Processing of proopiomelanocortin (POMC) approached by immunoelectron microscopy pre-embedding method.

Immunoelectron microscopy pre-embedding method was applied to study the processing of proopiomelanocortin (POMC). Premature pituitary cells and cancer cells showed POMC derived peptides in perinuclear spaces (PNS), rough endoplasmic reticula (RER) and in a few secretory granules (SG). These cells demonstrated immature processing of POMC and suggested constitutive pathway. Cultured mouse fibroblasts transfected with human POMC gene was a good model for this system. Mature pituitary cells and pituitary adenomas showed POMC derived peptides predominantly in SG which correlated with authentic processing of POMC. Cultured mouse AtT 20 cells transfected with human POMC gene showed similar secretory pathway and processing. These results emphasized that SG is mandatory for proper processing of POMC. SG is probably essential for the regulated system of secretion.