Role of IQGAP1 in Papillomavirus-Associated Head and Neck Tumorigenesis

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.

Role of IQGAP1 in Carcinogenesis

“…MmuPV1 can infect the mouse epithelium and cause cancers to arise in different anatomical sites in mice, including the head and neck region [104][105][106][107], which provides opportunities to study the pathogenesis of papillomavirus (PV) in a genetically manipulatable and trackable model organism. MmuPV1 infection upregulates PI3K signaling in keratinocytes [103], which is in line with a previous report showing that HPV16 pseudovirus infection upregulates PI3K signaling in vitro [108]. We also showed that this MmuPV1-induced PI3K signaling was greatly diminished in keratinocytes knocked out for IQGAP1 [103].…”

“…Given the importance of PI3K signaling in HPV-positive HNSCC and the role of IQGAP1 in scaffolding PI3K signaling [48], we hypothesized that IQGAP1 also plays a role in HPV-positive HNSCC. We found that HPV16 E6 upregulated PI3K signaling in normal oral keratinocytes, while E7 only mildly impacted its signaling [103]. Loss of IQGAP1 significantly reduced the PI3K signaling levels in both E6-and E7-expressing keratinocytes [103], indicating HPV16 oncoproteins regulate PI3K signaling in an IQGAP1dependent manner.…”

“…We found that HPV16 E6 upregulated PI3K signaling in normal oral keratinocytes, while E7 only mildly impacted its signaling [103]. Loss of IQGAP1 significantly reduced the PI3K signaling levels in both E6-and E7-expressing keratinocytes [103], indicating HPV16 oncoproteins regulate PI3K signaling in an IQGAP1dependent manner.…”

“…MmuPV1 infection upregulates PI3K signaling in keratinocytes [103], which is in line with a previous report showing that HPV16 pseudovirus infection upregulates PI3K signaling in vitro [108]. We also showed that this MmuPV1-induced PI3K signaling was greatly diminished in keratinocytes knocked out for IQGAP1 [103]. Utilizing the MmuPV1 infection-based HNSCC model, we infected the tongues of Iqgap1 +/+ (wild-type FVB strain) and Iqgap1 −/− mice with MmuPV1 (or PBS, mock infection), treated the mice with UVB, which induces systemic immunosuppression that facilitates persistence of infections, and the 4NQO carcinogen to induce HNSCC, and monitored the experimental mice for 6 months.…”

“…Utilizing the MmuPV1 infection-based HNSCC model, we infected the tongues of Iqgap1 +/+ (wild-type FVB strain) and Iqgap1 −/− mice with MmuPV1 (or PBS, mock infection), treated the mice with UVB, which induces systemic immunosuppression that facilitates persistence of infections, and the 4NQO carcinogen to induce HNSCC, and monitored the experimental mice for 6 months. Quantitative PCR (qPCR) analysis of DNA extracted from oral swabs collected at 3 weeks post-infection showed that both MmuPV1-infected Iqgap1 +/+ and Iqgap1 −/− mice carried similar copy numbers of the virus, indicating that IQGAP1 had no measurable effect on incidence of MmuPV1 infection in mice [103]. At 6 months post-infection, MmuPV1-infected Iqgap1 +/+ mice developed more severe tumor phenotypes, including tumor incidence, tumor multiplicity and disease severity, that were significantly higher than in MmuPV1-infected Iqgap1 −/− mice, which had tumor phenotypes very similar to those of mock-infected mice [103].…”