Activation of glucose uptake in adipocytes by receptor tyrosine kinase-mediated signaling cascades / Eileen Lisa Whiteman.

Whiteman, Eileen Lisa.
xiv, 199 p. ; 29 cm.
Medical subjects:
Cell and Molecular Biology.
Dissertations, Academic.
Local subjects:
Penn dissertations -- Cell and molecular biology.
Cell and molecular biology -- Penn dissertations.
Here, we have examined the signaling molecules involved in receptor tyrosine kinase (RTK)-mediated glucose uptake in 3T3-L1 adipocytes. In this model system, adipogenesis yields increased insulin responsiveness and the capacity for robust glucose transport. In the differentiated adipocyte, insulin uniquely directs the facilitative glucose transporter GLUT4 to the plasma membrane and instructs the cell to initiate increased hexose transport. The molecular determinants that provide a basis for this exquisite specificity and the fundamental requirements for hormone-mediated glucose transport are still largely undefined. We employed two approaches to address these outstanding issues. First, we analyzed the effect of differentiation on the activation of selected signaling molecules by insulin and platelet-derived growth factor (PDGF). Since both of these agonists often activate remarkably similar sets of signaling intermediates, a comparison of their effects enabled us to identify candidate molecules that might account for the specific metabolic effects of insulin in the differentiated adipocyte. We demonstrated that PDGF-mediated Akt activation is suppressed following differentiation, and insulin uniquely activates this enzyme in the adipocyte. This effect mirrors insulin's specific mediation of glucose transport in this cell type. Interestingly, PDGF can still activate other PI3'-Kinase effector molecules in adipocytes such as p70S6K and PHAS-I. Second, we potently activated the PDGF signaling pathway in adipocytes by overexpression of human PDGF receptors (hPDGFR) in order to evaluate both its capacity to stimulate glucose transport and the collection of effector molecules simultaneously activated. This strategy allowed us to identify common components involved in RTK-mediated glucose uptake and to discern which molecules may be required for this important biological response. We showed that PDGF-mediated glucose transport was always accompanied by PI3'-Kinase activation and the subsequent stimulation of Akt. However, we found that PDGF can effectively mimic these specific insulin effects by a mechanism that does not involve insulin receptor substrates (IRS). These results suggest that potent activation of PI3'-Kinase and specific PI3'-Kinase effectors, but not participation of IRS, are among the minimal requirements for RTK-mediated glucose transport.
Supervisor: Morris J. Birnbaum.
Thesis (Ph.D. in Cell and Molecular Biology) -- University of Pennsylvania, 2002.
Includes bibliographical references.
Local notes:
University Microfilms order no.: 3055012.
Birnbaum, Morris J., advisor.
University of Pennsylvania.
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