Pharmacological Research 60 (2009) 466–474
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The physiological and pathophysiological role of PRMT1-mediated protein
Thomas B. Nicholsona, Taiping Chena, Stéphane Richardb,∗
aDevelopmental and Molecular Pathways, Novartis Institutes for Biomedical Research, 250 Massachusetts Avenue, Cambridge, MA 02139, USA
bTerry Fox Molecular Oncology Group and the Bloomfield Center for Research on Aging, Segal Cancer Centre, Lady Davis Institute for Medical Research,
Sir Mortimer B. Davis Jewish General Hospital, and Departments of Oncology and Medicine, McGill University, Montréal, Québec, Canada H3T 1E2
a r t i c l e i n f o
Received 21 April 2009
Received in revised form 20 July 2009
Accepted 21 July 2009
a b s t r a c t
Post-translational modifications are well-known effectors in DNA damage signaling and epigenetic gene
expression. Protein arginine methylation is a covalent modification that results in the addition of methyl
groups to the nitrogen atoms of the arginine side chains and is catalyzed by a family of protein arginine
such as RNA-binding proteins and histones, but recent advances have revealed a plethora of arginine-
methylated proteins implicated in a variety of cellular processes including signal transduction, epigenetic
regulation and DNA repair pathways. Herein, we discuss these recent advances, focusing on the role of
PRMT1, the major asymmetric arginine methyltransferase, in cellular processes and its link to human
© 2009 Elsevier Ltd. All rights reserved.
Protein arginine methylation ........................................................................................................................
The PRMT family .....................................................................................................................................
PRMT1, the major asymmetric arginine MTase...................................................................................................... 468
PRMT1 substrates ....................................................................................................................................
Arginine methylation and disease ...................................................................................................................
PRMT1 inhibitors..................................................................................................................................... 471
Conclusions and future directions ...................................................................................................................
1. Protein arginine methylation
Post-translational protein modifications, including phosphory-
lation, methylation, ubiquitylation, sumoylation, and lipidation,
play key regulatory roles in determining enzyme/substrate speci-
onine; AMI, arginine methylase inhibitor; BTG, B-cell translocation gene; CARM1,
coactivator-associated arginine methyltransferase 1; GAR, glycine and arginine rich;
IFN, interferon; MMA, NG-monomethylarginine; MTase, methyltransferase; PRMT,
protein arginine N-methyltransferase; SAHase, S-adenosyl-l-homocysteine hydro-
lase; SDMA, NG,N?G-dimethylarginine; STAT, signal transducer and activator of
transcription; TCR, T-cell receptor.
∗Corresponding author at: Segal Cancer Centre, 3755 Côte Ste.-Catherine Road,
Montréal, Québec, Canada H3T 1E2. Tel.: +1 514 340 8260; fax: +1 514 340 8295.
E-mail address: email@example.com (S. Richard).
ADMA, NG,NG-dimethylarginine; AdoMet, S-adenosylmethi-
ficity, protein localization and stability. The biological roles of these
various modifications differ greatly, depending on the type of alter-
ation and the substrate being modified, allowing for a diversity
of effects for each post-translational modification. The addition
of methyl groups to various cellular substrates is gaining greater
appreciation as a widespread process, as it has been found to occur
on both DNA and proteins. DNA methylation generally occurs on
cytosines, and is associated with gene imprinting and silencing
[1,2]. Protein methylation can occur on both lysine and arginine
residues, offering a wide range of potential substrates in the cell,
including histones, RNA-binding proteins, and DNA damage regu-
S-Adenosylmethionine (AdoMet) is the methyl donor for the
methyltransferases (MTases). The enzymes that use AdoMet in this
manner have been classified into three separate categories . The
largest group (Class I) share a common ?-sheet structure, which
1043-6618/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
T.B. Nicholson et al. / Pharmacological Research 60 (2009) 466–474
is known as the AdoMet-dependent MTase-fold and is contained
in MTases that methylate DNA, RNA and proteins . The second
set of MTase enzymes (Class II) consists of the SET lysine MTases,
which share a common domain (the SET domain, so named due to
its presence in Su(var)3-9, Enhancer of zeste (E[z]), and trithorax)
of 130 amino acids with a large set of proteins that function to
ciated with the membrane such as the isoprenylcysteine carboxy
MTases . A subset of the Class I family is the protein arginine
N-MTases (PRMTs), whose members methylate proteins on argi-
nine residues. The PRMT family shares several conserved motifs
otes, especially in a core region of approximately 310 amino acids
that is involved in catalyzing the enzymatic activity of this family
. The non-core amino acids are most likely involved in substrate
specification and activity regulation. Arginines can be methy-
lated in three separate ways on the terminal guanidino nitrogen:
monomethylated (NG-monomethylarginine; MMA), symmetrically
dimethylated (NG,N?G-dimethylarginine; SDMA) and asymmetri-
cally dimethylated (NG,NG-dimethylarginine; ADMA) (Fig. 1). Each
Fig. 1. The methylation and demethylation of arginines. (A) Methylation of arginine proceeds by the addition of a methyl group, donated from AdoMet, to one ofthe guanidino
amino groups of arginine, generating monomethylarginine. Type I PRMT enzymes catalyze the formation of asymmetric DMA through the addition of a second methyl group
to the same nitrogen. Symmetric DMA is generated by type II PRMTs, which catalyze the addition of a methyl group to the other terminal nitrogen of the arginine. (B)
Monomethylarginine can be ‘demethylated’, via the process of deimination, by the enzyme PAD4, leading to the removal of methylamine and the generation of citrulline. The
conversion of citrulline to arginine then occurs via a currently unknown mechanism. (C) Specific demethylation of methylarginine may be catalyzed by JMJD6, an enzyme
that was also shown to hydroxylate lysine residues.
T.B. Nicholson et al. / Pharmacological Research 60 (2009) 466–474
of these arginine modifications leads to different functional out-
Arginine methylation impinges on multiple cellular processes,
including chromatin structure, signal transduction, transcriptional
regulation, RNA metabolism, and DNA damage repair [8,9]. Pro-
teomic analyses have revealed the existence of >200 proteins that
post-translational modification, as there are enzymes that likely
remove this modification (Fig. 1). Thus, arginine methylation may
represent a rapid modification of protein function. The study of
residues, where lysine-specific demethylase 1 (LSD1) and proteins
containing a JmjC-domain have been characterized as demethy-
lases of lysines . Arginine methylation is likely reversible and
one proposed candidate is the JmjC enzyme, JMJD6 ; how-
ever, recent data show that it is a lysine hydroxylase for U2AF65
. Similarly, the conversion of arginines to citrulline, in a pro-
cess known as deimination, antagonizes methylation by altering
lated [15,16]. Deimination can also occur on methylated arginines
found in histones, providing another mechanism for the removal of
methyl groups in a coordinated fashion [15,16]. The ability of the
cell to demethylate arginine residues is required for the dynamic
regulation of this modification.
As the roles of PRMTs continue to be better understood many
processes affected by arginine methylation are emerging. This
review will summarize the current knowledge regarding PRMT1
and the functional implications of methylation. We will explore
several emerging properties of PRMT1, including its role in signal
pathway. Furthermore, PRMT1 is beginning to be recognized as an
important player in several diseases, both in terms of its enzymatic
activity and its key role in the regulation of the metabolite, ADMA.
The use of PRMT1 inhibitors in the treatment and prevention of
several human diseases will also be discussed.
2. The PRMT family
There exist 11 members of the mammalian PRMT family (Fig. 2).
matic activity, while PRMT2, -10 and -11 have yet to be shown to
have enzymatic activity [8,17]. The PRMT family can be divided
into two major groups, type I and type II. Type I enzymes, which
Fig. 2. Schematic representation of the PRMT family. The 11 members of the PRMT
family are shown graphically, with key structural features of each protein indicated.
All members of the family contain a conserved catalytic domain. PRMT2 contains
an SH3 domain, while PRMT3 and PRMT9 contain zinc finger domains (Zn). PRMT9
also contains an F-box, while PRMT8 is myristoylated at its N-terminus.
include PRMT1, -2, -3, -4, -6, and -8, catalyze the addition of two
methyl groups to the same terminal nitrogen group of arginine,
generating ADMA . Conversely, type II enzymes (PRMT5, -7 and
-9, and F-box protein (FBXO) 11) add the second methyl group
to the other terminal nitrogen, generating SDMA. The dimethy-
lation of arginine by both type I and type II enzymes proceeds
through the generation of a monomethyl arginine intermediate.
The in vivo requirement for PRMT activity has been examined by
generating knockout mice lacking various members of the family.
As discussed in Section 3, the knockout of PRMT1 in mice results
in embryonic lethality [18,19]. PRMT2 mice are normal, despite
the observed interaction between PRMT2 and retinoblastoma (Rb)
and the dysregulation of E2F in knockout mouse embryonic fibrob-
lasts (MEFs) . Similarly, PRMT3 knockout mice are normal as
adults, although embryos are smaller during development and
the PRMT3 substrate ribosomal protein S2 (rpS2) is hypomethy-
lated . PRMT4 (also known as coactivator-associated arginine
methyltransferase 1, CARM1) knockout mice are smaller than their
littermates, have no methylation of CARM1-specific targets and die
soon after birth . These studies demonstrate the key role of
PRMT1 and CARM1 during mouse development. Excellent reviews
were recently written that cover all the PRMTs [8,9,23] and hence
the present manuscript will review the recent literature on PRMT1
and its link to certain diseases.
3. PRMT1, the major asymmetric arginine MTase
PRMT1 is thought to contribute to as much as 85% of all cellu-
lar PRMT activity . The PRMT1 mRNA is found in all embryonic
and adult tissues examined, demonstrating the widespread impor-
tance of this enzyme in cellular functions . The prmt1 gene is
composed of 12 coding exons , which are spliced into 7 differ-
ent isoforms . These isoforms vary in their N-terminal domain,
including one that contains a nuclear export sequence, and shows
a different catalytic activity and substrate specificity . These
To study PRMT1 activity in vivo, knockout mice were generated by
gene entrapment, resulting in the reduction of PRMT1 expression
indicating that PRMT1 is required during early development .
Embryonic stem (ES) cells generated from these mice are viable,
although they exhibit a significant decrease in protein arginine
methylation. Recently, we generated conditional PRMT1 knockout
MEFs by Cre-mediated recombination that showed hypomethyla-
tion of several proteins, as well as compromised cell survival and
DNA damage response signaling . Saccharomyces cerevisiae cells
lacking the PRMT1 homolog Hmt1/Rmt1 are viable, indicating that
PRMT1 is not essential for cell survival in yeast [28,29]. However,
the mislocalization of proteins within the cell  and chromatin
at glycine and arginine rich (GAR) motifs ; however, other pro-
tein motifs that can be methylated have recently been identified,
where the residues N-terminal to the arginine are also involved
in substrate recognition . This may be a major mechanism for
determining substrate identity, as the different abilities of PRMT1,
-3 and -6 to methylate specific arginines appears to reside in the
amino acids surrounding the arginine .
The activity of PRMT1 can be regulated in several fashions.
PRMT1 is present in both the cytoplasm and the nucleus, and is
highly mobile between these compartments . Its localization
may be regulated in part by associated proteins, as the pregnane
X receptor (PXR) can alter the localization of PRMT1, resulting in
its accumulation in the nucleus . PRMT1 activity is also stimu-
lated by binding to other proteins, such as B-cell translocation gene
T.B. Nicholson et al. / Pharmacological Research 60 (2009) 466–474
1 (BTG1), TIS2/BTG2 and CCR4-associated factor 1 (hCAF1) [36,37],
originally demonstrated to modulate the function of PRMT1 by
. Depletion of BTG2 leads to a specific decrease in methylated
arginines in the nucleus, but not the cytoplasm . This suggests
that modulators of PRMT1 function are present in different cellular
compartments. One of the first PRMT1 substrates to be identified
was interleukin enhancer binding factor 3 (ILF3), which binds to
PRMT1 and is its substrate . In turn, ILF3 appears to regulate
the activity of PRMT1 towards other substrates, suggesting that
a feedback loop exists between these proteins. A loss of PRMT1
oligomerization results in a decreased ability to function as both a
coactivator and a MTase, although monomeric PRMT1 also showed
elevated binding to other coactivators, increasing their function
. For example, binding between PRMT1 and the orphan nuclear
receptor TR3 does not lead to methylation, but stabilizes TR3 by
protecting it from degradation, increasing its expression level and
its activity . Interestingly, this study also demonstrated that
the binding between these proteins inhibits PRMT1 MTase activ-
ity, decreasing the methylation of several downstream substrates.
The PRMT family member CARM1 is phosphorylated, resulting in
modified in a rapid manner by phosphorylation . In summary,
a major mechanism by which the activity of PRMT1 is modulated
appears to be via its association with other proteins, which can
modulate both its activity and localization.
4. PRMT1 substrates
regulating gene expression . PRMT1 specifically dimethylates
histone H4 at arginine 3 (H4R3) [47,48]. In yeast cells Hmt1/Rmt1 is
involved in the maintenance of silent chromatin , while studies
involving the mammalian PRMT1 have shown mainly a coactivator
function for PRMT1 [49,50]. However, arginine methylation marks
on histones are either associated with gene repression and activa-
tion. The exact effect of protein arginine methylation depends on
the integration of methyl marks with other marks such as methy-
lated, acetylated or ubiquitinylated lysines. Addition of ADMA to
histones by PRMT1 and CARM1 generally serves as an activation
signal, while with the addition of SDMA to histones by PRMT5 is
suggested that PRMT1 and CARM1 can be also involved in gene
repression , indicating that the effect of PRMT1 modification
of histones is context-specific. Thus, one of the key functions of
PRMT1 is the regulation of transcription, and the correct spatio-
interactions with various transcription factors, including p53 
and YY1 . Moreover, p53 is arginine-methylated and this serves
to modulate p53-mediated gene expression . The recruitment
of PRMT1 is a dynamic process, as activation of the thyroid hor-
mone (T3) receptor (TR) results in transient association of PRMT1
with T3 response elements (TRE), serving as a coactivator of tran-
scription. Binding to these various transcription factors results in
the regulated recruitment of PRMT1 to specific genomic regions,
leading to alterations in histone methylation patterns that then
result in gene expression changes. Arginine methylation occurs on
other proteins with roles in transcription, including coactivators
[55,56], transcriptional elongation factors , and splicing fac-
tors [58,59]. The PRMT1-mediated methylation of TAF15, a nuclear
RNA-binding protein with gene regulatory functions, affects both
its subcellular localization and its activity . Methylation of the
transcription elongation factor SPT5 by PRMT1 regulates both its
promoter association and its interaction with RNA polymerase II
, while methylation of forkhead box O1 (FOXO1) blocks AKT-
mediated phosphorylation of this transcription factor, resulting in
its nuclear exclusion and degradation . The arginine methy-
lation of certain transcription factors regulates their activity and,
thus, PRMT1 is involved numerous levels to fine-tune the expres-
sion of various genes.
alter the cellular localization of its substrates [8,9,62]. For example,
Sam68 is an adaptor for Src kinases which contains proline-rich
regions that interact with the src-homology 3 (SH3) and WW
domains of several proteins . These proline-rich domains are
flanked by RG repeats, which were shown to be methylated by
PRMT1 [27,64]. Interestingly, this results in a selective decrease
in binding to SH3, but not WW, domains, allowing for the mod-
ulation of specific protein–protein interactions . PRMT1 adds
methyl groups to Arg296 and Arg299 of heterogeneous nuclear
ribonucleoprotein complex K (hnRNP K), which are present near
the SH3-binding domain of this protein, and as such may alter
its protein–protein interactions, in particular with Src family pro-
teins [65,66]. It has also been demonstrated that the survival
of motor neurons protein (SMN), which acts to assemble small
nuclear ribonucleoproteins (snRNPs), exhibits stronger binding to
the snRNP proteins SmD1 and SmD3 when these proteins contain
SDMA . Survival motor neuron (SMN) contains a Tudor domain,
which mediates its interaction with Sm proteins . The bind-
ing of Tudor domains to SDMA containing RG domains was then
expanded to encompass the splicing factor 30kDa (SPF30) and the
Tudor domain-containing 3 (TDRD3) proteins . Thus, arginine
methylation appears to play a role in determining protein–protein
interactions through several domains.
Arginines are present in nucleic acid binding domains and
have the potential to alter ionic interactions and hydrogen bond-
ing opportunities . Addition of a methyl group may prevent
hydrogen bonding, due to steric hindrance, or it may enhance van
der Waals interactions due to the increased hydrophobicity of the
arginine . There are a few examples, where the methylation
has been shown to influence association with RNA. For example,
PRMT1 methylation of Sam68 reduces its ability to bind to poly-
U sequences in RNA , the physiological significance of which
remains to be determined. PRMT1 binds directly to hnRNP K, and
may be involved in regulating the numerous functions of this pro-
tein, including regulating gene and protein expression, and serving
as a coactivator and a transactivator [66,72]. The activity of the
protein fragile X mental retardation syndrome 1 homolog (FMR1),
lation, is regulated by PRMT1-mediated methylation . These
by modifying protein–RNA interactions.
Arginine methylation is also involved in signaling downstream
of several receptors, including the T-cell receptor (TCR), cytokine
receptors, nerve growth factor (NGF) receptors, the interferon
receptor, the insulin receptor and various nuclear receptors .
Treating cells with insulin was reported to translocate PRMT1
to the plasma membrane, where it methylates several proteins
. Knock-down of PRMT1 expression by siRNA attenuates the
signaling cascade from the insulin receptor (IR), suggesting that
PRMT1 is a positive regulator of IR function . Methylation
of the estrogen receptor alpha (ER?) is required for its interac-
tion with phosphatidylinositol-3-kinase (PI3K) and Src and the
recruitment of focal adhesion kinase (FAK), leading to downstream
signaling . PRMT1 interacts with the cytoplasmic domain of
the interferon (IFN) receptor, and knock-down of PRMT1 by anti-
sense oligonucleotides interferes with the biological function of
this receptor . Upon ligand binding, the farnesoid X receptor
(FXR) nuclear receptor binds to PRMT1 and recruits it to specific
T.B. Nicholson et al. / Pharmacological Research 60 (2009) 466–474
DNA regions, leading to upregulation of gene expression through
H4R3 methylation . PGC-1? is a coactivator of nuclear recep-
tors, and methylation by PRMT1 is required for its ability to induce
target genes . PRMT1 regulates the orphan nuclear receptor
HNF4 by two mechanisms: the arginine methylation of the hep-
atocyte nuclear factor 4 (HNF4) DNA-binding domain increases its
binding affinity, while DNA-bound HNF4 recruits PRMT1 to sites of
activation, where PRMT1 generates asymmetric dimethylarginine
at H4R3 to increase transcription .
PRMT1 plays a role in TCR signaling, as well as signaling via the
IFN-STAT (signal transducer and activator of transcription) path-
way . In T cells, the arginine methylation was reported to be
necessary for the function of NIP45, a cofactor for NFAT (nuclear
factor of activated T cells) . This methylation regulates NIP45-
NFAT protein–protein interactions, enhancing the transcription of
several cytokines that are important for the humoral immune
tion of IFN?-inducible STAT1 target genes through effects on PIAS1
(protein inhibitor of activated STAT1) . PRMT1 was shown to
methylate PIAS1, resulting in the recruitment of this protein to spe-
cific promoters and the release of STAT1, a mechanism to terminate
transcription. The generation of a conditional allele of PRMT1 in
mice  will define the role of arginine methylation and its sub-
strates in lymphocytes.
Arginine methylation is required for double-strand DNA break
(DSBs) repair . DNA damage results in a complex cellular
signaling and repair of the DNA breaks . The initial response to
DSBs requires the orderly recruitment of many proteins including
protein kinases, sensors and adaptor molecules that will mediate
the signaling of DNA damage and its repair . One of the first
steps consists in the phosphorylation of a multitude of targets by
the PI3K-like kinase (PIKK) family members ataxia telangiectasia
mutated homolog (ATM), ataxia telangiectasia and Rad3 related
(ATR) and DNA-protein kinase (DNA-PK) . Immediately follow-
ing DNA damage, histone H2AX becomes phosphorylated by PIKK
on serine 139 surrounding the DNA breaks , which is followed
by the recruitment of several DNA damage response factors such
as mediator of DNA-damage checkpoint 1 (MDC1) , ring fin-
ger protein 8 (RNF8) [89,90], MRE11-NBS1-RAD50 (MRN) complex
[91,92], breast cancer 1 (BRCA1) , and 53BP1 . This well-
damage repair by non-homologous end joining (NHEJ) and homol-
ogous recombination (HR). Although DNA damage is induced with
chemotoxic agents like etoposide (a topoisomerase II inhibitor) or
?-irradiation it also occurs naturally in cells during replication fork
collapse , at telomeres  and during senescence [98–100].
ditional allele in mice leads to spontaneous DNA damage, cell cycle
progression delay, checkpoint defects, aneuploidy and polyploidy
. It was observed that the PRMT1 conditional knockout MEFs
had frequent aberrations, including a higher incidence of chromo-
some losses and gains with cells >90 chromosomes. The loss of
PRMT1 also resulted in the presence of several cells with unique
with centromeric fusions . These findings suggest that the loss
of PRMT1 leads to genomic instability.
PRMT1 likely methylates many proteins in the DNA damage
response pathway and two of its currently known substrates are
MRE11 and 53BP1 [83,101,102]. The proteomic identification of
the MRN complex with the antibody ASYM25 , suggested that
PRMT1 may be the enzyme responsible for MRE11 arginine methy-
lation. Indeed, PRMT1 methylates the MRE11 GAR motif in vitro
and in vivo . Arginine methylation of MRE11 is required for
its localization to DNA damage foci and for proper regulation of
its exonuclease activity . We have shown that the GAR motif
is sufficient to target MRE11 to DNA damage foci . Further-
more, the deletion of PRMT1 in MEFs impairs the recruitment of
RAD51 to DNA damage foci . Using a candidate approach, we
damage response [101,104]. The GAR motif of 53BP1 is methylated
by PRMT1 and regulates its ability to associate with DNA  and
to oligomerize . Methylation of polymerase ? by PRMT6 was
shown to increase its repair activity of damaged DNA, implicating
of PRMT6 in DNA damage and whether it influences the cell cycle
checkpoints has not been assessed.
5. Arginine methylation and disease
Epigenetic modifications, such as changes in DNA methylation
patterns and histone alterations, play important roles in cancer
[1,2]. Given the prevalence of PRMT1 substrates in the cell, it is
highly probable that PRMT1 and arginine methylation is linked to
many disease (for a review see Bedford and Richard ). In prostate
cancer, the methylation of H4R3 predicts the risk of prostate cancer
recurrence . Similarly, a recent study of colon cancer patients
demonstrated that the expression of one of the splice variants of
PRMT1 is associated with several clinical and pathological param-
eters . In contrast, the relative levels of PRMT1 isoforms are
isoforms down-regulated [25,26]. Therefore, it appears that PRMT1
expression in cancer cells may be altered depending on the tumor
type. Studies are beginning to examine the specific role of PRMT1
in cancer. PRMT1 is an essential component of a Mixed Lineage
Leukaemia (MLL) transcriptional complex that modifies histones
by methylation, at H4R3, and acetylation . This serves as the
first demonstration of a direct role for PRMT1-mediated transcrip-
tional upregulation during cancer progression. With the diverse set
of PRMT1 interactions and substrates in the cell, it will be of great
importance to examine its role in tumor initiation and progression.
PRMT1 is gaining recognition as an important link with non-
cancer related disorders. PRMT1, as well as PRMT3 and PRMT6,
located near its C-terminus . This domain is involved in the
aggregation of the PABPN1 protein; abnormal aggregation of this
involved in amyotrophic lateral sclerosis (ALS), TLS/FUS, translo-
of cancer and TLS/FUS often contains mutated arginines in cer-
tain familial forms of this disease [110,111]. These mutants are
retained in the cytoplasm, which is similar to several reports docu-
shuffling [27,30,60,112]. This may implicate PRMT1 function in
this disease, a hypothesis that is strengthened by previous reports
demonstrating that TLS/FUS is methylated on at least 20 arginine
Furthermore, altered levels of circulating ADMA, which is pro-
duced by the proteolysis of asymmetrically dimethylated proteins,
have been implicated in numerous diseases. ADMA levels are
nous competitive inhibitor of nitric oxide synthase (NOS), reducing
the production of nitric oxide (NO) . Nitric oxide functions as
a potent vasodilator in endothelial vessels, and as such inhibiting
its production may have major consequences on the cardiovascular
system. Since PRMT1 is the major enzyme that generates ADMA,
the dysregulation of its activity is likely to regulate cardiovas-
cular diseases [115–117], and other pathophysiological conditions
such as diabetes mellitus [118,119], kidney failure [120–122] and
T.B. Nicholson et al. / Pharmacological Research 60 (2009) 466–474
chronic pulmonary diseases . It has been demonstrated that
the expression of PRMT1 and PRMT3 are increased in coronary
heart disease . This is accompanied by a decrease in dimethy-
larginine dimethylaminohydrolase (DDAH)2, an enzyme involved
which is hypothesized to explain the increased amounts of oxida-
tive stress seen in this condition. ADMA elevation is also seen
in patients with renal failure, due to impaired clearance of this
metabolite from the circulation . In decompensated alcoholic
ADMA levels . Thus, circulating ADMA levels is observed in
many pathophysiological situations.
6. PRMT1 inhibitors
Given the diversity of PRMT1 substrates, and the emerging
role of arginine methylation in human health, recent work has
attempted to design inhibitors that alter PRMT1 activity. The first
inhibitor of PRMT1 to be identified, in 1978, was sinefungin, which
functions as an analog of AdoMet . More recently, in vitro
lular MTases. One of these classes of inhibitors include those that
results in the accumulation of S-adenosyl-l-homocysteine in the
cytoplasm, leading to the inhibition of methylation via a feedback
mechanism. Initial experiments designed to test the pharmacolog-
ical effects of PRMT1 inhibition demonstrated that the irreversible
inhibition of SAHase blocks methylation in the cell and both pre-
these types of inhibitors are non-specific in their interactions with
MTases, resulting in many undesired secondary effects upon their
inhibitors is a key objective in the field. The crystal structure of the
rat homolog of PRMT1, in complex with AdoMet and a 19 amino
acid substrate peptide, was recently solved, which will allow for
a more focused design of PRMT1 inhibitors . Among the con-
clusions drawn from this structure was the absolute requirement
for dimerization of PRMT1 prior to binding of AdoMet. Two glu-
tamate residues located in the active site are absolutely required
for enzymatic activity, while there are three channels in PRMT1
that are involved in peptide binding. Recently, the kinetic mech-
anism by which PRMT1 functions has also been examined, with
the demonstration that PRMT1 functions through a partially pro-
cessive mechanism [128,129]. Having this structural and enzymatic
information has provided a basis for the design of specific PRMT1
inhibitors, as it will allow for the rational design of compounds that
act on PRMT1.
he first reported high-throughput screen (HTS) for PRMT1
inhibitors led to the identification of arginine methylase inhibitor
1 (AMI-1) . AMI-1 does not compete for AdoMet and was
shown in a cell-based assay to inhibit a reporter gene responsive
to nuclear receptors, where PRMT1 is known to function as a coac-
tivator . Subsequent to this study, a more targeted approach
was taken, where the structure of the rat PRMT1 was used to model
both the human and Aspergillus nidulans PRMT1 . A virtual
screen was then performed to identify putative PRMT1 inhibitors,
which led to the identification of several compounds with the abil-
ity to inhibit enzymatic activity. Furthermore, treatment of these
of estrogen receptor activation. This virtual screening method was
then expanded to identify nine inhibitors of PRMT1 . While
many of these compounds are aromatic and aliphatic amines were
similarly potent. This suggests that several molecular structures
may be active in inhibiting PRMT1 function. Using rationale drug
design with the privileged structures of the AMIs, several addi-
tional PRMT1 inhibitors were generated and their critical contact
sites determined by modeling . Moreover, a virtual screen for
PRMT1 inhibitors identified several new compounds including stil-
IC50’s in the micromolar range and their biological actions remain
to be determined. PRMT1 inhibitors were also being generated in
situ using a substrate analog strategy with specificity and ∼10-fold
lower IC50’s than the AMIs [135,136].
Whether PRMT1 inhibitors will be feasible for the treatment
of certain human pathophysiological conditions and diseases is
unknown, especially due to the large number of PRMT1 cellular
substrates required for normal function. The key may lie in normal-
izing, rather than completely inhibiting, PRMT1 function, restoring
ADMA to normal levels without completely blocking PRMT1 func-
tion. In the case of diseases where ADMA is inhibiting NOS activity,
this could result in restored NO production, overcoming many of
the important secondary effects of diseases that affect, for exam-
ple, the kidneys. For other diseases, where arginine methylation
alters either protein function or gene expression, reducing PRMT1
activity may be sufficient to cross a threshold, whereby essential
protein function is maintained.
7. Conclusions and future directions
PRMT1 is an enzyme that generates methylated arginine
residues and directly regulates the levels of the key metabolite,
ADMA. Arginine methylation is a common post-translation mod-
ification that affects numerous events, both in the nucleus and
the cytoplasm. Among the many pathways that have been shown
to be modulated by arginine methylation include signal transduc-
tion, epigenetic regulation and DNA repair pathways. Because of
the widespread effects that are beginning to be described, much
remains to be learned about the physiological role of PRMT1. In
addition, the mechanisms behind the modulation and regulation of
PRMT1 function are beginning to come to light. Recent reports that
PRMTs are phosphorylated  opens the door to the possibility
that post-translational modifications may regulate PRMT function.
Understanding how various interacting partners and modifications
affect the function of PRMTs will therefore be of great impor-
Many questions remain to be answered with regard to PRMTs
and especially PRMT1. Notably, the determination of the role of
PRMT1 and ADMA in various diseases should provide a wealth
of information. Emerging evidence suggests that arginine methy-
lation is involved in a diverse set of conditions, including heart
disease and cancer. By exploring the role of PRMT1 in these dis-
eases, novel treatment modalities may emerge. This will evolve
in conjunction with current studies that are identifying chemical
inhibitors of PRMT1, which may be able to modulate its func-
tion. As we continue to improve our understanding of the role of
PRMT1 in various normal and disease states, it seems certain that
more properties of PRMT1 will be characterized. The generation
of improved inhibitors and new animal models along with a bet-
ter understanding of its mechanistic role in the cell is likely to
show the feasibility of targeting PRMT1 for therapeutic implica-
This work was supported by grants MOP93811 and MOP67070
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