Secretory pathways and processing of human proopiomelanocortin (POMC) using transformed mouse cultured fibroblasts (L cells) and AtT20 cells by human POMC gene--preembedding immunoelectron microscopic studies.

In order to elucidate the relationship between secretory pathway and processing for precursor molecule of peptide hormones, we performed immunoelectron microscopic studies to localize POMC-derived peptides in mouse cultured L cells (fibroblasts without secretory granules) and in mouse AtT20 cells (ACTH secreting pituitary tumor cells with secretory granules) which had been transformed with human POMC gene. From the electron microscopic localization patterns, L42 cells were considered to serve as a model of constitutive pathway without processing of POMC, and A53 cells were considered to serve as a model of transgranular (regulated) pathway with processing of POMC. Immunoblotting supported these interpretations.