Expression of adrenocortical steroidogenic acute regulatory (StAR) protein is influenced by chromaffin cells

Cell-cell interactions are crucial role for the proper functioning of endocrine glands. We recently demonstrated that interactions of chromaffin and cortical cells are important for adrenocortical steroidogenesis. However, the molecular mechanisms have not been elucidated and it is unclear if this involves acute and/or chronic processes. By Northern analysis and the quantitative technique of TaqMan PCR we investigated whether chromaffin cells influence the regulation of StAR and the peripheral benzodiazepine receptor (PBR), both required for the rate-limiting step, the delivery of cholesterol to the inner mitochondrial membrane. StAR mRNA levels in bovine adrenocortical cells were increased by incubation with chromaffin cell-conditioned medium (CCM). Short-term treatment for 4 h resulted in a greater stimulation (229+/-29% of basal, mean+/-SEM) than did longer incubation times of 8 h and 5 days (159+/-13 and 177+/-24%). Neither short nor a long-term treatment affected PBR expression. Consistently, the major secretion of chromaffin cells, epinephrine dose-dependently stimulated StAR expression with no effect on PBR mRNA. In conclusion, adrenomedullary secretory products are not necessary for the maintenance of PBR expression but facilitate steroid biosynthesis by increasing StAR mRNA expression and therefore can account for an ACTH-independent regulation of the rate-limiting step in steroidogenesis.