A-Myb Up-regulates Bcl-2 through a Cdx Binding Site in t(14;18) Lymphoma Cells

• Published in: The Journal of biological chemistry 2000-03, Vol.275 (9), p.6499-6508
• Main Authors: Heckman, Caroline A., Mehew, John W., Ying, Guo-Guang, Introna, Martino, Golay, Josee, Boxer, Linda M.
• Format: Article
• Language: English
• Subjects: A-Myb protein; Animals; B-Lymphocytes; Binding Sites; Cdx2 protein; CDX2 Transcription Factor; chromosome 14; chromosome 18; DNA-Binding Proteins - genetics; Gene Expression Regulation, Neoplastic - genetics; Homeodomain Proteins - genetics; Humans; Lymphoma, Follicular; Mutagenesis; Promoter Regions, Genetic; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - metabolism; Rats; RNA, Messenger - metabolism; Trans-Activators - metabolism; Transfection; Translocation, Genetic - genetics; Tumor Cells, Cultured; Ultraviolet Rays; Up-Regulation - genetics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.275.9.6499

In follicular lymphoma, bcl-2 is translocated to the immunoglobulin heavy chain locus leading to deregulation of bcl-2 expression. We examined the role of Myb proteins in the regulation of bcl-2 expression in lymphoma cells. We showed that A-Myb up-regulates bcl-2promoter activity. Northern and Western analyses demonstrated that A-Myb was expressed in the DHL-4 t(14;18) cell line. In t(14;18) cells and mature B cells, A-Myb up-regulated bcl-2 expression, whereas B- and c-Myb had little effect on bcl-2 gene expression. Deletion analysis of the bcl-2 5′-region identified a region responsive to A-Myb in t(14;18) cells. A potential binding site for the Cdx homeodomain proteins was located in this sequence. Analysis of the A-Myb-responsive region by UV cross-linking experiments revealed that a 32-kDa protein formed a complex with this region, but direct binding by Myb proteins could not be demonstrated. A-Myb could be recovered along with Cdx2 when nuclear extracts were passed over the Cdx site. Mutagenesis of the Cdx binding site abolished binding by the 32-kDa protein and significantly reduced the ability of A-Myb to induce bcl-2 expression. A strong induction ofbcl-2 P2 promoter activity was observed in cotransfection studies of DHL-4 cells with the A-Myb and Cdx2 expression vectors, and increased endogenous Bcl-2 protein expression was observed in B cells transfected with A-Myb and/or Cdx2 expression constructs.