Journal Article

A critical role of MYC for transformation of human cells by HPV16 E6E7 and oncogenic HRAS

Mako Narisawa-Saito, Yuki Inagawa, Yuki Yoshimatsu, Kei Haga, Katsuyuki Tanaka, Nagayasu Egawa, Shin-ichi Ohno, Hitoshi Ichikawa, Takashi Yugawa, Masatoshi Fujita and Tohru Kiyono

in Carcinogenesis

Volume 33, issue 4, pages 910-917
Published in print April 2012 | ISSN: 0143-3334
Published online February 2012 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/bgs104
A critical role of MYC for transformation of human cells by HPV16 E6E7 and oncogenic HRAS

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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 (HRASG12V) and MYC together with HPV16 E6E7 is sufficient for tumorigenic transformation of normal human cervical keratinocytes (HCKs). Here, we show that transduction of HRASG12V 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 HRASG12V 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 HRASG12V. 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.

Journal Article.  5285 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

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