Gerald V. Denis, Ph.D.
Scientific co-Director, Flow Cytometry Core
Faculty Member, Graduate Program in Molecular Medicine
A.B. Harvard College
M.Sc. University of Tokyo
Ph.D. University of California, Berkeley
We are interested in the immunological role of a novel transcriptional co-activator protein, called Brd2. This protein is closely related to the basal transcriptional co-activator TAFII250 and is a homolog of proteins that are important for development and homeosis in Drosophila and zebrafish. The human BRD2 gene is located within the class II major histocompatibility complex on Chromosome 6p, flanked by genes that are involved in antigen presentation, but quite surprisingly, Brd2 function appears to be involved in mitogenic signal transduction and has little to do with class II function directly. Brd2 harbors two bromodomains — a conserved protein motif comprised of about 110 amino acids that form four α-helices connected by two loops. Bromodomain proteins serve as adaptor or scaffolding modules that recruit transcription regulatory factors to chromatin to form protein complexes that regulate gene transcription in response to signal transduction. Brd2 has no sequence-specific DNA binding activity of its own, but its bromodomain motifs bind acetyl-lysine residues in the histones of nucleosomes or in transcription factors like p53, thus associating with promoter chromatin and controlling transcriptional status. We have used mass spectrometry analysis of multiprotein complexes to show that Brd2 also binds E2F proteins, histone acetylases and SWI/SNF complex components. Like the SWI/SNF complex, Brd2 can function as either a transcriptional co-activator or co-repressor, depending on the specific promoter and cellular context.
When expressed constitutively in the B cells of transgenic mice, Brd2 transactivates cyclin A to destabilize the cell cycle and cause B cell lymphoma and leukemia. When expressed acutely, Brd2 transactivates cell cycle genes, rendering cells hypersensitive to mitogens. We have recently reconstituted the murine immune system with hematopoietic stem cells transduced with lentiviruses for Brd2 overexpression or shRNA knockdown, and learned that Brd2 expression causes a dramatic expansion of the lymphoid compartment and B cell hypersensitivity to mitogens, nicely recapitulating the transgenic model, whereas Brd2 knockdown completely blocks lymphoid development, suggesting that this factor plays a crucial and fundamental role in normal immune biology and the processes of adaptive immunity, as well as in cancer. We are very actively engaged in elucidating the Brd2-specific transcriptional functions that have this major impact on B cell development and function.
Representative Publications:
1. Greenwald R., J. R. Tumang, A. Sinha, N. Currier, R. D. Cardiff, T. L. Rothstein, D. V. Faller and G. V. Denis (2004). Em-BRD2 transgenic mice develop B cell lymphoma and leukemia. Blood 103: 1475-1484. Sinha, A., D. V. Faller and G. V. Denis (2005). Bromodomain analysis of Brd2-dependent transcriptional activation of cyclin A. Biochem. J. 387: 257-269.
2. Denis, G. V., M. E. McComb, D. V. Faller, A. Sinha, P. B. Romesser and C. E. Costello (2006). Identification of transcription complexes that contain the double bromodomain protein Brd2 and chromatin remodeling machines. J. Proteome Res. 5: 502-511.
3. You, J., V. Srinivasan, G. V. Denis, W. J. Harrington Jr , M. E. Ballestas, K. M. Kaye and P. M. Howley (2006). The Kaposi’s Sarcoma-Associated Herpesvirus Latency-Associated Nuclear Antigen interacts with bromodomain protein Brd4 on host mitotic chromosomes. J. Virol. 80: 8909-8919.
4. Lenburg, M., A. Sinha, D. V. Faller and G. V. Denis (2007). Tumor-specific and proliferation-specific gene expression typifies murine transgenic B cell lymphomagenesis. J. Biol. Chem. 282: 4803-4811.
5. Longe, H., P. B. Romesser, A. Rankin, D. V. Faller, M. S. Eller, B. A. Gilchrest and G. V. Denis (2009). Telomere homolog oligonucleotides induce apoptosis in malignant but not in normal lymphoid cells: Mechanism and therapeutic potential. Int. J. Cancer. 124:473-482.
