Novel Molecular Biologic Mechanism of Growth Suppressive Regulation by Retinoid / Interferon in Cervical Cancer Cells

Kim, Soo Pyung; Namkoong, Sung Eun; Kim, Seung Jo; Kim, Eun Joo; Um, Soo Jong; Park, Jong Sup; Lee, Keun Ho; Kim, Chan Joo

Abstract

OBJECTIVE
Retinoic acids (RAs) and interferons (IFNs) have been implicated in the growth regulation of cervical cancer cells, which was suggested by clinical trials and in vitro experiments. However, the molecular mechanisms of growth regulation are not fully defined, The purpose of this study is to assess the effect of RA and/or IFN on human cervical carcinoma cells in vitro and to analyze their action mechanisms in HPV-positive cervical carcinoma cells by molecular biologic studies.
METHODS
HPV-positive (CaSki, HeLa), HPV-negative (C33A, HT-3), and non-cervical cancer Cos-1 cell lines were treated with RA and/ar IFN. Their effects on cell growth were evaluated by the cell pmliferation assay and the following BrdU DNA incorporation assay. The molecular mechanism was further investigated by a series of immunoblottings and transient cotransfection assays, which were conducted in HeLa cells and C33A cells using the CAT reporter gene assay. To observe the down regulation of HPV E6/E7 gene expression by RA/IFN, reverse transcription-polymerase chain reaction (RT-PCR) was perforned.
RESULTS
The powth of RA-treated cells was less suppressed than that of IFN-treated cells. Combined treatment of RA and IFN leads to additive effect on the growth suppression of HeLa and CaSki cells. The proliferation activity was most severely reduced in Hela cells by treatment of both all-trans-RA (AtRA) and IFN-r. Combined treatment of AtRA/IFN-r causes a great increase in the level of interferon regulatory factor-1 (IRF-1) protein in HeLa cells, whereas no induction of IRF-1 was observed in C33A cells. The CAT gene expression for IRF-1 was greatly induced by IFN-r in HeLa cells. Immunoblotting assays shows the concurrent induction of p21 CDK inhibitor and dephosphorylation of Rb protein in HeLa cells. In RT-PCR, an individual treatment of either RA or IFN reduced HPV E6/E7 mRNA levels and significantly cooperative when both RA and IFN were treated. By deaeasing E6 levels, the p53 level was increased in HeLs cells treated with RA and/or IFN. Transient cotransfection of IRF-1 and p53 as the transcription factors leads to the cooperative activation of a common p21 promoter to regulate the cell cycle.
CONCLUSION
RA/IFN suppressed the growth of HPV-positive cervical cancer cells. When they were both treated, additive suppressive effects were observed in cellular proliferation as well as DNA synthesis. The growth suppressive effect is likely to be related to the increased expression of IRF-1 and p21 (antitumoral effect; p53-independent). The down regulation of HPV E6 gene suppression may account for the resultant increase of p53 levels (antiviral effect; p53-dependent). Both induced IRF-1 and p53 cooperatively augument tbe suppession of p21 CDK inhibitor, which results in dephosphorylation of pRb. Although clinical effects are likely complex and may include interactions of in vitro growth inhibitory effects with immunomodulatory and antiangiogeaetic effect, tbese results suggest the optimal clinical role for the combination of RA/IFN in the treatment of cervical canccers.