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Abstract

Primary liver cancer (PLC) is a major health concern, being the fifth most occurring cancer and the second most lethal worldwide. However, due to the lack of targetable mutations in patient tumors, treatment options are still limited. Therefore, identifying and characterizing new targetable mutations in PLC is of the utmost importance. In the present study, I interrogated publicly available human PLC sequencing data to detect and functionally characterize recurring genetic alterations, with the overall aim of identifying potential biomarkers exploitable by precision medicine. PBRM1 is a component of the SWI/SNF epigenetic remodeling complexes and was found to be preferentially mutated in intrahepatic cholangiocarcinoma (iCCA) rather than hepatocellular carcinoma (HCC), thus suggesting a role as tumor initiator and/or cancer identity determinator. To gain further insight, I employed mouse models with liver-specific deletion or reversible downregulation of PBRM1 by CRISPR/Cas9 or RNA interference, respectively. In parallel, loss of PBRM1 was further investigated in these mouse models with NASH-inducing dietary models of HCC. Disrupting PBRM1 expression in vivo and in vitro showed no connection between PBRM1 expression status and its involvement in liver cancer initiation or liver cancer plasticity. RPS6KA3 is a kinase protein that acts as an effector and negative feedback regulator of RAS/MAPK pathway. The results from this dissertation demonstrated that RPS6KA3 loss contributes to tumorigenicity in vivo and that the loss of RPS6KA3 leads to an upregulation of the MAPK pathway both in vivo and in vitro with murine and human HCC cell lines. Moreover, RPS6KA3-depleted murine xenograft tumors and orthotopically transplanted human HCC cells lines with low RPS6KA3 levels responded remarkably to trametinib, a FDA-approved MEK inhibitor. Thus, the results not only reveal RPS6KA3 as an important tumor suppressor in HCC but also implicate RPS6KA3 as a novel biomarker for MAPK pathway inhibitors in HCC patients.