Oncogenic Ras and?Np63a cooperate to recruit immunosuppressive polymorphonuclear myeloid-derived suppressor cells in a mouse model of squamous cancer pathogenesis

Introduction Amplification of human chromosome 3q26-29, which encodes oncoprotein ?Np63 among other isoforms of the p63 family, is a feature common to squamous cell carcinomas (SCCs) of multiple tissue origins. Along with overexpression of ?Np63, activation of the protooncogene, RAS, whether by overexpression or oncogenic mutation, is frequently observed in many cancers. In this study, analysis of transcriptome data from The Cancer Genome Atlas (TCGA) demonstrated that expression of TP63 mRNA, particularly ?Np63 isoforms, and HRAS are significantly elevated in advanced squamous cell carcinomas of the head and neck (HNSCCs), suggesting pathological significance. However, how co-overexpressed ?Np63 and HRAS affect the immunosuppressive tumor microenvironment (TME) is incompletely understood.Methods Here, we established and characterized an immune competent mouse model using primary keratinocytes with retroviral-mediated overexpression of?Np63a and constitutively activated HRAS (v-ras(Ha) G12R) to evaluate the role of these oncogenes in the immune TME.Results In this model, orthotopic grafting of wildtype syngeneic keratinocytes expressing both v-ras(Ha) and elevated levels of ?Np63a consistently yield carcinomas in syngeneic hosts, while cells expressing v-ras(Ha) alone yield predominantly papillomas. We found that polymorphonuclear (PMN) myeloid cells, experimentally validated to be immunosuppressive and thus representing myeloid-derived suppressor cells (PMN-MDSCs), were significantly recruited into the TME of carcinomas arising early following orthotopic grafting of ?Np63a/v-ras(Ha)-expressing keratinocytes. ?Np63a/v-ras(Ha)-driven carcinomas expressed higher levels of chemokines implicated in recruitment of MDSCs compared to v-ras(Ha)-initiated tumors, providing a heretofore undescribed link between ?Np63a/HRAS-driven carcinomas and the development of an immunosuppressive TME.Conclusion These results support the utilization of a genetic carcinogenesis model harboring specific genomic drivers of malignancy to study mechanisms underlying the development of local immunosuppression.

Automated summary

This study established an immune competent mouse model to evaluate the immune suppressive role of ?Np63a and HRAS in the tumor microenvironment. Orthotopic grafting of keratinocytes overexpressing ?Np63a and HRAS resulted in the recruitment of immunosuppressive PMN-MDSCs cells and the development of an immunosuppressive tumor microenvironment.