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.

The lysine acetyltransferase GCN5 contributes to human papillomavirus oncoprotein E7‐induced cell proliferation via up‐regulating E2F1

“…However, another study found that c‐Myc overacetylation at K323 may reduce its stability . c‐Myc plays a critical role for transformation of human cells by HPV E6 and E7 . c‐Myc interacts with and forms a specific complex with high‐risk type HPV E7 that augmented c‐Myc transactivation activity .…”

“…53 c-Myc plays a critical role for transformation of human cells by HPV E6 and E7. 72,73 c-Myc interacts with and forms a specific complex with high-risk type HPV E7 that augmented c-Myc transactivation activity. 74 The expression of c-Myc correlated to HR-HPV (including HPV-16 and HPV-18)-infected epithelium compared with HR-HPVnegative epithelium.…”

Signaling pathways in HPV‐associated cancers and therapeutic implications

“…However, E6 and E7 together are not sufficient, requiring introduction of another cancer risk factor for tumor formation. For example, oncogene Ras has been shown to cause cancer together with E6 and E7 . Deletion of tumor suppressor gene RXRα and expression of E6 and E7 together have also been shown to cause malignant lesions of cervical tissue .…”

Roles of the PDZ‐binding motif of HPV 16 E6 protein in oncogenic transformation of human cervical keratinocytes

“…We previously demonstrated that transduction of oncogenic HRAS (HRAS G12V ) and MYC together with HPV16 E6E7 is sufficient for highly tumorigenic transformation of primary human cervical keratinocytes (HCKs) . More recently, we found HRAS G12V and HPV16 E6E7 is sufficient for tumorigenic transformation of HCKs . Having taken advantage of this system, we found the PDZ domain‐binding motif plays an important role in tumorigenic transformation of primary HCKs, and further investigated which PDZ domain‐containing target(s) are critical for HPV‐induced cervical carcinogenesis.…”