IL-1 induces expression of p21(WAF1) independently of p53 in high-passage human embryonic fibroblasts WI38

We tested the effect of IL-1 on the expression of p21(WAF1) in human embryo nic fibroblasts WI38. Exposure to IL-1 caused induction of p21(WAF1) protei n in high-passage WI38 cells but not in early-passage cells. However, IL-1 did not stimulate the transcription of a CAT-reporter gene having two copie s of the p53-responsive element on its promoter or the p53-binding capacity of nuclear extracts, although it increased transcriptional rate of p21(WAF 1) in these high-passage cells. These results suggest that the induction of p21(WAF1) 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 p21(WAF1) resulted in only a slight delay of cell growth, while the level of p21(WAF1) coprecipitated wi th cyclin-dependent kinase-2 (Cdk2) was increased by IL-1. Moreover, a kina se assay of Cdk2 immunoprecipitates showed that IL-1 did not reduce the kin ase activity, and IL-1 did not affect the status of phosphorylation of the retinoblastoma gene product (Rb). These findings imply that despite the ind uction of p21(WAF1), this cannot fully account for the growth arrest in hig h-passage WI38 cells. Thus, IL-1 mediates p21(WAF1) induction through a p53 -independent pathway(s) in high-passage WI38 cells, but the cell cycle is r egulated independently of p21(WAF1).