The Polycomb group protein Enhancer of Zeste 2: its links to DNA repair and breast cancer

MiRNA-506 presents multiple tumor suppressor activities by targeting EZH2 in nasopharyngeal carcinoma

OBJECTIVE

MiR-506 has been reported to be associated with multiple malignancies, but its roles in nasopharyngeal cancer (NPC) are not fully understood. Our objective is to demonstrate its effects on NPC and the underlying mechanisms.

METHODS

Totally fifteen pairs of NPC and adjacent non-tumorous tissues were collected for the detection of miR-506 and enhancer of zeste homolog 2 (EZH2) expression. Dual luciferase reporter assay was employed for verifying the relationship between miR-506 and EZH2. The flow cytometry and MTT assays were employed to explore the effects of miR-506 and EZH2 on the cell apoptosis and proliferation, respectively. Wound closure and transwell assays were used to evaluate the cell migration and invasion abilities. Western blotting or RT-qPCR assays were applied to detect the alterations of miR-506, EZH2 and epithelial-mesenchymal transition (EMT)-related markers. Morphological changes of cells with EMT were assessed by light microscopy.

RESULTS

MiR-506 was significantly decreased and EZH2 was obviously increased in NPC tissues. Overexpression of miR-506 decreased the EZH2 level, promoted apoptosis, inhibited proliferation, invasion and migration of NPC cells. Accordingly, miR-506 overexpression attenuated EMT process of NPC cells as demonstrated by the alterations of EMT-related markers and the morphological changes. In addition, the luciferase assay proved that miR-506 directly targeted EZH2. Furthermore, the overexpression of EZH2 reversed the tumor-suppressive effects induced by miR-506 mimics.

CONCLUSION

MiR-506 acted as a tumor suppressor to promote apoptosis and inhibit invasion and migration via directly targeting EZH2. MiR-506 can be a candidate target for gene therapy against NPC.

XRCC2 (X-ray repair cross complementing 2)

XRCC2 is one of five somatic RAD51 paralogs, all of which have Walker A and B ATPase motifs. Each of the paralogs, including XRCC2, has a function in DNA double-strand break repair by homologous recombination (HR). However, their individual roles are not as well understood as that of RAD51 itself. The XRCC2 protein forms a complex (BCDX2) with three other RAD51 paralogs, RAD51B, RAD51C and RAD51D. It is believed that the BCDX2 complex mediates HR downstream of BRCA2 but upstream of RAD51, as XRCC2 is involved in the assembly of RAD51 into DNA damage foci. XRCC2 can bind DNA and, along with RAD51D, can promote homologous pairing in vitro. Consistent with its role in HR, XRCC2-deficient cells have increased levels of spontaneous chromosome instability, and exhibit hypersensitivity to DNA interstrand crosslinking agents such as mitomycin C and cisplatin as well as ionizing radiation, alkylating agents and aldehydes. XRCC2 also functions in promoting DNA replication and chromosome segregation. Biallelic mutation of XRCC2 (FANCU) causes the FA-U subtype of FA, while heterozygosity for deleterious mutations in XRCC2 may be associated with an increased breast cancer risk. XRCC2 appears to function 'downstream' in the FA pathway, since it is not required for FANCD2 monoubiquitination, which is the central step in the FA pathway. Clinically, the only known FA-U patient in the world exhibits severe congenital abnormalities, but had not developed, by seven years of age, the bone marrow failure and cancer that are often seen in patients from other FA complementation groups.

The polycomb group protein EZH2 induces epithelial-mesenchymal transition and pluripotent phenotype of gastric cancer cells by binding to PTEN promoter

BACKGROUND

The influences of oncogenic Ezh2 on the progression and prognosis of gastric cancer (GC) and the underlying mechanisms are still poorly understood. Here, we aimed at investigating clinicopathological significance of Ezh2 in GC and the mechanisms underlying its function in GC development.

METHODS

The expression level of Ezh2 was determined by qRT-PCR, immunoblot, and immunohistochemistry analysis in 156 pairs of GC tissues and adjacent normal gastric mucosa tissues. The biological functions of Ezh2 were assessed by in vitro and in vivo functional experiments. Chromatin immunoprecipitation (ChIP), luciferase, and Western blotting analyses were utilized to identify the relationship between Ezh2 and the PTEN/Akt signaling.

RESULTS

The expression of Ezh2 was higher in gastric cancer tissues in comparison with para-nontumorous epithelium. High expression of Ezh2 was associated with more aggressive biological behavior and poor prognosis in GC. In vitro studies indicated that Ezh2 promoted GC cells' proliferation and clonogenicity. Besides, Ezh2 led to the acquisition of epithelial-mesenchymal transition (EMT) phenotype of GC cells and enhanced GC cell migration and invasion capacity. In particular, Ezh2 strengthened sphere-forming capacity of GC cells, indicating its role in the enrichment of GC stem cells. Furthermore, we found that PTEN/Akt signaling contributed to the effects of Ezh2 on cancer stem cells (CSC) and EMT phenotype in GC cells, and blocking PTEN signaling significantly rescued the effects of Ezh2.

CONCLUSIONS

Taken together, Ezh2 has a central role in regulating diverse aspects of the pathogenesis of GC in part by involving PTEN/Akt signaling, indicating that it could be an independent prognostic factor and potential therapeutic target.

Identification of Polycomb Group Protein EZH2-Mediated DNA Mismatch Repair Gene MSH2 in Human Uterine Fibroids

Uterine fibroids (UFs) are benign smooth muscle neoplasms affecting up to 70% of reproductive age women. Treatment of symptomatic UFs places a significant economic burden on the US health-care system. Several specific genetic abnormalities have been described as etiologic factors of UFs, suggesting that a low DNA damage repair capacity may be involved in the formation of UF. In this study, we used human fibroid and adjacent myometrial tissues, as well as an in vitro cell culture model, to evaluate the expression of MutS homolog 2 (MSH2), which encodes a protein belongs to the mismatch repair system. In addition, we deciphered the mechanism by which polycomb repressive complex 2 protein, EZH2, deregulates MSH2 in UFs. The RNA expression analysis demonstrated the deregulation of MSH2 expression in UF tissues in comparison to its adjacent myometrium. Notably, protein levels of MSH2 were upregulated in 90% of fibroid tissues (9 of 10) as compared to matched adjacent myometrial tissues. Human fibroid primary cells treated with 3-deazaneplanocin A (DZNep), chemical inhibitor of EZH2, exhibited a significant increase in MSH2 expression (P < .05). Overexpression of EZH2 using an adenoviral vector approach significantly downregulated the expression of MSH2 (P < .05). Chromatin immunoprecipitation assay demonstrated that enrichment of H3K27me3 in promoter regions of MSH2 was significantly decreased in DZNep-treated fibroid cells as compared to vehicle control. These data suggest that EZH2-H3K27me3 regulatory mechanism dynamically changes the expression levels of DNA mismatch repair gene MSH2, through epigenetic mark H3K27me3. MSH2 may be considered as a marker for early detection of UFs.

Polycomb Group (PcG) Proteins and Human Cancers: Multifaceted Functions and Therapeutic Implications

Polycomb group (PcG) proteins are transcriptional repressors that regulate several crucial developmental and physiological processes in the cell. More recently, they have been found to play important roles in human carcinogenesis and cancer development and progression. The deregulation and dysfunction of PcG proteins often lead to blocking or inappropriate activation of developmental pathways, enhancing cellular proliferation, inhibiting apoptosis, and increasing the cancer stem cell population. Genetic and molecular investigations of PcG proteins have long been focused on their PcG functions. However, PcG proteins have recently been shown to exert non-classical-Pc-functions, contributing to the regulation of diverse cellular functions. We and others have demonstrated that PcG proteins regulate the expression and function of several oncogenes and tumor suppressor genes in a PcG-independent manner, and PcG proteins are associated with the survival of patients with cancer. In this review, we summarize the recent advances in the research on PcG proteins, including both the Pc-repressive and non-classical-Pc-functions. We specifically focus on the mechanisms by which PcG proteins play roles in cancer initiation, development, and progression. Finally, we discuss the potential value of PcG proteins as molecular biomarkers for the diagnosis and prognosis of cancer, and as molecular targets for cancer therapy.

Prognostic value of COX-2, P53, and EZH-2 evaluated by quantitative image analysis in premalignant and malignant breast lesions

BACKGROUND

Cytological differential diagnosis of atypical hyperplasia and well differentiated breast carcinoma may be challenging, because sometimes there is an overlap between the cytomorphological features of these lesions. The aim of the study was to investigate COX-2, EZH-2, p53 expression in carcinomas and the gray zone of breast cytology categories of atypical hyperplastic lesions with regard to biological behavior of the tumor.

METHODS

FNA speciments from 100 patients with breast hyperplastic lesions and cancer were investigated by immunocytochemistry and a quantitative analysis for COX-2, p53, and EZH-2.

RESULTS

Extent of staining for COX-2 correlated with percentage of positive for EZH-2 (P < 0.0001) and p53 nuclei (P < 0.001). The intensity of COX-2 was lower in the carcinoma group (118.57 ± 12.43) than in the hyperplastic (127.16 ± 11.71) group (P = 0.006). On the contrary the mean value of staining extent was greater in the adenocarcinoma cases (15.96 ± 13.03) than in hyperplastic (4.04 ± 1.94) cases (P < 0.0001). The percentage of EZH-2 and p53 positive cells correlated with the histological type of the lesions (P = 0.001 and P = 0.011, respectively). There was also a statistically significant relation between tumor size and expression of COX-2 (P = 0.007) and EZH-2 (P = 0.010).

CONCLUSION

Our study showed that the expression of COX-2, EZH-2, and p53 as determined by immunocytochemistry at quantitative level may be a predictor for distinguishing cytologically atypical hyperplastic from malignant breast lesions and may be regarded as potential prognostic factor in breast cancer patients.

A potential antitumor ellagitannin, davidiin, inhibited hepatocellular tumor growth by targeting EZH2

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and is the third most common cause of cancer-related deaths. Currently available treatment options for HCC patients are scarce resulting in an urgent need to develop a novel effective cure. Polygonum capitatum is a medicinal herb which has been used to treat inflammatory diseases in Miao nationality of China. We recently isolated a pure compound davidiin from P. capitatum extract. Four HCC cell lines were treated with davidiin. Cell viability was recorded by MTT assay. siRNAs targeting enhancer of zeste homolog 2 (EZH2) were applied to modulate the expression of EZH2. Established xenograft mice models of HCC were applied to evaluate the in vivo anticancer activity of davidiin. We investigated the anticancer activity and the underlying mechanism of davidiin. The compound inhibited HCC cell growth and also suppressed tumor growth in xenografted HCC mouse. Such inhibition was facilitated by specifically downregulation on EZH2. The compound possesses anticancer activity both in vitro and in vivo which warrants further clinical investigation as a potential anti-HCC agent.

RAD51C-deficient cancer cells are highly sensitive to the PARP inhibitor olaparib

A PARP inhibitor is a rationally designed targeted therapy for cancers with impaired DNA repair abilities. RAD51C is a paralog of RAD51 that has an important role in the DNA damage response. We found that cell lines sensitive to a novel oral PARP inhibitor, olaparib, had low levels of RAD51C expression using microarray analysis, and we therefore hypothesized that low expression of RAD51C may hamper the DNA repair process, resulting in increased sensitivity to olaparib. Compared with the cells with normal RAD51C expression levels, RAD51C-deficient cancer cells were more sensitive to olaparib, and a higher proportion underwent cell death by inducing G2-M cell-cycle arrest and apoptosis. The restoration of RAD51C in a sensitive cell line caused attenuation of olaparib sensitivity. In contrast, silencing of RAD51C in a resistant cell line enhanced the sensitivity to olaparib, and the number of RAD51 foci decreased with ablated RAD51C expression. We also found the expression of RAD51C was downregulated in cancer cells due to epigenetic changes and RAD51C expression was low in some gastric cancer tissues. Furthermore, olaparib significantly suppressed RAD51C-deficient tumor growth in a xenograft model. In summary, RAD51C-deficient cancer cells are highly sensitive to olaparib and offer preclinical proof-of-principle that RAD51C deficiency may be considered a biomarker for predicting the antitumor effects of olaparib.

Functional characterization of EZH2β reveals the increased complexity of EZH2 isoforms involved in the regulation of mammalian gene expression

BACKGROUND

Histone methyltransferase enhancer of zeste homologue 2 (EZH2) forms an obligate repressive complex with suppressor of zeste 12 and embryonic ectoderm development, which is thought, along with EZH1, to be primarily responsible for mediating Polycomb-dependent gene silencing. Polycomb-mediated repression influences gene expression across the entire gamut of biological processes, including development, differentiation and cellular proliferation. Deregulation of EZH2 expression is implicated in numerous complex human diseases. To date, most EZH2-mediated function has been primarily ascribed to a single protein product of the EZH2 locus.

RESULTS

We report that the EZH2 locus undergoes alternative splicing to yield at least two structurally and functionally distinct EZH2 methyltransferases. The longest protein encoded by this locus is the conventional enzyme, which we refer to as EZH2α, whereas EZH2β, characterized here, represents a novel isoform. We find that EZH2β localizes to the cell nucleus, complexes with embryonic ectoderm development and suppressor of zeste 12, trimethylates histone 3 at lysine 27, and mediates silencing of target promoters. At the cell biological level, we find that increased EZH2β induces cell proliferation, demonstrating that this protein is functional in the regulation of processes previously attributed to EZH2α. Biochemically, through the use of genome-wide expression profiling, we demonstrate that EZH2β governs a pattern of gene repression that is often ontologically redundant from that of EZH2α, but also divergent for a wide variety of specific target genes.

CONCLUSIONS

Combined, these results demonstrate that an expanded repertoire of EZH2 writers can modulate histone code instruction during histone 3 lysine 27-mediated gene silencing. These data support the notion that the regulation of EZH2-mediated gene silencing is more complex than previously anticipated and should guide the design and interpretation of future studies aimed at understanding the biochemical and biological roles of this important family of epigenomic regulators.

Detection of long non-coding RNA in archival tissue: correlation with polycomb protein expression in primary and metastatic breast carcinoma

A major function of long non-coding RNAs (lncRNAs) is regulating gene expression through changes in chromatin state. Experimental evidence suggests that in cancer, they can influence Polycomb Repressive Complexes (PRC) to retarget to an occupancy pattern resembling that of the embryonic state. We have previously demonstrated that the expression level of lncRNA in the HOX locus, including HOTAIR, is a predictor of breast cancer metastasis. In this current project, RNA in situ hybridization of probes to three different lncRNAs (HOTAIR, ncHoxA1, and ncHoxD4), as well a immunohistochemical staining of EZH2, is undertaken in formalin-fixed paraffin-embedded breast cancer tissues in a high throughput tissue microarray format to correlate expression with clinicopathologic features. Though overall EZH2 and HOTAIR expression levels were highly correlated, the subset of cases with strong HOTAIR expression correlated with ER and PR positivity, while the subset of cases with strong EZH2 expression correlated with an increased proliferation rate, ER and PR negativity, HER2 underexpression, and triple negativity. Co-expression of HOTAIR and EZH2 trended with a worse outcome. In matched primary and metastatic cancers, both HOTAIR and EZH2 had increased expression in the metastatic carcinomas. This is the first study to show that RNA in situ hybridization of formalin fixed paraffin-embedded clinical material can be used to measure levels of long non-coding RNAs. This approach offers a method to make observations on lncRNAs that may influence the cancer epigenome in a tissue-based technique.

Progress in understanding the role of EZH2 in the pathogenesis of hepatocellular carcinoma

Primary hepatocellular carcinoma (HCC) is one of the most common malignancies, with a multifaceted molecular pathogenesis. The activation of proto-oncogenes and the inactivation of tumor suppressor genes induced by genetic and epigenetic alterations are major mechanisms of hepatocarcinogenesis. The Polycomb-group gene EZH2 is a newly identified oncogene with gene silencing function, which is mediated by intrinsic histone methyltransferase activity for trimethylation of histone h3 lysine 27 (H3K27me3) and involved in regulation of X-inactivation, cell differentiation and embryonic development. In recent years, EZH2 has been reported to be highly expressed in HCC and is closely related to hepatocarcinogenesis by aberrant regulation of tumor-associated gene expression. In this paper we give an overview of the role of EZH2 in the development of HCC.

Polycomb and the emerging epigenetics of pancreatic cancer

INTRODUCTION

The revolution of epigenetics has revitalized cancer research, shifting focus away from somatic mutation toward a more holistic perspective involving the dynamic states of chromatin. Disruption of chromatin organization can directly and indirectly precipitate genomic instability and transformation.

DISCUSSION

One group of epigenetic mediators, the Polycomb group (PcG) proteins, establishes heritable gene repression through methylation of histone tails. Although classically considered regulators of development and cellular differentiation, PcG proteins engage in a variety of neoplastic processes, including cellular proliferation and invasion. Due to their multifaceted potential, PcG proteins rest at the intersection of transcriptional memory and malignancy. Expression levels of PcG proteins hold enormous diagnostic and prognostic value in breast, prostate, and more recently, gastrointestinal cancers.

CONCLUSION

In this review, we briefly summarize the function of PcG proteins and report the latest developments in understanding their role in pancreatic cancer.

Polycomb group protein EZH2 is frequently expressed in inflammatory breast cancer and is predictive of worse clinical outcome

BACKGROUND

Enhancer of zeste homolog 2 (EZH2), a member of polycomb group proteins, is involved in the regulation of cell cycle progression and has been implicated in various human malignancies, including breast cancer, and also has been associated with aggressive tumor behavior. However, the clinical significance of EZH2 expression in inflammatory breast cancer (IBC), a rare but aggressive type of breast carcinoma, has not been explored. In this retrospective study, the authors examined EZH2 expression in IBC tumors and evaluated the relation between EZH2 expression and patient survival.

METHODS

Tissue microarrays of 88 surgically resected IBC tumors were stained immunohistochemically for EZH2, and the authors evaluated the association of EZH2 expression status with clinicopathologic factors and clinical outcome.

RESULTS

The median follow-up for the entire cohort was 45.7 months, and the 5-year overall survival (OS) rate was 45%. EZH2 was expressed frequently in IBC tumors (75.7%) and was associated significantly with unfavorable prognostic factors, such as higher tumor grade, negative estrogen receptor status, and triple-negative status (ie, negative for the estrogen, progesterone, and human epidermal growth factor 2 receptors). Univariate survival analysis indicated that patients who had EZH2-positive IBC had a significantly lower 5-year OS rate than patients who had EZH2-negative IBC (P = .01). In multivariate analysis, only positive EZH2 status remained an independent predictor of worse OS.

CONCLUSIONS

EZH2 was expressed frequently in IBC tumors. The current results indicated that EZH2 expression status may be used to identify a subset of patients with IBC who have a relatively worse prognosis. Targeting EZH2 also may provide a novel strategy for improving the clinical outcome of patients with IBC.

FOXC1, a target of polycomb, inhibits metastasis of breast cancer cells

Polycomb group (PcG) proteins have recently been shown related to cancer development. The PcG protein EZH2 is involved in progression of prostate and breast cancers, and has been identified as a molecular marker in breast cancer. Nevertheless, the molecular mechanism by which PcG proteins regulate cancer progression and malignant metastasis is still unclear. PcG proteins methylate H3K27 in undifferentiated epithelial cells, resulting in the repression of differentiation genes such as HOX. FOXC1 is a member of the Forkhead box transcription factor family, which plays an important role in differentiation, and is involved in eye development. We discovered in this study that the expression of FOXC1 gene was negatively correlated to that of PcG genes, i.e., Bmi1, EZH2, and SUZ12, in MCF-7 and MDA-MB-231 cells. To investigate the regulatory effects of PcG proteins on FOXC1 gene, the two cell lines were transfected with either expression plasmids or siRNA plasmids of Bmi1, EZH2, and SUZ12, and we found that PcGs, especially EZH2, could repress the transcription of FOXC1 gene. Chromatin immunoprecipitation (ChIP) assay showed that histone methylation and acetylation modifications played critical roles in this regulatory process. When FOXC1 was stably transfected into MDA-MB-231 cells, the migration and invasion of the cells were repressed. Moreover, the tumorigenicity and the spontaneous metastatic capability regulated by FOXC1 were determined by using an orthotropic xenograft tumor model of athymic mice with the FOXC1-MDA-MB-231HM and the GFP-MDA-MB-231HM cells, and the results showed that FOXC1 in MDA-MB-231HM cells inhibited migration and invasion in vitro and reduced the pulmonary metastasis in vivo. Data presented in this report contribute to the understanding of the mechanisms by which EZH2 participates in tumor development.

The overexpression of polycomb group proteins Bmi1 and EZH2 is associated with the progression and aggressive biological behavior of hepatocellular carcinoma

Polycomb-group proteins Bmi1 and EZH2 are involved in the malignant transformation and biological aggressiveness of several human carcinomas. We herein examined the significance of the Bmi1 and EZH2 expression in hepatocellular carcinoma (HCC) and its preneoplastic lesions, dysplastic nodules. The expression of Bmi1 and EZH2 were examined immunohistochemically in HCC (n=27) and dysplastic nodules (n=14), and combined hepatocellular and cholangiocarcinoma (HC-CC) (n=14). The effect of Bmi1 and EZH2 knockdown was examined in cultured HCC cells (HuH7 and HepG2) using siRNA. It was determined that Bmi1 was constantly expressed in cholangiocytes, but not in hepatocytes, and EZH2 was detected in neither cholangiocytes nor hepatocytes. Bmi1 and EZH2 were overexpressed in HCC and more extensively in HC-CC (P<0.01). Interestingly, Bmi1 and EZH2 were not overexpressed in the dysplastic nodules. The expression of Bmi1 and EZH2 was heterogeneous and associated with vascular infiltration, the histological grades, and the cell proliferation activity in HCC and HC-CC. In cultured carcinoma cells overexpressing Bmi1 and EZH2, knockdown of Bmi1 and EZH2 resulted in decreased cell proliferation activities. Therefore, the overexpression of polycomb-group proteins Bmi1 and EZH2 is associated with the malignant progression of HCC, thereby reflecting the aggressive biological behavior in HCC and HC-CC.

A polycomb group protein, PHF1, is involved in the response to DNA double-strand breaks in human cell

DNA double-strand breaks (DSBs) represent the most toxic DNA damage arisen from endogenous and exogenous genotoxic stresses and are known to be repaired by either homologous recombination or nonhomologous end-joining processes. Although many proteins have been identified to participate in either of the processes, the whole processes still remain elusive. Polycomb group (PcG) proteins are epigenetic chromatin modifiers involved in gene silencing, cancer development and the maintenance of embryonic and adult stem cells. By screening proteins responding to DNA damage using laser micro-irradiation, we found that PHF1, a human homolog of Drosophila polycomb-like, Pcl, protein, was recruited to DSBs immediately after irradiation and dissociated within 10 min. The accumulation at DSBs is Ku70/Ku80-dependent, and knockdown of PHF1 leads to X-ray sensitivity and increases the frequency of homologous recombination in HeLa cell. We found that PHF1 interacts physically with Ku70/Ku80, suggesting that PHF1 promotes nonhomologous end-joining processes. Furthermore, we found that PHF1 interacts with a number of proteins involved in DNA damage responses, RAD50, SMC1, DHX9 and p53, further suggesting that PHF1, besides the function in PcG, is involved in genome maintenance processes.

Laser capture microdissection and microarray analysis of dividing neural progenitor cells from the adult rat hippocampus

Neural progenitor cells reside in the hippocampus of adult rodents and humans and generate granule neurons throughout life. Knowledge about the molecular processes regulating these neurogenic cells is fragmentary. In order to identify genes with a role in the proliferation of adult neural progenitor cells, a protocol was elaborated to enable the staining and isolation of such cells under RNA-preserving conditions with a combination of immunohistochemistry and laser capture microdissection. We increased proliferation of neural progenitor cells by electroconvulsive treatment, one of the most effective antidepressant treatments, and isolated Ki-67-positive cells using this new protocol. RNA amplification via in vitro transcription and subsequent microarray analysis revealed over 100 genes that were differentially expressed in neural progenitor cells due to electroconvulsive treatment compared to untreated control animals. Some of these genes have already been implicated in the functioning of neural progenitor cells or have been induced by electroconvulsive treatment; these include brain-derived neurotrophic factor (Bdnf), PDZ-binding kinase (Pbk) and abnormal spindle-like microcephaly-associated (Aspm). In addition, genes were identified for which no role in the proliferation of neurogenic progenitors has been described so far, such as enhancer of zeste homolog 2 (Ezh2).

Proteomic analysis of EZH2 downstream target proteins in hepatocellular carcinoma

Enhancer of zeste homolog 2 (EZH2) is suggested to be a potential therapeutic target and a diagnostic marker for cancer. Our previous study also showed the critical role of EZH2 in hepatocellular carcinoma (HCC) tumorigenesis. The present study is aimed at revealing the comprehensive downstream pathways of EZH2 by functional proteomic profiling. Lentivirus mediated RNA interference (RNAi) was employed to knockdown EZH2 in HCC cells. The 2-DE was employed to compare the expression profile difference between parental and EZH2-knockdown HCC cells. In total, 28 spots were differentially expressed during EZH2 inhibition. Among all, 18 proteins were identified by PMF with MALDI-TOF MS. Western blotting further validated upregulation of 60S acidic ribosomal protein P0 (L10E), and downregulation of two proteins with EZH2 inhibition: stathmin1 and probable protein disulfide isomerase (PDI) ER-60 precursor (ERp57). Moreover, L10E was downregulated with overexpression of EZH2 in hepatocytes, and L10E reversed the effect of EZH2 on cell proliferation, suggesting it a downstream target of EZH2. The comprehensive and comparative analyses of proteins associated with EZH2 could further our understanding on the downstream signal cascade of EZH2 leading to tumorigenesis.

EZH2 promotes proliferation and invasiveness of prostate cancer cells

BACKGROUND

The transcriptional repressor EZH2 is implicated in control of cell proliferation in embryonic, immortalized and transformed cells. EZH2 expression in prostate cancer correlates with progression to hormone-refractory and metastatic disease, but it is unknown whether EZH2 plays a specific role in the acquisition of an advanced prostate cancer phenotype.

METHODS

Using siRNA knockdown, we investigated the role of EZH2 in maintenance of prostate cancer cell proliferation and invasiveness. Using LNCaP cells with inducible EZH2 overexpression, we investigated whether EZH2 upregulation promotes an aggressive phenotype.

RESULTS

Knockdown of endogenous EZH2 reduced proliferation of androgen-responsive and androgen-independent prostate cancer cells. EZH2 knockdown also inhibited prostate cancer cell invasion. However, overexpression of EZH2 in androgen-responsive cancer cells did not appreciably affect either proliferation or invasiveness.

CONCLUSIONS

EZH2 promotes proliferation and invasion of prostate cancer cells, which can account for the correlation between EZH2 expression levels and an adverse prostate cancer prognosis.