Parathyroid hormone-related protein (PTHrP) is a newly identified tumor peptide which causes hypercalcemia in patients with the syndrome of humoral hypercalcemia of malignancy. Unlike its relative PTH, PTHrP is produced in many normal tissues and emerging evidence suggests that smooth muscle is a main site of production and activity of PTHrP. Our recent studies show that PTHrP is abundantly expressed in vascular smooth muscle cells and subject to regulation by Ang II and other vasoconstrictor peptides. Since both PTH and PTHrP exhibit vasorelaxant activity, we hypothesize that this protein is produced to counter balance the effects of either humoral or mechanical vasoconstrictor signals. The overall goals of this project, are to: 1) determine the mechanisms which control PTHrP gene expression in vascular smooth muscle; 2) characterize the secreted form(s) of the protein and; 3) study its activity in vascular smooth muscle cells and in intact aortic strips. Using a well characterized rat aortic smooth muscle cell culture model we will study the mechanisms by which Ang II regulates PTHrP gene expression in smooth muscle cells (SMC) and establish the relative importance of transcriptional and post-transcriptional control. Separate studies will apply gene transfer and molecular biological techniques to identify cis-acting elements in the PTHrP promoter and 3' UTR which account for the induction of gene expression. We will also examine regulation of PTHrP expression in rat aortic strips in vitro in response to vasoactive agents. We plan to characterize the secreted forms of PTHrP using region-specific RIAs and determine its glycosylation status. In parallel studies, PTHrP and putative N-and C-terminal fragments will be evaluated for their ability to bind to and activate established intracellular signaling pathways in SMC and to affect selected markers for the differentiated SMC phenotype. We will use specific PTHrP antagonists and the aortic strip technique to directly test the hypothesis of local production of PTHrP. In summary, we believe that our findings will implicate PTHrP as an autocrine regulator of vascular smooth muscle tone and finally explain the long-recognized but under-appreciated effects of PTH-related peptides in this tissue.
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