Biosynthesis of proTRH-derived peptides in prohormone convertase 1 and 2 knockout mice

Abstract

Prohormone convertases (PCs) 1 and 2 are the primary endoproteases involved in the post-translational processing of proThyrotropin Releasing Hormone (proTRH) to give rise to TRH and other proposed biologically active non-TRH peptides. Previous evidence suggests that PC1 is responsible for most proTRH cleavage events. Here, we used the PC1 and PC2 knockout (KO) mouse models to examine the effects of PC1 or PC2 loss on proTRH processing. The PC1KO mouse presented a decrease in five proTRH-derived peptides, whereas the PC2KO mouse showed only lesser reduction in three TRH (Gln-His-Pro), TRH-Gly (Gln-His-Pro-Gly), and the short forms preproTRH178–184 (pFQ7) and preproTRH186–199 (pSE14) of pFE22 (preproTRH178–199). Also, PC1KO and not PC2KO showed a decrease in pEH24 indicating that PC1 is more important in generating this peptide in the mouse, which differs from previous studies using rat proTRH. Furthermore, downstream effects on thyroid hormone levels were evident in PC1KO mice, but not PC2KO mice suggesting that PC1 plays the more critical role in producing bioactive hypophysiotropic TRH. Yet loss of PC1 did not abolish TRH entirely indicating a complementary action for both enzymes in the normal processing of proTRH. We also show that PC2 alone is responsible for catalyzing the conversion of pFE22 to pFQ7 and pSE14, all peptides implicated in regulation of suckling-induced prolactin release. Collectively, results characterize the specific roles of PC1 and PC2 in proTRH processing in vivo.