A-Myb up-regulates Bcl-2 through a Cdx binding site in t(14;18) lymphoma cells.
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-2 promoter 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 of bcl-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.
Heckman
C A
CA
Center for Molecular Biology in Medicine, Veterans Affairs Palo Alto Health Care System and the Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.
Mehew
J W
JW
Ying
G G
GG
Introna
M
M
Golay
J
J
Boxer
L M
LM
D000818:Animals; D001402:B-Lymphocytes; D001665:Binding Sites; D000071616:CDX2 Transcription Factor; D004268:DNA-Binding Proteins / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D008224:Lymphoma, Follicular; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D014178:Translocation, Genetic / Q000235:genetics*; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays; D015854:Up-Regulation / Q000235:genetics
D000071616:CDX2 Transcription Factor; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C088831:MYBL1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D015534:Trans-Activators