Regulation by steroid hormones of phosphorylation of specific protein common to several target organs.

Abstract

The effect of in vivo administration of steroid hormones on the endogenous phosphorylation of individual proteins in cell sap from several target tissues was studied using the technique of discontinuous sodium dodecyl sulfate-polyacrylamide gel eletrophoresis. The hormones studied (and their respective target organs) were 17.beta.-estradiol [1,3,5(10)-estratriene-3, 17.beta.-diol] (rat uterus); testosterone (17.beta.-hydroxy-4-androsten-3-one) (rat ventral prostate and seminal vesicle); cortisol (11.beta.,17.alpha., 21-trihydroxy-4-pregnene-3,20-dione) (rat liver); aldosterone (the 18,11-hemiacetal of 11.beta.,21-dihydroxy-3,20-dioxo-4-pregnen-18-al) (toad bladder). In each of the 5 target organs studied, pretreatment with the appropriate hormone reduced the amount of 32P incorporated from [.gamma.-32P]ATP into an apparently common protein band present in the cytosol fraction. The endogenous phosphorylation and dephosphorylatin of this protein was also regulated by cyclic AMP (cAMP). This protein, designated SCARP (steroid and cyclic adenosine 3'':5'' monophosphate regulated phosphoprotein), was estimated to have an apparent molecular weight of 54,000 in the gel electrophoresis system used. The effect of the steroid hormones in decreasing the phosphorylation of SCARP was specific for their respective target tissues. The effect of 17.beta.-estradiol and of testosterone on SCARP could be observed as early as 2 h after a single dose of the steroid. A protein synthesis inhibitor, cycloheximide, abolished the effect of the steroid hormones, but not that of cAMP, on the endogenous phosphorylation of SCARP. Steroid hormones may regulate either the amount of SCARP or its ability to become phosphorylated. This regulation of a single species of protein by several types of steroid hormones in different target organs raises the possibility that this common biochemical action may be a component of the mechanism by which these steroids achieve some of their biological effects.