Phospholipid Scramblase is a newly-identified gene family, whose proteins (PLSCR1-4) were proposed to mediate accelerated transbilayer movement of plasma membrane phospholipids in cells exposed to elevated intracellular Ca2+. The first identified member of this family, PLSCR1, was shown to be a Ca2+-binding endofacial plasma membrane protein that partitions into cholesterol and sphingomyelin-enriched lipid rafts when palmitoylated, and to traffic into the nucleus to influence gene transcription when not palmitoylated. Cellular expression of PLSCR1 is highly induced by the interferons, as well as by various growth factors, and deletion of PLSCR1 results in defective cell maturation and proliferation in response to these same growth factors. Finally, we have evidence that PLSCR1 plays a central role in receptor signaling and transactivation, through its recruitment of the adapter Shc and the activation of c-Src tyrosine kinase. We have now turned our attention to the role of another member of the PLSCR gene family, PLSCR3. Mice with targeted deletion of PLSCR3 show a marked increase in abdominal fat on a standard (~5% fat) diet, with elevated plasma glucose, cholesterol, triglycerides, and free fatty acids relative to WT controls. These mice also show distinctly abnormal glucose tolerance with evidence of insulin resistance, mimicking Metabolic Syndrome in man (obesity-related insulin resistance with dyslipidemia). Adipocytes from these mice are engorged with lipid and show a marked increase in expression of PPAR? and in genes regulated by this nuclear transcription factor. In this Proposal, we aim (1) To determine whether observed lipid engorgement, insulin resistance, and elevation of PPAR? in PLSCR3-/- adipose represent primary defects of PLSCR3 deficiency in the pre-adipocyte; (2): To determine which properties identified or suspected in the case of PLSCR1 are conserved with respect to PLSCR3; [unreadable] (3) To identify the mechanism by which PLSCR3 - through its activity at the plasma membrane or nucleus - attenuates both PPAR? expression and lipid accumulation in the adipocyte. It is proposed that these experiments will provide new insight into the cellular function of PLSCR3 and into a novel class of genes that appear to influence the accumulation of lipid in adipose tissue and the risk for acquiring the Metabolic Syndrome. [unreadable] [unreadable] [unreadable] [unreadable]
NIH ExPorter
NIH ExPorter