CELLULAR-LOCALIZATION OF THE PROHORMONE CONVERTASES IN THE HYPOTHALAMIC PARAVENTRICULAR AND SUPRAOPTIC NUCLEI - SELECTIVE REGULATION OF PC1IN CORTICOTROPIN-RELEASING HORMONE PARVOCELLULAR NEURONS MEDIATED BY GLUCOCORTICOIDS

The prohormone convertases (PCs) are processing enzymes that activate proproteins via cleavage at specific single or pairs of basic residues . The hypothalamic paraventricular nucleus (PVN) and supraoptic nucleu s (SON) are primary sites of biosynthesis of several neuroendocrine ho rmone precursors, including provasopressin (pro-AVP), pro-oxytocin (pr o-OT), and procorticotrophin-releasing hormone (pro-CRH), which requir e post-translational processing to yield active products. Using in sit u hybridization, we observed PC1 and PC5 mRNAs in PVN and SON magnocel lular neurons, while PC2 mRNA was observed in both magnocellular and p arvocellular PVN neurons as well as magnocellular SON neurons. Similar to furin, PC7 mRNA was expressed throughout the PVN and SON, whereas PACE4 mRNA levels were undetectable. Both immunohistochemical and West ern blot studies were performed to demonstrate the presence of PC prot eins and forms in the PVN and SON. Using double-labeling in situ hybri dization, we examined the cellular colocalization of each PC mRNA with pro-AVP, pro-OT, and pro-CRH mRNAs in PVN and SON. PCI mRNA was coloc alized with both AVP and OT mRNA in PVN and SON magnocellular neurons. All AVP, OT, and CRH neurons expressed PC2. In contrast, PC5 mRNA was colocalized only with OT mRNA. We examined the effects of adrenalecto my (ADX) on PVN PC mRNA levels. PCI mRNA levels were increased selecti vely within CRH/AVP parvocellular neurons but were unchanged in PVN ma gnocellular AVP or OT neurons. These results established the anatomica l organization of each convertase and proneuropeptide substrates in th e PVN and SON and suggested potential roles for each enzyme under rest ing and stimulated conditions.