Glucocorticoids Stimulate p21 Gene Expression by Targeting Multiple Transcriptional Elements within a Steroid Responsive Region of the p21 Promoter in Rat Hepatoma Cells

Abstract

Glucocorticoids can induce a G 1 arrest in the cell cycle progression of BDS1 rat hepatoma cells. In these cells, dexamethasone, a synthetic glucocorticoid, stimulated a rapid and selective increase in expression of the p21 cyclin-dependent kinase (CDK) inhibitor mRNA and protein and virtually abolished CDK2 phosphorylation of the retinoblastoma protein. Expression of the p27 CDK inhibitor, and other G 1 -acting cell cycle proteins, remained unaffected. Dexamethasone stimulated p21 promoter activity in a p53-independent manner that required functional glucocorticoid receptors. Transforming growth factor-␤, which also induced a G 1 cell cycle arrest of the hepatoma cells, failed to elicit this response. Analysis of 5 deletions of the p21 promoter uncovered a glucocorticoid responsive region between nucleotides ؊1481 and ؊1184, which does not contain a canonical glucocorticoid response element but which can confer dexamethasone responsiveness to a heterologous promoter. Fine mapping of this region uncovered three distinct 50 -60-base pair transcriptional elements that likely function as targets of glucocorticoid receptor signaling. Finally, ectopic expression of p21 had no effect on hepatoma cell growth in the absence of glucocorticoids but facilitated the ability of dexamethasone to inhibit cell proliferation. Thus, our results have established a direct transcriptional link between glucocorticoid receptor signaling and the regulated promoter activity of a CDK inhibitor gene that is involved in the cell cycle arrest of hepatoma cells.

Glucocorticoid receptor functions as a potent suppressor of mouse skin carcinogenesis

“…Moreover, TPA-induced skin tumorigenesis was significantly reduced when v-Ha-ras transgene was transferred to cyclin D1-deficient genetic background (Robles et al, 1998). Glucocorticoids or GR overexpression have been reported to induce a G1 cell cycle arrest via an increased expression of p21 that has GRE in its promoter (Ramalingam et al, 1997;Rogatsky et al, 1997Rogatsky et al, , 1999Cha et al, 1998;Park et al, 2001;Terada et al, 2001). The alternative mechanism may involve the transcriptional repression of kB-dependent cyclin D1 (Guttridge et al, 1999).…”

“…Glucocorticoids induce G1 cell cycle arrest in some cell types through the activation of cyclin-dependent kinase (CDK) inhibitors p21/Cip1 and p27/Kip1 (Rogatsky et al, 1997;Cha et al, 1998;Rogatsky et al, 1999;Samuelsson et al, 1999;Park et al, 2001;Terada et al, 2001). Thus, we analysed whether GR affected the expression of p21 and p27 CDK inhibitors, as well as cyclin D1, which is usually overexpressed in skin papillomas (Robles and Conti, 1995).…”

C/EBPα Regulates Formation of S-Phase-Specific E2F-p107 Complexes in Livers of Newborn Mice

“…The transcriptional regulation of specific genes by C/EBP␣ has been found to be a major mechanism in the control of adipose tissue differentiation and energy metabolism. However, the regulation of cell proliferation by C/EBP␣ is more complicated and involves both transcriptional control (3,5,36) and interaction with proteins that regulate cell cycle progression (34). The expression of C/EBP␣ and C/EBP␤ proteins has been shown to be increased in the liver before birth (2).…”

“…It has been shown that C/EBP␣ up-regulates p21 mRNA transiently, but protein level elevation occurs primarily via the stabilization of p21 protein (36). It has been recently shown that C/EBP␣ can also up-regulate p21 protein in hepatoma cells (3,5). In the liver, C/EBP␣ regulates p21 protein levels presumably through a protein-protein interaction (34).…”

Cell Cycle Arrest by Glucocorticoids May Protect Normal Tissue and Solid Tumors from Cancer Therapy

“…48 Similarly, GCs stimulated p21 gene expression by targeting multiple transcriptional elements within a steroid responsive region of the p21 WAF1/CIP1 promoter in rat hepatoma cells. 49 Another possibility, not examined in this study, is that DEX may have upregulated some drug-detoxifying factors such as found for metallothionein, [50][51][52] O6-methylguanine-DNA methyltransferase (MGMT), 53-55 P-glycoprotein 56,57 or glutathione, 58 which may have influenced the effectiveness of chemotherapy. 59…”