Altered processing of pro-orphanin FQ/nociceptin and pro-opiomelanocortin-derived peptides in the brains of mice expressing defective prohormone convertase 2

The bioactivity of neuropeptides can be regulated by a variety of post-tran slational modifications, including proteolytic processing. Here, gene-targe ted mice producing defective prohormone convertase 2 (PC2) were used to exa mine the post-translational processing of two neuroendocrine prohormones, p ro-opiomelanocortin (POMC) and pro-orphanin FQ (pOFQ)/nociceptin (N), in th e brain. Reversed-phase HPLC and gel-exclusion chromatography were combined with specific radioimmunoassays to analyze the processing patterns of thes e two prohormones in the hypothalamus and the amygdala. In the case of POMC , the lack of PC2 activity completely prevented carboxy-shortening of beta -endorphins and greatly diminished conversion of beta -lipotropin to gamma -lipotropin and beta -endorphin. Although conversion of beta -lipotropin to beta -endorphin decreased, the lack of PC2 activity caused an increase in beta -lipotropin and beta -endorphin levels in the mutant animals, but no i ncreases in POMC or biosynthetic intermediates were seen. The extent of OFQ /N production was significantly lower in PC2-deficient mice and there was a n accumulation of relatively large amounts of pOFQ/N and biosynthetic inter mediates. These results demonstrate that PC2 is directly involved in the bi ogenesis of two brain neuropeptides in vivo and suggest that the specific p ro-hormone and cellular context influences neuropeptide processing by PCs.