Defining Gene Regulatory Mechanisms
Paul A. Wade, Ph.D.
Tel (919) 541-3392
Fax (919) 541-0146
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Research Triangle Park, North Carolina 27709
The Eukaryotic Transcriptional Regulation Group is interested in defining gene regulatory mechanisms and identifying key regulatory molecules with a focus on chromatin modification. Currently, the group’s studies center on the Mi-2/NuRD complex, a multi-subunit chromatin modification enzyme (Wade et al., 1998). The complex consists of a SNF2-related chromatin remodeling ATPase (Mi-2), a member of the MBD family of methyl CpG binding domain proteins (MBD3), histone deacetylases (HDAC1 and HDAC2), a histone binding protein (RbAp46/p48), a protein of unknown function (known as p66), and an interesting subunit encoded by one of three genes (MTA1, MTA2, or MTA3) in mammals (Wade et al., 1999).
The group has proposed that members of the metastasis associated protein (MTA) family constitute alternative subunits of the complex (Bowen et al., 2004). This hypothesis predicts that individual MTA family members impart functional specificity on the complexes of which they are a component. The group’s recent work has involved establishment of systems to test this hypothesis. This research has led to the development of two unique systems for the analysis of Mi-2/NuRD complex function.
MI-2/NURD Complex Function in Breast Cancer
In the context of breast cancer cells, group members found that synthesis of MTA3 is directly regulated by the estrogen receptor and by estradiol (Fujita et al., 2004a). Further, the Eukaryotic Transcriptional Regulation Group conclusively demonstrated that MTA3 is a bona fide component of Mi-2/NuRD in estrogen receptor positive breast cancer cells (Fujita et al., 2003). As predicted by the group’s hypothesis, MTA3 is not found in association with either MTA1 or MTA2. Using a candidate approach, Snail was identified as a direct target of the transcriptional repression function of Mi-2/NuRD in breast cancer cells (Fujita et al., 2003). Snail is a transcription factor that initiates epithelial to mesenchymal transitions in normal development and in cancer. Thus, MTA3 and the Mi-2/NuRD complex are intimately involved in the genetic program downstream of estrogen receptor in breast cancer. At least one function of the complex is to repress genes critical to epithelial to mesenchymal transition, a critical component of invasion and metastasis.
MI-2/NURD Complex Function in the Immune System
The Eukaryotic Transcriptional Regulation Group has identified a second biological system that it intends to utilize to study Mi-2/NuRD complex function, the immune system. MTA3 is expressed in a very specific and tightly regulated pattern during development and differentiation of B lymphocytes. B lymphocytes develop from a common lymphoid precursor, ultimately differentiating into antibody secreting plasma cells following encounter with antigen in germinal centers. Germinal center B lymphocytes undergo a remarkable series of biological events, including somatic hypermutation and isotype switching, that results in affinity selection of immunoglobulins. These events are integral to acquired immunity. MTA3 is expressed in the B lymphocyte lineage solely in cells resident in the germinal center, mirroring the expression of the master regulator of B cell differentiation, the proto-oncogene BCL-6 (Figure 2).
The group discovered that MTA3 interacts directly with the transcriptional repressor BCL-6 in germinal center B lymphocytes. This interaction occurs through a novel repression domain located in the central region of BCL-6. Importantly, the interaction between MTA3 and BCL-6 is biologically regulated by acetylation of BCL-6 itself (Fujita et al., 2004b). BCL-6 and the MTA3 containing version of the Mi-2/NuRD complex are involved in repression of genes integral to the plasma cell transcriptional program. Thus, these two molecules participate in regulation of cell fate. When the appropriate biological cues are received, these cells change their transcriptional program to that of the terminally differentiated plasma cell. During this process, expression of both MTA3 and BCL-6 is extinguished.
Summary & Prospectives
The Eukaryotic Transcriptional Regulation Group is currently investigating transcriptional regulation and epigenetic mechanisms using these two rather disparate biological systems. It hopes to determine the roles of individual subunits in the biological function(s) of Mi-2/NuRD and define their biological regulation. Of particular interest in this regard is the coupling of a chromatin remodeling enzyme (the Mi-2 ATPase) to histone deacetylases.
Major areas of research:
Paul A. Wade, Ph.D., leads the Eukaryotic Transcriptional Regulation Group within the Laboratory of Molecular Carcinogenesis. He earned his Ph.D. in 1994 from Indiana University, Bloomington, Indiana and received postdoctoral training in the laboratory of the late Alan Wolffe at NICHD. He has published more than 50 peer-reviewed articles in leading biomedical journals as well as several book chapters. He served as an Assistant Professor in the Department of Pathology and Laboratory Medicine at Emory University before joining NIEHS in October, 2004.