Cellular localization and role of prohormone convertases in the processingof pro-melanin concentrating hormone in mammals

Melanin concentrating hormone (MCH) and neuropeptide EI (NEI) are two pepti des produced from the same precursor in mammals, by cleavage at the Arg(145 ) Arg(146) Site and the Lys(129)-Arg(130) site, respectively. We performed co-localization studies to reveal simultaneously the expression of MCH mRNA and proconvertases (PCs) such as PC1/3 or PC2. In the rat hypothalamus, PC 2 was present in all MCH neurons, and PC1/3 was present in about 15-20% of these cells. PC1/3 or PC2 was not found in MCH-positive cells in the spleen . In GH(4)C(1) cells co-infected with vaccinia virus (VV):pro-MCH along wit h VV:furin, PACE4, PC1/3, PC2, PC5/6A, PC5/6B, or PC7, we observed only eff icient cleavage at the Arg(145)-Arg(146) Site to generate mature MCH. Co-ex pression of pro-MCH together with PC2 and 7B2 resulted in very weak process ing to NEI. Comparison of pro-MCH processing patterns in PC1/3- or PC2-tran sfected PC12 cells showed that PC2 but not PC1/3 generated NEI. Finally, we analyzed the pattern of pro-MCH processing in PC2 null mice. In the brain of homozygotic mutants, the production of mature NEI was dramatically reduc ed. In contrast, MCH content was increased in the hypothalamus of PC2 null mice. In the spleen, a single large MCH-containing peptide was identified i n both wild type and PC2 nub mice, Together, our data suggest that pra-MCH is processed differently in the brain and in peripheral organs of mammals. PC2 is the key enzyme that produces NEI, whereas several PCs may cleave at the Arg(145)-Arg(146) Site to generate MCH in neuronal cell types.