Abstract PO019: Gas6/Axl signaling induces PRAME expression in hepatocellular carcinoma

Abstract The receptor tyrosine kinase Axl, binding to its ligand Gas6, fosters oncogenic effects during the progression of hepatocellular carcinoma (HCC) which is accompanied by increased mortality of patients. The specific role of Gas6/Axl signaling in neoplastic hepatocytes and its pathophysiological consequences are poorly understood at the current stage of research. We aimed at identifying and functionally analyzing targets of Gas6/Axl signaling in HCC by exploiting well-characterized human HCC tumor models. HCC cells transformed by epithelial to mesenchymal transition (EMT) and expressing high levels of Axl or harboring CRISPR/Cas9-mediated Axl deficiency, the latter in absence or presence of Axl reconstitution, were subjected to Gas6 stimulation and subsequent RNA-seq analysis. Bioinformatics and VENN relations were applied to identify novel targets of the Gas6/Axl axis. Expression of Gas6/Axl targets was assessed in publicly available HCC patient datasets and in HCC tissue microarrays. In vitro analysis was performed including gain and loss of functions studies to unravel target genes contribution to EMT and HCC progression. RNA-seq analyses revealed PRAME (preferentially expressed antigen in melanoma) and C15orf48 among others as novel targets of Gas6/Axl. Notably, these target genes showed elevated expression levels in Axl-stratified HCC patients and significant impact on patient survival. Pharmacological or genetic interference with Axl signaling resulted in strongly reduced expression of PRAME and C15orf48, suggesting bona fide targets of Gas6/Axl signaling. PRAME expression positively regulated 2D cell migration and invasion of 3D hepatospheres while proliferation and survival of HCC cells remained unaffected by altered PRAME levels. In accordance, PRAME expression strongly associated with a mesenchymal-like phenotype in human HCC. Intriguingly, HCC patients expressing PRAME correlated with Axl expression and vascular invasion in a large proportion of HCC patients. Our study demonstrates that PRAME is a novel target of Gas6/Axl signaling in HCC linked to EMT. Translation of in vitro findings into the HCC patient situation provides first insights that PRAME plays a crucial role in HCC progression. Citation Format: Viola Hedrich, Doris Chen, Heidemarie Huber, Wolfgang Mikulits. Gas6/Axl signaling induces PRAME expression in hepatocellular carcinoma [abstract]. In: Proceedings of the AACR Special Conference: Advances in the Pathogenesis and Molecular Therapies of Liver Cancer; 2022 May 5-8; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(17_Suppl):Abstract nr PO019.