Role of Autophagy in Bortezomib-induced HNSCC Apoptosis

University Of California Los Angeles, Los Angeles CA

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Abstract

? DESCRIPTION (provided by applicant): Head and Neck Squamous Cell Carcinoma (HNSCC) comprise 90% of head and neck cancer and typically presents poor prognosis and resistant to chemotherapy. Hence, the development of more effective therapeutic strategy is critical. Previously, Bortezomib has been proposed as an alternate chemotherapeutic agent to conventional chemotherapy in HNSCC, but infers chemoresistance through a largely unknown pathway. The main objectives of this application are to investigate the potential utilization of Trichostatin A (TSA) and Bortezomib (aka PS-341) combinatory regimen to treat HNSCC and to understand the molecular mechanisms by which TSA enhances Bortezomib-induced apoptosis to effectively overcome chemoresistance. Our preliminary studies suggest that histone deacetylase 6 (HDAC6) promotes autophagy to reduce the Bortezomib cytotoxicity. When we abolished expression of HDAC6 in HNSCC cells, autophagy induction was inhibited and the Bortezomib cytotoxicity was significantly enhanced. Based on these novel findings, we hypothesize that TSA may enhance antitumor effects of Bortezomib through inhibition of HDAC6 activity, which may serve as a critical causal link between autophagy, apoptosis, and cellular survival response in HNSCC. Our hypotheses will be addressed in the following specific aims: (1) Determine if TSA enhances Bortezomib- induced apoptosis while inhibiting HDAC6-mediated autophagy; and (2) Investigate the molecular mechanisms by which HDAC6 initiates autophagy induced by Bortezomib in HNSCC. This plan will utilize several features from both basic science and translational medicine aspects: Green fluorescent protein (GFP) - LC3 puncta formation assay, flow cytometry, western blotting, real-time qRT-PCR, chromatin immunoprecipitation, and immunofluorescence staining will be used to examine changes in expression of molecules associated with HDAC6-induced autophagy and accumulation of cytotoxic protein aggregates. Further, we plan to utilize xenotransplantation of HDAC6-depleted human HNSCC cells in nude mice to investigate molecular and cellular changes associated with autophagy, endoplasmic reticulum stress, and apoptosis. This research strategy is an integral component of a research training plan designed to develop the trainee's expertise in molecular/cellular biology and genetics of head and neck carcinogenesis, chemoresistance, and apoptosis and will prepare the trainee for an academic career as an independent researcher.