Molecular analysis of B-cell malignant lymphoma-related oncogenes and its clinical application for diagnosis and treatment.

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1) BCL6. The BCL-6/LAZ3 gene encodes a zinc-finger transcriptional repressor and is located at the breakpoint of the 3q27-associated translocations that occur most frequently in non-Hodgkin's lymphomas (NHLs To examine cell responses and target genes related to the BCL-6 signaling pathway, we established Ba/F3 pro-B cells carrying a human BCL-6 transgene that is inducible under control of the lactose operon. Using a CDNA array hybridization technique, we found that the induced BCL-6 protein can downregulate the expressions of the genes, cyclin A2, chemokine receptor CXCR4, and insulin-like growth factor binding protein-4 (IGFBP-4) in the Ba/F3 cells. Northern blot analysis established that the expressions of these genes were indeed downregulated by the induced BCL-6 protein but in a somewhat different manner. The induced BCL-6 protein also inhibited cell proliferation of Ba/F3 cells. These findings strongly suggest that three key genes, namely cyclin A2, CXCR4 and IGFBP-4 may play a ro … More le in the downstream of the BCL-6 signaling pathway during B - lymphoid differentiation.2) API2-MALT1. t(11;18)(q21;q21) is a characteristic chromosomal translocation in mucosa-associated lymphoid tissue (MALT) type lymphoma, and this translocation results in chimeric transcript of API2 (Apoptosis Inhibitor 2, also known as c-IAP2) - MALT1 (Mucosa-Associated Lymphoma Translocation gene 1). To identify proteins that bind API2-MALT1 chimeric protein, we employed coimmunoprecipitation and SDS PAGE analysis, followed by liquid chromatography-electrospray ionization tandem mass spectrometry. As a result, Smac, Htra2, and TRAF2 were identified as API2-MALT1-binding proteins. Immunoprecipitation analysis demonstrated that ectopically expressed API2-MALT1 protein indeed binds to these endogeneous proteins. Furthermore, API2-MALT1 protein significantly inhibited Smac-promoted apoptosis in UV irradiated HeLa cells. These data strongly suggest that API2-MALT1 can block apoptosis, at least in part, by inhibiting Smac-mediated apoptotic pathway. Less