p57(Kip2), a glucocorticoid-induced inhibitor of cell cycle progression inHeLa cells

Glucocorticoids exert antiproliferative effects on a number of cell types, including the HeLa cervical carcinoma cell line, However, the mechanism res ponsible for the antiproliferative effect is poorly understood. In this rep ort we have investigated the role of the recently identified cyclin-depende nt kinase inhibitor (CDI) p57(Kip2) in the antiproliferative effect conferr ed by glucocorticoids, When HeLa cells were treated with the synthetic gluc ocorticoid dexamethasone (DEX), the doubling time of exponentially growing cells increased 2-fold. Within 11 h of DEX treatment, this was accompanied by an accumulation of cells in the G(1) phase of the cell cycle with a corr esponding decreased proportion of cells in the S phase and decreased CDK2 a ctivity. DEX treatment of the HeLa cells dramatically induced the protein a nd mRNA expression of the CDI p57(Kip2), This induction was seen within 4 h of DEX treatment, preceding a major DEX-induced accumulation of cells in t he G(1) phase. DEX-induced mRNA expression of p57(Kip2) did not require de novo protein synthesis, and the transcription of the p57(Kip2) gene was inc reased as determined by a run-on transcription assay. Furthermore, DEX indu ction of p57(Kip2) was not a consequence of the cell cycle arrest, since ot her growth inhibition signals did not result in strong p57(Kip2) induction. Overexpression of p57(Kip2) using HeLa cells stably transfected with a tet racycline-inducible vector showed that p57(Kip2) is sufficient to reconstit ute an antiproliferative effect similar to that seen in DEX-treated cells. Selective p57(Kip2) expression by the tetracycline analog doxycycline to le vels comparable to those observed on DEX induction resulted in a 1.7-fold i ncrease in the doubling time and a shift of HeLa cells to the G(1) phase as well as a decrease in CDK2 activity. Taken together, these results suggest that glucocorticoid treatment directly induces transcription of the p57(Ki p2) gene and that the p57(Kip2) protein is involved in the glucocorticoid-i nduced antiproliferative effect.