Response of adrenal tumor cells to adrenocorticotropin: site of inhibition by cytochalasin B

Abstract

The ability of cytochalasin B to inhibit the steroidogenic response of mouse adrenal tumor cells (Y-1) to ACTH was examined with 2 aims: to consider the specificity of the inhibitor and to determine at what point(s) in the steroidogenic pathway it acts. Cytochalasin B did not inhibit protein synthesis or transport of [3H]-cholesterol into the cells nor did it alter total cell concentration of ATP. Together with previous evidence, this suggests that the effects of cytochalasin observed are relatively specific in these cells. Cytochalasin inhibits the increase in conversion of [3H]cholesterol to 20.alpha.-[3H]dihydroprogesterone (20.alpha.-hydroxypregn-4-en-3-one; a major product of the steroid pathway in Y-1 cells) produced by ACTH but does not inhibit conversion of cholesterol to pregnenolone by mitochondrial and purified enzyme preparations from Y-1 cells and bovine adrenal, respectively. Cytochalasin does not inhibit the conversion of pregnenolone to 20.alpha.-dihydroprogesterone but inhibited increased transport of [3H]cholesterol to mitochondria resulting from the action of ACTH. These findings indicate that cytochalasin acts after cholesterol has entered the cells and before it is subjected to side chain cleavage in mitochondria. In view of the known action of cytochalasin on microfilaments, these organelles are necessary for the transport of cholesterol to the mitochondrial cleavage enzyme and at least 1 effect of ACTH (and cyclic AMP) is exerted on this transport process. The specificity of the effects of cytochalasin is considered in relation to this conclusion.