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Volume 272, Number 40, Issue of October 3, 1997 pp. 24921-24926
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

The DNA Binding Domain of the A-MYB Transcription Factor Is Responsible for Its B Cell-specific Activity and Binds to a B Cell 110-kDa Nuclear Protein

(Received for publication, May 7, 1997, and in revised form, June 24, 1997)

Guo-Guang Ying , Marcello Arsura ^§ , Martino Introna and Josée Golay

From the  Laboratory of Molecular Immunohematology, Department of Immunology and Cell Biology, Istituto Ricerche Farmacologiche "Mario Negri," via Eritrea 62, 20157 Milano, Italy and the ^§ Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118-2394

Expression studies as well as the use of transgenic animals have demonstrated that the A-MYB transcription factor plays central and specific role in the regulation of mature B cell proliferation and/or differentiation. Furthermore, it is highly expressed in Burkitt's lymphoma cells and may participate in the pathogenesis of this disease. We have therefore investigated the transcriptional activity of A-MYB and its regulation in several human lymphoid cell lines using co-transfection assays and show that A-MYB is transcriptionally active in all the B cell lines studied, but not in T cells. In particular the best responder cell line was the Burkitt's cell line Namalwa. The activity of A-MYB in B and not T cells was observed when either an artificial construct or the c-MYC promoter was used as a reporter. Furthermore, the functional domains responsible for DNA binding, transactivation, and negative regulation, previously characterized in a fibroblast context, were found to have similar activity in B cells. The region of A-MYB responsible for the B cell specific activity was defined to be the N-terminal 218 amino acids containing the DNA binding domain. Finally, a 110-kDa protein has been identified in the nuclei of all the B, but not T, cell lines that specifically binds to this A-MYB N-terminal domain. We hypothesize that this 110-kDa protein may be a functionally important B cell-specific co-activator of A-MYB.

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