Most cells depend on glucose as their primary substrate for energy production and carbon storage. In addition, glucose serves a role in regulating the expression of proteins involved in its own metabolism. These include the proteins involved in glucose transport, which is often the rate-limiting step in its metabolism. Animal studies suggest that basal glucose uptake in adipose tissue is directly related to the expression and activity of GLUT1, the """"""""constitutive"""""""" glucose transporter. We have focused specifically on the regulation of GLUT1 by glucose, itself. To accomplish this, we have used 3T3-L1 adipocytes which afford characterization over extended time in a controlled environment. In cells deprived of glucose, we have shown that transport activity increases by 20-fold, not an insignificant change. The relevance to this observation is that a 4-fold change is observed over the physiological extremes of circulating glucose. Because GLUT1 expression does not change, this led to the hypothesis that GLUT1 is activated in response to glucose deprivation. We now know that a proportion of the GLUT1 pool in plasma membranes resides in lipid rafts. This percentage increases in response to deprivation. New data demonstrate that GLUT1 reconstituted from lipid rafts isolated from glucose-deprived cells exhibits higher """"""""intrinsic activity"""""""" than that observed from control cells. Interestingly, we are able to demonstrate a specific interaction between GLUT1 and stomatin, a protein that exists almost exclusively in the lipid raft fraction. Glucose-deprivation increases this interaction, which infers that stomatin and GLUT1 interact within lipid rafts. Together, these data suggest that the environment of lipid rafts plays a role in GLUT1 function. These novel observations have led to new directions in our attempts to understand the nutrient-dependent control of glucose transport.
In Specific Aim 1, we focus on the targeting of GLUT1 to lipid rafts.
In Specific Aim 2, we explore the role of lipids in rafts on transport function.
In Specific Aim 3, we identify proteins unique to lipid rafts using a novel proteomics approach which may regulate GLUT1. Finally in Specific Aim 4, we use the stomatin knockout mouse to determine the role of stomatin on GLUT1 targeting and function.
Showing the most recent 10 out of 15 publications
