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

Cell-cell interactions are crucial role for the proper functioning of endoc rine glands. We recently demonstrated that interactions of chromaffin and c ortical cells are important for adrenocortical steroidogenesis. However, th e molecular mechanisms have not been elucidated and it is unclear if this i nvolves acute and/or chronic processes. By Northern analysis and the quanti tative technique of TaqMan PCR we investigated whether chromaffin cells inf luence the regulation of StAR and the peripheral benzodiazepine receptor (P BR), both required for the rate-limiting step, the delivery of cholesterol to the inner mitochondrial membrane. StAR mRNA levels in bovine adrenocorti cal cells were increased by incubation with chromaffin cell-conditioned med ium (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 tre atment affected PER expression. Consistently, the major secretion of chroma ffin cells, epinephrine dose-dependently stimulated StAR expression with no effect on PER mRNA. In conclusion, adrenomedullary secretory products are not necessary for the maintenance of PER expression but facilitate steroid biosynthesis by increasing StAR mRNA expression and therefore can account f or an ACTH-independent regulation of the rate-limiting step in steroidogene sis. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserve d.