329 Sands Bldg.
Duke University Med. Center
Durham, NC 27710
Email: richard DOT premont AT duke DOT edu
Medicine, Division of Gastroenterology, School of Medicine
My research focuses on the regulation of cell surface receptors coupled to GTP-binding proteins and the intracellular signaling networks downstream of these receptors.
Research area 1: G protein-coupled receptor kinases (GRKs) and G protein-coupled receptor signaling and regulation. GPCRs on the cell surface activate both heterotrimeric G protein and non-traditional, non-G protein pathways. GRKs phosphorylate activated GPCRs, initiating both desensitization of the receptor through uncoupling from downstream G proteins, as well as initiating receptor signaling to non-G protein pathways and trafficking of the receptor from the cell surface. Both events require the arrestin adaptor proteins, which bind to GRK-phosphorylated receptors. We have created lines of knockout mice lacking genes for GRK4, GRK5 and GRK6, and used these to assess the function and redundancy of GRK regulation and signaling. Our major findings thus far are that a particular receptor can be regulated by distinct GRKs in different tissues and organs, rather than by the same GRK in all locations throughout the body; and that receptor types vary in the degree to which they are regulated by GRKs, so that one receptor type can be regulated primarily by one GRK type (i.e., striatal D2 dopamine receptors and GRK6) while other receptor types are regulated by multiple GRKs acting together such that loss of any one appears to have no effect on function (i.e., BC-opioid receptor). One clinically relevant receptor we have focused on is the D2 dopamine receptor regulated by GRK6. Our initial investigations revealed that function of D2 dopamine receptors in the striatum was augmented in mice lacking GRK6. We are now pursuing the identification of small molecule GRK6 inhibitors as therapeutics for Parkinson's disease, where inhibition of GRK6 would augment the function of the remaining dopaminergic cells. We envisage that this would be most effective in combination with the standard therapy of L-DOPA replacement, allowing a reduction of L-DOPA dosage and staving off dyskinetic side effects.
Research area 2: GIT/PIX complexes, signaling scaffolds and small GTP-binding protein regulators at the crossroads of cellular signaling. Using a screen for signaling molecules interacting with GRKs to search for potential arrestin-independent signaling partners of GRKs, we identified the GIT proteins, GIT1 and GIT2. We showed that GIT proteins are GTPase-activating proteins (GAPs) for the ADP-ribosylation factor (Arf) family of small GTP-binding proteins, and turn off Arf protein signaling, for all three subclasses of Arf proteins. We showed that rather than acting alone, GIT proteins form oligomeric complexes with another family of proteins, the PIX proteins B1-PIX and B2-PIX; the PIX proteins are guanine nucleotide exchange factors (GEFs) for another small GTP-binding protein family, namely the Rho family members Rac1 and Cdc42. Together, GIT and PIX proteins are the two constituent subunits of oligomeric GIT/PIX complexes. GIT/PIX complexes function as recruitable signaling scaffolds by binding to a large number of signaling proteins (mainly protein kinases) and binding to a number of localizing partners at defined cellular locations, as well as being coordination centers for small GTP-binding protein activity. Our current research is focused on understanding the physiological and pathophysiological roles of GIT proteins, particularly on brain function and behavior, using GIT1 and GIT2 knockout mice lines we have developed. Despite nearly identical distribution throughout the brain, GIT1 and GIT2 serve very distinct functions. GIT1 knockout mice have normal emotionality but reduced cognitive function, while GIT2 knockout mice exhibit anxiety in a variety of tests but appear to have normal cognition. We are investigating the behavior, brain function and signaling differences between GIT1 and GIT2 knockouts to understand the mechanisms and consequences of distinct, non-overlapping functions between these two closely-related proteins. Tests of hyperarousal, fear-potentiated startle, fear conditioning and fear extinction indicate that GIT2 knockout mice massively over-respond to traumatic experiences by overgeneralizing fear and failing to forget fearful experiences. We are therefore developing the GIT2 knockout mice as a model for post-traumatic stress disorder. In particular, we are characterizing the brain signaling changes that accompany the development of the PTSD-like state in these mice to identify pathways mis-regulated in PTSD, as well as those brain signaling changes that underlie altered responses to abused drugs as a way to understand the very high incidence of substance abuse among PTSD patients. Both GIT1 and GIT2 mice are being studied as models of abnormal synaptic development and plasticity, as well.
Ph.D., Mount Sinai School of Medicine, City University of New York, Pharmacology 1992
M.Ph., Mount Sinai School of Medicine, City University of New York,1990
B.S., California Institute of Technology, Biology & Chemistry, 1985
L. Li, I. Rasul, J. Liu, B. Zhao, R. Tang, R.T. Premont , and W.Z. Suo, "Augmented axonal defects and synaptic degenerative changes in female GRK5 deficient mice." (2009) Brain Research Bulletin 78(4-5):145-51.
R. Schmalzigaug, R.M. Rodriguiz, L.E. Phillips, C.E. Davidson, W.C. Wetsel, and R.T. Premont , "Anxiety-like behaviors in mice lacking GIT2." (2008) Neuroscience Letters 451(2):156-161.
R. Schmalzigaug, H. Phee, C. E. Davidson, A. Weiss and R. T. Premont, "Differential Expression of the Arf GAP Genes GIT1 and GIT2 in Mouse Tissues." (2007) The Journal of Histochemistry and Cytochemistry 55(10): 1039-1048.
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