Defective prodynorphin processing in mice lacking prohormone convertase PC2

Prodynorphin, a multifunctional precursor of several important opioid pepti des, is expressed widely in the CNS. It is processed at specific single and paired basic sites to generate various biologically active products. Among the prohormone convertases (PCs), PC1 and PC2 are expressed widely in neur oendocrine tissues and have been proposed to be the major convertases invol ved in the biosynthesis of hormonal and neural peptides. In this study we h ave examined the physiological involvement of PC2 in the generation of dyno rphin (Dyn) peptides in mice tacking active PC2 as a result of gene disrupt ion. Enzymological and immunological assays were used to confirm the absenc e of active PC2 in these mice. The processing profiles of Dyn peptides extr acted from brains of these mice reveal a complete lack of Dyn A-8 and a sub stantial reduction in the levels of Dyn A-17 and Dyn B-13, Thus, PC2 appear s to be involved in monobasic processing, leading to the generation of Dyn A-8, Dyn A-17, and Dyn B-13 from prodynorphin under physiological condition s. Brains of heterozygous mice exhibit only half the PC2 activity of wild-t ype mice; however, the levels of Dyn peptides in these mice are similar to those of wild-type mice, suggesting that a 50% reduction in PC2 activity is not sufficient to significantly reduce prodynorphin processing. The disrup tion of the PC2 gene does not lead to compensatory up-regulation in the lev els of other convertases with similar substrate specificity because we find no significant changes in the levels of PC1, PC5/PC6, or furin in these mi ce as compared with wild-type mice. Taken together, these results support a critical role for PC2 in the generation of Dyn peptides.