Role of IQGAP1 in Papillomavirus-Associated Head and Neck Tumorigenesis

SIMPLE SUMMARY: Human papillomaviruses (HPVs) are the most common sexually transmitted pathogens in the United States and are associated with 25% of head and neck cancers (HNCs). To study the genesis of papillomavirus-associated HNC in a physiologically relevant pre-clinical model, we recently developed an infection-based murine model that uses the recently discovered mouse papillomavirus, MmuPV1. In this MmuPV1 HNC model, as in HPV-associated HNCs, the PI3K/AKT/mTOR signaling pathway is upregulated. Components of this pathway are known to be assembled by the scaffolding protein IQGAP1. Utilizing our MmuPV1 HNC model, we tested and demonstrated the importance of IQGAP1 in papillomavirus-induced HNC, in which IQGAP1 is required for optimal induction of the PI3K/AKT/mTOR pathway by MmuPV1 and contributes quantitatively to MmuPV1-induced HNC. Further investigation into how IQGAP1 promotes disease progression may shed additional insights into papillomavirus-induced carcinogenesis and provide new drug targets for treating HPV-associated neoplastic disease. ABSTRACT: Approximately 25% of head and neck squamous cell carcinomas (HNSCC) are associated with human papillomavirus (HPV) infection. In these cancers as well as in HPV-associated anogenital cancers, PI3K signaling is highly activated. We previously showed that IQ motif-containing GTPase activating protein 1 (IQGAP1), a PI3K pathway scaffolding protein, is overexpressed in and contributes to HNSCC and that blocking IQGAP1-mediated PI3K signaling reduces HPV-positive HNSCC cell survival and migration. In this study, we tested whether IQGAP1 promotes papillomavirus (PV)-associated HNSCCs. IQGAP1 was necessary for optimal PI3K signaling induced by HPV16 oncoproteins in transgenic mice and MmuPV1 infection, a mouse papillomavirus that causes HNSCC in mice. Furthermore, we found that, at 6 months post-infection, MmuPV1-infected Iqgap1(−/−) mice developed significantly less severe tumor phenotypes than MmuPV1-infected Iqgap1(+/+) mice, indicating a role of IQGAP1 in MmuPV1-associated HNSCC. The tumors resulting from MmuPV1 infection showed features consistent with HPV infection and HPV-associated cancer. However, such IQGAP1-dependent effects on disease severity were not observed in an HPV16 transgenic mouse model for HNC. This may reflect that IQGAP1 plays a role in earlier stages of viral pathogenesis, or other activities of HPV16 oncogenes are more dominant in driving carcinogenesis than their influence on PI3K signaling.