title: Human papillomavirus type 16 E6 amino acid 83 variants enhance E6-mediated MAPK signaling and differentially regulate tumorigenesis by notch signaling and oncogenic Ras.
abstract: Oncogenically high-risk human papillomaviruses (HPVs) are causally associated with the progression of major human neoplasia-like cancers of the cervix. Several studies have defined functions of the key E6 and E7 oncoproteins in epithelial cell immortalization. The roles of these oncogenes in the progression of immortalized epithelial cells to invasive tumors are still poorly understood. Here, we establish a novel link between the E6 oncoprotein and activation of mitogen-activated protein kinase (MAPK) signaling and show that this signaling involves Rap1. We find that activated MAPK signaling cooperates with deregulated Notch1 signaling to recreate features of HPV-driven invasive cervical carcinomas. We extend our analysis to evaluate an E6 (amino acid [aa] 83) variant that has been linked to invasive tumors. The variant enhances MAPK signaling and cooperative transformation with deregulated Notch1 signaling. Unlike E6, this variant surprisingly inhibits oncogenic Ras-mediated transformation. Our data reveal that the quantitative differences in activation of MAPK signaling by E6 and its variant correlate with differences in cooperative transformation with other signaling pathways, thus suggesting that thresholds of MAPK activation may define permissive conditions for other signaling pathways in tumorigenesis. Epidemiological studies have suggested the importance of E6 aa 83 variants in invasive carcinomas; our data support a key deterministic role for this variant in human cervical tumorigenesis. These observations, along with our recent data showing that deregulated Notch signaling activates phosphatidylinositol 3-kinase signaling, strengthen the possibility of the existence of Ras-independent mechanisms to recreate signaling through classical Ras effector pathways.
authors.affiliation: National Centre for Biological Sciences, TIFR, UAS-GKVK Campus, Bangalore 560065, India. oishee@ncbs.res.in
authors.forename: Oishee
authors.initials: O
authors.lastname: Chakrabarti
authors.forename: Karthikeyan
authors.initials: K
authors.lastname: Veeraraghavalu
authors.forename: Vinay
authors.initials: V
authors.lastname: Tergaonkar
authors.forename: Yun
authors.initials: Y
authors.lastname: Liu
authors.forename: Elliot J
authors.initials: EJ
authors.lastname: Androphy
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Stanley
authors.forename: Sudhir
authors.initials: S
authors.lastname: Krishna
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D005260:Female; D011905:Genes, ras / Q000502:physiology*; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009856:Oncogene Proteins, Viral / Q000737:chemistry* / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface / Q000502:physiology*; D012097:Repressor Proteins; D013329:Structure-Activity Relationship; D014157:Transcription Factors; D014412:Tumor Virus Infections / Q000209:etiology*; D002583:Uterine Cervical Neoplasms / Q000209:etiology*
chemical_list: C068651:E6 protein, Human papillomavirus type 16; C497761:NOTCH1 protein, human; C497762:Notch1 protein, mouse; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface; D012097:Repressor Proteins; D014157:Transcription Factors; C059731:oncogene protein E7, Human papillomavirus type 16