The effect of all-trans and 9-cis retinoic acid on the steady state level of HPV16 E6/E7 mRNA and cell cycle in cervical carcinoma cells

• Published in: Life sciences (1973) Vol. 63; no. 7; pp. 565 - 573
• Main Authors: Narayanan, Bhagavathi A., Holladay, E.Blair, Nixon, Daniel W., Maure, Charles T.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 1998
• Subjects: 9-cis retinoic acid; Alitretinoin; Cell Cycle - drug effects; cervical carcinoma; Female; Flow Cytometry; Human papillomavirus 16; Humans; Oncogene Proteins, Viral - genetics; Papillomavirus E7 Proteins; Polymerase Chain Reaction; Repressor Proteins; retinoids; RNA, Messenger - metabolism; Tretinoin - pharmacology; Tumor Cells, Cultured; Uterine Cervical Neoplasms - genetics; Uterine Cervical Neoplasms - virology; vitamin A; 9-cis retinoic acid; vitamin A; retinoids; cervical carcinoma
• ISSN: 0024-3205; 1879-0631
• DOI: 10.1016/S0024-3205(98)00307-5

Retinoids, including natural vitamin A and its analogs, have been closely studied as chemopreventive drugs. The mechanism of action of retinoids, however, is not completely understood. Our study evaluated the effects of all-trans (high affinity ligand for both RAR and RXR receptors) and 9-cis retinoic acid (binds only with RXR receptors) on E6–E7 transcription, cell proliferation, cell cycle distribution, and p53 expression in CaSki cells, a cell line derived from cervical carcinoma containing 600 copies of the HPV-16 genome. Using quantitative RT-PCR analysis, we found that CaSki cells treated with all trans retinoic acid (ATRA) for seven days had a remarkably low level of E6–E7 transcription at 10
−5 M to 10
−5 M concentrations. A smaller inhibitory effect was observed on the E6–E7 transcription at a concentration of 10
−5 M with only 9-cis retinoic acid. Flow cytometric analysis revealed that cells treated with both all trans and 9-cis RA showed an increase in the mean percentage (93.5% and 86.1% respectively) of cells in the G1 phase as compared to untreated CaSki cells (55%) and normal keratinocytes (58%). The percentage of cells in the S phase decreased from a mean percentage of 28 and 26.5 to 5.8 and 5, respectively, after treatment with all trans retinoic acid and 9-cis retinoic acid. An increase in the level of immunophenotypic expression of wild type p53 was also noted after treatment with all trans retinoic acid and 9-cis retinoic acid. All trans and 9-cis retinoic acid may act on highly proliferating tumor cells by initially arresting DNA synthesis and inducing G1 arrest. In addition, they may be inducing a p53 dependent cell cycle arrest and thus suggests that all-trans and 9-cis retinoic acid may have a cytostatic effect rather than a cytotoxic effect on CaSki cells. The increased expression of p53 positive cells and the inhibition of E6/E7 transcription after treatment with these retinoids may indicate the potential role of all trans and 9-cis retinoic acid as a cell cycle regulator and an antiviral chemoprevention agent.