Human papillomavirus (HPV) type 18 E7 protein is a short-lived steroid-inducible phosphoprotein in HPV-transformed cell lines.
We used a capture ELISA to quantify the E7 protein of human papillomavirus type 18 (HPV-18). In HeLa cells, which express low levels of immunoreactive E7 protein (iE7), iE7 had a mean half-life of 13.5 min. In HPV-18 E7 recombinant baculovirus (E7rec BV)-infected Sf21 cells, which express higher levels of E7, the half-life of iE7 was much longer (90 min and > 24 h, with two different E7rec BVs). For two transformed human cervical cell lines expressing HPV-18 E7, exposure of the cells to hydrocortisone resulted in a twofold increase in steady-state levels of the E7 protein: no similar effect was observed with progesterone, oestrogen or testosterone. The half-life of iE7 was unaltered by hydrocortisone or progesterone exposure. An immunoassay which distinguished Ser33-phosphorylated E7 from E7 not phosphorylated at this residue (Ser33dephospho-E7), showed that in HeLa and Sf21 cells the majority of E7 was phosphorylated: the half-life of both species of E7 was similar in HeLa cells, but the half-life of Ser33dephospho-E7 was much shorter (90 min) in Sf21 cells than that of Ser33phospho-E7 (> 24 h). A HeLa-fibroblast fusion cell line with tumorigenic potential (CGL-1) had a similar ratio of dephospho-E7 to total E7 (0.06), as a similar fusion cell line (CGL-4) with no tumorigenic potential (0.03). We conclude that E7 is a labile phosphoprotein, and that the expression and steady-state level of the E7 protein in eukaryotic cells may be influenced by the hormonal environment of the cells.
Papillomavirus Research Unit, Lions Human Immunology Laboratories, University of Queensland, Princess Alexandra Hospital, Woolloongabba, Australia.
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Selvey
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Park
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D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D002460:Cell Line; D002461:Cell Line, Transformed; D003350:Cortodoxone / Q000494:pharmacology; D004268:DNA-Binding Proteins; D004958:Estradiol / Q000494:pharmacology; D015870:Gene Expression; D006207:Half-Life; D006367:HeLa Cells; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D008969:Molecular Sequence Data; D009856:Oncogene Proteins, Viral / Q000032:analysis / Q000378:metabolism*; D027383:Papillomaviridae / Q000378:metabolism*; D010766:Phosphorylation; D011374:Progesterone / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013256:Steroids / Q000494:pharmacology*; D013739:Testosterone / Q000494:pharmacology
D000911:Antibodies, Monoclonal; D004268:DNA-Binding Proteins; C052633:E7 protein, Human papillomavirus type 18; D009856:Oncogene Proteins, Viral; D011993:Recombinant Fusion Proteins; D013256:Steroids; D013739:Testosterone; D012694:Serine; D011374:Progesterone; D004958:Estradiol; D003350:Cortodoxone; D006854:Hydrocortisone