David C. Pallas, PhD
Emory University School of Medicine
Office: 4125 Rollins Research Center
Emory University Department of Biochemistry
1510 Clifton Rd.
Rollins Research Center
Atlanta, GA 30322
Research FocusThe primary purpose of the research in my laboratory is to understand the molecular basis of the control of cell proliferation and of mechanisms by which this control is circumvented in neoplastic cell growth. Our approach has been to investigate the roles of a set of cellular proteins which associate with polyomavirus small and/or middle tumor (T) antigens. Middle T antigen (MT) is capable of transforming a wide variety of cell types to a state of uncontrolled cell proliferation. In some cases MT requires the help of the small T antigen (ST) for full transformation to occur. These proteins appear to exert their effects by associating with and altering the function of cellular proteins that are important players in the control of cell proliferation. Most of our recent efforts have focused on one of the proteins that we identified in complex with the T antigens, protein phosphatase 2A (PP2A). Our goal is to understand the roles of PP2A, a multisubunit, multifunctional phosphatase, in normal and T antigen-perturbed cell proliferation. Precipitating antibodies have been used, in combination with mutational analysis, to probe the regulation of PP2A subunit assembly and PP2A association with MT. We have used catalytically inactive mutants to study the role of PP2A activity in MT complex assembly and function. In addition to forming complexes with the normal PP2A regulatory subunits, the catalytically inactive mutants complex with several cellular proteins which do not bind active, wild-type PP2A. These proteins represent potential substrates or regulators of PP2A and are being isolated and studied. We have identified the first of these as a PP2A methylesterase, an enzyme which removes a regulatory methyl group from the carboxy-terminus of the PP2A catalytic subunit. The cloning of this methylesterase, the first mammalian protein methylesterase to be cloned, and the production of monoclonal antibodies capable of distinguishing the methylation state of PP2A together have facilitated many new experiments investigating the role of PP2A methylation. Our mutational analyses have also generated a series of mutants that are defective in binding of one or more regulatory subunits and/or in methylation. These mutants are being analyzed in yeast and in mammalian cells to investigate the roles of these different subunits and of methylation in regulating PP2A activity, localization, and the formation of PP2A complexes. Finally, we have identified a new family of PP2A regulatory subunits that appear to be scaffolding proteins involved in targeting PP2A to different cellular compartments and are likely involved in integrating PP2A phosphatase activity with the activity of cellular kinases. The roles and regulation of these complexes are being investigated.
Current Lab Members
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