[Show abstract][Hide abstract] ABSTRACT: Cancer cells with stem cell-like properties contribute to the development of resistance to chemotherapy and eventually to tumor relapses. The current study investigated the potential of curcumin to reduce breast cancer stem cell (BCSC) population for sensitizing breast cancer cells to mitomycin C (MMC) both in vitro and in vivo. Curcumin improved the sensitivity of paclitaxel, cisplatin, and doxorubicin in breast cancer cell lines MCF-7 and MDA-MB-231, as shown by the more than 2-fold decrease in the half-maximal inhibitory concentration of these chemotherapeutic agents. In addition, curcumin sensitized the BCSCs of MCF-7 and MDA-MB-231 to MMC by 5- and 15-fold, respectively. The BCSCs could not grow to the fifth generation in the presence of curcumin and MMC. MMC or curcumin alone only marginally reduced the BCSC population in the mammospheres; however, together, they reduced the BCSC population in CD44+CD24-/low cells by more than 75% (29.34% to 6.86%). Curcumin sensitized BCSCs through a reduction in the expression of ATP-binding cassette (ABC) transporters ABCG2 and ABCC1. We demonstrated that fumitremorgin C, a selective ABCG2 inhibitor, reduced BCSC survival to a similar degree as curcumin did. Curcumin sensitized breast cancer cells to chemotherapeutic drugs by reducing the BCSC population mainly through a reduction in the expression of ABCG2.
[Show abstract][Hide abstract] ABSTRACT: CCNE1 gene amplification is present in 15-20% ovary tumor specimens. Here, we showed that Cyclin E1 (CCNE1) was overexpressed in 30% of established ovarian cancer cell lines. We also showed that CCNE1 was stained positive in over 40% of primary ovary tumor specimens regardless of their histological types while CCNE1 staining was either negative or low in normal ovary and benign ovary tumor tissues. However, the status of CCNE1 overexpression was not associated with the tumorigenic potential of ovarian cancer cell lines and also did not correlate with pathological grades of ovary tumor specimens. Subsequent experiments with CCNE1 siRNAs showed that knockdown of CCNE1 reduced cell growth only in cells with inherent CCNE1 overexpression, indicating that these cells may have developed an addiction to CCNE1 for growth/survival. As CCNE1 is a regulatory factor of cyclin-dependent kinase 2 (Cdk2), we investigated the effect of Cdk2 inhibitor on ovary tumorigenecity. Ovarian cancer cells with elevated CCNE1 expression were 40 times more sensitive to Cdk2 inhibitorSNS-032 than those without inherent CCNE1 overexpression. Moreover, SNS-032 greatly prolonged the survival of mice bearing ovary tumors with inherent CCNE1 overexpression. This study suggests that ovary tumors with elevated CCNE1 expression may be staged for Cdk2-targeted therapy.
[Show abstract][Hide abstract] ABSTRACT: Radix Glycyrrhiza has been used in China for thousand years to treat cancer. However, focus on its tumor-suppressing mechanism has been concentrated on its effect on tumor cell growth and apoptosis.
With the aid of a panel of human breast cancer cell lines, we reveal that glycyrrhetinic acid (GA), a major component of Radix Glycyrrhiza, is actually a significantly more potent agent to suppress invasion than cell survival.
GA effectively inhibits breast cancer cell MMP-2/MMP-9 expression; GA-induced reduction in the MMP-2/9 expression is apparently mediated by GA's ability to specifically inhibit the p38 MAPK activity and its downstream AP1 activation. Moreover, we show that GA down regulates the levels of Fra-1 and c-Jun, two main components of AP1 transcription complex in invasive breast cancer cells and that AP1-specific inhibitor abrogates breast cancer cell invasion. These results suggest that GA impairs the p38 MAPK-AP1 signaling axis, leading to the repression of breast cancer cell invasion. Finally, we demonstrate that GA effectively suppresses breast tumor outgrowth and pulmonary metastasis without causing animal weight loss or eliciting liver/kidney toxicity to the recipient animals.
This study indicates that GA represents a good candidate compound for the potential development of therapeutic drug.
No preview · Article · Mar 2015 · Expert Opinion on Therapeutic Targets
[Show abstract][Hide abstract] ABSTRACT: MicroRNAs have added a new dimension to our understanding of tumorigenesis and associated processes like epithelial-to-mesenchymal transition (EMT). Here, we show that miR-375 is elevated in epithelial-like breast cancer cells, and ectopic miR-375 expression suppresses EMT in mesenchymal-like breast cancer cells. We identified short stature homeobox 2 (SHOX2) as a miR-375 target, and miR-375-mediated suppression in EMT was reversed by forced SHOX2 expression. Ectopic SHOX2 expression can induce EMT in epithelial-like breast cancer cells, whereas SHOX2 knockdown diminishes EMT traits in mesenchymal-like breast cancer cells, demonstrating SHOX2 as an EMT inducer. We show that SHOX2 acts as a transcription factor to upregulate transforming growth factor β receptor I (TβR-I) expression, and TβR-I inhibitor LY364947 abolishes EMT elicited by ectopic SHOX2 expression, suggesting that transforming growth factor β signaling is essential for SHOX2-induced EMT. Manipulating SHOX2 abundance in breast cancer cells impact in vitro invasion and in vivo dissemination. Analysis of breast tumor microarray database revealed that high SHOX2 expression significantly correlates with poor patient survival. Our study supports a critical role of SHOX2 in breast tumorigenicity.
Full-text · Article · Apr 2014 · Neoplasia (New York, N.Y.)
[Show abstract][Hide abstract] ABSTRACT: MicroRNAs (miRNAs) play key roles in inflammatory responses of macrophages. However, the function of miRNAs in macrophage-derived foam cell formation is unclear. Here, we investigated the role of miRNAs in macrophage-derived foam cell formation and atherosclerotic development.Methods and ResultsUsing quantitative reverse transcription-PCR (qRT-PCR), we found that level of miR-155 expression was increased significantly in both plasma and macrophages from atherosclerosis (ApoE(-/-)) mice. We identified that oxidized LDL (oxLDL) induced the expression and release of miR-155 in macrophages, and that miR-155 was required to mediate oxLDL-induced lipid uptake and reactive oxygen species (ROS) production of macrophages. Further, ectopic overexpression and knockdown experiments identified that HMG box-transcription protein1 (HBP1) is a novel target of miR-155. Knockdown of HBP1 enhanced lipid uptake and ROS production in oxLDL-stimulated macrophages, and overexpression of HBP1 repressed these effects. Furthermore, bioinformatics analysis identified three YY1 binding sites in the promoter region of pri-miR-155 and verified YY1 binding directly to its promoter region. Detailed analysis showed that the YY1/HDAC2/4 complex negatively regulated the expression of miR-155 to suppress oxLDL-induced foam cell formation. Importantly, inhibition of miR-155 by a systemically delivered antagomiR-155 decreased clearly lipid-loading in macrophages and reduced atherosclerotic plaques in ApoE(-/-) mice. Moreover, we observed that the level of miR-155 expression was upregulated in CD14(+) monocytes from patients with coronary heart disease.
Our findings reveal a new regulatory pathway of YY1/HDACs/miR-155/HBP1 in macrophage-derived foam cell formation during early atherogenesis and suggest that miR-155 is a potential therapeutic target for atherosclerosis.
Preview · Article · Mar 2014 · Cardiovascular Research
[Show abstract][Hide abstract] ABSTRACT: Cell-cell adhesion molecule cadherin-11(CDH11) is preferentially expressed in basal-like breast cancer cells and facilitates breast cancer cell migration by promoting small GTPase Rac activity. However, how the expression of CDH11 is regulated in breast cancer cells is not understood. Here, we show that CDH11 is transcriptionally controlled by homeobox C8 (HOXC8) in human breast cancer cells. HOXC8 serves as a CDH11-specific transcription factor and binds to the site of nucleotides -196 to -191 in the CDH11 promoter. Depletion of HOXC8 leads to the decrease in anchorage-independent cell growth, cell migration/invasion and spontaneous metastasis of breast cancer cells; however, suppressed tumorigenic events were fully rescued by ectopic CDH11 expression in HOXC8-knockdown cells. These results indicate that HOXC8 impacts breast tumorigenesis through CDH11. The analysis of publically available human breast tumor microarray gene expression database demonstrates a strong positive linear association between HOXC8 and CDH11 expression ( = 0.801, p < 0.001). Survival analysis (Kaplan-Meier method, log-rank test) show that both high HOXC8 and CDH11 expression correlate with poor recurrence-free survival rate of patients. Together, our study suggests that HOXC8 promotes breast tumorigenesis by maintaining high level of CDH11 expression in breast cancer cells.
[Show abstract][Hide abstract] ABSTRACT: Increased activation of the serine-glycine biosynthetic pathway is an integral part of cancer metabolism that drives macromolecule synthesis needed for cell proliferation. Whether this pathway is under epigenetic control is unknown. Here we show that the histone H3 lysine 9 (H3K9) methyltransferase G9A is required for maintaining the pathway enzyme genes in an active state marked by H3K9 monomethylation and for the transcriptional activation of this pathway in response to serine deprivation. G9A inactivation depletes serine and its downstream metabolites, triggering cell death with autophagy in cancer cell lines of different tissue origins. Higher G9A expression, which is observed in various cancers and is associated with greater mortality in cancer patients, increases serine production and enhances the proliferation and tumorigenicity of cancer cells. These findings identify a G9A-dependent epigenetic program in the control of cancer metabolism, providing a rationale for G9A inhibition as a therapeutic strategy for cancer.
[Show abstract][Hide abstract] ABSTRACT: Cellular differentiation is characterized by the acquisition of specialized structures and functions, cell cycle exit, and global attenuation of the DNA damage response. It is largely unknown how these diverse cellular events are coordinated at the molecular level during differentiation. We addressed this question in a model system of neuroblastoma cell differentiation induced by HOXC9.
We conducted a genome-wide analysis of the HOXC9-induced neuronal differentiation program. Microarray gene expression profiling revealed that HOXC9-induced differentiation was associated with transcriptional regulation of 2,370 genes, characterized by global upregulation of neuronal genes and downregulation of cell cycle and DNA repair genes. Remarkably, genome-wide mapping by ChIP-seq demonstrated that HOXC9 bound to 40% of these genes, including a large number of genes involved in neuronal differentiation, cell cycle progression and the DNA damage response. Moreover, we showed that HOXC9 interacted with the transcriptional repressor E2F6 and recruited it to the promoters of cell cycle genes for repressing their expression.
Our results demonstrate that HOXC9 coordinates diverse cellular processes associated with differentiation by directly activating and repressing the transcription of distinct sets of genes.
[Show abstract][Hide abstract] ABSTRACT: Ovarian cancer is a highly lethal gynecological cancer and its causes remain to be understood. Using a recently identified tumor suppressor gene GT198 (PSMC3IP) as unique marker, we search for the identity of GT198 mutant cells in ovarian cancer. GT198 has germline mutations in familial and early-onset breast and ovarian cancers and recurrent somatic mutations in sporadic fallopian tube cancers. GT198 protein has been shown as a steroid hormone receptor coregulator and also as a crucial factor in DNA repair. In this study, using GT198 as a marker for microdissection, we find that ovarian tumor stromal cells harboring GT198 mutations are present in various types of ovarian cancer including high- and low-grade serous, endometrioid, mucinous, clear cell, granulosa cell carcinomas, and in precursor lesions such as inclusion cysts. The mutant stromal cells consist of a luteinized theca cell lineage at various differentiation stages including CD133+, CD44+, CD34+ cells; although the vast majority of them are differentiated overexpressing steroidogenic enzyme CYP17, a theca cell-specific marker. In addition, wild type GT198 suppresses whereas mutant GT198 protein stimulates CYP17 expression. The chromatin-bound GT198 on the human CYP17 promoter is decreased by overexpressing mutant GT198 protein, implicating the loss of wild type suppression in mutant cells. Together, our results suggest that GT198 mutant luteinized theca cells overexpressing CYP17 are common in ovarian cancer stroma. Since first-hit cancer gene mutations would specifically mark cancer-inducing cells, the identification of mutant luteinized theca cells may add a crucial evidence in understanding the cause of human ovarian cancer.
Full-text · Article · Oct 2013 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: High abundance of c-Jun is detected in invasive breast cancer cells and aggressive breast tumor malignancies. Here, we demonstrate that a major cause of high c-Jun abundance in invasive breast cancer cells is prolonged c-Jun protein stability owing to poor poly-ubiquitination of c-Jun. Among the known c-Jun-targeting E3 ligases, we identified constitutive photomorphogenesis protein 1 (COP1) as an E3 ligase responsible for c-Jun degradation in less invasive breast cancer cells because depletion of COP1 reduced c-Jun poly-ubiquitination leading to the stabilization of c-Jun protein. In a panel of breast cancer cell lines, we observed an inverse association between the levels of COP1 and c-Jun. However, overexpressing COP1 alone was unable to decrease c-Jun level in invasive breast cancer cells, indicating that efficient c-Jun protein degradation necessitates an additional event. Indeed, we found that glycogen synthase kinase 3 (GSK3) inhibitors elevated c-Jun abundance in less invasive breast cancer cells and that GSK3β nonphosphorylable c-Jun-T239A mutant displayed greater protein stability and poorer poly-ubiquitination compared to the wild-type c-Jun. The ability of simultaneously enforced expression of COP1 and constitutively active GSK3β to decrease c-Jun abundance in invasive breast cancer cells allowed us to conclude that c-Jun is negatively regulated through the coordinated action of COP1 and GSK3β. Importantly, co-expressing COP1 and active GSK3β blocked in vitro cell growth/migration and in vivo metastasis of invasive breast cancer cells. Gene expression profiling of breast tumor specimens further revealed that higher COP1 expression correlated with better recurrence-free survival. Our study supports the notion that COP1 is a suppressor of breast cancer progression.
Full-text · Article · Sep 2013 · Neoplasia (New York, N.Y.)
[Show abstract][Hide abstract] ABSTRACT: Elevated level of urokinase receptor (uPAR) is detected in various aggressive cancer types and is closely associated with poor prognosis of cancers. Binding of uPA to uPAR triggers the conversion of plasminogen to plasmin and the subsequent activation of metalloproteinases. These events confer tumor cells with the capability to degrade the components of the surrounding extracellular matrix, thus contributing to tumor cell invasion and metastasis. uPA-uPAR interaction also elicits signals that stimulate cell proliferation/survival and the expression of tumor-promoting genes, thus assisting tumor development. In addition to its interaction with uPA, uPAR also interacts with vitronectin and this interaction promotes cancer metastasis by activating Rac and stimulating cell migration. Although underlying mechanisms are yet to be fully elucidated, uPAR has been shown to facilitate epithelial-mesenchymal transition (EMT) and induce cancer stem cell-like properties in breast cancer cells. The fact that uPAR lacks intracellular domain suggests that its signaling must be mediated through its co-receptors. Indeed, uPAR interacts with diverse transmembrane proteins including integrins, ENDO180, G protein-coupled receptors and growth factor receptors in cancer cells and these interactions are proven to be critical for the role of uPAR in tumorigenesis. Inhibitory peptide that prevents uPA-uPAR interaction has shown the promise to prolong patients' survival in the early stage of clinical trial. The importance of uPAR's co-receptor in uPAR's tumor-promoting effects implicate that anti-cancer therapeutic agents may also be developed by disrupting the interactions between uPAR and its functional partners.
[Show abstract][Hide abstract] ABSTRACT: Xiao Chai Hu Tang (XCHT), a compound formula originally recorded in an ancient Chinese medical book Shanghanlun, has been used to treat chronic liver diseases for a long period of time in China. Although extensive studies have been demonstrated the efficacy of this formula to treat chronic hepatitis, hepatic fibrosis, and hepatocarcinoma, how it works against these diseases still awaits full understanding. Here, we firstly present an overview arranging from the entire formula to mechanism studies of single herb in XCHT and their active components, from a new perspective of "separation study," and we tried our best to both detailedly and systematically organize the antihepatocarcinoma effects of it, hoping that the review will facilitate the strive on elucidating how XCHT elicits its antihepatocarcinoma role.
Full-text · Article · Jun 2013 · Evidence-based Complementary and Alternative Medicine
[Show abstract][Hide abstract] ABSTRACT: The importance of microRNAs (miRNAs) in biological and disease processes necessitates a better understanding of the mechanisms that regulate miRNA abundance. We showed that the activities of the mitogen-activated protein kinase (MAPK) p38 and its downstream effector kinase MAPK-activated protein kinase 2 (MK2) were necessary for the efficient processing of a subset of primary miRNAs (pri-miRNAs). Through yeast two-hybrid screening, we identified p68 (also known as DDX5), a key component of the Drosha complex that processes pri-miRNAs, as an MK2-interacting protein, and we found that MK2 phosphorylated p68 at Ser197 in cells. In wild-type mouse embryonic fibroblasts (MEFs) treated with a p38 inhibitor or in MK2-deficient (MK2-/-) MEFs, expression of a phosphomimetic mutant p68 fully restored pri-miRNA processing, suggesting that MK2-mediated phosphorylation of p68 was essential for this process. We found that, whereas p68 was present in the nuclei of wild-type MEFs, it was found mostly in the cytoplasm of MK2-/- MEFs. Nuclear localization of p68 depended on MK2-mediated phosphorylation of Ser197. In addition, inhibition of p38 MAPK promoted the growth of wild-type MEFs and breast cancer MCF7 cells by enhancing the abundance of c-Myc through suppression of the biogenesis of the miRNA miR-145, which targets c-Myc. Because pri-miRNA processing occurs in the nucleus, our findings suggest that the p38 MAPK-MK2 signaling pathway promotes miRNA biogenesis by facilitating the nuclear localization of p68.
No preview · Article · Mar 2013 · Science Signaling
[Show abstract][Hide abstract] ABSTRACT: Traditional Chinese medicine (TCM) ZHENG as the key pathological principle is to understand the human homeostasis and guide TCM treatment. Here, circulating microRNAs (miRNAs) were utilized to differentiate between ZHENGs including liver-gallbladder dampness-heat syndrome (LGDHS) and liver-kidney yin deficiency syndrome (LKYDS) in chronic hepatitis B (CHB). Sera samples of CHB patients with LGDHS (n = 35), LKYDS (n = 24), and healthy controls (Ctrls, n = 21) were analyzed by microarray and real-time RT-PCR. Receiver-operator characteristic (ROC) curves were established to evaluate the levels of serum miRNA for discriminating LGDHS and LKYDS. The target genes of miRNAs were predicted by TargetScan. Gene Ontology (GO) and pathways were analyzed using DAVID tool. The results showed that 22 miRNAs were differentially expressed between LGDHS and LKYDS (fold change >2.0 and P < 0.01). Circulating miR-583 and miR-663 were significantly higher (P < 0.001) in CHB patients with LGDHS than those with LKYDS and Ctrls. ROC curve analysis revealed that miR-583 and miR-663 were sensitive and specific enough to distinguish LGDHS from LKYDS. Pathway enrichment analysis indicated that 354 putative targets for miR-583 and 68 putative targets for miR-663 were mainly involved in Axon guidance, Neurotrophin, and MAPK signaling pathway. miR-583 and miR-663 may be potential markers for ZHENG differentiation in CHB.
Full-text · Article · Mar 2013 · Evidence-based Complementary and Alternative Medicine
[Show abstract][Hide abstract] ABSTRACT: In this study we performed a systematic evaluation of functional miRNA-mRNA interactions associated with the invasiveness of breast cancer cells using a combination of integrated miRNA and mRNA expression profiling, bioinformatics prediction, and functional assays. Analysis of the miRNA expression identified 11 miRNAs that were differentially expressed, including 7 down-regulated (miR-200c, miR-205, miR-203, miR-141, miR-34a, miR-183, and miR-375) and 4 up-regulated miRNAs (miR-146a, miR-138, miR-125b1 and miR-100), in invasive cell lines when compared to normal and less invasive cell lines. Transfection of miR-200c, miR-205, and miR-375 mimics into MDA-MB-231 cells led to the inhibition of in vitro cell migration and invasion. The integrated analysis of miRNA and mRNA expression identified 35 known and novel target genes of miR-200c, miR-205, and mir-375, including CFL2, LAMC1, TIMP2, ZEB1, CDH11, PRKCA, PTPRJ, PTPRM, LDHB, and SEC23A. Surprisingly, the majority of these genes (27 genes) were target genes of miR-200c, suggesting that miR-200c plays a pivotal role in regulating the invasiveness of breast cancer cells. We characterized one of the target genes of miR-200c, CFL2, and demonstrated that CFL2 is overexpressed in aggressive breast cancer cell lines and can be significantly down-regulated by exogenous miR-200c. Tissue microarray analysis further revealed that CFL2 expression in primary breast cancer tissue correlated with tumor grade. The results obtained from this study may improve our understanding of the role of these candidate miRNAs and their target genes in relation to breast cancer invasiveness and ultimately lead to the identification of novel biomarkers associated with prognosis.
Full-text · Article · Mar 2013 · Journal of Translational Medicine
[Show abstract][Hide abstract] ABSTRACT: Loss of function in either VHL or Nek1 leads to cyst formation in tissues, especially in kidneys. Whether there is a connection between pVHL and Nek1 regulation is unknown. Here, we report that the VHL protein (pVHL) may be a substrate of Nek1. While Nek1 can phosphorylate pVHL at multiple sites, the phosphorylation at serine-168 results in pVHL degradation. Nek1-mediated phosphorylation of pVHL does not significantly affect hypoxia-inducible factors (HIF), a known target of pVHL. However, non-phosphorylable pVHL reconstituted in VHL-deficient cells induces more stable cilia than wild-type VHL during serum stimulation and Nocodazole treatment. The results suggest a possible regulation of pVHL by Nek1 that may contribute to ciliary homeostasis and cystogenesis.
[Show abstract][Hide abstract] ABSTRACT: To investigate whether circulating microRNAs (miRNAs) can serve as molecular markers to predict liver injury resulted from chronic hepatitis B (CHB).
The profiles of serum miRNA expression were first generated with serum samples collected from 10 patients with CHB and 10 healthy donors (Ctrls) by microarray analysis. The levels of several miRNAs were further quantitated by real-time reverse transcription polymerase chain reaction with serum samples from another 24 CHB patients and 24 Ctrls. Serum samples of 20 patients with nonalcohlic steatohepatitis (NASH) were also included for comparison. The comparison in the levels of miRNAs between groups (CHB, NASH and Ctrl) was analyzed with Mann-Whitney U-test. The correlation between miRNAs and clinical pathoparameters was analyzed using Spearman correlation analysis or canonical correlation analysis. The receiver-operator characteristic (ROC) curves were also generated to determine the specificity and sensitivity of each individual miRNA in distinguishing patients with CHB from Ctrls.
miRNA profile analysis showed that 34 miRNAs were differentially expressed between CHB and Ctrl subjects, in which 12 were up-regulated and 22 down-regulated in CHB subject (fold change > 2.0 and P < 0.01). The median levels of miR-122, -572, -575 and -638 were significantly higher (P < 1.00 × 10(-5)) while miR-744 significantly lower (P < 1.00 × 10(-6)) in CHB compared with the Ctrl. The levels of miR-122, -572 and -638 were also higher (P < 1.00 × 10(-3)) while the level of miR-744 lower in CHB (P < 0.05) than in NASH, although the difference between them was not as significant as that between CHB and Ctrl. ROC curve analysis revealed that the levels of miR-122, -572, -575, -638 and -744 in serum were sensitive and specific enough to distinguish CHB, NASH and Ctrl. Multivariate analysis further showed that the levels of these miRNAs were correlated with the liver function parameters. Most significantly, it was the scatter plot of principal component with the levels of these miRNAs, but not the parameters of liver function, which clearly distinguished CHB, NASH and Ctrl subjects.
Serum levels of miR-122, -572, -575, -638 and -744 are deregulated in patients with CHB or NASH. The levels of these miRNAs may serve as potential biomarkers for liver injury caused by CHB and NASH.
Full-text · Article · Oct 2012 · World Journal of Gastroenterology
[Show abstract][Hide abstract] ABSTRACT: Retinoic acid (RA) can induce growth arrest and neuronal differentiation of neuroblastoma cells and has been used in clinic for treatment of neuroblastoma. It has been reported that RA induces the expression of several HOXD genes in human neuroblastoma cell lines, but their roles in RA action are largely unknown. The HOXD cluster contains nine genes (HOXD1, HOXD3, HOXD4, and HOXD8-13) that are positioned sequentially from 3' to 5', with HOXD1 at the 3' end and HOXD13 the 5' end. Here we show that all HOXD genes are induced by RA in the human neuroblastoma BE(2)-C cells, with the genes located at the 3' end being activated generally earlier than those positioned more 5' within the cluster. Individual induction of HOXD8, HOXD9, HOXD10 or HOXD12 is sufficient to induce both growth arrest and neuronal differentiation, which is associated with downregulation of cell cycle-promoting genes and upregulation of neuronal differentiation genes. However, induction of other HOXD genes either has no effect (HOXD1) or has partial effects (HOXD3, HOXD4, HOXD11 and HOXD13) on BE(2)-C cell proliferation or differentiation. We further show that knockdown of HOXD8 expression, but not that of HOXD9 expression, significantly inhibits the differentiation-inducing activity of RA. HOXD8 directly activates the transcription of HOXC9, a key effector of RA action in neuroblastoma cells. These findings highlight the distinct functions of HOXD genes in RA induction of neuroblastoma cell differentiation.
[Show abstract][Hide abstract] ABSTRACT: Cell-cell contact formation following cadherin engagement requires actomyosin contraction along the periphery of cell-cell contact. The molecular mechanisms that regulate myosin activation during this process are not clear. In this paper, we show that two polarity proteins, partitioning defective 3 homologue (Par3) and mammalian homologues of Drosophila Lethal (2) Giant Larvae (Lgl1/2), antagonize each other in modulating myosin II activation during cell-cell contact formation in Madin-Darby canine kidney cells. While overexpression of Lgl1/2 or depletion of endogenous Par3 leads to enhanced myosin II activation, knockdown of Lgl1/2 does the opposite. Intriguingly, altering the counteraction between Par3 and Lgl1/2 induces cell-cell internalization during early cell-cell contact formation, which involves active invasion of the lateral cell-cell contact underneath the apical-junctional complexes and requires activation of the Rho-Rho-associated, coiled-coil containing protein kinase (ROCK)-myosin pathway. This is followed by predominantly nonapoptotic cell-in-cell death of the internalized cells and frequent aneuploidy of the host cells. Such effects are reminiscent of entosis, a recently described process observed when mammary gland epithelial cells were cultured in suspension. We propose that entosis could occur without matrix detachment and that overactivation of myosin or unbalanced myosin activation between contacting cells may be the driving force for entosis in epithelial cells.
Preview · Article · Apr 2012 · Molecular biology of the cell