Type 2 diabetes is a genetically programmed disease that primarily develops in adult life. Insulin resistance is a predisposing factor for diabetes and can be induced by impaired biogenesis of the insulin receptor, a transmembrane protein tyrosine kinase. The goal of this proposal is to analyze the physiological control and molecular determinants of insulin receptor biogenesis. Recently, we demonstrated that calnexin and calreticulin, both glucose-regulated proteins, control receptor expression through interactions with specific asparagine-linked glycans in the nascent receptor. Analysis of human mutant insulin receptors has further demonstrated that insulin receptor maturation and degradation is critically dependent upon furin, a serine protease in the secretory pathway. What is still not well understood is the molecular mechanism linking glucose metabolism, proteolytic processing and degradation in living cells and in the whole animal.
The first aim of this proposal is to examine the """"""""real-time"""""""" dynamics of insulin receptor biogenesis using novel insulin receptor-green fluorescent protein chimeras and to manipulate components in the cell quality control pathway in vivo in attempts to enhance the expression of cell surface receptors.
Our second aim i s to further identify the molecular effectors of the degradation pathway and to elucidate the function of furin and cytoplasmic heat shock proteins in this process.
The third aim will be to develop knock-in mice with loss-of-function mutations in the insulin receptor that recapitulate late-onset congenital insulin resistance, providing a new molecular and pathophysiological model of type 2 diabetes.
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