SELECTIVE REDUCTION OF PROADRENOCORTICOTROPIN-ENDORPHIN PROTEINS AND MESSENGER RIBONUCLEIC-ACID ACTIVITY IN MOUSE PITUITARY-TUMOR CELLS BY GLUCOCORTICOIDS

Mouse pituitary tumor cells (line AtT-20/D16v) were used as a model system for studying the mechanism of the glucocorticoid-mediated decrease in adrenocorticotropin (ACTH) and β-endorphin production. Glucocorticoids decrease by 50-60% the levels of ACTH, β-endorphin, and the amino-terminal fragment of the common precursor of these peptides as measured by radioimmunoassay. Isoelectric focusing and sodium dodecyl sulfate (NaDodSO4) gel electrophoresis of ACTH, endorphin, or N-terminal specific immunoprecipitated radioactive AtT-20 cell extracts showed that glucocorticoids had essentially no effect on the processing of the precursor other than to reduce by 50% the amount of label incorporated into pro-ACTH/endorphin proteins. The effect of the steroid was highly specific for the precursor and its end products as detected by two-dimensional gel analysis of pulse-labeled cellular proteins. Dexamethasone specifically reduced the total level of translatable ACTH/endorphin messenger ribonucleic acid (mRNA) with a half-maximal effective concentration at 3 nM, a 16-h half-time of dein-duction, and no detectable influence on the proportion of translatable mRNA in the polysomes. The ACTH/endorphin precursor forms synthesized in the presence and absence of glucocorticoids are similar by every analytical technique used, suggesting that they are the same protein. Thus, glucocorticoids appear to reduce ACTH and β-endorphin production in AtT-20 cells by specifically decreasing ACTH/endorphin mRNA and not by altering the processing of the precursor. © 1979, American Chemical Society. All rights reserved.