Antiproliferative effects of retinoic acid/interferon in cervical carcinoma cell lines: Cooperative growth suppression of IRF-1 and p53

Retinoids and interferons have been implicated in the growth regulation of cervical cancer cells. However, the molecular mechanisms are not fully defi ned. To analyze detailed mechanisms, HPV-positive (HeLa, CaSki), HPV-negati ve (C33A, HT-3) and non-cervical Cos-1 cell lines were treated with I mu M all-trans-retinoic acid (RA) and/or 10 ng/ml interferon-gamma (IFN-gamma). The growth of RA-treated HeLa cells was less effectively suppressed than th at of IFN-gamma-treated ones. A combination of RA and IFN-gamma leads to an additive antiproliferative effect on the cell growth. CaSki cell growth wa s also inhibited by IFN-gamma but was little stimulated by RA treatment, an d the IFN effect was attenuated when IFN-gamma was combined with RA. HPV-ne gative C33A and HT-3 cells, which are defective in p53 and Rb, and Cos-1 ce lls were weakly or not responsive to all combined treatments. The molecular mechanism underlying the differential effects of RA/IFN on HeLa and C33A c ells was investigated. Combined RA/IFN-gamma treatment caused a marked incr ease in the level of IFN regulatory factor-1 (IRF-1) in HeLa, whereas no in duction of IRF-1 was observed in C33A, consistent with the findings that IF N signaling is functional in HeLa but is defective in C33A cells. The incre ase of p53 in HeLa cells might account for the down-regulation of HPV-18 E6 gene expression by RA/IFN-gamma. Furthermore, RA/IFN-gamma treatment resul ted in the concurrent induction of p21(WAF1) CDK inhibitor and dephosphoryl ation of Rb protein. Transient co expression of IRF-1 and p53 led to the co operative activation of the p21(WAF1) promoter, Our results indicate that 2 transcription factors, increased in response to RA/IFN-gamma, cooperate fu nctionally to regulate the cell cycle through the activation of a common p2 1(WAF1) gene in HeLa cells. (C) 2000 Wiley-Liss, Inc.