p53 Stimulates Promoter Activity of the sgk Serum/Glucocorticoid-inducible Serine/Threonine Protein Kinase Gene in Rodent Mammary Epithelial Cells

Abstract

sgk is a novel member of the serine/threonine protein kinase gene family that is transcriptionally regulated by serum and glucocorticoids in mammary epithelial cells. To functionally determine if the sgk promoter is regulated by the p53 tumor suppressor protein in mammary cells, a series of sgk promoter fragments with 5 -deletions were linked to the bacterial chloramphenicol acetyltransferase gene (sgk-CAT) and transiently cotransfected into nontumorigenic NMuMG or transformed Con8Hd6 mammary epithelial cells with p53 expression plasmids. Wild-type p53, but not mutant p53, strongly stimulated sgk promoter activity in both mammary epithelial cell lines. These effects were mediated by specific regions within the sgk promoter containing p53 DNA-binding sites. The sgk p53 sequence at ؊1380 to ؊1345 (site IV) was sufficient to confer p53-dependent transactivation to a heterologous promoter, and p53 was capable of binding to this sequence in vitro as assessed by gel shift analysis. In the nontumorigenic NMuMG epithelial cell line, cotransfection of wild-type p53 strongly stimulated the activities of both the sgk promoter and the well characterized p53-responsive p21/ Waf1 promoter, whereas in Rat-2 fibroblasts, wild-type p53 repressed the basal activities of both promoters, revealing that sgk and p21/Waf1 are similarly regulated in a cell type-specific manner. Taken together, these results demonstrate that sgk is a new transcriptional target of p53 in mammary epithelial cells and represent the first example of a hormone-regulated protein kinase gene with a functionally defined p53 promoter recognition element.An intricate network of protein kinases and phosphatases propagates various extracellular growth and differentiation signals from the plasma membrane into the nucleus, leading to changes in the phosphorylation status and the function of discrete sets of transcription factors. The catalytic activities of most protein kinases are regulated by specific interactions with regulatory proteins (1-3) and/or by phosphorylation (4, 5). Recent studies have uncovered a newly emerging subfamily of serine/threonine protein kinase genes, including snk, sgk, plk, and fnk, that are predominantly regulated at the transcriptional level by hormone-and/or mitogen-induced pathways (6 -13). Our previous studies have identified the sgk (serum-and glucocorticoid-inducible protein kinase) serine/threonine protein kinase gene, which is transcriptionally regulated by serum and/or glucocorticoids in mammary epithelial cells and Rat-2 fibroblasts (12, 13), as the second member of this subfamily of transcriptionally regulated protein kinase genes. sgk encodes a 49-kDa putative protein kinase that shares 45-55% homology with the catalytic domain of protein kinase C, the cAMP-dependent protein kinase A, the rac protein kinases, and the ribosomal protein S6 kinase (13). We have documented that sgk transcripts are expressed in a variety of adult rat tissues, with the highest expression in the thymus, lung, and ovary and detectable levels in the ma...

Deregulated expression of pro-survival and pro-apoptotic p53-dependent genes upon Elongator deficiency in colon cancer cells

“…Of note, SGK expression was not induced upon daunomycin treatment (Fig. 4B) and this observation may reflect the inability of p53 to induce SGK expression in fibroblasts, as previously reported in the Rat-2 fibroblasts-derived cell line [32]. Finally, SGK expression was not daunomycin-inducible in colon cancer-derived HT29 cells where p53 is not functional and SGK expression was modestly enhanced in Elongator deficient cells despite robust IKAP/ hELP1 depletion (Fig.…”

“…4A). Because SGK expression is p53-inducible in some cell types [32], we next determined whether the enhanced SGK expression seen upon Elongator deficiency also occurred in p53 deficient HCT116 cells. Interestingly, SGK mRNA levels were not induced in daunomycin-treated HCT116 cells lacking p53 and IKAP/hELP1 depletion did not cause increased SGK expression in such cells (Fig.…”

Many forks in the path: cycling with FoxO

“…Indeed, p53 may induce the expression of serum and glucocorticoid-regulated kinase, resulting in the phosphorylation and nuclear exclusion of FoxO3a (Maiyar et al, 1996), and FoxO3a may inhibit p53-mediated repression of SIRT1 expression, which binds to, and deacetylates p53. (Campisi, 2005;van der Horst and Burgering, 2007).…”

Hyperosmotic Stress Stimulates Promoter Activity and Regulates Cellular Utilization of the Serum- and Glucocorticoid-inducible Protein Kinase (Sgk) by a p38 MAPK-dependent Pathway

“…The various sgk promoter-CAT deletions down to Ϫ236 sgk-CAT were generated utilizing the Erase-a-Base system (Promega, Madison, WI) and are further described (32). The Ϫ78 sgk-CAT was generated as described (38).…”

“…We have recently shown that Sgk enzymatic activity, phosphorylation and subcellular localization is regulated by PI 3-kinase signaling through PDK1, suggesting a possible role for Sgk in a cell survival pathway (31). Moreover, the physiological stress hormones, glucocorticoids, stimulate sgk promoter activity through a glucocorticoid response element, and sgk is a transcriptional target of the p53 tumor suppressor gene, a known target of genotoxic stress (28,32). Consistent with a role for Sgk in the cellular stress response, sgk transcripts have been shown to be elevated in response to ischemic injury of the brain, changes in cell volume, and inflammatory disease and in a screen for transcripts involved in wound repair in fibroblasts (33)(34)(35)(36).…”