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.
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(-9) 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.
Narayanan
B A
BA
Hollings Cancer Center and Department of Medical Laboratory Sciences, Medical University of South Carolina, Charleston, USA.
Holladay
E B
EB
Nixon
D W
DW
Mauro
C T
CT
D000077556:Alitretinoin; D002453:Cell Cycle / Q000187:drug effects; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000235:genetics*; D050725:Papillomavirus E7 Proteins; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism*; D012097:Repressor Proteins; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D002583:Uterine Cervical Neoplasms / Q000235:genetics / Q000821:virology*
C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; D000077556:Alitretinoin; D014212:Tretinoin