Phone: (303) 492-6166
GOLD A345C (GOLD A3B40 for Express Mail)
Ph.D. Columbia University, 2004
Signal transduction across membranes; Auto-feedback cellular homeostasis systems.
One hallmark during the evolution of life on the earth is the acquisition of a selectively-permeable lipid bilayer (cell membrane) that sequesters the cell from its surrounding environment. A eukaryotic cell is further subdivided by an extensive internal membrane network, creating compositionally distinct chemical reaction "vessels", or organelles. We are interested in how membrane proteins form molecular machines to maintain cellular homeostasis.
Regulation of GLUT4 exocytosis
Regulated vesicle exocytosis is a stimulus-dependent membrane fusion event that allows the cells to be in constant communication with their environment. One prominent example of regulated exocytosis is the insulin-triggered trafficking of the glucose transporter GLUT4. Following a meal, insulin promotes the uptake of glucose into adipocytes and muscle cells by relocating GLUT4 from intracellular reservoirs to the cell surface. Imbalances in GLUT4 exocytosis result in insulin resistance and type 2 diabetes.
Insulin modulates multiple stages of GLUT4 trafficking, in which vesicle fusion (merging of GLUT4-containing vesicles with the plasma membrane) is a key regulatory step. The regulatory mechanisms of GLUT4 vesicle fusion remain largely unknown due to a lack of mechanistic studies in minimal functional systems. GLUT4 vesicle fusion requires three SNARE proteins - syntaxin-4, SNAP-23, and VAMP2/synaptobrevin, as well as a large number of regulatory factors. Our long-term vision is to understand: a) how SNAREs and regulatory factors act in concert to mediate and regulate the fusion of GLUT4 vesicles, and b) how imbalances in GLUT4 vesicle fusion cause glucose intolerance and type 2 diabetes. We are addressing this problem from a novel angle by reconstituting GLUT4 vesicle fusion in vitro using purified components. Findings from the reconstitution studies will be verified in vivo using GLUT4 translocation assays in adipocytes. We also collaborate with physiologists to investigate the alterations of GLUT4 vesicle fusion in diabetes.
General principles of intracellular vesicle fusion in physiology and disease
It is challenging to elucidate the molecular basis of vesicle fusion proteins because members of the same protein family may possess both conserved and divergent functions. Our group is interested in dissecting and comparing vesicle fusion proteins from multiple transport pathways to establish their general as well as specialized mechanisms. In addition to GLUT4 exocytosis, we also investigate neurotransmitter release at the chemical synapse, yeast exocytosis, as well as intracellular fusion pathways (e.g. lysosomal fusion).
Currently we focus on the Sec1/Munc18 (SM) family proteins, soluble factors of 60-70 kDa. First discovered by Randy Schekman (University of California-Berkeley) in his classic yeast genetic screens, SM proteins are required for every pathway of intracellular vesicle trafficking. Mutations of SM proteins give rise to a number of devastating diseases including epilepsy, immune disorders, and ARC syndrome. We aim to understand the molecular mechanisms and physiological regulations of SM proteins using biochemical reconstitution, biophysical analysis, high-resolution imaging, and mammalian cell genetics.
Selective activation of cognate SNAREpins by Sec1/Munc18 proteins.
Shen, J, Tareste, DC, Paumet, F, Rothman, JE, and Melia, TJ Cell, 128(1):183-95. 2007
ER stress regulation of ATF6 localization by dissociation of BiP/GRP78 binding and unmasking of Golgi localization signals.
Shen, J, Chen, X, Hendershot, L, and Prywes, R Dev Cell, 3(1):99-111. 2002