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Breast Disease 1(2019) 1–12 1
DOI 10.3233/BD-190409
IOS Press
Role of CD44 in breast cancer
Nihad Al-Othmana,∗, Ala’ Alhendia, Manal Ihbaishaa, Myassar Barahmeha, Moath Alqaralehband
Bayan Z. Al-Momanyb
aDivision of Anatomy, Biochemistry, and Genetics, Faculty of Medicine and Health Sciences, An-Najah National
University, Nablus, Palestine
bSchool of Science, The University of Jordan, Amman, Jordan
Abstract. Breast cancer (BC) is among the most prevalent type of malignancy affecting females worldwide. BC is classified into
different types according to the status of the expression of receptors such as estrogen receptor (ER), human epidermal growth
factor receptor 2 (HER2), and progesterone receptor (PR). Androgen receptor (AR) appears to be a promising therapeutic target
of breast cancer. Binding of 5α-dihydrotestosterone (DHT) to AR controls the expression of microRNA (miRNA) molecules in
BC, consequently, affecting protein expression. One of these proteins is the transmembrane glycoprotein cluster of differentiation
44 (CD44). Remarkably, CD44 is a common marker of cancer stem cells in BC. It functions as a co-receptor for a broad diversity
of extracellular matrix ligands. Several ligands, primarily hyaluronic acid, can interact with CD44 and mediate its functions.
CD44 promotes a variety of functions independently or in cooperation with other cell-surface receptors through activation of
varied signaling pathways like Rho GTPases, Ras-MAPK, and PI3K/AKT pathways to regulate cell adhesion, migration, survival,
invasion, and epithelial–mesenchymal transition. In this review, we present the relations between AR, miRNA, and CD44 and
their roles in BC.
Keywords: Breast cancer, CD44, miRNA, hyaluronic acid, matrix metalloproteinase
1. Introduction
BC is the most prominent cause of mortality among
women in most developed countries[1]. It is deemed
to be a greatly heterogeneous group of cancers that
develop from varied cell types, each having its particu-
lar clinical consequences[2] and is composed of sev-
eral biologically various entities with discrete patho-
logical features and response to treatment[3,4]. There-
fore, the precise grouping of BC into clinically related
subtypes is of real importance for therapeutic deci-
sion[5]. Conventional Immunohistochemistry (IHC)
markers including estrogen receptor (ER), human epi-
dermal growth factor receptor 2 (HER2), and proges-
terone receptor (PR) are applied to patient progno-
sis and management[6,7]. The forthcoming of high-
throughput schemesof gene expression profiling have
*Corresponding author: Nihad Al-Othman, Division of Anatomy,
Biochemistry, and Genetics, Faculty of Medicine and Health Sci-
ences, An-Najah National University, Nablus, Palestine. Tel.: +970
598776995; E-mail: n.othman@najah.edu.
revealed that tumor cell response to treatment is not
entrenched using anatomical predicted features, rather
fundamental molecular features that can be explored
using molecular techniques[4,8]. Therefore, during the
past 15 years, modulation of BC classifications has
been in progress from histopathological typing to the
molecular classification[5]. For instance, ER-positive
and ER-negative BCs comprise different diseases[9].
Besides, the existence of four essential subtypes of
BC including luminal A, luminal B, HER2-enriched,
and basal-like has been established[10]. The Cancer
Genome Atlas Network (TCGA) has designated a broad
profiling for BC at the DNA, RNA, and protein lev-
els[10] whereby the luminal BC subtype can be divided
into at least two subgroups, each with a distinctive
mRNA profile[11]. Each subtype manifests differ-
ent prognosis, incidence, treatment response, preferred
metastatic sites, and disease-free survival rates[12].
CD44 is an integral membranous protein with a
multi-structure and multi-functions. It been found to
play a role in tethering cells to the extracellular matrix
(ECM) via mediating complex formation between
0888-6008/19/$35.00 © 2019 – IOS Press and the authors. All rights reserved
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2N. Al-Othman etal./Role of CD44 in breast cancer
Table1
Effect of different exon number on CD44v characteristics
Variant exon number Features added to CD44
V1 Not expressed in human CD44 variants.
V2 Gives additional sites for O- and N-glycosylation[122].
V3 - Gives a motif for GAGs addition (as heparan sulfate that confers CD44 the ability to bind to heparin-binding
growth factors and chemokines)[122].
- Mediates cell-cell adhesion that was dependent on HA[123].
- Mediates Met receptor activation and binding to its ligands (SF/ HGF)[124]
V4 - Enhances phosphorylation of CD44 cytoplasmic tail[26]
V5 - Enhances malignancy and invasiveness of some tumors[125].
- Enhances phosphorylation of CD44 cytoplasmic tail[26].
V6 - Broadens the ligand specificity to include GAGs other than HA[126].
- Makes CD44 able to form a complex with hepatocyte growth factor (HGF) and its receptor Met[14].
- Enhances phosphorylation of CD44 cytoplasmic tail[26].
V7 - Mediates cell survival by osteopontin[127].
- Enhances phosphorylation of CD44 cytoplasmic tail[26].
V8 - Gives additional sites of O-lycosylation (its extensive O-glycosylation inhibits CD44 binding HA[122].
V9 - Gives additional sites of O-lycosylation (its extensive O-glycosylation inhibits CD44 binding HA[122].
V10 - Gives additional sites of O-lycosylation (its extensive O-glycosylation inhibits CD44 binding HA[122].
extracellular components and intracellular cytoskeletal
elements. This role is no less important than its function
in cellular signaling and cell-cell communication[13].
It senses the changes in ECM and cell’s microenvi-
ronment that in turn influences many cell aspects, for
example and not as a limitation: cell survival, growth,
differentiation and motility[14].
2. CD44 structure
As mentioned previously, CD44 consists of three
domains: the extracellular domain (ECD), trans-
membrane domain (TMD), and intracellular domain
(ICD)[15]. The ECD includes the amino termi-
nal globular domain where HA, glycosaminoglycans
(GAGs) and other ligands bind such as hyaluronic acid
(HA)[16]. The TMD is sponsible for CD44 oligomer-
ization[17]. Palmitoylation can occur reversibly for
that domain. Several studies reported that this mod-
ification could impair signal transduction in lympho-
cytes and promote CD44 association with ankyrin and
ezrin, radixin, and moesin (ERM) proteins[18,19].
The cytoplasmic domain, also called the ICD, has two
configurations, short- and long-tail configurations[20].
This domain is essential in many cellular aspects
including subcellular localization of CD44 into the
basolateral side of polarized epithelia[21] and lead-
ing edge of lamellipodia during cell migration, sig-
naling, cytoskeletal organization and gene transcrip-
tion[22]. A number of factors, such as mitogens and
membrane-type 1 matrix MMP (MT-1 MMP), promote
the cleavage of cytoplasmic tail[20]. Translocation of
that cleaved tail into the nucleus influences the tran-
scription of many genes including CD44 itself in a pos-
itive feedback pattern[23]. The cytoplasmic domain
displays a divergent role in signaling. It alters CD44
affinity to bind ligands “inside-out signaling” and also
mediates downstream signaling upon CD44 binding
ligands “outside-in signaling”[19].
3. CD44 isoforms
The mechanisms that account for heterogeneity of
CD44 are alternative splicing, N-glycosylation, O-
glycosylation and palmitoylation[24,25]. CD44 gene is
composed of 20 exons. Exons (1–5), (16–18) and (20)
produce CD44s (the long-tail configuration), which is
the smallest compared to other isoforms. Exons 6–15,
designated as (v1-10), are variable with various combi-
nations produced by alternative splicing The addition of
one or more of the exons (v2-v10) to CD44s generates
other CD44 isoforms with larger molecular mass (up
to 381 amino acids long). Take into consideration that
expressing v1 exon would yield a truncated protein
due to presence of a stop codon and therefore, it is
not expressed in human CD44v[26]. Table1 displays
the different features of CD44v depending on its exon
number.
Whether post translation modification or the alter-
native splicing affects the binding affinity of CD44 or
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increases its affinity for its ligands is not clear. How-
ever, what is clear is that both processes are depen-
dent on cell type, cell growth condition, environment,
and oncogenic pathways such as the Ras-MAPK cas-
cade[24,27]. Though, CD44s is expressed remarkably
in most tissues, whereas CD44 variants are expressed
mainly in tumor cells[15,24]. On the other hand, other
studies have reported that CD44 variants are expressed
in normal and the tumor cells at different levels sug-
gesting that they are also necessary for normal cellu-
lar functions[28,29]. CD44s and its variants take part
in cancer invasiveness. For instance, CD44v8-10 and
CD44v9 are expressed in high amounts in pancreatic
and colorectal cancers respectively[20]. CD44v6 and
soluble (cleaved) CD44 were seen in prostate cancer
cell derived from bone metastasis. Switching between
CD44 isoforms, as observed in prostate cancerous
cells when CD44s is replaced by CD44v6, promotes
adhesion and survival[30]. Comparing benign with
the malignant forms of prostate cancer, CD44v5 and
CD44s are highly expressed in these forms, respec-
tively[31]. A few studies showed that CD44v promotes
some cancer types progression and metastasis[32,33],
while others indicated that they are tumor suppressors
in other types of cancers[34,35]. This discrepancy
of findings may stem from applying different means
for detecting CD44 (e.g. polymerase chain reaction or
IHC) or using different primary anti-CD44 antibod-
ies that may not recognize the CD44v epitopes[29].
For more detailed information regarding some cancer
type’s relation with CD44v, see Table2.
4. CD44 ligands
Several ligands can interact with CD44 and mediate
its functions. Osteopontin, collagens, growth factors,
fibronectin and MMP can bind to CD44, although HA
is the principal one[20].
4.1. HA
HA is one of the mucopolysaccharides or GAGs
found mainly in the ECM, pericellular matrix, and can
be found intracellularly[36]. It is an unbranched, non-
sulfated, anionic heteropolysaccharide with a molec-
ular weight up to 10,000KDa[24]. HA is composed
of a repeated units of disaccharide; β-D-glucuronic
acid and D-N-acetylglucosamine and is abundant in
soft connective, epithelial and neural tissues[36]. It is
synthesized by an integral membrane enzyme called
hyaluronic acid synthase (HAS) followed by a direct
release into the ECM[37]. Many cells have the abil-
ity to synthesize HA, but mesenchymal cells are the
main ones[38]. Using CD44-nul COS-7 cells trans-
fected with human CD44s plasmids, cells gained HA-
binding ability and were able to internalize a conjugated
HA[39,40]. This experiment strengthens the idea that
HA turnover and internalization correlate with CD44
expression level. Researchers exploit that notion in their
attempt to improve cancer treatment by conjugating
drugs to HA to improve its delivery and internaliza-
tion into cancerous cells that have high expression of
CD44[41].
The enzymes that are involved in HA degradation
are hyaluronidases (HYALs), β-d-glucuronidase, and
β-N-acetyl-hexosaminidase[37]. These enzymes are
found intracellularly and in the serum. HYALs cleave
high molecular weight HA (HMW) into smaller lower
molecular weight (LMW) oligosaccharides while β-
d-glucuronidase and β-N-acetylhexosaminidase addi-
tionally degrade the oligosaccharide fragments[36].
Some studies defined HMW HA as HA molecule
with a molecular mass >500KDa. Human HYALs are
encoded by six genes: hyall1, hyal2, and hyal3[37].
HYAL1 and HYAL2 are the main hyaluronidases in
most tissues; HYAL2 is responsible for cleaving HMW
HA that is bound to CD44 receptor. The resulting HA
fragments are further degraded by HYAL1 generating
HA oligosaccharides[42].
HA can perform many functions. It binds to a num-
ber of keratin sulfate and chondroitin sulfate molecules
and from proteoglycan aggregates in the ECM. If it
is not linking with other molecules, it will bind to
water and maintains tissue hydration and osmotic bal-
ance[36]. HA contributes in many other physiolog-
ical and pathological cellular processes such as cell
adhesion, migration, cancer progression and inflam-
mation[36,38]. CD44 can bind HA and mediates a
host of cellular functions[36]. Furthermore, most of
HA functions in most tissues are related to CD44-HA
interactions[36]. Based on CD44 affinity to HA, CD44
can be classified into three forms: the low affinity form
that is expressed in normal cells[43], the inflammation-
induced high affinity form, and the constitutive high
affinity form that is expressed all the time in cancerous
cells[29,44].
In addition, several studies have reported that many
of HA effects are related to its molecular weight.
HMW-HA provokes distinct effects compared to those
mediated by LMW-HA on the same cell. For exam-
ple, LMW-HA reduces CD44 clustering and increases
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Table2
Contribution of CD44v in different type of cancer
Cancer type CD44 isoform Isoform contribution
Colorectal Cancer CD44v3 - Activates invasion and resistance to apoptosis.
CD44v6 - Associated with tumor metastasis.
- Essential for their migration and generation of metastatic tumors[30,128,129].
CD44v8–10 - Has a role in metastasis[130].
CD44v2 - Is overexpressed & upregulated in CRC.
- Significantly worse prognosis[131].
Lung cancer CD44v5
CD44v6
- Promotes squamous cell carcinoma metastasis In[132,133].
CD44v7
CD44v3
- Are expressed in non-small cell lung carcinomas[134,135].
CD44v5
CD44v6
- CD44v6 is associated with lymph node metastasis and poor survival[136,137].
Breast Cancer CD44v3, CD44v5, and
CD44v6
- Promotes metastasis[138].
CD44v5, CD44v6, and
CD44v7-8
- Are associated with axillary lymph node metastasis[139].
CD44v3 - Enhances metastases to the lymph nodes[140].
CD44v2–10
CD44v3–10
- High expression is correlated to positive steroid receptor status, low proliferation,
and luminal A subtype[114].
CD44v8-10 - Is correlated to positive EGFR, negative/low HER2 status, and basal-like
subtype[114].
Leukemia CD44v3,
CD44v6, CD44v9, and
CD44v10
- Are expressed in bone marrow progenitors[141].
CD44v3, CD44v6, and
CD44v9
- Are expressed in lymphocytes and monocytes following stimulation with
inflammatory cytokines[141].
Non-Hodgkin’s
lymphoma and myeloma
CD44v6, CD44v9, and
CD44v10
- Are overexpressed and associated with poor prognosis[142].
Acute myeloid leukemia CD44v6 - Is associated with poor prognosis and shorter survival rate[142].
Pancreatic Cancer CD44v6 - Is expressed in primary and metastatic human pancreatic CA[143].
CD44v5 - Is strongly expressed on adenocarcinomas[144].
CD44v6 And
CD44v2
- Are expressed on tumor cells and correlated with decreased overall survival[145].
CD44v6,
CD44v9
- Promotes metastasis
- CD44v6 is a risk factor affecting overall survival[146].
CD44v9 - Their expression is upregulated[147].
Head and Neck Cancer CD44v3 - Leads to a significant increase in migration[148].
CD44v3, CD44v6, and
CD44v10
- Are associated with lymph node metastasis, perineural invasion, decreased
survival, distant metastasis and radiation failure[149,150].
CD44v6 - Is correlated with tumor invasion, lymph node metastasis, and shorter
survival[151].
Prostate cancer CD44v6 - Promotes cell survival[30]
cell adhesion, while HMW-HA induces CD44 clus-
tering[24,45]. It is the vast length of HMW-HA that
enables it to bind and bridge higher number of receptors
over large cell area[36]. HMW-HA stimulates Ras-
CD44 in ovarian tumor cell[46], inhibits tumor growth
in schwannomas[47] as well as inhibits neovascu-
larization in breast cancerous cells[20]. Furthermore,
HMW-HA fragments have anti-inflammatory role[48]
and support tissue integrity[36,48]. In contrast, LMW-
HA stimulates expression of genes required for inflam-
mation[49]. In cancer cells, LMW-HA suppresses anti-
apoptotic signaling pathways and inhibits the activ-
ity of transporters that enhances multidrug resistances
to some chemotherapeutic agents[50,51], inhibits
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Table3
Functions of HMW-HA and LMW-HA
LMW-HA roles HMW-HA roles
Reduces CD44 clustering[24,45]. Induces CD44 clustering[24,45].
Provokes an inflammatory response and stimulates expression of genes
required for inflammation[48,49].
Has anti-inflammatory role and supports tissue integrity[48].
Induces wound site inflammation and scar formation[38]. Induces wound healing with minimal inflammation and scar
formation[38].
Induces tumor regression[53]. Inhibits tumor growth in schwannomas[47].
Interrupts HA-CD44 interaction in breast CA → Inhibits cell growth,
motility, and invasion[55].
Bridges high number of receptors over large cell area[36].
Enhances CD44 break down and angiogenesis[27]. Inhibits neovascularization[152].
Suppresses anti-apoptotic signaling pathways in cancer cells[50,51]. Stimulates Ras-CD44 in ovarian tumor cell[46].
Inhibits HA synthesis[52]. Limits viral infections of further neighboring T- cells[48].
Inhibits multidrug resistances transporter[50,51].
Disassembles CD44-multidrug transporter complex and tyrosine kinase
receptor complexes[52].
HA synthesis[52] and induces tumor regression[53].
Moreover, LMW-HA leads to the “degradation of
CD44-multidrug transporter complex and receptor
tyrosine kinase (TRK) complexes, internalization of
these disassembled structures, and sapping of their
role”[52]. Furthermore, LMW-HA blocks dissemi-
nation of an ovarian cancer cells who are induced
artificially to metastasize[54]. Disaccharides of HA
compared to HMW-HA and other HA oligosaccha-
rides fragments/length shows the ability to inhibit cell
growth, motility, and invasion significantly in BC via
disturbance of the interaction of endogenous HA-CD44
complex[55]. LMW-HA enhances CD44 break down
and angiogenesis and attenuates cell adhesion in breast
cancer[20]. Note that studies that discussed LMW-
and HMW-HA cellular effects did not define the type
of receptor that is involved in their functions[24].
Table3 summarizes functions of both HMW-HA and
LMW-HA.
5. Role of CD44 and HA in cancer signaling
CD44 promotes a variety of functions independently
or in cooperation with various cell-surface receptors
through triggering a number of signaling pathways
via Rho GTPases, Ras-MAPK, and PI3K/AKT among
others[24,56]. CD44 functions as a growth or arrest
sensor according to signals from the microenviron-
ment that can influence cancer progression[57]. The
protein directly intercedessignal transduction pathways
through triggering of LMW-HA when bound to CD44.
It also recruits signaling mediators to the cytoplasmic
tail of CD44 that controls the activity of regulatory
signaling molecules such as Tiam1, p115, Rac1, Rho
GEFs, Rho-associated protein kinase, and cSrc[27].
Interactions with these signaling proteins lead to induc-
tion of the PI3K pathway that activates a number of cel-
lular behavior including cell survival and invasion[58].
In addition, CD44 stimulates RhoA independently of
HA binding, which triggers CD44 involvement with
ankyrin resulting in creation of membrane projections
and stimulation of migration[59]. Furthermore, CD44
mediates actin cytoskeleton remodeling and invasion by
interaction with ERM protein complex. The latter com-
plex induces the re-formation of the actin cytoskele-
ton and facilitates cell adhesion cell motility[60]. The
ERM proteins compete with another protein known
as merlin, which acts as a tumor suppressor. Through
binding to CD44 cytoplasmic tail, merlin can either
facilitate or inhibit cell growth and motility. In addi-
tion to HMW-HA, merlin combines with CD44 shift-
ing ERM and, subsequently, suppressing Ras path-
way[61]. Activation of PI3K leads to phosphorylation
and deactivation of merlin by p21-associated kinase
(Pak2), which obstructs merlin binding to CD44. As
a result, ankyrin and ERM proteins become free to
bind CD44 cytoplasmic tail to the actin cytoskeleton
enhancing cell invasion[62]. Several studies revealed
that collagen-embedded HMW-HA can hinder the
induction of epidermal growth factor receptor (EGFR)
and inhibitfilopodia formation in MDA-MB-231 cells
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6N. Al-Othman etal./Role of CD44 in breast cancer
grown on collagen[63]. Merlin attaches to CD44 and
prevents ERM, N-Wasp, and Grb2 complexing, which
leads to inactivation of Ras pathway and suppression
of cell invasion, motility, and growth[27]. Alteration
of CD44-mediated biology is a result of the expression
of differentially spliced isoforms; alternative expres-
sion has been proposed to be associated with amplified
metastatic behavior[27,64].
Furthermore, CD44 inhibits cancer progression,
whereby when it attaches to merlin, it functions as
a growth/arrest sensor in relation to signals from the
microenvironment and has a function in contact repres-
sion[65].
6. Androgen receptor (AR)
AR is a member of the steroid hormone nuclear
receptors family that also includes ER and PR[66–
68]. Although the main functions of androgens and
their receptor are associated with male sexual differ-
entiation, AR and its ligands, testosterone and its more
potent product, dihydrotestosterone, are critical in the
development of the mammary gland. Androgens effect
various sites throughout the body: the hypothalamus
and amygdala in the brain, breast, bone, skin, adipose
tissues, skeletal muscles, vascular and genital tissues,
and in women ovaries and extra-gonadal tissues in
which androgens are the essential precursors for estro-
gen biosynthesis[69,70]. Thus, androgens influence
sexual desire and function, mineral density in bones,
muscle mass and strength, the distribution of adipose
tissue, energy, mood and psychological well-being as
well[71].
7. AR expression in BC
AR expression has been identified in 60–85% of
breast tumors[72]. However, the expression of AR is
different among the different subtypes. Approximately
70 to 90% of ER-positive cancers are AR-positive
as well[73,74]. Indeed, there is a significant associ-
ation between the expression of both ER and AR. In
addition, approximately 60% of ERBB2-positive breast
cancers overexpress AR[73,75]. On the other hand,
the prevalence of AR expression in triple-negative BC
(TNBC) is less frequently reported, ranging from 13 to
65%[76]. This variability may be due to the differences
in the techniques or criteria used to define AR positiv-
ity[76,77].
8. AR as a therapeutic target
Historically, androgens such as fluoxymesterone,
testolactone, and calusterone were used for the treat-
ment of advanced breast cancer resulting in about 18–
39% clinical responses[78]. However, the undesirable
masculinity side effects of these agents have limited
their routine use in the treatment of breast cancer
especially in the advent of newer, less toxic endocrine
agents. There is a renewed interest in the use of AR-
targeted agents in the treatment of breast cancer given
the improvement in treating prostate cancer using such
agents and the significance of AR signaling pathway in
breast cancer. This is true particularly for TNBC. The
fact that AR-positive TNBCs have preserved andro-
genic signaling suggests that AR can be used as a
possible therapeutic target similar to ER-positive breast
cancer targeting[79,80]. However, the use of AR as
a potential therapeutic target in breast cancer has yet
to be established due to the difficulties in both the
identification of the patients who might be benefit
from AR-targeted therapies and the development of the
right combination of therapeutic agents based on AR-
targeted therapies[73,75,81].
9. Androgen regulation of miRNA
miRNAs are short, single-stranded, non-coding
RNA molecules of 20–25 nucleotides that are widely
conserved among species[82]. They regulate cell func-
tion via negatively targeting the stability of mRNAs
and/or their use in protein synthesis. Interestingly, a
correlation has been found in the expression of miR-
NAs in androgen-dependent and independent prostate
cancers, in addition to benign and malignant prostate
tissues[83]. In addition, miRNAs have been found to
regulate the long AR 3’untranslated region (UTR)[84],
suggesting a functional regulation by AR. This is not
surprising given that primary function of AR as a tran-
scription regulatory protein.
More than 50% of all human gene translation is
thought to be regulated by miRNA[85]. This extra
level of gene regulation is involved in the cell signaling
pathways in both normal and tumor tissues[86,87].
Moreover, each miRNA can regulate numerous target
genes, and, vice versa, the same target gene can also
be regulated by several types of miRNAs, creating a
complex network[88–90]. It is of note that miRNA
is not always associated with inhibitory or down reg-
ulatory effects. In rare circumstances, depending on
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7N. Al-Othman etal./Role of CD44 in breast cancer
the cell cycle and protein co-factors, a miRNA can
activate mRNA translation and, hence, increase protein
levels[91]. The inherent complexity of this regulatory
system allows miRNAs to control the global activity
of the cell, including cell differentiation, proliferation,
stress response, metabolism, cell cycle, apoptosis, and
angiogenesis.
Different miRNA expression profiles between can-
cerous cells and paired normal tissues from the same
organ and cancer types have been documented in a
number of studies[92,93]. Some miRNAs are down-
regulated in a number of different tumors, and their re-
introduction weakens the viability of cancer cells since
they function as tumor-suppressor genes with an anti-
proliferative and pro-apoptotic activity role[92,93]. In
contrast to the tumor-suppressor miRNAs, oncogenic
miRNAs, oroncomiRs, display an antiapoptotic activity
and are over-expressed in cancer cells. Therefore, alter-
ations in the expression of these miRNAs can stimulate
tumorigenesis[56].
In 2011, Waltering etal.examined androgen regula-
tion of miRNAs using one of the first miRNA microar-
ray showing that DHT positively regulates 17 miRNAs
in metastatic prostate VCaP tumor cells and causes
high expression in 42 miRNAs[94]. Further works
by several independent groups have demonstrated
that miRNAs such as miR-19a, miR-148, miR-27a,
miR-125b, miR-135a, MiR-32 and miR-21 are andro-
gen inducible[95–101]. Other miRNAs are down-
regulated by androgens such as the well-established
oncogenes miR-221 and miR-222, which are located
on the X chromosome and are over-expressed in pan-
creatic, breast, liver, and lung cancer[100,102,103].
Other miRNAs that are down-regulated by andro-
gens include miR-126-5p, miR-146b, miR-219-5p,
miR181b-1, miR-181c, and miR-221[104].
On the other hand, many studies have examined the
role of miRNAs in controlling the AR pathway. Using
a miRNA library, Ostling etal.reported the ability of
71 unique miRNAs to influence the function of AR
with 52 decreasing and 19 increasing its RNA and pro-
tein levels[84]. Since then, several miRNAs have been
described to have a role in the regulation of AR activity
directly or indirectly via co-regulators[105,106]. MiR-
205 was found to exhibit a negative correlation to AR
through binding to the receptor’s 3’UTR and decrease
its transcript and protein levels[107], and there is a sta-
tistically significant inverse association exists between
miR-34a and AR[84]. In addition to those examples,
let-7c determines prostate tumor suppression through
AR, and this mechanism is linked to the capability
of this tumor-suppressing miRNA to target c-MYC, a
molecule that is required for the correct transcription
of AR[108].
However, miRNAs do not only have direct effects,
rather they can use alternative routes to control andro-
gen signaling such as those mediated by the ERBB-
2 and PI3K/AKT. The tyrosine receptor ERBB-2 is
often elevated in prostate cancer, whereas the activation
of PI3K/AKT signaling is associated with prolifera-
tion, metastasis, apoptosis resistance and angiogenesis
in prostate cancer[109]. The latter study has shown
that the 3′-UTR of ERBB-2 mRNA contains two spe-
cific target sites for miR-331-3p, which suppresses the
expression of ERBB-2 at both the transcript and protein
levels. The same group also illustrated that miR-331-
3p is involved in the downstream PI3K/AKT signal-
ing in multiple prostate cancer cell lines[109]. MiR-
488* directly affects AR signaling by targeting the 3′-
UTR of AR and down-regulates AR protein expression
in both androgen-sensitive and -insensitive prostate
cancer cells inhibiting cellular growth and inducing
apoptosis[110]. Another miRNA miR-17-5p, has been
shown to target PCAF, a coactivator of AR, and to
support the development of prostate tumor[111].
10. AR and CD44
Treatment of breast MDA-MB-231 cancer cells with
DHT alters CD44 expression at both the RNA and
protein levels[112]. The expression of the different
variants of CD44 is regulated at the post-transcriptional
level. Moreover, MDA-MB-231 cells express elevated
levels of CD44 in contrast to other BC cell lines[113].
The high levels of CD44 could be due to the large
number of miRNA types such as miR-512-3p, miR-
328, miR-491, and miR-671 that bind to 3’UTR of
CD44 in these cells[86]. The levels of these miR-
NAs could also be regulated by DHT. Understanding
the role of CD44 in cancer progression must take in
consideration the existence of different CD44 isoforms
as the antibodies in the majority of the earlier studies
identifies an epitope located in a non-variable region of
CD44 of cancer stem cells, so they cannot differentiate
between different CD44 isoforms[114]. Not all CD44
proteins bind to HA. In facts, three isoforms of CD44
cannot interact with HA unless activated by physio-
logical stimuli, and constitutive binding[115]. CD44
switching from the inactive state (low-affinity incapable
of binding and internalizing HA) to the active state
(high-affinity with ability to bind and internalize HA)
uncorrected proof version
8N. Al-Othman etal./Role of CD44 in breast cancer
Table4
miRNAs that regulate CD44 expression in BC cells
miRNA Role in BC Experimental model Reference
miR-143 ∙Increase in S-phase population of cancer cells
∙Reduces stem cell properties such as:
self-renewal and sphere formation abilities
∙Reduces cancer cell proliferation (in vivo)
∙Suppresses epithelial-mesenchymal transition
and metastasis
∙Tested on BT474, MDA231, MDA468, MCF7,
SUM102 and SKBR3 human breast cancer cell line
in vitro
[120]
miR-373 ∙Increase invasion and migration by suppressing
CD44, promoting metastasis
∙No effect on cell cycle or cell proliferation
∙Tested on MCF-7 human breast cancer cell line
in vitro and in vivo (transplanted into SCID mice)
∙Expressed by MDA-MB-435 human breast cancer
cell line and DU-145 human prostate cancer cell
line and is responsible for their migratory ability
∙Overexpressed by lymph-node metastatic breast
cancer samples compared to primary tumors
[153]
miR-520c ∙Increase invasion and migration by suppressing
CD44, promoting metastasis
∙No effect on cell cycle or cell proliferation
∙Tested on MCF-7 human breast cancer cell line
in vitro and in vivo (transplanted into SCID mice)
[153]
miR-34a ∙Inhibits tumor growth and survival
∙Induces cell cycle arrest and senescence
∙Reduces metastasis (in vivo) and invasion
∙Inhibits stem cell properties like holoclone and
sphere formation
∙LAPC4, LAPC9 &Du145 xenograft models of
human prostate cancer in vitro
∙In vivo models of prostate cancer in NOD-SCID
mice
[154]
SCID: severe combined immunodeficiency
NOD: non-obese diabetic
requires posttranslational modification including gly-
cosylation of the extracellular domain and/or phospho-
rylation of specific serine residues in the cytoplasmic
domain[26,116]. This modification is vital for cellular
migration that allows CD44 to be inserted into the
leading border of the cells and lamellipodia[117].
11. MiRNA and CD44
Seventy miRNAs control CD44 expression levels in
different tissues[118]. Different types of miRNAs reg-
ulate the expression of CD44 (Table4). A study on BC
MCF-7 cells showed another HA/CD44 signaling path-
way that is initiated by activation of protein kinase C
(PKC). The latter kinase promotes phosphorylation of
the stem cell marker Nanog, which is a transcriptional
growth factor that plays a role in the self-regeneration of
pluripotency in embryonic stem cells. Phosphorylated
Nanog can then translocate from the cytosol into the
nucleus and associate with RNAase III (DROSHA)
and the RNA helicase (p68), which together lead to
up-regulation of miRNA-21. The latter molecule then
down-regulates the tumor suppressor protein, program
cell death 4 (PDCD4), induces expression of inhibitor
of apoptosis protein (IAPs) as well as X-linked inhibitor
of apoptosis protein (XIAP), and promotes chemore-
sistance by stimulating the expression of MDR1 (P-
gp)[119].
Recently, numerous miRNAs have been identified to
affect cancer progression; miRNA-143 directly binds
the 3’ UTR region of CD44 resulting in reduction of
its expression and the capability of BC cells to metas-
tasize. These effects are as a result of the tumor sup-
pressing activity of miRNA-143[120]. Furthermore, it
has been found that miRNA-520a-3p acts as a tumor
suppressor and CD44 gene as one of its targets in BC
tissues and numerous cell lines including MCF-7 and
MDA-MB-231 cells[121].
12. Conclusion
CD44 is an integral membranous protein with a
multi-structure and multi-functions. The multifunc-
tional glycoprotein CD44 can undergo alternative splic-
ing events to produce CD44 variant isoforms that are
more restricted in their distribution as compared to the
standard CD44 isoforms. Different CD44 isoforms are
expressed differentially in different types of cancers.
The binding of CD44 to its ligand “HA” has a major
function in BC progression, cell adhesion, behavior,
uncorrected proof version
9N. Al-Othman etal./Role of CD44 in breast cancer
motility, and morphology. In addition, various miR-
NAs regulate CD44 expression via binding of DHT
to AR. As a result, alteration in the expression of
miRNAs that control CD44 expression can influence
tumorigenicity of BC and other types of cancer.
Conflict of interest
There is no conflict of interest to declare.
References
[1] Childers CP et al., National estimates of genetic testing in
women with a history of breast or ovarian cancer, J Clin
Oncol, 35(34): 3800, 2017.
[2] Grunewald TG et al., Understanding tumor heterogeneity as
functional compartments-superorganisms revisited, Journal
of Translational Medicine, 9(1): 79, 2011.
[3] Weigelt B, Baehner FL, Reis-Filho JS, The contribution of
gene expression profiling to breast cancer classification, prog-
nostication and prediction: a retrospective of the last decade,
The Journal of Pathology: A Journal of the Pathological
Society of Great Britain and Ireland, 220(2): 263–280, 2010.
[4] Reis-Filho JS et al., Molecular profiling: moving away
from tumor philately, Science Translational Medicine, 2(47):
47ps43, 2010.
[5] Dai X et al., Breast cancer intrinsic subtype classification,
clinical use and future trends, Am J Cancer Res, 5(10): 2929,
2015.
[6] Vallejos CS et al., Breast cancer classification according
to immunohistochemistry markers: subtypes and associa-
tion with clinicopathologic variables in a peruvian hospital
database, Clin Breast Cancer, 10(4): 294–300, 2010.
[7] Cheang MC et al., Ki67 index, HER2 status, and prognosis of
patients with luminal B breast cancer, JNCI: Journal of the
National Cancer Institute, 101(10): 736–750, 2009.
[8] Sotiriou C, Pusztai L, Gene-expression signatures in breast
cancer, N Engl J Med, 360(8): 790–800, 2009.
[9] Yan Y, Zuo X, Wei D, Concise review: emerging role of CD44
in cancer stem cells: a promising biomarker and therapeutic
target, Stem Cells Translational Medicine, 4(9): 1033–1043,
2015.
[10] C.G.A. Network. Comprehensive molecular portraits of
human breast tumours, Nature, 490(7418): 61, 2012.
[11] Sørlie T et al., Gene expression patterns of breast carcinomas
distinguish tumor subclasses with clinical implications, Proc
Natl Acad Sci, 98(19): 10869–10874, 2001.
[12] Parker JS et al., Supervised risk predictor of breast cancer
based on intrinsic subtypes, J Clin Oncol, 27(8): 1160, 2009.
[13] Waugh DJ et al. Adhesion and penetration: two sides of CD44
signal transduction cascades in the context of cancer cell
metastasis. Hyaluronan in Cancer Biology. . Elsevier; 109–
125. 2009.
[14] Orian-Rousseau V et al., CD44 is required for two consecutive
steps in HGF/c-Met signaling, Genes Dev, 16(23): 3074–
3086, 2002.
[15] Miwa T et al., Isoform switch of CD44 induces different
chemotactic and tumorigenic ability in gallbladder cancer, Int
J Oncol, 51(3): 771–780, 2017.
[16] Bajorath J, Molecular organization, structural features, and
ligand binding characteristics of CD44, a highly variable cell
surface glycoprotein with multiple functions, Proteins: Struc-
ture, Function, and Bioinformatics, 39(2): 103–111, 2000.
[17] Liu D, Sy M-S, Phorbol myristate acetate stimulates the
dimerization of CD44 involving a cysteine in the transmem-
brane domain, J Immunol, 159(6): 2702–2711, 1997.
[18] Bourguignon LY et al., Rho-kinase (ROK) promotes CD44v3,
8–10- ankyrin interaction and tumor cell migration in
metastatic breast cancer cells, Cytoskeleton, 43(4): 269–287,
1999.
[19] Thorne RF, Legg JW, Isacke CM, The role of the CD44
transmembrane and cytoplasmic domains in co-ordinating
adhesive and signalling events, J Cell Sci, 117(3): 373–380,
2004.
[20] Senbanjo LT, Chellaiah MA, CD44: a multifunctional cell
surface adhesion receptor is a regulator of progression and
metastasis of cancer cells, Front Cell Dev Biol, 5: 18, 2017.
[21] Neame SJ, Isacke CM, The cytoplasmic tail of CD44 is
required for basolateral localization in epithelial MDCK cells
but does not mediate association with the detergent-insoluble
cytoskeleton of fibroblasts, J Cell Biol, 121(6): 1299–1310,
1993.
[22] Cywes C, Stamenkovic I, Wessels MR, CD44 as a receptor for
colonization of the pharynx by group A Streptococcus, J Clin
Invest, 106(8): 995–1002, 2000.
[23] Okamoto I et al., Proteolytic release of CD44 intracellular
domain and its role in the CD44 signaling pathway, J Cell Biol,
155(5): 755–762, 2001.
[24] Ponta H, Sherman L, Herrlich PA, CD44: from adhesion
molecules to signalling regulators, Nature Rev Mol Cell Biol,
4(1): 33, 2003.
[25] Wang X et al., Expression of CD44 standard form and variant
isoforms in human bone marrow stromal cells, Saudi Pharma-
ceutical Journal, 25(4): 488–491, 2017.
[26] Naor D, Sionov RV, Ish-Shalom D. CD44: structure, function
and association with the malignant process. Advances in Can-
cer Research. . Elsevier; 241–319. 1997.
[27] Louderbough JM, Schroeder JA, Understanding the dual
nature of CD44 in breast cancer progression, Mol Cancer Res,
9(12): 1573–1586, 2011.
[28] Wang SJ, Bourguignon LY, Role of hyaluronan-mediated
CD44 signaling in head and neck squamous cell carcinoma
progression and chemoresistance, Am J Pathol, 178(3): 956–
963, 2011.
[29] Thapa R, Wilson GD, The importance of CD44 as a stem
cell biomarker and therapeutic target in cancer, Stem Cells Int,
20162016.
[30] Todaro M et al., CD44v6 is a marker of constitutive and repro-
grammed cancer stem cells driving colon cancer metastasis,
Cell Stem Cell, 14(3): 342–356, 2014.
[31] Gupta A et al., Promising noninvasive cellular phenotype in
prostate cancer cells knockdown of matrix metalloproteinase
9, Sci World J, 20132013.
[32] Döme B et al., Expression of CD44v3 splice variant is
associated with the visceral metastatic phenotype of human
melanoma, Virchows Archiv, 439(5): 628–635, 2001.
[33] Li X-D et al., Clinical significance of CD44 variants expres-
sion in colorectal cancer, Tumori J, 99(1): 88–92, 2013.
[34] Sato S et al., Reduced expression of CD44 variant 9 is related
to lymph node metastasis and poor survival in squamous cell
carcinoma of tongue, Oral Oncol, 36(6): 545–549, 2000.
[35] Diaz LK et al., CD44 expression is associated with increased
survival in node-negative invasive breastcarcinoma, Clin Can-
cer Res, 11(9): 3309–3314, 2005.
uncorrected proof version
10 N. Al-Othman etal./Role of CD44 in breast cancer
[36] Necas J et al., Hyaluronic acid (hyaluronan): a review, Veteri-
narni Medicina, 53(8): 397–411, 2008.
[37] Karbownik MS, Nowak JZ, Hyaluronan: towards novel anti-
cancer therapeutics, Pharmacological Reports, 65(5): 1056–
1074, 2013.
[38] Jordan AR et al., The role of CD44 in disease pathophysiology
and targeted treatment, Front Immunol, 6: 182, 2015.
[39] Ghosh SC, Neslihan Alpay S, Klostergaard J, CD44: a val-
idated target for improved delivery of cancer therapeutics,
Expert Opinion on Therapeutic Targets, 16(7): 635–650,
2012.
[40] Rios de la Rosa JM et al., The CD44-mediated uptake of
hyaluronic acid-based carriers in macrophages, Advanced
Healthcare Materials, 6(4)2017.
[41] Cai S et al., Cellular uptake and internalization of hyaluronan-
based doxorubicin and cisplatin conjugates, Journal of Drug
Targeting, 22(7): 648–657, 2014.
[42] Chanmee T, Ontong P, Itano N, Hyaluronan: a modulator
of the tumor microenvironment, Cancer Lett, 375(1): 20–30,
2016.
[43] Maiti A, Maki G, Johnson P, TNF-𝛼induction of CD44-
mediated leukocyte adhesion by sulfation, Science,
282(5390): 941–943, 1998.
[44] Cichy J, Puré E, The liberation of CD44, J Cell Biol, 161(5):
839–843, 2003.
[45] Yang C et al., The high and low molecular weight forms of
hyaluronan have distinct effects on CD44 clustering, J Biol
Chem, 287(51): 43094–43107, 2012.
[46] Bourguignon LY et al., Hyaluronan promotes CD44v3-Vav2
interaction with Grb2-p185HER2 and induces Rac1 and Ras
signaling during ovarian tumor cell migration and growth, J
Biol Chem, 276(52): 48679–48692, 2001.
[47] Morrison H et al., The NF2 tumor suppressor gene product,
merlin, mediates contact inhibition of growth through inter-
actions with CD44, Genes Dev, 15(8): 968–980, 2001.
[48] Turville S. Blocking of HIV Entry through CD44–Hyaluronic
Acid Interactions. . Nature Publishing Group; 2014.
[49] Ohkawara Y et al., Activation and transforming growth factor-
𝛽production in eosinophils by hyaluronan, American Journal
of Respiratory Cell and Molecular Biology, 23(4): 444–451,
2000.
[50] Toole BP, Ghatak S, Misra S, Hyaluronan oligosaccharides
as a potential anticancer therapeutic, Current Pharmaceutical
Biotechnology, 9(4): 249–252, 2008.
[51] Toole BP, Slomiany MG, Hyaluronan, CD44 and Emmprin:
partners in cancer cell chemoresistance, Drug Resistance
Updates, 11(3): 110–121, 2008.
[52] Slomiany MG et al., Abrogating drug resistance in malignant
peripheral nerve sheath tumors by disrupting hyaluronan-
CD44 interactions with small hyaluronan oligosaccharides,
Cancer Res, 69(12): 4992–4998, 2009.
[53] Gilg AG et al., Targeting hyaluronan interactions in malignant
gliomas and their drug-resistant multipotent progenitors, Clin
Cancer Res, 14(6): 1804–1813, 2008.
[54] Ween MP et al., Versican induces a pro-metastatic ovarian
cancer cell behavior which can be inhibited by small hyaluro-
nan oligosaccharides, Clinical & Experimental Metastasis,
28(2): 113–125, 2011.
[55] Urakawa H et al., Inhibition of hyaluronan synthesis in breast
cancer cells by 4-methylumbelliferone suppresses tumori-
genicity in vitro and metastatic lesions of bone in vivo, Int
J Cancer, 130(2): 454–466, 2012.
[56] Marhaba R, Zöller M, CD44 in cancer progression: adhesion,
migration and growth regulation, J Mol Histol, 35(3): 211–
231, 2004.
[57] Hanahan D, Weinberg RA, The hallmarks of cancer, Cell,
100(1): 57–70, 2000.
[58] Bourguignon LY et al., Hyaluronan-CD44 interaction pro-
motes c-Src-mediated twist signaling, microRNA-10b expres-
sion, and RhoA/RhoC up-regulation, leading to Rho-kinase-
associated cytoskeleton activation and breast tumor cell inva-
sion, J Biol Chem, 285(47): 36721–36735, 2010.
[59] Bourguignon LY et al., Hyaluronan-mediated CD44 interac-
tion with RhoGEF and Rho kinase promotes Grb2-associated
binder-1 phosphorylation and phosphatidylinositol 3-kinase
signaling leading to cytokine (macrophage-colony stimulating
factor) production and breast tumor progression, J Biol Chem,
278(32): 29420–29434, 2003.
[60] Bretscher A, Edwards K, Fehon RG, ERM proteins and mer-
lin: integrators at the cell cortex, Nature Rev Mol Cell Biol,
3(8): 586, 2002.
[61] Morrison H et al., The NF2 tumor suppressor gene product,
merlin, mediates contact inhibition of growth through inter-
actions with CD44, Genes Dev, 15(8): 968–980, 2001.
[62] Kissil JL et al., Merlin phosphorylation by p21-activated
kinase 2 and effects of phosphorylation on merlin localization,
J Biol Chem, 277(12): 10394–10399, 2002.
[63] Louderbough JM, Lopez JI, Schroeder JA, Matrix hyaluronan
alters epidermal growth factor receptor-dependent cell mor-
phology, Cell Adh Migr, 4(1): 26–31, 2010.
[64] Brown RL et al., CD44 splice isoform switching in human
and mouse epithelium is essential for epithelial-mesenchymal
transition and breast cancer progression, J Clin Invest, 121(3):
1064–1074, 2011.
[65] Herrlich P et al., CD44 acts both as a growth- and
invasiveness-promoting molecule and as a tumor-suppressing
cofactor, Ann N Y Acad Sci, 910: 106–118, 2000.
[66] Lubahn DB et al., Sequence of the intron/exon junctions of
the coding region of the human androgen receptor gene and
identification of a point mutation in a family with complete
androgen insensitivity, Proc Natl Acad Sci, 86(23): 9534–
9538, 1989.
[67] Olsen JR et al., Context dependent regulatory patterns of the
androgen receptor and androgen receptor target genes, BMC
Cancer, 16(1): 377, 2016.
[68] Toocheck C et al., Mouse spermatogenesis requires classical
and nonclassical testosterone signaling, Biology of Reproduc-
tion, 94(1): 11, 2016. 1–14.
[69] Davis S, Androgen replacement in women: a commentary,
The Journal of Clinical Endocrinology & Metabolism, 84(6):
1886–1891, 1999.
[70] Simpson E, Role of aromatase in sex steroid action, J Mol
Endocrinol, 25(2): 149–156, 2000.
[71] Somboonporn W, Bell RJ, Davis SR, Testosterone for peri
and postmenopausal women, Cochrane Database Systematic
Reviews (4), 2005.
[72] Niemeier LA et al., Androgen receptor in breast cancer:
expression in estrogen receptor-positive tumors and in estro-
gen receptor-negative tumors with apocrine differentiation,
Modern Pathology, 23(2): 205, 2010.
[73] Collins LC et al., Androgen receptor expression in breast
cancer in relation to molecular phenotype: results from the
Nurses’ Health Study, Modern Pathology, 24(7): 924, 2011.
[74] Huo L, Androgen receptor expression in breast cancer in rela-
tion to molecular phenotype: results from the Nurses’ Health
Study: Collins LC, Cole KS, Marotti JD, et al (Beth Israel
Deaconess Med Ctr and Harvard Med School, Boston, MA;
Dartmouth-Hitchcock Med Ctr, Lebanon, NH) Mod Pathol
24: 924–931, 2011 §, Breast Diseases: A YB Quarterly, 23(2):
155–156, 2012.
uncorrected proof version
11N. Al-Othman etal./Role of CD44 in breast cancer
[75] Park S et al., Androgen receptor expression is significantly
associated with better outcomes in estrogen receptor-positive
breast cancers, Ann Oncol, 22(8): 1755–1762, 2011.
[76] Asano Y et al., Expression and clinical significance of andro-
gen receptor in triple-negative breast cancer, Cancers, 9(1): 4,
2017.
[77] Mohammadizadeh F et al., Androgen receptor expression and
its relationship with clinicopathological parameters in an Ira-
nian population with invasive breast carcinoma, Adv Biomed
Res, 3, 2014.
[78] Ingle JN et al., Combination hormonal therapy with tamox-
ifen plus fluoxymesterone versus tamoxifen alone in post-
menopausal women with metastatic breast cancer. An updated
analysis, Cancer, 67(4): 886–891, 1991.
[79] Lehmann BD et al., Identification of human triple-negative
breast cancer subtypes and preclinical models for selection of
targeted therapies, J Clin Invest, 121(7): 2750–2767, 2011.
[80] Gucalp A et al., Phase II trial of bicalutamide in patients
with androgen receptor–positive, estrogen receptor–negative
metastatic breast cancer, Clin Cancer Res, 19(19): 5505–
5512, 2013.
[81] Elebro K et al., Combined androgen and estrogen receptor
status in breast cancer: treatment prediction and prognosis
in a population-based prospective cohort, Clin Cancer Res,
21(16): 3640–3650, 2015.
[82] Christodoulatos GS, Dalamaga M, Micro-RNAs as clinical
biomarkers and therapeutic targets in breast cancer: Quo
vadis?, World J Clin Oncol, 5(2): 71, 2014.
[83] Shi G-M et al., Identification of side population cells in human
hepatocellular carcinoma cell lines with stepwise metastatic
potentials, J Cancer Res Clin Oncol, 134(11): 1155, 2008.
[84] Östling P et al., Systematic analysis of microRNAs targeting
the androgen receptor in prostate cancer cells, Cancer Res,
71(5): 1956–1967, 2011.
[85] Shu J et al., Dynamic and modularized microRNA regulation
and its implication in human cancers, Sci Rep, 7(1): 13356,
2017.
[86] Rutnam ZJ, Yang BB, The non-coding 3′UTR of CD44
induces metastasis by regulating extracellular matrix func-
tions, J Cell Sci, 125(8): 2075–2085, 2012.
[87] Subtil FS et al., Carbon ion radiotherapy of human lung
cancer attenuates HIF-1 signaling and acts with considerably
enhanced therapeutic efficiency, FASEB J, 28(3): 1412–1421,
2014.
[88] Esteller M, Non-coding RNAs in human disease, Nature Rev
Genet, 12(12): 861, 2011.
[89] Spizzo R et al., Long non-coding RNAs and cancer: a new
frontier of translational research?, Oncogene, 31(43): 4577,
2012.
[90] Mendell JT, Olson EN, MicroRNAs in stress signaling and
human disease, Cell, 148(6): 1172–1187, 2012.
[91] Vasudevan S, Tong Y, Steitz JA, Switching from repression to
activation: microRNAs can up-regulate translation, Science,
318(5858): 1931–1934, 2007.
[92] Lu J et al., MicroRNA expression profiles classify human
cancers, Nature, 435(7043): 834, 2005.
[93] Zhu J et al., Different miRNA expression profiles between
human breast cancer tumors and serum, Front Genet, 5: 149,
2014.
[94] Waltering KK et al., Androgen regulation of micro- RNAs in
prostate cancer, The Prostate, 71(6): 604–614, 2011.
[95] Murata T et al., miR-148a is an androgen-responsive
microRNA that promotes LNCaP prostate cell growth by
repressing its target CAND1 expression, Prostate Cancer and
Prostatic Diseases, 13(4): 356, 2010.
[96] Fletcher CE et al., Androgen-regulated processing of the
oncomir miR-27a, which targets Prohibitin in prostate cancer,
Hum Mol Genet, 21(14): 3112–3127, 2012.
[97] Mo W et al., Identification of novel AR-targeted microR-
NAs mediating androgen signalling through critical pathways
to regulate cell viability in prostate cancer, PloS one, 8(2):
e56592, 2013.
[98] Ribas J et al., miR-21: an androgen receptor–regulated
microRNA that promotes hormone-dependent and hormone-
independent prostate cancer growth, Cancer Res, 69(18):
7165–7169, 2009.
[99] Takayama K et al., Integration of cap analysis of gene expres-
sion and chromatin immunoprecipitation analysis on array
reveals genome-wide androgen receptor signaling in prostate
cancer cells, Oncogene, 30(5): 619, 2011.
[100] Jalava S et al., Androgen-regulated miR-32 targets BTG2
and is overexpressed in castration-resistant prostate cancer,
Oncogene, 31(41): 4460, 2012.
[101] Kroiss A et al., Androgen-regulated microRNA-135a
decreases prostate cancer cell migration and invasion through
downregulating ROCK1 and ROCK2, Oncogene, 34(22):
2846, 2015.
[102] Garofalo M et al., miR221/222 in cancer: their role in tumor
progression and response to therapy, Curr Mol Med, 12(1):
27–33, 2012.
[103] Gui B et al., Androgen receptor-mediated downregulation of
microRNA-221 and-222 in castration-resistant prostate can-
cer, PloS One, 12(9): e0184166, 2017.
[104] Ambs S et al., Genomic profiling of microRNA and messenger
RNA reveals deregulated microRNA expression in prostate
cancer, Cancer Res, 68(15): 6162–6170, 2008.
[105] Gao L, Alumkal J, Epigenetic regulation of androgen receptor
signaling in prostate cancer, Epigenetics, 5(2): 100–104, 2010.
[106] Shih J-W et al., Non-coding RNAs in castration-resistant
prostate cancer: regulation of androgen receptor signaling
and cancer metabolism, Int J Mol Sci, 16(12): 28943–28978,
2015.
[107] Hagman Z et al., miR-205 negatively regulates the androgen
receptor and is associated with adverse outcome of prostate
cancer patients, Br J Cancer, 108(8): 1668, 2013.
[108] Nadiminty N et al., MicroRNA let-7c suppresses androgen
receptor expression and activity via regulation of Myc expres-
sion in prostate cancer cells, J Biol Chem, 287(2): 1527–1537,
2012.
[109] Epis MR et al., miR-331-3p regulates ERBB-2 expression and
androgen receptor signaling in prostate cancer, J Biol Chem,
284(37): 24696–24704, 2009.
[110] Sikand K et al., miR 488* inhibits androgen receptor expres-
sion in prostate carcinoma cells, Int J Cancer, 129(4): 810–
819, 2011.
[111] Gong A-Y et al., miR-17-5p targets the p300/CBP-associated
factor and modulates androgen receptor transcriptional activ-
ity in cultured prostate cancer cells, BMC Cancer, 12(1): 492,
2012.
[112] Al-Othman N, Hammad H, Ahram M, Dihydrotestosterone
regulates expression of CD44 via miR-328-3p in triple-
negative breast cancer cells, Gene, 675: 128–135, 2018.
[113] Smith SM, Cai L, Cell specific CD44 expression in breast
cancer requires the interaction of AP-1 and NFkappaB with
a novel cis-element, PLoS One, 7(11): 30, 2012.
[114] Olsson E et al., CD44 isoforms are heterogeneously expressed
in breast cancer and correlate with tumor subtypes and cancer
stem cell markers, BMC Cancer, 11(1): 418, 2011.
uncorrected proof version
12 N. Al-Othman etal./Role of CD44 in breast cancer
[115] Lesley J et al., Hyaluronan binding by cell surface CD44, J
Biol Chem, 275(35): 26967–26975, 2000.
[116] Skelton TP et al., Glycosylation provides both stimulatory and
inhibitory effects on cell surface and soluble CD44 binding to
hyaluronan, J Cell Biol, 140(2): 431–446, 1998.
[117] Zohar R et al., Intracellular osteopontin is an integral compo-
nent of the CD44- ERM complex involved in cell migration,
J Cell Physiol, 184(1): 118–130, 2000.
[118] G.T.H.G. Database, GeneCards®: The Human Gene
Database, 2019. [cited 2019; Available from:
https://www.genecards.org.
[119] Bourguignon LY et al., Hyaluronan-CD44 interaction with
protein kinase C𝜖promotes oncogenic signaling by the stem
cell marker Nanog and the production of microRNA-21,
leading to down-regulation of the tumor suppressor protein
PDCD4, anti-apoptosis, and chemotherapyresistance in breast
tumor cells, J Biol Chem, 284(39): 26533–26546, 2009.
[120] Yang Z et al., MicroRNA- 143 targets CD44 to inhibit breast
cancer progression and stem cell-like properties, Mol Med
Rep, 13(6): 5193–5199, 2016.
[121] Li J et al., Suppressing role of miR-520a-3p in breast cancer
through CCND1 and CD44, American Journal of Transla-
tional Research, 9(1): 146, 2017.
[122] Bennett KL et al., Regulation of CD44 binding to hyaluronan
by glycosylation of variably spliced exons, J Cell Biol, 131(6):
1623–1633, 1995.
[123] Milstone LM et al., Epican, a heparan/chondroitin sulfate
proteoglycan form of CD44, mediates cell-cell adhesion, J
Cell Sci, 107(11): 3183–3190, 1994.
[124] Kurz SM et al., The impact of c- met/scatter factor receptor on
dendritic cell migration, Eur J Immunol, 32(7): 1832–1838,
2002.
[125] Cheng C, Sharp PA, Regulation of CD44 alternative splicing
by SRm160 and its potential role in tumor cell invasion, Mol
Cell Biol, 26(1): 362–370, 2006.
[126] Sleeman JP et al., Variant exons v6 and v7 together expand
the repertoire of glycosaminoglycans bound by CD44, J Biol
Chem, 272(50): 31837–31844, 1997.
[127] Lee J-L et al., Osteopontin promotes integrin activation
through outside-in and inside-out mechanisms: OPN-CD44V
interaction enhances survival in gastrointestinal cancer cells,
Cancer Res, 67(5): 2089–2097, 2007.
[128] Kuhn S et al., A complex of EpCAM, claudin-7, CD44 variant
isoforms, and tetraspanins promotes colorectal cancer pro-
gression, Mol Cancer Res, 5(6): 553–567, 2007.
[129] Kuniyasu H et al., Heparan sulfate enhances invasion by
human colon carcinoma cell lines through expression of CD44
variant exon 3, Clin Cancer Res, 7(12): 4067–4072, 2001.
[130] Yamaguchi A et al., Expression of a CD44 variant containing
exons 8 to 10 is a useful independent factor for the prediction
of prognosis in colorectal cancer patients, J Clin Oncol, 14(4):
1122–1127, 1996.
[131] Ozawa M et al., Prognostic significance of CD44 variant 2
upregulation in colorectal cancer, Br J Cancer, 111(2): 365,
2014.
[132] Pirinen R et al., Reduced expression of CD44v3 variant iso-
form is associated with unfavorable outcome in non–small cell
lung carcinoma, Hum Pathol, 31(9): 1088–1095, 2000.
[133] Mizera-Nyczak E et al., Isoform expression of CD44 adhesion
molecules, Bcl-2, p53 and Ki-67 proteins in lung cancer,
Tumor Biol, 22(1): 45–53, 2001.
[134] Zhao S et al., Prognostic value of CD44 variant exon 6 expres-
sion in non-small cell lung cancer: a meta-analysis, Asian Pac
J Cancer Prev, 15(16): 6761–6766, 2014.
[135] Ruibal Á et al., Cell membrane CD44v6 levels in squamous
cell carcinoma of the lung: association with high cellular
proliferation and high concentrations of EGFR and CD44V5,
Int J Mol Sci, 16(3): 4372–4378, 2015.
[136] Miyoshi T et al., The expression of the CD44 variant exon 6 is
associated with lymph node metastasis in non-small cell lung
cancer, Clin Cancer Res, 3(8): 1289–1297, 1997.
[137] Jiang H, Zhao W, Shao W, Prognostic value of CD44
and CD44v6 expression in patients with non-small cell
lung cancer: meta-analysis, Tumor Biol, 35(8): 7383–7389,
2014.
[138] Kaufmann M et al., CD44 variant exon epitopes in primary
breast cancer and length of survival, The Lancet, 345(8950):
615–619, 1995.
[139] Tempfer C et al., Prognostic value of immunohistochemically
detected CD44 isoforms CD44v5, CD44v6 and CD44v7–8
in human breast cancer, Eur J Cancer, 32(11): 2023–2025,
1996.
[140] Rys J et al., The role of CD44v3 expression in female breast
carcinomas, Pol J Pathol, 54(4): 243–247, 2003.
[141] Bendall L, Gottlieb D, CD44 and adhesion of normal and
leukemic CD34+ cells to bone marrow stroma, Leukemia &
Lymphoma, 32(5–6): 427–439, 1999.
[142] Legras S et al., A strong expression of CD44-6v correlates
with shorter survival of patients with acute myeloid leukemia,
Blood, 91(9): 3401–3413, 1998.
[143] Rall CJ, Rustgi AK, CD44 isoform expression in primary and
metastatic pancreatic adenocarcinoma, Cancer Res, 55(9):
1831–1835, 1995.
[144] Gansauge F et al., Differential expression of CD44 splice
variants in human pancreatic adenocarcinoma and in normal
pancreas, Cancer Res, 55(23): 5499–5503, 1995.
[145] Gotoda T et al., Expression of CD44 variants and its associ-
ation with survival in pancreatic cancer, Cancer Sci, 89(10):
1033–1040, 1998.
[146] Li Z et al., CD44v/CD44s expression patterns are associated
with the survival of pancreatic carcinoma patients, Diagn
Pathol, 9(1): 79, 2014.
[147] Kiuchi S et al., Pancreatic cancer cells express CD44
variant 9 and multidrug resistance protein 1 during
mitosis, Experimental and Molecular Pathology, 98(1):
41–46, 2015.
[148] Reategui EP et al., Characterization of CD44v3 containing
isoforms in head and neck cancer, Cancer Biol Ther, 5(9):
1163–1168, 2006.
[149] Wang SJ et al., CD44 variant isoforms in head and neck squa-
mous cell carcinoma progression, The Laryngoscope, 119(8):
1518–1530, 2009.
[150] Wang SJ, Wreesmann VB, Bourguignon LY, Association of
CD44 V3- containing isoforms with tumor cell growth, migra-
tion, matrix metalloproteinase expression, and lymph node
metastasis in head and neck cancer, Head & Neck, 29(6): 550–
558, 2007.
[151] Kawano T et al., Expression of E-cadherin, and CD44s and
CD44v6 and its association with prognosis in head and neck
cancer, Auris Nasus Larynx, 31(1): 35–41, 2004.
[152] Slevin M et al., Hyaluronan-mediated angiogenesis in vascular
disease: uncovering RHAMM and CD44 receptor signaling
pathways, Matrix Biol, 26(1): 58–68, 2007.
[153] Huang Q et al., The microRNAs miR-373 and miR-520c
promote tumour invasion and metastasis, Nature Cell Biol,
10(2): 202, 2008.
[154] Liu C et al., Identification of miR-34a as a potent inhibitor
of prostate cancer progenitor cells and metastasis by directly
repressing CD44, Nature Med, 17(2): 211–215, 2011.
