CANCER BIOLOGY: The human papillomavirus E6/E7 genes induce discordant changes in the expression of cell growth regulatory proteins

Abstract

The E6/E7 oncoproteins of human papillomavirus (HPV) types 16 and 18 are responsible for the efficient immortalization of human genital keratinocytes and we have recently reported that such immortalized cells display alterations in the expression of cyclin A, cyclin B, and cdc-2. To determine whether these alterations were the consequence of E6/E7 protein expression or whether they resulted from the process of cellular immortalization, we multiply-infected primary genital keratinocytes with a retrovirus expressing the HPV-18 E6/E7 genes and examined the cells for acute, pre-immortalization changes in several critical cell growth regulatory proteins including cyclin A, cyclin B, cdc-2, p53 and c-myc. In addition, we simultaneously evaluated the expression of the E6/E7, bcl-2 and involucrin genes to determine whether there were accompanying alterations in the expression of viral genes or in cellular genes related to cell apoptosis and the state of keratinocyte differentiation. The cell cycle regulating proteins (cyclin A, cyclin B, cdc-2 and p53) change significantly within days after retroviral infection. Cyclin B and cdc-2 increase over 4-fold by three passages and remain relatively constant thereafter through passage 21, whereas the levels of p53 protein decrease 25% by passage three. Increases in the expression of cyclin A, cyclin B and cdc-2, and decreases in p53 are therefore among the earliest observable changes in cell regulatory proteins following E6/E7 gene expression and may be important contributors to the development of cell immortalization. The expressions of viral E6/E7 genes, c-myc, bcl-2 and involucrin exhibit progressive changes with increased passage numbers until passage 21, presumably reflecting the selective outgrowth of immortalized cells.

The RPTEC/TERT1 cell line models key renal cell responses to the environmental toxicants, benzo[a]pyrene and cadmium

“…The HK-2 cell line, isolated in 1994 from human renal proximal tubule cells, was immortalized with the human papilloma virus 16 (HPV16) E6 and E7 genes. While studies characterizing the HK-2 cell line have demonstrated their ability to reproduce results seen in isolated proximal tubule cells, the transformation with E6/E7 genes is now known to lead to aberrant cell growth, signaling, and in vitro properties that may not correctly reflect normal proximal tubule cells [26], [28].…”

Squamous metaplasia induced by transfection of human papillomavirus DNA into cultured adenocarcinoma cells

“…The HPV integration site in chromosomes varies from case to case, although Cannizzaro and colleagues 57 58 have reported integration at the chromosome 3p fragile site. It is thought that HPV infects epithelial cells and that the viral gene, especially the E6, E7 and E2 products, 59 induces the abrogation of the cell cycle, 46 60 and that in this process squamous metaplasia is induced, and dysplasia and neoplasia develop through further gene alterations. Recently Graham and colleagues 49 have indeed reported that additional genetic alterations in HPV infected cells are thought to be required for the development of a carcinogenic genotype.…”

Differential patterns of cell cycle regulatory proteins expression in transgenic models of thyroid tumours

“…The inactivation of Rb, by phosphorylation, mutation, gene deletion or viral oncogenes leads in most cell types to increased proliferation. It also causes overexpression of the di erent cyclins and cdk(s) expressed in late G1 Herrera et al, 1996;Pei, 1996;Tiainen et al, 1996).…”