Bmi-1 promotes invasion and metastasis, and its elevated expression is correlated with an advanced stage of 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/GSK3ß 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/GSK3ß/Snail pathway. CONCLUSIONS: This study demonstrates that Bmi-1 promotes the invasion and metastasis of human breast cancer and predicts poor survival.

Epstein-Barr virus-encoded LMP2A induces an epithelial-mesenchymal transition and increases the number of side population stem-like cancer cells in nasopharyngeal carcinoma.

It has been recently reported that a side population of cells in nasopharyngeal carcinoma (NPC) displayed characteristics of stem-like cancer cells. However, the molecular mechanisms underlying the modulation of such stem-like cell populations in NPC remain unclear. Epstein-Barr virus was the first identified human tumor virus to be associated with various malignancies, most notably NPC. LMP2A, the Epstein-Barr virus encoded latent protein, has been reported to play roles in oncogenic processes. We report by immunostaining in our current study that LMP2A is overexpressed in 57.6% of the nasopharyngeal carcinoma tumors sampled and is mainly localized at the tumor invasive front. We found also in NPC cells that the exogenous expression of LMP2A greatly increases their invasive/migratory ability, induces epithelial-mesenchymal transition (EMT)-like cellular marker alterations, and stimulates stem cell side populations and the expression of stem cell markers. In addition, LMP2A enhances the transforming ability of cancer cells in both colony formation and soft agar assays, as well as the self-renewal ability of stem-like cancer cells in a spherical culture assay. Additionally, LMP2A increases the number of cancer initiating cells in a xenograft tumor formation assay. More importantly, the endogenous expression of LMP2A positively correlates with the expression of ABCG2 in NPC samples. Finally, we demonstrate that Akt inhibitor (V) greatly decreases the size of the stem cell side populations in LMP2A-expressing cells. Taken together, our data indicate that LMP2A induces EMT and stem-like cell self-renewal in NPC, suggesting a novel mechanism by which Epstein-Barr virus induces the initiation, metastasis and recurrence of NPC.

Pre-malignant nasopharyngeal epithelial cell models.

Experimental models that allow investigation of nasopharyngeal carcinoma(NPC) progression could provide valuable insights of the molecular mechanism of nasopharyngeal carcinogenesis as well as potential clinical intervention. Because Epstein-Barr virus only infects humans and a few species of monkeys, representative NPC animal models have not been available so far. Attempts to provide cell models for early nasopharyngeal carcinogenesis have involved in the studies of in vitro transformation of normal finite lifespan human nasopharyngeal epithelial cells (NPEC) to immortality. The first two immortalized NPECs were established by introduction of ectopic SV40T or HPV E6/E7. In order to avoid the unrelated molecular alterations caused by the viral oncogenes, we established and characterized two immortalized NPECs by introduction of Bmi-1, an oncogene which has been demonstrated to be overexpressed in NPC cells and specimens. In addition, human telomerase reverse transcriptase (hTERT) immortalized NPECs have been established in both Tsao's and our laboratory. Unlike the immortalized cells induced by viral oncogenes, these immortal NPECs maintain a normal p53 checkpoint, and are unlikely to have other undefined genetic lesions except presenting some molecular alterations which have been observed in NPC. Thus, the establishment of the immortalized NPECs can be used to further study the mechanism of NPC development using defined genetic elements, particularly in elucidating the role of EBV infection in NPC development.

Bmi-1 expression predicts prognosis for patients with gastric carcinoma.

BACKGROUND AND OBJECTIVE: The Bmi-1 gene is a transcriptional repressor involved in oncogenesis in various human cancers. Here, we examine Bmi-1 expression in gastric carcinoma (GC) and investigates whether its expression correlates with patient prognosis. METHODS: Immunohistochemistry was performed using an anti-Bmi-1 antibody on primary tumor samples of 146 cases of GC. The association between Bmi-1 expression and the clinicopathological status and prognosis of GC patients was statistically analyzed. Furthermore, reverse transcription-PCR (RT-PCR) and Western blotting were performed to determine the expression levels of Bmi-1 in an additional 8 GC and the adjacent non-cancerous samples. RESULTS: Using immunohistochemistry, we found that 99 of 146 paraffin-embedded GC samples expressed Bmi-1 extensively. Statistical analysis showed that Bmi-1 overexpression was highly correlated with tumor size, clinical stage, lymph node metastasis and T classification (P < 0.05), Patients with Bmi-1 expression had shorter overall survival time than those without Bmi-1 expression (P < 0.01). Multivariate analysis indicated that Bmi-1 expression is an independent prognostic factor of GC. RT-PCR and Western blotting showed that Bmi-1 was up-regulated at both the transcriptional and translational levels in the GC tissues compared with the adjacent non-cancerous tissues. CONCLUSIONS: Bmi-1 may serve as a valuable marker for diagnosis and prognosis of GC.

Mel-18 acts as a tumor suppressor by repressing Bmi-1 expression and down-regulating Akt activity in breast cancer cells.

The Bmi-1 oncogene is overexpressed in a number of malignancies including breast cancer. In addition to Bmi-1, mammalian cells also express four other polycomb group (PcG) proteins that are closely related to Bmi-1. Virtually nothing is known about the role of these PcG proteins in oncogenesis. We have recently reported that Mel-18, a Bmi-1-related PcG protein, negatively regulates Bmi-1 expression, and that its expression negatively correlates with Bmi-1 in proliferating and senescing human fibroblasts. Here, we report that the expression of Bmi-1 and Mel-18 inversely correlates in a number of breast cancer cell lines and in a significant number of breast tumor samples. Overexpression of Mel-18 results in repression of Bmi-1 and reduction of the transformed phenotype in malignant breast cancer cells. Furthermore, the repression of Bmi-1 by Mel-18 is accompanied by the reduction of Akt/protein kinase B (PKB) activity in breast cancer cells. Similarly, Bmi-1 knockdown using RNA interference approach results in down-regulation of Akt/PKB activity and reduction in transformed phenotype of MCF7 cells. Importantly, we show that overexpression of constitutively active Akt overrides tumor-suppressive effect of Mel-18 overexpression and the knockdown of Bmi-1 expression. Thus, our studies suggest that Mel-18 and Bmi-1 may regulate the Akt pathway in breast cancer cells, and that Mel-18 functions as a tumor suppressor by repressing the expression of Bmi-1 and consequently down-regulating Akt activity.

[Expression and significance of Bmi-1 in breast cancer].

BACKGROUND & OBJECTIVE: Bmi-1, a putative oncogene, is a member of the polycomb group genes family. It is widely expressed in many kinds of tumors. This study was to investigate the expression and significance of Bmi-1 in breast cancer. METHODS: The expression of Bmi-1 protein in 58 specimens of breast cancer was detected by immunohistochemistry. The correlation of Bmi-1 expression to clinicopathologic features of breast cancer was analyzed. RESULTS: The intensive positive rate of Bmi-1 in breast cancer was 82.8%. The intensive expression of Bmi-1 was positively correlated to clinical stage and lymph node metastasis (P < 0.05), but not to tumor size, estrogen receptor (ER), progesterone receptor (PR), c-erbB-2 and vascular endothelial growth factor (VEGF) expression (P>0.05). CONCLUSIONS: The intensive expression of Bmi-1 in breast cancer is related to tumor progression. Bmi-1 may serve as a new molecular marker of metastasis of breast cancer.

Centromere protein H is a novel prognostic marker for nasopharyngeal carcinoma progression and overall patient survival.

PURPOSE: The aim of the present study was to analyze the expression of Centromere protein H (CENP-H), one of the fundamental components of the human active kinetochore, in nasopharyngeal carcinoma (NPC) and to correlate it with clinicopathologic data, including patient survival. EXPERIMENTAL DESIGN: Using reverse transcription-PCR and Western blot, we detected the expression of CENP-H in normal nasopharyngeal epithelial cells, immortalized nasopharyngeal epithelial cell lines, and NPC cell lines. Using immunohistochemistry, we analyzed CENP-H protein expression in 160 clinicopathologically characterized NPC cases. Statistical analyses were applied to test for prognostic and diagnostic associations. RESULTS: Reverse transcription-PCR and Western blot showed that the expression level of CENP-H was higher in NPC cell lines and in immortalized nasopharyngeal epithelial cells than in the normal nasopharyngeal epithelial cell line at both transcriptional and translational levels. By immunohistochemical analysis, we found that 76 of 160 (47.5%) paraffin-embedded archival NPC biopsies showed high expression of CENP-H. Statistical analysis showed that there was a significant difference of CENP-H expression in patients categorized according to clinical stage (P = 0.024) and T classification (P = 0.027). Patients with higher CENP-H expression had shorter overall survival time, whereas patients with lower CENP-H expression had better survival. A prognostic value of CENP-H was also found of the subgroup of N(0)-N(1) tumor classification. Multivariate analysis showed that CENP-H expression was an independent prognostic indicator for patient's survival. CONCLUSIONS: Our results suggest that CENP-H protein is a valuable marker of NPC progression. High CENP-H expression is associated with poor overall survival in NPC patients.