Repression of Glucocorticoid Receptor Transactivation and DNA Binding of a Glucocorticoid Response Element within the Serum/Glucocorticoid-Inducible Protein Kinase (<i>sgk</i>) Gene Promoter by the p53 Tumor Suppressor Protein

414

339

The early phase of the stimulatory effect of aldosterone on sodium reabsorption in renal epithelia is thought to involve activation of apical sodium channels. However, the genes initiating this effect are unknown. We used a combination of polymerase chain reaction-based subtractive hybridization and differential display techniques to identify aldosterone-regulated immediate early genes in renal mineralocorticoid target cells. We report here that aldosterone rapidly increases mRNA levels of a putative Ser/Thr kinase, sgk (or serum-and glucocorticoid-regulated kinase), in its native target cells, i.e. in cortical collecting duct cells. The effect occurs within 30 min of the addition of aldosterone, is mediated through mineralocorticoid receptors, and does not require de novo protein synthesis. The fulllength sequences of rabbit and mouse sgk cDNAs were determined. Both cDNAs show significant homology to rat and human sgk (88 -94% at the nucleotide level, and 96 -99% at the amino acid level). Coexpression of the mouse sgk in Xenopus oocytes with the three subunits of the epithelial Na ؉ channel results in a significantly enhanced Na ؉ current. These results suggest that sgk is an immediate early aldosterone-induced gene, and this protein kinase plays an important role in the early phase of aldosterone-stimulated Na ؉ transport.

Section: Discussionmentioning

confidence: 86%

sgk Is an Aldosterone-induced Kinase in the Renal Collecting Duct

Náray-Fejes-Tóth¹,

Canessa

Cleaveland³

et al. 1999

414

339

“…To confirm that the transfected cell clones remained generally glucocorticoid responsive, the dexamethasone stimulated expression of the endogenous serum-glucocorticoid inducible protein kinase (SGK) was examined in the recovered transfected cell lines. We have previously established that SGK is under direct glucocorticoid receptor transcriptional control due to a glucocorticoid response element in its promoter (78,79). As shown in Fig.…”

Section: Ectopic Expression Of Full-length Fascin Prevents the Glucocmentioning

confidence: 92%

Glucocorticoid Down-regulation of Fascin Protein Expression Is Required for the Steroid-induced Formation of Tight Junctions and Cell-Cell Interactions in Rat Mammary Epithelial Tumor Cells

Wong¹,

Ching²,

McCrea³

et al. 1999

Self Cite

Glucocorticoid hormones, which are physiological regulators of mammary epithelium development, induce the formation of tight junctions in rat Con8 mammary epithelial tumor cells. We have discovered that, as part of this process, the synthetic glucocorticoid dexamethasone strongly and reversibly down-regulated the expression of fascin, an actin-bundling protein that also interacts with the adherens junction component ␤-catenin.

“…p53 has also been demonstrated to interact with other transcription factors: Sp1 (37), CCAAT-binding factor (38), cAMP response element-binding protein (39), and glucocorticoid receptors (40). Taken together these observations strongly imply that p53 interacts directly with the transcription machinery to modulate gene expression.…”

mentioning

confidence: 92%

p53 Down-regulates Human Matrix Metalloproteinase-1 (Collagenase-1) Gene Expression

Sun¹,

Sun²,

Wenger³

et al. 1999

128

105

We hypothesize that the abnormality of p53 seen in RA synovium may contribute to joint degeneration through the regulation of human matrix metalloproteinase-1 (hMMP-1, collagenase-1) gene expression. Transcription assays were performed with luciferase reporters driven by the promoter of the hMMP-1 gene or by a minimal promoter containing tandem repeats of the consensus binding sequence for activator protein-1, cotransfected with p53-expressing plasmids. The results revealed that (i) wild-type (wt) p53 down-regulated the promoter activity of hMMP-1 in a dose-dependent fashion; (ii) four of six p53 mutants (commonly found in human cancers) lost this repression activity; and (iii) this p53 repression activity was mediated at least in part by the activator protein-1 sites found in the hMMP-1 promoter. These findings were further confirmed by Northern analysis. The down-regulation of hMMP-1 gene expression by endogenous wtp53 was shown by treatment of U2-OS cells, a wt-p53-containing osteogenic sarcoma line, and Saos-2 cells, a p53-negative osteogenic sarcoma line, with etoposide, a potent inducer of p53 expression. p53, activated by etoposide, appears to block hMMP-1 promoter activity induced by etoposide in U2-OS cells. In summary, we have shown for the first time that the hMMP-1 gene is a p53 target gene, subject to p53 repression. Because MMP-1 is principally responsible for the irreversible destruction of collagen in articular tissue in RA, abnormality of p53 may contribute to joint degeneration through the regulation of MMP-1 expression.Rheumatoid arthritis (RA) 1 is marked by destruction of the extracellular matrix and it is believed that, among other factors, matrix metalloproteinases (MMPs) play an important role in mediating the degradation of connective tissue matrix components such as collagens and proteoglycans (4, 5). Collagenase-1 (MMP-1), stromelysin (MMP-3), gelatinase A and B (MMP-2 and MMP-9), and collagenase-3 (MMP-13) are all present at significantly elevated levels in cartilage, synovial membranes, and synovial fluid of patients with RA (6 -8). The synovium produces substantial amounts of MMP-1, the major matrix metalloproteinase involved in the degradation of interstitial collagens, specifically, types I-III. MMP-1 expression has been shown to be stimulated by native collagen type I and collagen fragments, phorbol esters, growth factors, and cytokines such as interleukin 1␤ (IL-1␤) and tumor necrosis factor-␣ (9 -12). The activity of MMP-1 is stringently regulated at three levels: the promoter, the activation of proenzyme, and the inhibition of active enzyme. The activator protein-1 (AP-1) binding sites found in the promoters of human collagenase have been shown to be critical to the expression of human collagenase (13-16).The protein product of the p53 tumor suppressor gene plays a very important role in cell growth control, DNA repair, and apoptosis (17). It has been proposed that p53 acts as an "emergency brake" inducing G1 arrest and apoptosis after DNA damage, either by halting cell divi...