Immunolocalization of secretogranin II and insulin in a nerve growth factor-differentiated insulinoma cell line

RINm5F, a rat insulin-secreting pancreatic cell line, responds to nerve growth factor (NGF) by extending neurite-like processes. Secretogranin II (SgII), a marker of neuroendocrine secretory organelles, has recently been found to be a good marker of neuronal differentiation in both human neuroblastoma and rat pheochromocytoma cells. The present paper reports the results obtained from immunocytochemical studies, which show that NGF increases the expression of SgII-immunolabeled organelles in RINm5F cells. We also demonstrate that NGF increases the expression of insulin and that SgII and insulin are predominantly, but not always, colocalized. These results suggest that this insulinoma cell line may be a good model for studying the role of SgII in neuroendocrine secretion mechanisms.