title: HPV16 E7 protein and hTERT proteins defective for telomere maintenance cooperate to immortalize human keratinocytes.
abstract: Previous studies have shown that wild-type human telomerase reverse transcriptase (hTERT) protein can functionally replace the human papillomavirus type 16 (HPV-16) E6 protein, which cooperates with the viral E7 protein in the immortalization of primary keratinocytes. In the current study, we made the surprising finding that catalytically inactive hTERT (hTERT-D868A), elongation-defective hTERT (hTERT-HA), and telomere recruitment-defective hTERT (hTERT N+T) also cooperate with E7 in mediating bypass of the senescence blockade and effecting cell immortalization. This suggests that hTERT has activities independent of its telomere maintenance functions that mediate transit across this restriction point. Since hTERT has been shown to have a role in gene activation, we performed microarray studies and discovered that E6, hTERT and mutant hTERT proteins altered the expression of highly overlapping sets of cellular genes. Most important, the E6 and hTERT proteins induced mRNA and protein levels of Bmi1, the core subunit of the Polycomb Group (PcG) complex 1. We show further that Bmi1 substitutes for E6 or hTERT in cell immortalization. Finally, tissue array studies demonstrated that expression of Bmi1 increased with the severity of cervical dysplasia, suggesting a potential role in the progression of cervical cancer. Together, these data demonstrate that hTERT has extra-telomeric activities that facilitate cell immortalization and that its induction of Bmi1 is one potential mechanism for mediating this activity.
authors.affiliation: Department of Pathology, Georgetown University Medical Center, Washington, D.C., United States of America.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Miller
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Dakic
authors.forename: Renxiang
authors.initials: R
authors.lastname: Chen
authors.forename: Nancy
authors.initials: N
authors.lastname: Palechor-Ceron
authors.forename: Yuhai
authors.initials: Y
authors.lastname: Dai
authors.forename: Bhaskar
authors.initials: B
authors.lastname: Kallakury
authors.forename: Richard
authors.initials: R
authors.lastname: Schlegel
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Liu
mesh_terms: D002472:Cell Transformation, Viral; D052162:Human papillomavirus 16 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000502:physiology*; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D050725:Papillomavirus E7 Proteins / Q000235:genetics / Q000378:metabolism*; D063150:Polycomb Repressive Complex 1 / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000235:genetics / Q000502:physiology
chemical_list: C069077:BMI1 protein, human; C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012333:RNA, Messenger; D012097:Repressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16; D063150:Polycomb Repressive Complex 1; C509186:TERT protein, human; D019098:Telomerase