Glucocorticoid-induced messenger ribonucleic acids in rat thymic lymphocytes: rapid primary effects specific for...

We examined the mechanism underlying the rapid (15-120 min) glucocorticoid-mediated increase in the synthesis of proteins envisioned as mediators of the initial steroid effects in thymic lymphocytes. Analysis of about 1500 in vitro translation products on giant two-dimensional gels revealed rapid hormonal influences on only 7 mRNAs, 6 whose translation products have mol wt and pIs identical to those proteins whose synthesis has been found to be increased after the addition of glucocorticoids to thymus cells. The additional mRNA codes for glucocortin, whose induction in thymus as well as other target cells has been reported. mRNA inductions for proteins 1, 2, and 1N are detectable 15-30 min after the addition of dexamethasone to isolated thymus cells and continue to increase until 2 h, whereas the mRNAs for proteins 4 and 5 are not increased until after 1 h. The mRNA for protein 3 is elevated by 1 h, but attempts to quantitate the change at earlier times have failed because this protein focuses poorly. The parallel between these in vitro translation results and the increased synthesis of individual proteins seen in whole cells demonstrates that increased mRNA levels underlie the cellular changes. Other hormones, such as estradiol, testosterone, and T3, at 10(-6) M and deoxycorticosterone at 10(-8) M do not induce these messages. Partial inductions of 1 and 2, but not 1N, are seen with deoxycorticosterone at 10(-6) M, consistent with its classification as a partial glucocorticoid agonist. Cycloheximide does not block the rise in mRNA for the most rapid inductions, 1, 2, and 1N. The results indicate that dexamethasone rapidly and specifically induces 6 thymus cell mRNAs in addition to the one coding for glucocortin. The cycloheximide results suggest that at least 3 of these represent primary steroid hormone responses.