Regulation of cell growth and HPV genes by exogenous estrogen in cervical cancer cells

Cj. Kim et al., Regulation of cell growth and HPV genes by exogenous estrogen in cervical cancer cells, INT J GYN C, 10(2), 2000, pp. 157-164
Citations number
Categorie Soggetti
Reproductive Medicine
Journal title
ISSN journal
1048-891X → ACNP
Year of publication
157 - 164
SICI code
Human papillomavirus (HPV) infection is known as the major cause of the dev elopment of cervical cancer. The E6 and E7 proteins of oncogenic HPV can pl ay critical roles in immortalization and malignant transformation of cervic al epithelial cells. From the previous epidemiologic data, it has been dete rmined that long-term use of oral contraceptives may be a risk factor for c ervical cancer. Investigation of the estrogenic and antiestrogenic effects on the proliferation of cervical cancer cells and the gene expression of HP V would help to explain the role of estrogen in the HPV-associated pathogen esis of cervical cancer. In this study, cervical cancer cells (HeLa, CaSki, and C33A) were cultured in vitro in the presence of 17 beta-estradiol or t amoxifen to observe their regulatory growth effect and HPV E6/E7 gene expre ssion. The estrogenic effect on the promoter activity of HPV URR was furthe r confirmed by transient transfection assay, which was conducted in C33A ce lls using the HPV-18 URR-CAT reporter plasmid. The supplemental effect of e strogen receptors on URR promoter activity was also evaluated. The prolifer ation of HeLa and CaSki cells was stimulated by estradiol at physiologic co ncentration levels (less than or equal to 1 x 10(-6) M). At a low concentra tion (0.1 x 10(-6) M), tamoxifen also stimulated the proliferation of HeLa and CaSki cells. In contrast to HPV-positive cervical cells, the proliferat ion of C33A was not influenced by exogenous estradiol or tamoxifen, indicat ing that HPV might play a role in the hormonal stimulation of cell growth. Interestingly, the proliferation of HeLa was markedly suppressed at high co ncentrations of estradiol and tamoxifen (5 and 10 x 10(-6) M). The levels o f HPV-18 E6 and E7 mRNA were significantly increased by estradiol at a conc entration of 0.5 x 10(-6) M. Transient transfection experiments using the H PV URR-CAT reporter plasmid in C33A cells indicated that the expression of HPV E6/E7 genes was increased by the treatment of estradiol and tamoxifen. Co-transfection of estrogen receptors (ER) and URR-CAT leads to a fourfold increase in CAT activity by estradiol or tamoxifen at physiologic concentra tions. When estradiol or tamoxifen was administered at high concentrations (5 x 10(-6) M), a DNA ladder, typically indicative of apoptosis, was observ ed in HeLa cells. In conclusion, estradiol stimulated the growth of HPV-pos itive cervical cancer cells, as did tamoxifen at low concentrations (0.1 x 10(-6) M). The growth stimulation of HPV-positive cervical cancer cells by estrogen appeared to be related to the increased expression of HPV E6/E7. G rowth suppression observed at high concentrations of estradiol and tamoxife n in HeLa cells might be a result of apoptosis. Taken together, these data suggested that exogenous estradiol might be a risk factor in HPV-mediated c ervical carcinogenesis.