Although major improvements have been made in chemotherapeutic, radiotherapeutic and surgical management of head and neck squamous cell carcinoma, morbidity and mortality from these lesions remain unacceptable. Moreover, in spite of major advances in therapy of other cancers, many head and neck cancers remain refractory to treatment with standard agents. The likelihood that subpopulations of cancer cells with self- renewal properties ("cancer stem cells" or cancer-initiating cells [CICs]) are responsible for resistance to therapy is becoming increasingly recognized, although little is known about the molecular pathways that determine the CIC phenotype. Our previous work identified EPS8, a mediator of growth factor receptor signaling, as being central to oral cancer cell growth and motility. We also found that EPS8 stimulates the expression of pluripotency-related transcription factors, and that binding sites for these exist within the EPS8 promoter. Moreover, we found that p63, a reported marker of keratinocyte stem cells, acts as a repressor of EPS8 expression, and that RNAi-mediated knockdown of p63 results in elevated levels of EPS8, promoting cell growth. This has led us to propose the hypothesis that elevated expression of EPS8 through relief of p63-mediated repression activates pathways promoting self-renewal and enhanced tumorigenic capacity. The proposed study has three objectives: first, to determine the mechanism through which p63 regulates EPS8;second, to define the role of EPS8 as a driver of the malignant phenotype of oral CICs;and, third, to understand how EPS8 expression and activity in oral CICs modulates their response to the microenvironment. Achieving these objectives will allow us to identify pathways responsible for the malignant properties of CICs that are likely to underpin tumor recurrence. Ultimately, this will uncover rational therapeutic targets to improve the quality of life of those affected by head and neck squamous cell carcinoma.
Our recent work has identified EPS8 as a novel oncogene that contributes to oral carcinogenesis, and which promotes expression of regulators of pluripotency and stem cell-like properties. The goals of the proposed study are to understand how EPS8 is regulated in cancer initiating cells, how it drives malignancy, and how it participates in the response of cancer initiating cells to microenvironmental conditions. At the study's conclusion, we will have identified rational targets for therapy directed at eradicating orl cancer-initiating cells.