The JAK-STAT signaling pathway is the major pathway for most cytokine and growth factors. Signals from extracellular ligands binding to cell surface receptors are directly transduced to the nucleus by STATs (Signal Transducer and Activator of Transcription), a family of transcription factors, resulting in the transcriptional activation of specific sets of genes. The focus of our research is to understand how STATs communicate the signals to the RNA polymerase machinery to induce gene expression. Biochemical approaches were used to characterize the transcription activation domain (TAD) of Stat1 and to purify specific Stat1 TAD-interacting proteins that might be co-activators involved in transcriptional activation in response to interferon-gamma. We have identified a group of nuclear proteins that potentially form a novel complex in the process of Stat1-induced transcriptional activation, specifically through chromatin remodeling. One member of this group is CBP/p300, a general transcription co-activator providing histone acetylase activity in disrupting nucleosome structure. A second protein, MCM5, previously known to be required for DNA replication, was shown to be involved in interferon-gamma-stimulated transcriptional activation by Stat1, probably to provide a helicase activity in the unwinding of the DNA duplex to facilitate transcription initiation. These novel findings not only provide a beginning in revealing the molecular mechanism of communication between STATs and the basal transcription machinery they also suggest new mechanisms for the anti-viral and growth-inhibitory effect of interferon-gamma.

Our current research includes further characterization of the above mentioned group of Stat1-interacting nuclear protein and functional analyses of their involvement in transcriptional activation by Stat1 through analyses of complex formation, enzymatic activities, role in chromatin remodeling and in vitro transcription system with chromatin templates. In addition, we are studying the JAK-STAT pathway in a new biological system, the IgH (immunoglobulin heavy chain) locus. STAT proteins are the major players in cytokine-regulated biological processes in the immune system. In particular, generation of specific isotypes of antibodies in B cells requires cytokine-regulated STAT-dependent transcriptional activation in the IgH locus under the control of two enhancers. For example, one member of family, Stat6, and the transcription activation mediated by Stat6 in the IgH locus is induced by interleukin-4 and required for generation of IgE, the isotype of antibodies involved in allergic response. Another member of STATs, Stat1, mediates IFN-gamma-induced transcription and generation of IgG2a, the isotype of antibody involved in anti-viral response. A locus control region has been proposed to regulate the expression of these genes, possibly mediated by STATs. It is likely that in response to different cytokines, different STAT proteins recruit specific proteins including chromatin remodeling factors to the locus to participate in the regulation of expression of specific genes. Studies of STAT-interacting proteins will not only contribute to the understanding of general mechanisms of chromatin remodeling in the process of transcriptional activation, it will also provide ways to develop potentially highly-specific therapeutic methods for diseases involving the immune system, such allergy and autoimmune problems, through disruption/inhibition of the interactions.