648

BMI1

BMI1 proto-oncogene, polycomb ring finger;BMI1;BMI1 proto-oncogene, polycomb ring finger

B lymphoma Mo-MLV insertion region 1 homolog|BMI1 polycomb ring finger oncogene|BMI1 polycomb ring finger proto-oncogene|flvi-2/bmi-1|murine leukemia viral (bmi-1) oncogene homolog|polycomb complex protein BMI-1|polycomb group RING finger protein 4|polyco

10p11.23

protein-coding

B-lymphoma Moloney murine leukaemia virus insertion region-1 (BMI1) is a member of the polycomb group of transcription repressors, which functions in stem cell maintenance and oncogenesis through the inhibition of the INK4A/ARF tumour suppressor locus. Overexpression of BMI1 is associated with poor prognosis in several human cancers, including breast cancer. We have previously shown that BMI1 collaborates with H-RAS to induce transformation of MCF10A human mammary epithelial cells through dysregulation of multiple growth pathways independent of the INK4A/ARF locus. In this study, we show that BMI1 collaborates with H-RAS to promote increased proliferation, invasion and resistance to apoptosis in vitro, and an increased rate of spontaneous metastases from mammary fat pad xenografts including novel metastases to the brain. Furthermore, in collaboration with H-RAS, BMI1 induced fulminant metastatic disease in the lung using a tail vein model of haematogenous spread through accelerated cellular proliferation and inhibition of apoptosis. Finally, we show that knockdown of BMI1 in several established breast cancer cell lines leads to decreased oncogenic behaviour in vitro and in vivo. In summary, BMI1 collaborates with H-RAS to induce an aggressive and metastatic phenotype with the unusual occurrence of brain metastasis, making it an important target for diagnosis and treatment of aggressive breast cancer.

BACKGROUND: B-lymphoma Moloney murine leukemia virus insertion region-1 (Bmi-1) acts as an oncogene in various tumors, and its overexpression correlates with a poor outcome in several human cancers. Ectopic expression of Bmi-1 can induce epithelial-mesenchymal transition (EMT) and enhance the motility and invasiveness of human nasopharyngeal epithelial cells (NPECs), whereas silencing endogenous Bmi-1 expression can reverse EMT and reduce the metastatic potential of nasopharyngeal cancer cells (NPCs). Mouse xenograft studies indicate that coexpression of Bmi-1 and H-Ras in breast cancer cells can induce an aggressive and metastatic phenotype with an unusual occurrence of brain metastasis; although, Bmi-1 overexpression did not result in oncogenic transformation of MCF-10A cells. However, the underlying molecular mechanism of Bmi-1-mediated progression and the metastasis of breast cancer are not fully elucidated at this time. RESULTS: Bmi-1 expression is more pronouncedly increased in primary cancer tissues compared to matched adjacent non-cancerous tissues. High Bmi-1 expression is correlated with advanced clinicopathologic classifications (T, N, and M) and clinical stages. Furthermore, a high level of Bmi-1 indicates an unfavorable overall survival and serves as a high risk marker for breast cancer. In addition, inverse transcriptional expression levels of Bmi-1 and E-cadherin are detected between the primary cancer tissues and the matched adjacent non-cancerous tissues. Higher Bmi-1 levels are found in the cancer tissue, whereas the paired adjacent non-cancer tissue shows higher E-cadherin levels. Overexpression of Bmi-1 increases the motility and invasive properties of immortalized human mammary epithelial cells, which is concurrent with the increased expression of mesenchymal markers, the decreased expression of epithelial markers, the stabilization of Snail and the dysregulation of the Akt/GSK3beta pathway. Consistent with these observations, the repression of Bmi-1 in highly metastatic breast cancer cells remarkably reduces cellular motility, invasion and transformation, as well as tumorigenesis and lung metastases in nude mice. In addition, the repression of Bmi-1 reverses the expression of EMT markers and inhibits the Akt/GSK3beta/Snail pathway. CONCLUSIONS: This study demonstrates that Bmi-1 promotes the invasion and metastasis of human breast cancer and predicts poor survival.

AIM: It has been reported that BMI-1, a gene transcription promoter overexpressed in various human cancers, is associated with poor survival. We investigated whether BMI-1 is a marker for cervical cancer by detecting the expression of BMI-1 in cervical cancer. METHODS: An immunohistochemistry (IHC) streptavidin-peroxidase technique was used to identify BMI-1 protein expression in 302 cervical cancer specimens. Reverse transcription polymerase chain reaction and Western blot were employed to measure BMI-1 mRNA and protein level. The correlation between BMI-1 expression and clinicopathological factors was analyzed. RESULTS: Both BMI-1 mRNA and protein expression were evident in cervical carcinoma tissues. An intense positive rate of 55.3% (167/302) was observed by IHC. High BMI-1 expression was correlated with clinical stage, lymph node metastasis, vascular invasion and human papillomavirus (HPV) infection (P < 0.05), but there is insufficient evidence to confirm its value in tumor size, age, estrogen or progesterone receptor (P > 0.05). The BMI-1 protein level was positively correlated with the clinical stages of cervical carcinoma and a high BMI-1 expression was associated with poor prognosis (P < 0.05). CONCLUSION: The high expression of BMI-1 in cervical cancer is related to tumor progression, lymph node metastasis and HPV infection, suggesting that cervical cancer with excessive BMI-1 expression possesses high metastases potential and that BMI-1 may be a promising biomarker for predicting metastasis in cervical cancer.

BACKGROUND & OBJECTIVE: Bmi-1, a putative oncogene, is a member of the polycomb group genes, and is expressed in many human tumors. Ki67 is an important nuclear antigen associated with cell proliferation. This study was to investigate the expression, significance and correlation of Bmi-1 and Ki67 in colorectal carcinoma (CRC) tissues. METHODS: Protein expressions of Bmi-1 and Ki67 in sixty CRC, 30 adenomas and 20 normal colorectal mucosal tissues were detected using immunohistochemistry. Correlations of the expression of Bmi-1 and Ki67 to clinicopathological features and survival of patients were analyzed. RESULTS: The expression rates of Bmi-1 and Ki67 were 25.0%, 6.7%, 0% and 18.3%, 3.3% and 0% in CRC, adenomas and normal colorectal mucosal tissues, respectively. The expression of Bim-1 and Ki67 were significantly higher in CRC than in adenomas and normal colorectal mucosal tissues (P<0.05). Chi-square test revealed that the overexpression of Bmi-1 protein in CRC was correlated to distant metastasis (P<0.01) and TNM stage (P<0.05), while the overexpression of Ki67 protein was associated with age, distant metastasis and TNM stage (P<0.05). Further logistic regression analysis showed that only distant metastasis was correlated with Bmi-1 overexpression (P<0.01,OR>1), and only age was correlated with Ki67 overexpression(P<0.05, OR<1). Kaplan-Meier survival analysis showed that the survival was significantly shorter in CRC patients with overexpression than low expression of Bmi-1 and Ki67 (P<0.05). CONCLUSIONS: Overexpression of Bmi-1 and Ki67 protein are significantly correlated with tumorigenesis, metastasis and prognosis of CRC. Bmi-1 and Ki67 might be used to predict the prognosis of CRC. Bmi-1 might regulate the expression of Ki67 indirectly in CRC patients.

OBJECTIVE: To investigate the expression of B cell specific MLV integration site-1 (Bmi-1) in colorectal cancer (CRC) and its correlation to the clinicopathological features and prognosis of CRC. METHODS: Sixty CRC, 30 adenomas and 20 normal colorectal mucosal tissues were collected to detect the expression of Bmi-1 protein using immunohistochemistry, and the results were analyzed in comparison with the clinicopathological features and survival rate of patients. RESULTS: The positivity rate of Bmi-1 expression in CRC tissue was 51.7%. In CRC, the rate of Bmi-1 overexpression was 25.0%, significantly higher than that in the adenomas and normal colorectal mucosal tissues (6.67% and 0%, respectively, P<0.05). The overexpression of Bmi-1 protein in CRC was obviously associated with distant metastasis and the TNM stage (P<0.05), but not with gender, age, tumor size, tumor site, histological type, differentiation degree and lymph node metastasis (P>0.05). But logistic regression analysis showed that Bmi-1 protein overexpression in CRC was associated only with distant metastasis (P<0.01,OR>1); Kaplan-Meier survival analysis showed that the survival rate of the patients with high Bmi-1 expression was significantly lower than that in patients with low expression (P<0.05). CONCLUSION: The overexpression of Bmi-1 protein was significantly correlated to the tumorigenesis, metastasis and prognosis of CRC, and may serve as an indicator for evaluating the prognosis of CRC.

OBJECTIVE: To investigate the association of B cell-specific MLV integration site-1 (Bmi-1) mRNA expression level with the differentiation, metastasis and prognosis of gastric carcinoma. METHODS: Tissue specimens were obtained from 42 patients undergoing surgery for gastric carcinomas. Reverse transcriptional PCR (RT-PCR) was performed for amplification of Bmi-1 mRNA from the 42 tumor tissues and matched adjacent normal tissues, and the differential Bmi-1 mRNA expression was analyzed for its association with the clinical manifestations of the patients. RESULTS: Bmi-1 mRNA expression was detected in all the gastric carcinoma tissues and normal tissues adjacent to the carcinoma using fluorescence method, and in 29 cases, Bmi-1 mRNA expression was significantly higher in the tumor tissues than in the adjacent tissues. expression of Bmi-1 mRNA was highly correlated with tumor size, lymph node metastasis and T classification (P<0.05), but not with the patients' gender, age, or tumor differentiation (P>0.05). The survival rate was much lower in patients positive for Bmi-1 mRNA expression than in those without Bmi-1 mRNA expression. CONCLUSIONS: Bmi-1 mRNA expression is correlated to differentiation and metastasis of gastric carcinoma and may facilitate its prognostic evaluation. Bmi-1 may serve as a marker for assessing the progression of gastric carcinoma and provide assistance for clinical therapeutic decisions.

AIM: To evaluate the impact of Bmi-1 on cell senescence and metastasis of human gastric cancer cell line BGC823. METHODS: Two pairs of complementary small hairpin RNA (shRNA) oligonucleotides targeting the Bmi-1 gene were designed, synthesized, annealed and cloned into the pRNAT-U6.2 vector. After DNA sequencing to verify the correct insertion of the shRNA sequences, the recombinant plasmids were transfected into BGC823 cells. The expression of Bmi-1 mRNA and protein was examined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. The effects of Bmi-1 knockdown on cell senescence and metastasis were determined by the beta-Gal activity assay and Boyden chamber assay, respectively. RESULTS: The double-stranded oligonucleotide fragments of Bmi-1 short interfering RNA (siRNA) cloned into pRNAT-U6.2 vector conformed to the inserted sequence. RT-PCR and Western blotting indicated that the expression levels of Bmi-1 gene mRNA and protein were markedly decreased in transfected BGC823 cells with pRNAT-U6.2-si1104 and pRNAT-U6.2-si1356, especially in transfected BGC823 cells with pRNAT-U6.2-si1104, compared with two control groups (empty vector and blank group). In particular, Bmi-1 protein expression was almost completely abolished in cells transfected with the recombinant vector harboring shRNA targeting the sequence GGAGGAGGTGAATGATAAA (nt1104-1122). Compared with untransfected cells and cells transfected with the empty vector, the mean percentage of senescent cells increased and the number of cells passing through the Matrigel decreased in cells transfected with the recombinant vectors. CONCLUSION: Silencing Bmi-1 by RNA interference can increase the senescent cell rate and effectively reduce the metastasis of gastric cancer cells.

Bmi-1 has been implicated in cancer cell growth and metastasis in a variety of tumor types. In this study, we sought to evaluate the expression of Bmi-1 in lung adenocarcinoma samples, and to determine if a correlation exists between Bmi-1 expression and clinical features of lung cancer, such as metastasis. Our results showed that Bmi-1 expression is increased in lung cancer tissues compared to adjacent non-cancerous tissues, and is associated with clinical features of lung cancer, including clinical stage and distant metastasis. We were then interested in determining if shRNA-mediated knockdown of Bmi-1 would inhibit metastasis of lung adenocarcinoma cells. To this end, we chose the most efficient shRNA duplexes targeting Bmi-1, and constructed two stably transfected lung adenocarcinoma cell lines (A549 and SPCA1). The shRNA-mediated knockdown of Bmi-1 significantly reduced migration in vitro, and metastasis in vivo, of A549 and SPCA1 cells. More importantly, knockdown of Bmi-1 also upregulated PTEN expression, and downregulated p-Akt and VEGF expression. These data support the hypothesis that Bmi-1 regulates key pathways involved in the metastasis of lung adenocarcinoma cells.

AIM: Enhancer of zeste homolog-2 (EZH2) and B lymphoma Mo-MLV insertion region-1 homolog (BMI1) are members of the polycomb group of proteins, which function as transcriptional repressors through chromatin modification. EZH2 forms part of the polycomb repressive complex (PRC)-2, while BMI1 is a component of PRC1. Previous studies have shown that EZH2 is highly expressed in various type of cancers. expression of EZH2 is reported to be regulated by the P53-E2F/retinoblastoma (RB)-related pathway, and a correlation between P53 mutation and EZH2 expression was recently found in breast cancer. Here, we examined the relationship between P53 and EZH2 in oral squamous cell carcinoma (OSCC). MATERIALS AND METHODS: Using immunohistochemistry, we investigated the expression of EZH2 and BMI1 in 99 surgically-resected OSCC and 34 epithelial dysplasia samples. We analyzed associations between aberrant expression of EZH2 and BMI1, and clinicopathological findings and patient outcome. P53 expression was also examined and analyzed in relation to EZH2 and BMI1 expression. RESULTS: EZH2 and BMI1 protein were up-regulated in OSCC tissues compared with epithelial dysplasia and normal epithelium. Aberrant EZH2 and BMI1 protein expression was observed in 32 and 59 of the 99 OSCC samples, respectively. Aberrant EZH2 and BMI1 expression was significantly associated with mode of invasion, but not with lymph node metastasis or survival rate. Aberrant EZH2 expression was associated with P53 alteration in OSCC tissue. expression of EZH2 mRNA in SAS/neo cells, which have wild-type P53, was significantly lower than in SAS/mp53 cells that have a mutant P53 gene. CONCLUSION: P53 alteration may be involved in dysregulated EZH2 expression, and aberrant expression of EZH2 may play a role in carcinogenesis of OSCC.

The Polycomb group (PcG) gene BMI1 is required for the proliferation and self-renewal of normal and leukemic stem cells. Overexpression of Bmi1 oncogene causes neoplastic transformation of lymphocytes and plays essential role in pathogenesis of myeloid leukemia. Another PcG protein, Ezh2, was implicated in metastatic prostate and breast cancers, suggesting that PcG pathway activation is relevant for epithelial malignancies. Whether an oncogenic role of the BMI1 and PcG pathway activation may be extended beyond the leukemia and may affect progression of solid tumors as well remains unknown. Here we demonstrate that activation of the BMI1 oncogene-associated PcG pathway plays an essential role in metastatic prostate cancer, thus mechanistically linking the pathogenesis of leukemia, self-renewal of stem cells, and prostate cancer metastasis. To characterize the functional status of the PcG pathway in metastatic prostate cancer, we utilized advanced cell- and whole animal-imaging technologies, gene and protein expression profiling, stable siRNA-gene targeting, and tissue microarray (TMA) analysis in relevant experimental and clinical settings. We demonstrate that in multiple experimental models of metastatic prostate cancer both BMI1 and Ezh2 genes are amplified and gene amplification is associated with increased expression of corresponding mRNAs and proteins. For the first time, we provide images of human prostate carcinoma metastasis precursor cells isolated from blood and shown to overexpress both BMI1 and Ezh2 oncoproteins. Consistent with the PcG pathway activation hypothesis, increased BMI1 and Ezh2 expression in metastatic cancer cells is associated with elevated levels of H2AubiK119 and H3metK27 histones. Quantitative immunofluorescence colocalization analysis and expression profiling experiments documented increased BMI1 and Ezh2 expression in clinical prostate carcinoma samples and demonstrated that high levels of BMI1 and Ezh2 expression are associated with markedly increased likelihood of therapy failure and disease relapse after radical prostatectomy. Gene-silencing analysis reveals that activation of the PcG pathway is mechanistically linked with highly malignant behavior of human prostate carcinoma cells and is essential for in vivo growth and metastasis of human prostate cancer. We conclude that the results of experimental and clinical analyses indicate the important biological role of the PcG pathway activation in metastatic prostate cancer. Our work suggests that the PcG pathway activation is a common oncogenic event in pathogenesis of metastatic solid tumors and provides justification for development of small molecule inhibitors of the PcG chromatin silencing pathway as a novel therapeutic modality for treatment of metastatic prostate cancer.