Parathyroid hormone-related protein (PTH-P) undergoes extensive posttranslational endoproteolytic processing in the pancreatic islet to yield a family of at least four distinct mature peptides. One of the endoproteolytic processing sites appears to be a single basic amino acid, Arg37, the cleavage of which leads to the generation of PTHrP(1-36) and a mid-region form of the peptide which begins at Ala38. Following this and a number of other complex posttranslational processing steps, mature PTHrPs are secreted by a large number of different cell types, some of which employ the regulated secretory pathway, and others of which typically employ the constitutive secretory pathway. The pathways through which the various mature PTHrP secretory forms are secreted in the pancreatic islet, as is the case in other cell types, is unknown. In addition, while it is now well established that the PTHrP gene is expressed in the pancreatic islet, its function in the islet is unknown. In order to study the normal physiologic role of PTHrP in the pancreatic islet in vivo, we have developed a transgenic mouse model in which PTHrP is targeted to, and overexpressed in, the pancreatic beta cell using the rat insulin promoter (RIP). These RIP-PTHrP mice have only recently been established, but already display a striking phenotype: they appear to be hypoglycemic relative to their normal littermates, have a high perinatal mortality, and are markedly stunted in size.
The aims of this proposal follow from the above considerations and are: 1. To study the role of monobasic endoproteolytic posttranslational processing enzymes in the posttranslational processing of PTHrP in the pancreatic beta cell, and to study the mechanisms of secretion of PTHrP by the pancreatic beta cell. 2. To evaluate the physiologic roles of PTHrP in the pancreatic islet using a) pancreatic beta cell-targetted, PTHrP-overexpressing transgenic mice, and b) the PTHrP """"""""knockout"""""""" mouse. Preliminary data summarized within the proposal indicate that the reagents and techniques required to accomplish these goals are available in the applicant's laboratory. Identification of the processing steps: and secretory mechanisms of PTHrP as well as its normal physiologic role in the islet will have critical importance, and may well yield insight into the regulation of insulin secretion and the pathogenesis and treatment of diabetes.
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