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.
Selvey
L A
LA
Papillomavirus Research Unit, Lions Human Immunology Laboratories, University of Queensland, Princess Alexandra Hospital, Woolloongabba, Australia.
Dunn
L A
LA
Tindle
R W
RW
Park
D S
DS
Frazer
I H
IH
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