Expression of the polycomb-group gene BMI1 is related to an unfavourable prognosis in primary nodal DLBCL.

BACKGROUND: Clinical outcome in patients with diffuse large B cell lymphomas (DLBCL) is highly variable and poorly predictable. Microarray studies showed that patients with DLBCL with a germinal centre B cell-like (GCB) phenotype have a better prognosis than those with an activated B cell-like (ABC) phenotype. The BMI1 proto-oncogene was identified as one of the genes present in the signature of the ABC type of DLBCL, associated with a poor prognosis. OBJECTIVES: (1) To investigate, in primary nodal DLBCL, the expression of BMI1 and its association with clinical outcome and DLBCL signature; (2) to look for an association between BMI1 expression and the expression of its putative downstream targets p14ARF and p16INK4a. RESULTS: BMI1 expression was found to be associated with poor clinical outcome, but not clearly with an ABC-like phenotype of DLBCL. Expression of BMI1 was frequently, but not always, related to low levels of expression of p14ARF and p16INK4a. CONCLUSION: Expression of BMI1 is associated with an unfavourable clinical outcome of primary nodal DLBCL.

Of mice, flies, and man: the emerging role of polycomb-group genes in human malignant lymphomas.

Genes belonging to the Polycomb group (PcG) are responsible for the maintenance of cell identity and are directly involved in epigenetic gene silencing. They perform a vital role in the regulation of embryogenesis but also contribute to various adult processes, including regulation of the cell cycle and lymphopoiesis. Experimental model systems have demonstrated that enhanced expression of individual PcG genes, such as Bmi1, results in the development of B-cell and T-cell lymphomas. In humans, a growing body of work has now linked human PcG genes to various hematologic and epithelial cancers. This review focuses on the emerging role of PcG genes in the development of human malignant lymphomas.

Poorly differentiated breast carcinoma is associated with increased expression of the human polycomb group EZH2 gene.

Polycomb group (PcG) genes contribute to the maintenance of cell identity, cell cycle regulation, and oncogenesis. We describe the expression of five PcG genes (BMI-1, RING1, HPC1, HPC2, and EZH2) innormal breast tissues, invasive breast carcinomas, and their precursors. Members of the HPC-HPH/PRC1 PcG complex, including BMI-1, RING1, HPC1, and HPC2, were detected in normal resting and cycling breast cells. The EED-EZH/PRC2 PcG complex protein EZH2 was only found in rare cycling cells, whereas normal resting breast cells were negative for EZH2. PcG gene expression patterns in ductal hyperplasia (DH), well-differentiated ductal carcinoma in situ (DCIS), and well-differentiated invasive carcinomas closely resembled the pattern in healthy cells. However, poorly differentiated DCIS and invasive carcinomas frequently expressed EZH2 in combination with HPC-HPH/PRC1 proteins. Most BMI-1/EZH2 double-positive cells in poorly differentiated DCIS were resting. Poorly differentiated invasive carcinoma displayed an enhanced rate of cell division within BMI-1/EZH2 double-positive cells. We propose that the enhanced expression of EZH2 in BMI-1(+) cells contributes to the loss of cell identity in poorly differentiated breast carcinomas, and that increased EZH2 expression precedes high frequencies of proliferation. These observations suggest that deregulated expression of EZH2 is associated with loss of differentiation and development of poorly differentiated breast cancer in humans.

Increased expression of the EZH2 polycomb group gene in BMI-1-positive neoplastic cells during bronchial carcinogenesis.

Polycomb group (PcG) genes are responsible for maintenance of cellular identity and contribute to regulation of the cell cycle. Recent studies have identified several PcG genes as oncogenes, and a role for PcG proteins in human oncogenesis is suspected. We investigated the expression of BMI-1 and EZH2 PcG oncogenes in human bronchial squamous cell carcinomas (SCCs) and bronchial premalignant precursor lesions (PLs). Whereas normal bronchial epithelium was associated with widespread expression of BMI-1 in resting EZH2-negative cells, neoplastic cells in lung carcinomas displayed altered expression of both BMI-1 and EZH2. Two patterns of abnormal PcG expression were observed: increased expression of BMI-1 in dividing neoplastic cells of PLs and SCCs, and enhanced expression of EZH2 and Ki-67 in BMI-1-positive cells according to severity of the histopathologic stage. We propose that altered expression of BMI-1 and EZH2 is an early event that precedes high rates of proliferation in lung cancer. Because PcG complexes are normally involved in the maintenance of cell characteristics, abnormal PcG expression may contribute to loss of cell identity.

TCRBV CDR3 diversity of CD4+ and CD8+ T-lymphocytes in HIV-infected individuals.

TCRBV CDR3 repertoire diversity was analyzed in a cross-sectional study of HIV-infected individuals by CDR3 fingerprinting/spectratyping and single strand conformation polymorphism (SSCP). Most TCRBV families were detected in CD4+ cells of HIV-infected patients with CD4 counts ranging from 35 to 1103. In patients with CD4 counts >500, CD4+ TCRBV CDR3 fingerprinting profiles contained subtle variations with generally gaussian-distributed sizes. Lower CD4 counts coincided with more fragmented TCRBV CDR3 repertoires, containing dominant bands and bands missing from the CDR3 profiles. The CD8+ population of the same patients exhibited skewed CDR3 profiles of the majority of TCR BV families at CD4 counts >500. Irregularity of CD8+ CDR3 size distribution was most profound at low CD4 counts and suggested domination of the CD8+ TCRBV repertoire by a limited number of clones. Skewed patterns of CDR3 diversity probably reflect (oligo)clonal expansion of particular CD4+ and CD8+ cell populations during chronic infection with HIV. In addition, irregular CDR3 profiles of CD4+ and CD8+ at low CD4 counts suggest diminished TCR repertoire diversity, which may contribute to immunodeficiency.

Polycomb-group oncogenes EZH2, BMI1, and RING1 are overexpressed in prostate cancer with adverse pathologic and clinical features.

OBJECTIVES: Polycomb group (PcG) proteins are involved in maintenance of cell identity and proliferation. The protein EZH2 is overexpressed in disseminated prostate cancer, implicating a role of PcG complexes in tumor progression. In this study, we evaluated the expression of eight members of both PcG complexes in clinicopathologically defined prostate cancer. METHODS: Components of both PcG protein complexes PRC2 (EZH2, EED, YY1) and PRC1 (BMI1, RING1, HPH1, HPC1, HPC2) were immunohistochemically identified in tissue microarrays of 114 prostate cancer patients. Protein expression was semi-quantitatively scored and correlated with pathologic parameters and recurrence of prostate-specific antigen (PSA). RESULTS: Whereas BMI1, RING1, HPC1 and HPH1 were all abundantly present in normal and malignant prostate epithelium, expression of EZH2 occurred in only <10% of cells. Expression of EZH2, BMI1 and RING1 were all significantly enhanced in tumours with Gleason score (GS) > or = 8, extraprostatic extension, positive surgical margins, and PSA recurrence. When only the subgroup of GS < or = 6 was considered, representing the tumour grade in the majority of needle biopsies, EZH2 and BMI1 were also predictive for PSA recurrence. In a multivariable analysis, BMI1 was the only PcG protein with an independent prognostic value. CONCLUSIONS: PcG proteins EZH2, BMI1, and RING1 are associated with adverse pathologic features and clinical PSA recurrence of prostate cancer. Whereas BMI1 and RING1 are abundantly present in prostate cancer, EZH2 is expressed at relatively low levels, making it a less obvious target for therapy.

Deregulated expression of Polycomb-group oncogenes in human malignant lymphomas and epithelial tumors.

Genes belonging to the Polycomb-group (PcG) are epigenetic gene silencers with a vital role in the maintenance of cell identity. They contribute to regulation of various processes in both embryos and adults, including the cell cycle and lymphopoiesis. A growing body of work has linked human PcG genes to various hematological and epithelial cancers, identifying novel mechanisms of malignant transformation and paving the way to development of new cancer treatments and identification of novel diagnostic markers. This review addresses the current insights in the role of PcG genes in development of human malignancies.

Self-renewal of hematopoietic and leukemic stem cells: a central role for the Polycomb-group gene Bmi-1.

Self-renewal of hematopoietic stem cells is vital for the sustained daily production of blood cells. Two recent studies have shown that the Polycomb-group gene Bmi-1 is indispensable for regulation of self-renewal by normal and leukemic stem cells. This identifies Polycomb-group genes as potential targets for therapeutic intervention in leukemia, and possibly other forms of cancer.

Distinct expression patterns of polycomb oncoproteins and their binding partners during the germinal center reaction.

Polycomb group (PcG) genes encode two chromatin-binding protein complexes, the PRC1 and the PRC2 PcG complexes, which are essential for the maintenance of cell identity and play a role in oncogenesis. PcG complexes were recently identified as novel regulators of hematopoiesis, and appear to be expressed in a non-overlapping pattern in resting and mature follicular B cells. Using highly specific antisera in combination with immunohistochemistry and triple immunofluorescence, we investigated the expression pattern of nine human PcG genes in germinal center (GC) B cells and highly purified germinal center B cell subpopulations. PcG proteins were detected in characteristic binding patterns that were not necessarily related to mutually exclusive expression of the two PcG complexes. We conclude that the two PcG complexes are expressed throughout GC development, and that the fine composition of each complex is determined by the differentiation status of the cell. In addition, a subset of dividing cells with a centrocyte CD marker profile was identified that co-expresses core components of the PRC1 and PRC2 complex. We propose that these cells reflect a transitional stage between resting and dividing follicular B lymphocytes, and that they possibly represent the healthy precursors of nodal large B cell lymphomas.

Unique polycomb gene expression pattern in Hodgkin's lymphoma and Hodgkin's lymphoma-derived cell lines.

Human Polycomb-group (PcG) genes play a crucial role in the regulation of embryonic development and regulation of the cell cycle and hematopoiesis. PcG genes encode proteins that form two distinct PcG complexes, involved in maintenance of cell identity and gene silencing patterns. We recently showed that expression of the BMI-1 and EZH2 PcG genes is separated during normal B-cell development in germinal centers, whereas Hodgkin/Reed-Sternberg (H/RS) cells co-express BMI-1 and EZH2. In the current study, we used immunohistochemistry and immunofluorescence to determine whether the binding partners of these PcG proteins are also present in H/RS cells and H/RS-derived cell lines. PcG expression profiles were analyzed in combination with expression of the cell cycle inhibitor p16INK4a, because experimental model systems indicate that p16 is a downstream target of Bmi-1. We found that H/RS cells and HL-derived cell lines co-express all core proteins of the two known PcG complexes, including BMI-1, MEL-18, RING1, HPH1, HPC1, and -2, EED, EZH2, YY1, and the HPC2 binding partner, CtBP. Expression of HPC1 has not been found in normal mature B cells and other malignant lymphomas of B-cell origin, suggesting that the PcG expression profile of H/RS is unique. In contrast to Bmi-1 transgenic mice where p16INK4a is down-regulated, 27 of 52 BMI-1POS cases of HL revealed strong nuclear expression of p16INK4a. We propose that abnormal expression of BMI-1 and its binding partners in H/RS cells contributes to development of HL. However, abnormal expression of BMI-1 in HL is not necessarily associated with down-regulation of p16INK4a.

Site-specific expression of polycomb-group genes encoding the HPC-HPH/PRC1 complex in clinically defined primary nodal and cutaneous large B-cell lymphomas.

Polycomb-group (PcG) genes preserve cell identity by gene silencing, and contribute to regulation of lymphopoiesis and malignant transformation. We show that primary nodal large B-cell lymphomas (LBCLs), and secondary cutaneous deposits from such lymphomas, abnormally express the BMI-1, RING1, and HPH1 PcG genes in cycling neoplastic cells. By contrast, tumor cells in primary cutaneous LBCLs lacked BMI-1 expression, whereas RING1 was variably detected. Lack of BMI-1 expression was characteristic for primary cutaneous LBCLs, because other primary extranodal LBCLs originating from brain, testes, and stomach were BMI-1-positive. Expression of HPH1 was rarely detected in primary cutaneous LBCLs of the head or trunk and abundant in primary cutaneous LBCLs of the legs, which fits well with its earlier recognition as a distinct clinical pathological entity with different clinical behavior. We conclude that clinically defined subclasses of primary LBCLs display site-specific abnormal expression patterns of PcG genes of the HPC-HPH/PRC1 PcG complex. Some of these patterns (such as the expression profile of BMI-1) may be diagnostically relevant. We propose that distinct expression profiles of PcG genes results in abnormal formation of HPC-HPH/PRC1 PcG complexes, and that this contributes to lymphomagenesis and different clinical behavior of clinically defined LBCLs.

Evidence for at least three alternative mechanisms targeting the p16INK4A/cyclin D/Rb pathway in penile carcinoma, one of which is mediated by high-risk human papillomavirus.

A comprehensive analysis of 53 penile carcinomas was performed to determine which mechanisms might be involved in the disruption of the p16(INK4A)/cyclin D/Rb pathway. To that end, human papillomavirus (HPV) presence, p16(INK4A) expression and promoter methylation, and expression of the BMI-1 polycomb gene product were studied. Sixteen (30%) of the carcinomas were found to harbour high-risk HPV DNA, 15 of which contained HPV 16. HPV 16 E6/E7 oncogene transcripts were detected in 13 (87%) of the carcinomas that contained HPV 16. Strong immunostaining for p16(INK4A) was significantly more frequent in carcinomas that contained high-risk HPV DNA (p < 0.001) and amongst those with HPV 16 DNA, it was more frequent in lesions in which E6/E7 transcripts were detectable (p = 0.029). This supports an active role for HPV E7 in interfering with the p16(INK4A)/cyclin D/Rb pathway. Methylation of the p16(INK4A) promoter or overexpression of the BMI-1 polycomb gene product may provide alternative modes of interference with this pathway. These phenomena were mutually exclusive and found in the absence of HPV in 15% and 10% of the penile carcinomas, respectively. These data indicate that there are at least three plausible mechanisms by which the p16(INK4A)/cyclin D/Rb pathway can become disrupted during penile carcinogenesis.