MANIPULATION OF DISULFIDE BONDS DIFFERENTIALLY AFFECTS THE INTRACELLULAR-TRANSPORT, SORTING, AND PROCESSING OF NEUROENDOCRINE SECRETORY PROTEINS

To investigate if the prevention of disulfide bond formation affects t he intracellular transport, sorting, and processing of a distinct set of neuroendocrine proteins in the regulated secretory pathway, we have treated Xenopus intermediate pituitaries with the thiol-reducing agen t dithiothreitol. Pulse-chase incubations in combination with immunopr ecipitation analysis were used to monitor the fates of the prohormone proopiomelanocortin (POMC), prohormone convertase PC2 and its helper p rotein 7B2, as well as secretogranin iii. Manipulation of the disulfid e bonds in POMC and proPC2 blocked their transport to the trans-Golgi network and strongly inhibited their processing. Reduction of the sing le disulfide bond in 7B2 did not disturb its transport and cleavage, b ut caused its missorting to the constitutive secretory pathway. Moreov er, the liaison between proPC2 and 7B2 was prevented. Dithiothreitol d id not affect transport, sorting, and cleavage of secretogranin iii, w hich lacks disulfide bonds. When the reducing agent was washed away, P OMC processing, proPC2 maturation, and the association between proPC2 and 7B2 were reestablished. Collectively, our findings indicate that m anipulation of disulfide bonds differentially affects the fates of neu roendocrine proteins during their transit through the secretory pathwa y.