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.
Regulation of GLUT4 exocytosisAs the epidemic of insulin resistance and type 2 diabetes emerges worldwide, there is an urgent need to understand how insulin maintains blood glucose homeostasis at the molecular level. A major function of insulin is to promote glucose uptake into muscle and adipose tissues, a process mediated by the glucose transporter GLUT4. Upon insulin stimulation, GLUT4 is relocated from intracellular storage vesicles to the cell surface through regulated exocytosis.
We are still at a very early stage of understanding the molecular basis of insulin-regulated GLUT4 trafficking. Our group investigates the biochemical properties of vesicle fusion proteins involved in GLUT4 exocytosis using both recombinant proteins and native proteins isolated from mouse adipocytes. We begin with known regulatory factors and continuously incorporate new factors identified in our ongoing genome-wide genetic screens. Our long-term vision is to map the protein-protein networks that mediate and regulate GLUT4 trafficking steps including protein sorting, motor-powered movements on cytoskeletons, exocytosis, endocytosis/recycling, and coupling to insulin signaling cascades. We also aim to understand how the networks are compromised in insulin resistance and type 2 diabetes.
Genome-wide mapping of membrane trafficking pathways
In the next chapter of membrane trafficking research, one of the most exciting directions is to unravel how the now-familiar core engines of vesicle transport are controlled by regulatory networks to achieve integrated physiological responses. Regulated membrane trafficking plays central roles in nearly every aspect of human physiology but we have very little knowledge about most of these physiological pathways. For instance, considering the vast complexity of synaptic exocytosis (neurotransmitter), what we know about GLUT4 trafficking and other mammalian exocytic pathways is just tip of the iceberg. Classic biochemical and biophysical approaches have been pivotal to our past studies and will continue to play essential roles in our research. However, by definition, these reductionist approaches are useful only to the studies of known factors. Therefore, it is critical to systematically identify and characterize all the components associated with a membrane trafficking pathway. A powerful way to dissect a biological pathway is unbiased genome-wide genetic screens. Many core membrane trafficking mediators were identified by classic genetic screens in model organisms, mainly in the yeast Saccharomyces cerevisiae. Mammalian trafficking pathways, however, are often significantly more complex, equipped with additional regulatory layers. RNA interference has been instrumental in unraveling mammalian gene functions but its broad applications in mammalian cell genetics are limited by incomplete gene silencing and extensive off-target effects.
The recent development of two revolutionary technologies – haploid genetics and CRISPR-Cas9 – enabled us to perform genome-wide genetic screens in mammalian cells in a similar way as in yeasts. Haploid genetics takes advantage of haploid cell lines including human cancer cells and murine pluripotent stem cells. Gene-trap mutations in haploid genetic screens can be precisely mapped to genomic locations such that the screens do not suffer the off-target effects observed in other genetic approaches. Another notable feature of haploid genetics is its ability to interrogate the whole genome, rather than being restricted to known coding regions. CRISPR-Cas9, on the other hand, allows for genetic screens in virtually any proliferating cell type including certain primary cells. We are using haploid genetics and CRISPR-Cas9 to dissect a range of mammalian membrane pathways including insulin-controlled GLUT4 trafficking. We aim to establish comprehensive maps of these pathways and define the functional interactions among the components.
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