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Abstract

In an effort to identify novel targets during HCC, previous work from the lab has shown that TRIP13, a member of the AAA+-ATPase family was significantly upregulated in DEN-induced HCC in mice and in human HCC. TRIP13 has been described to be an important regulator of chromosomal events during meiosis and mitosis. An induced expression of TRIP13 has been reported in several cancer entities however its cancer-related role remains marginally understood. Interestingly, TRIP13 forms part of the chromosomal instability (CIN) gene signature that is commonly seen in tumour cells and has DNA-damage repair functions in head and neck carcinoma cells (SSCHN). Unpublished data from the lab was the first to have confirmed the growth-promoting role of TRIP13 in liver, which was unveiled during hepatocyte regeneration and tumourigenesis using various mouse models of HCC. Here, we aim to dissect the mechanism through which TRIP13 exerts its pro-proliferative effects in HCC and to identify novel signalling pathways through which TRIP13 could exert its function. In this study, we showed that TRIP13 is essential during cell growth and proliferation, proliferation was severely impaired by Trip13 knockdown in all mouse and human HCC cells lines under investigation. Conversely, the overexpression of Trip13 in non-tumourigenic AML12 liver cells stimulated cell proliferation significantly, with upregulated expression of oncogenic factors like c-MYC, EGFR and cyclin D1. We identified an unexpected functional relevance of the interaction between TRIP13 and SIN3A, which was enriched during a MS screen for Trip13 interaction partners previously performed in the lab. SIN3A has been commonly described as a transcriptional repressor due to its HDAC-related roles. Strikingly, a concomitant depletion of SIN3A reverses the growth defect of TRIP13-depleted HCC cells, despite accumulated DNA damages (from TRIP13 depletion) still apparent in these growth-rescued cells. This growth rescue was paralleled by a partial restoration of c-MYC expression levels, which were significantly depleted during TRIP13-KD alone. We further demonstrated that the overexpression of c-MYC was able to rescue the growth defect seen in TRIP13-depleted cells. Taken together, this study is the first to report on an oncogenic, pro-proliferative role of TRIP13 in liver cancer using both human HCC cells and mice HCC models. An inhibition of c-MYC and its downstream targets might account for the growth arrest and apoptotic cell death during TRIP13-depletion. Along with the reported roles of SIN3A as a c-MYC antagonist, further work is required to decipher a possible cross talk between TRIP13, SIN3A and c-MYC and its functional relevance during hepatocarcinogenesis.