University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
Cancer Testis Antigens (CTAs) are a group of genes defined by their unique expression pattern, normally expressed nearly exclusively in gametogenic tissues they are also found aberrantly expressed in malignant tissues throughout the body. As a result of the immune-privileged nature of their normal site of expression in the testis, CTAs are capable of eliciting an immune response when expressed within tumors. As a result of their antigenicity, CTAs have been the intense studied as potential immunotherapy targets since their discovery in the early 1990s; however, in this time their possible functional contributions to tumorigenesis have been woefully under investigated. Here, we undertook the first comprehensive approach to define the functional contribution of CTAs to tumorigenesis. This screen identified numerous CTAs that support aspects of tumorigenesis. Further studies demonstrated that the uncharacterized CTA Fetal and Adult Testis-Expressed 1 (FATE1) is a major contributor to tumor cell fitness across multiple cancer lineages. We found that FATE1 is a mitochondrial protein that interacts with Mitochondrial Fission Factor (MFF) a mediator of mitochondrial fission and that expression of FATE1 is capable of altering mitochondrial morphology. Within the transformed cellular background, we find that FATE1 regulates protein levels of the tumor suppressor, Bcl-2 Interacting Killer (BIK), a pro-apoptotic member of the Bcl-2 protein family. We also found that BIK protein is degraded by the FATE1-interactor RNF183 a previously uncharacterized E3- ligase. We found further in vitro and clinical data that supports the hypothesis that FATE1 and RNF183 form a functionally relevant complex within tumors. Like their functional roles, the mechanisms by which CTAs are activated within tumors is currently unclear. Although demethylation plays a large role, epigenetic alterations alone are not sufficient to drive expression of all CTAs indicating that trans-acting factors are required. Here we find that FATE1 is a direct target of chimeric transcription factor EWS-FLI1, the oncogene responsible for the pediatric bone and soft tissue tumor Ewing sarcoma. FATE1 expression is required for short and long term viability of Ewing sarcoma derived cell lines. By leveraging a previously published EWS-FLI1 ChIP-seq dataset we nominate three additional CTAs (BORIS, MAGE-A4, and SPATA19) as EWS-FLI1 targets, two of which, MAGE-A4 and SPATA19 are required to maintain Ewing sarcoma cell viability. The results of these studies argue that not only do CTAs function to support tumor cell fitness but as targets of oncogenes they may potentially be key functional drivers in the early stages of tumorigenesis.Doctor of Philosoph
