A common 43 K protein induced by glucocorticoids in a variety of cells and tissues

A secreted Mr approximately 40,000 glycoprotein specifically induced by glucocorticoids in a rat colon carcinoma cell line

Glucocorticoid hormones are thought to play a role in carcinogenesis, as they regulate cell differentiation and proliferation. We have previously shown that dexamethasone inhibits the growth of a rat colon carcinoma cell line, and induces the secretion of an Mr approximately 40,000 protein. We now report that the synthesis and the release in the culture medium of this protein is stimulated specifically by glucocorticoid agonists, and not by other steroid hormones. The anti-glucocorticoid RU 38486 is inefficient and suppresses the induction of this protein by dexamethasone. Induction is sensitive to actinomycin D, suggesting that regulation may be exerted by altering the rate of mRNA synthesis. Characterization of culture medium from dexamethasone-treated cells revealed that the Mr approximately 40,000 protein is glycosylated, and can be further separated from other secreted proteins by high-performance anion-exchange chromatography.

Glucocorticoid effects and receptors in two rat colon carcinoma cell lines differing by their tumorigenicity

Steroid hormones, regulators of cell differentiation and proliferation, are believed to play a role in carcinogenesis. Glucocorticoid hormones in particular modulate the expression of a number of proteins implicated in this process. We have investigated the effect of dexamethasone on two cell lines derived from a colon carcinoma, which differ by their tumorigenicity. Dexamethasone was found to inhibit growth of both the progressive (PROb) and the regressive clone (REGb). Upon hormonal treatment, glucocorticoid hormones induced fibronectin secretion by the two clones, whereas PROb cells were found to secrete an additional Mr approximately 43,000 protein. The cellular effect of glucocorticoid hormones being mediated through a specific soluble receptor, we have characterized this protein. The progressive cells (PROb) contained more specific glucocorticoid-binding sites (approximately 170,000 sites per cell) than the regressive ones (REGb cells; approximately 100,000 sites per cell). In both clones, the receptor was associated with the Mr approximately 90,000 heat shock protein to yield large complexes (Stokes radius Rs approximately 7.5 nm), which were dissociated to the same extent upon heat- and salt-treatment. The steroid- and DNA-binding unit of the receptor, characterized under denaturing conditions using an anti-receptor monoclonal antibody was found to be more degraded in the progressive cell line.

Characterization of a glucocorticoid-sensitive hippocampal protein

Increased synthesis of a rat hippocampal protein with an apparent molecular weight (Mr) of 35,000 Da occurs in response to elevation of serum corticosterone levels. Subcellular fractionation has localized this protein in the cytosol. Two-dimensional gel electrophoresis indicated that this protein has an isoelectric point (IEP) of 6.6. A similar protein in liver has a slightly higher Mr and an IEP of 6.8. Increased synthesis of one additional hippocampal protein with an Mr of 46,000 Da and an IEP of 6.2 and of two other liver proteins, one with an Mr of 53,000 Da and an IEP of 6.2 and the other with an Mr of 45,000 Da and a range of IEPs from 8.7 to 7.8, was also seen after injection of corticosterone into rats. One possible identity of the 35,000 Da protein is glycerol 3-phosphate dehydrogenase (GPDH), based upon the reported Mr and IEP of this enzyme. The 35,000 Da hippocampal protein co-eluted from a gel filtration column with GPDH activity. No alteration of hippocampal GPDH activity was seen in intact rats 4 or 24 h after injection of either corticosterone or the type II receptor-specific agonist RU 28362. However, daily administration of corticosterone to rats beginning 10 days after adrenalectomy returned hippocampal GPDH activity to normal values after 2-3 days. In contrast, synthesis of the 35,000 Da protein was maximally increased 4 h after a single injection of steroid and not elevated at later times.

Glucocorticoid-mediated induction of glucocortin: a rapid primary response common to major target tissues

Glucocorticoids are known to rapidly induce four proteins in rat thymus cells in time to account for the earliest known metabolic hormone effects. We report here an additional protein, which we refer to as "glucocortin" (Mr = 17,000, pI = 4.7). It is of special interest since it is the only protein rapidly induced in all of the glucocorticoid target cells we have examined. We have characterized the kinetics of glucocortin mRNA induction in isolated thymus cells. Giant two-dimensional gel electrophoretic analysis of in vitro translation products reveals a 2-fold increase in the level of translatable mRNA within 15 min of dexamethasone addition, with maximal stimulation (approximately equal to 7-fold) by 45 min. Cycloheximide does not reduce the hormone-mediated increase in glucocortin mRNA, suggesting that the induction represents a primary response to glucocorticoids. This protein is induced by dexamethasone in a dose-dependent manner, with maximal induction at 10(-6) M and partial inductions at concentrations as low as 10(-10) M. It is strongly induced by cortisol at 10(-6) M, but it is not induced by estradiol or testosterone or by thyroid hormone, even at concentrations as high as 10(-6) M. Deoxycorticosterone has no effect at 10(-8) M but does generate a half-maximal effect at 10(-6) M, a finding consistent with its status as a partial glucocorticoid agonist. In summary, glucocortin appears to be a primary glucocorticoid-induced protein that represents the most rapid induction so far detected, and it appears to be the only one that may be common to all glucocorticoid target cells.