Cytostatic effect of TNFα on cancer cells is independent of p21^WAF1

Abstract

Tumor necrosis factor α (TNFα) is a cytotoxic/cytostatic compound for a variety of human cancer cells. The p21^WAF1 protein is a cyclin-dependent kinase inhibitor (CDKI) that binds to cyclin/cyclin-dependent kinase (CDK) complexes and inhibits their kinase activities, thereby leading to cell cycle arrest. We found that the cytostatic effect of TNFα on the cervical cancer cell line, ME180, was concomitant with an arrest of these cells in the G0/G1 phase of the cell-cycle. This corresponded with an increase in both p21^WAF1 mRNA and protein levels which likely occurred via a p53-independent pathway since ME180 is infected with the human papilloma virus. To elucidate the role of p21^WAF1 in the TNFα-mediated growth and cell cycle arrest, we stably transformed ME180 cells with an antisense p21^WAF1-expression vector. Two clones with reduced levels of p21^WAF1 both in their basal state as well as after their exposure to TNFα were selected. The growth of these cells was still inhibited by TNFα and they arrested in G0/G1 similar to wildtype or empty vector transfected cells. These results indicate that although p21^WAF1 expression increases dramatically with TNFα treatment, it may not play a critical role in the cytostatic effect of TNFα on ME180 cervical cancer cells.