Lipoprotein lipase (LPL) is a central enzyme in lipid metabolism, in adipocyte lipid accumulation, and in diseases such as diabetes, atherosclerosis, and obesity. The mechanism of LPL regulation is complex. Depending on the regulator or the cell type, LPL regulation may be due to changes at the mRNA level or at numerous post-transcriptional sites. The applicant and others have recently described several instances of regulation of LPL translation. In response to glucose, thyroid hormone, and catecholamines, there were 3- to 5-fold changes in LPL synthesis, with no changes in adipocyte LPL mRNA levels. When diabetic patients were treated with insulin or drugs, there was an increase in LPL translation.The applicant has evidence for the presence of a cytoplasmic RNA binding protein that interacts with the 3'UTR of the LPL mRNA, resulting in an inhibition of LPL translation. This project is intended to better characterize this binding protein and the RNA motif, and to determine the precise physiologic significance of the LPL 3' UTR. Hypothesis 1. A specific and novel RNA binding protein interacts with the 3'UTR. The synthesis or activation of the protein increases following epinephrine-mediated changes in LPL translation. They plan to characterize the 3'UTR motif and clone the RNA binding protein. Hypothesis 2. The 3'UTR plays an important role in the physiologic regulation of LPL translation. The investigators plan on making stable transfectants of cells that express an LPL construct lacking the proximal 3'UTR and will study the response in vitro to known regulators of LPL. They will produce transgenic mice expressing in adipose tissue an LPL construct lacking the proximal 3'UTR and examine the effects of diabetes, epinephrine, and T3 in these mice. Hypothesis 3. Translational regulation of LPL in humans by improved control involves elements on the 3'UTR mRNA. The applicants will determine whether the same regions of the LPL mRNA that control epinephrine-mediated translational regulation are involved in human diabetes. They will determine whether translational regulation in humans is due to preferential transcription of a longer mRNA species controlled by alternate poly A sites.
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