Induction of cell-cycle arrest in cervical cancer cells by the human immunodeficiency virus type 1 viral protein R

Objective: To determine the ability of the human immunodeficiency virus typ e 1 (HIV-1) gene vpr to induce cell-cycle arrest in cervical cancer cells w ith or without human papillomavirus (HPV) type 16 E6 or E7 expression. Methods: High- and low-level expression vectors for vpr (designated pVPR(HI GH) and pVPR(LOW), respectively) were used in conjunction with HPV-16 E6 or E7 vectors to trans; feet HPV-negative C33A cervical cancer cells. Vpr exp ression vectors encode a cell surface marker gene, murine Thy-1, for specif ic detection of transfected cells. Dual staining for the surface molecule T hy-1 and DNA content was used to determine cell-cycle profile and G(2)-phas e arrest(.) Results: C33A cells not expressing HPV-16 E6 showed some but not maximal G( 2)-phase arrest when transfected with pVPR(HIGH) alone (43.2% of cells in t he G(2) phase). Addition of HPV-16 E6 or E6 plus E7 to pVPR(HIGH) substanti ally increased the percentages of cells in the G2 phase (51.3% and 53.0%, r espectively). Cotransfection with pVPR(HIGH) and HPV-16 E7 did not increase significantly the percentage of cells in the G(2) phase compared with pVPR (HIGH) alone (40.6% versus 43.2%). In transfections involving pVPR(LOW) a s light degree of G(2)-phase arrest was observed when Vpr was expressed alone (29.0% of cells in the G(2) phase) or in cotransfection with HPV-16 E7 (33 .2% of cells), and G(2)-phase arrest was augmented with the addition of HPV -16 E6 (41.7%) or E6 plus E7 (45.7%). Conclusion: Cervical cancer cells are susceptible to cell-cycle arrest indu ced by HIV-1 vpr. This effect is exacerbated by coexpression of HPV-16 E6, although E6 alone is incapable of inducing any detectable G(2)-phase arrest , suggesting that E6 and VPR share links in cell-cycle signaling pathways. (Obstet Gynecol 2000;95:141-6. (C) 2000 by The American College of Obstetri cians and Gynecologists.).