2000 Volume 127 Issue 5 Pages 883-893
We tested the effect of IL-1 on the expression of p21WAF1 in human embryonic fibroblasts W138. Exposure to IL-1 caused induction of p21WAF1 protein in high-passage W138 cells but not in early-passage cells. However, IL-1 did not stimulate the transcription of a CAT-reporter gene having two copies of the p53-responsive element on its promoter or the p53-binding capacity of nuclear extracts, although it increased transcriptional rate of p21WAF1 in these high-passage cells. These results suggest that the induction of p21WAF1 by IL-1 occurs at the transcriptional level, but p53 function is not required in these cells. Further studies found that IL-1 did not cause cell-cycle arrest, and the overexpression of p21WAF1 resulted in only a slight delay of cell growth, while the level of p21WAF1 coprecipitated with cyclin-dependent kinase-2 (Cdk2) was increased by IL-1. Moreover, a kinase assay of Cdk2 immunoprecipitates showed that IL-1 did not reduce the kinase activity, and IL-1 did not affect the status of phosphorylation of the retinoblastoma gene product (Rb). These findings imply that despite the induction of p21WAF1, this cannot fully account for the growth arrest in high-passage W138 cells. Thus, IL-1 mediates p21WAF1 induction through a p53-independent pathway (s) in high-passage W138 cells, but the cell cycle is regulated independently of p21WAF1.
