title: Human papillomavirus type 16 E6 inactivation of p53 in normal human mammary epithelial cells promotes tamoxifen-mediated apoptosis.
abstract: Aberrant p53 expression is frequently observed in mammary epithelial cells obtained from women at high risk for developing breast cancer and is a predictor for the subsequent development of malignancy. Tamoxifen has recently been shown to reduce the incidence of noninvasive breast cancer in high-risk women, but the molecular mechanism of tamoxifen chemoprevention in mammary epithelial tissue that does not overexpress the estrogen receptor is poorly understood. We suppressed p53 expression by retroviral-mediated expression of human papillomavirus type-16 E6 protein (HPV-16 E6) in human mammary epithelial cells (HMECs) to develop an in vitro model of tamoxifen chemoprevention in the context of p53 loss. Early passage p53(-) HMEC-E6-transduced cells treated with 1.0 microM tamoxifen rapidly underwent apoptosis. In contrast, early passage p53(+) HMEC-LXSN vector controls treated with 1.0 microM tamoxifen underwent G1-G0-phase arrest but did not undergo apoptosis. p53(-) HMEC-E6 cells rapidly acquired resistance to tamoxifen-mediated apoptosis after 10 passages in culture (in the absence of tamoxifen). Both p53(+) and p53(-) HMECs exhibited a low level of estrogen receptor staining and minimal estrogen binding, characteristic of proliferating normal luminal mammary epithelial cells. Tamoxifen-mediated apoptosis in p53(-) HMEC-E6 cells was not blocked by inhibitors of transcription and protein synthesis. These data suggest that the acute loss of p53 function in HMECs by expression of HPV-16 E6 results in marked sensitivity to tamoxifen-mediated apoptosis but that resistance to apoptosis rapidly develops within 10 passages in vitro. Observations in our model system predict a critical role for the early institution of tamoxifen chemoprevention.
authors.affiliation: Division of Medical Oncology, Duke University Medical Center, Durham, North Carolina 27710, USA. seewa001@mc.duke.edu
authors.forename: V L
authors.initials: VL
authors.lastname: Seewaldt
authors.forename: K
authors.initials: K
authors.lastname: Mrózek
authors.forename: E C
authors.initials: EC
authors.lastname: Dietze
authors.forename: M
authors.initials: M
authors.lastname: Parker
authors.forename: L E
authors.initials: LE
authors.lastname: Caldwell
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001667:Binding, Competitive; D015153:Blotting, Western; D001940:Breast / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D020732:Cytogenetic Analysis; D004274:DNA, Recombinant; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D004967:Estrogens / Q000378:metabolism; D015870:Gene Expression; D020868:Gene Silencing; D005822:Genetic Vectors / Q000235:genetics; D005838:Genotype; D006801:Humans; D008854:Microscopy, Electron; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins; D013629:Tamoxifen / Q000378:metabolism / Q000494:pharmacology*; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D004274:DNA, Recombinant; C068651:E6 protein, Human papillomavirus type 16; D004967:Estrogens; D009856:Oncogene Proteins, Viral; D011960:Receptors, Estrogen; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D013629:Tamoxifen