title: A critical role of MYC for transformation of human cells by HPV16 E6E7 and oncogenic HRAS.
abstract: Human papillomaviruses (HPVs) are the primary causal agents for development of cervical cancer, and deregulated expression of two viral oncogenes E6 and E7 is considered to contribute to disease initiation. Recently, we have demonstrated that transduction of oncogenic HRAS (HRAS(G12V)) and MYC together with HPV16 E6E7 is sufficient for tumorigenic transformation of normal human cervical keratinocytes (HCKs). Here, we show that transduction of HRAS(G12V) on the background of E6E7 expression causes accumulation of MYC protein and tumorigenic transformation of not only normal HCKs but also other normal primary human cells, including tongue keratinocytes and bronchial epithelial cells as well as hTERT-immortalized foreskin fibroblasts. Subcutaneous transplantation of as few as 200 HCKs expressing E6E7 and HRAS(G12V) resulted in tumor formation within 2 months. Dissecting RAS signaling pathways, constitutively active forms of AKT1 or MEK1 did not result in tumor formation with E6E7, but tumorigenic transformation was induced with addition of MYC. Increased MYC expression endowed resistance to calcium- and serum-induced terminal differentiation and activated the mammalian target of rapamycin (mTOR) pathway. An mTOR inhibitor (Rapamycin) and MYC inhibition a level not affecting proliferation in culture both markedly suppressed tumor formation by HCKs expressing E6E7 and HRAS(G12V). These results suggest that a single mutation of HRAS could be oncogenic in the background of deregulated expression of E6E7 and MYC plays a critical role in cooperation with the RAS signaling pathways in tumorigenesis. Thus inhibition of MYC and/or the downstream mTOR pathway could be a therapeutic strategy not only for the MYC-altered but also RAS-activated cancers.
authors.affiliation: Division of Virology, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
authors.forename: Mako
authors.initials: M
authors.lastname: Narisawa-Saito
authors.forename: Yuki
authors.initials: Y
authors.lastname: Inagawa
authors.forename: Yuki
authors.initials: Y
authors.lastname: Yoshimatsu
authors.forename: Kei
authors.initials: K
authors.lastname: Haga
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Tanaka
authors.forename: Nagayasu
authors.initials: N
authors.lastname: Egawa
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Ohno
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Ichikawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Yugawa
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Fujita
authors.forename: Tohru
authors.initials: T
authors.lastname: Kiyono
mesh_terms: D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D052162:Human papillomavirus 16 / Q000502:physiology*; D006801:Humans; D050725:Papillomavirus E7 Proteins / Q000502:physiology*; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*
chemical_list: D050725:Papillomavirus E7 Proteins; D016271:Proto-Oncogene Proteins c-myc; D016283:Proto-Oncogene Proteins p21(ras)