Loss of p53 protein in human papillomavirus type 16 E6-immortalized human mammary epithelial cells

Abstract

We have shown previously that introduction of the human papillomavirus type 16 (HPV16) or HPV18 genome into human mammary epithelial cells induces their immortalization. These immortalized cells have reduced growth factor requirements. We report here that transfection with a single HPV16 gene E6 is sufficient to immortalize these cells and reduce their growth factor requirements. The RB protein is normal in these cells, but the p53 protein is sharply reduced, as shown by immunoprecipitation with anti-p53 antibody (pAB 421). We infer that the E6 protein reduces the p53 protein perhaps by signalling its destruction by the ubiquitin system. The HPV-transforming gene E7 was unable to immortalize human mammary epithelial cells. Thus, cell-specific factors may determine which viral oncogene plays a major role in oncogenesis. Human papillomavirus types 16 and 18 (HPV16 and HPV18) have been associated with cervical carcinoma, although most of the 65 or more known HPV types are restricted to small benign epidermal lesions, such as warts and papillomas (14). New HPV types and new associations with oral as well as genital carcinomas are being reported (14), but no evidence for an association of HPV with breast cancer has yet been found. Indeed, it has been postulated that the narrow host range of HPV, apparently limited to squamous epithelial cells, may reflect a specific cellular interaction provided by these cells.

Ubiquitin‐immunoreactive degradation products of cytokeratin 8/18 correlate with aggressive breast cancer

“…17) The Ub-dependent degradation pathway has also been shown to be involved in the turnover of p53 by others. 18,19) Following our earlier results, 17) we were interested in determining whether increased Ub-dependent proteolysis shortens the half-lives of other cellular proteins, thereby causing a reorganization of the cellular structure which would in turn contribute to the characteristics of the cancerous state. Therefore, in the present study, we used two-dimensional (2-D) polyacrylamide gel electrophoresis (PAGE) followed by immunoblot analysis with anti-Ub mAbs, together with sequencing analysis, in an attempt to identify tumor-specific Ub-conjugated proteins in breast cancer tissue.…”

Does telomere shortening drive selection for p53 mutation in human cancer?

“…The best direct evidence for this idea so far comes from in vitro gene transfer experiments. A variety of DNA tumor virus oncogenes have long been known to abrogate senescence (MI) in human fibroblasts [29], a property initially thought to require inhibition of function of at least two tumor suppressor genes (TSGs), i.e., pl05rb as well asp53 [30-321. Using the ability of amphotropic retroviral vectors to manipulate near-senescent cells, however, we recently demonstrated unequivocally that this can be achieved by expression of mutant p53 alone [l], a result that agrees with more indirect evidence from experiments using human papillomavirus E6 to abrogate p53 function in breast epithelial cells [32,33].…”

Preferential chromosome loss in human papilloma virus DNA‐lmmortalized mammary epithelial cells

“…Cytogenetic analyses of nine independent HPV-immortalized human mammary epithelial cell lines were performed as summarized in Table 1. The HPV-HMECs are derived from a series of calcium phosphate-mediated transfections of normal mammary epithelial cells (76N) with plasmid-containing HPV DNA (Band et al, 1990(Band et al, , 1991. Immortal clones could be derived from independent transfections with either HPV 16 or HPV 18 DNA (Band et al, 1990).…”

“…Immortal clones could be derived from independent transfections with either HPV 16 or HPV 18 DNA (Band et al, 1990). When these studies were extended to determine which spe-cific HPV genes were necessary for immortalization, Band et al (1991) determined that only the E6 gene was required.…”

“…Both normal 76N cells and HPV-immortalized 76N cells were grown in DFCI-1 medium, a semidefined medium that supports the propagation of human mammary epithelial cells (Band and Sager, 1989). Most cell strains derived from reduction mammoplasty or from cell lines of HPV-immortalized mammary epithelial cells have been described previously and are listed in Table 1 (Band et al, 1990(Band et al, , 1991. A brief description of the lines follows.…”