Tumor necrosis factor-? promotes human papillomavirus (HPV) E6/E7 RNA expression and cyclin-dependent kinase activity in HPV-immortalized keratinocytes by aras-dependent pathway

Publisher Website
Google Scholar
Abstract
Tumor necrosis factor‐α (TNF‐α) inhibits growth of normal cervical keratinocytes but stimulates proliferation of human papillomavirus (HPV)–immortalized and cervical carcinoma–derived cell lines when mitogens such as epidermal growth factor (EGF) or serum are depleted. Current work identifies the mechanism of growth stimulation. TNF‐α promoted cell cycle progression by increasing expression of HPV‐16 E6/E7 RNAs and enhancing activity of cyclin‐dependent kinase (cdk)2 and cdc2 after 3 d. Increased kinase activity was mediated by upregulation of cyclins A and B and decreases in cdk inhibitors p21waf and p27kip. TNF‐α stimulated these changes in part by increasing transcription and stabilization of RNA for amphiregulin, an EGF receptor ligand, and amphiregulin directly increased HPV‐16 E6/E7 and cyclin A RNAs. To define which components of the EGF receptor signaling pathway were important, HPV‐immortalized cells were transfected with activated or dominant negative mutants of Ha‐ras, raf, or MAPKK. Expression of activated Ha‐ras maintained HPV‐16 and cyclin gene expression and promoted rapid growth in the absence of EGF. Furthermore, ras activation was necessary for TNF‐α mitogenesis as transfection with a dominant negative ras mutant (Asn‐17) strongly inhibited growth. Thus, activation of ras promotes expression of HPV‐16 E6/E7 RNAs, induces cyclins A and B, and mediates growth stimulation of immortal keratinocytes by TNF‐α. These studies define a pathway by which ras mutations, which occur in a subset of cervical cancers, may contribute to pathogenesis. Mol. Carcinog. 27:97–109, 2000. Published by Wiley‐Liss, Inc.