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Abstract

Background & Aims: Hepatocellular carcinoma (HCC) is the most frequently diagnosed liver cancer and a leading cause of cancer-related death. Paired related homeobox 1 (PRRX1) is a transcriptional co-activator, which regulates cell growth, differentiation and, as I could recently show, is also linked to epithelial to mesenchymal transition (EMT). EMT is a hallmark of cancer progression, paving the way to tumor cell spreading into surrounding tissue, vessels and other organs. The transforming growth factor-β (TGF-β) is a known EMT inducer that also plays important roles in HCC. Whether PRRX1 has a functional relevance in HCC is still unknown. Thus, the aim of my work was to perform an in-depth analysis of PRRX1 expression and its co-expressed genes in HCC samples, as well as to clarify its function in liver carcinogenesis.

Methods: The expression of PRRX1 in human HCC was assessed in online databases, including Oncomine, cBioPortal, and in microarray datasets encompassing > 1,400 liver tumor profiles. Bioinformatics analyses were performed for functional annotation of genes correlated with PRRX1 in HCC, and followed by Kaplan-Meier overall survival analyses. In vitro, PRRX1 expression was analyzed in HCC cell lines, treated or not with TGF-β, its receptor inhibitor Galunisertib. Further, PRRX1 expression was inhibited with small interfering RNA and the functional impact on cell migration, proliferation, clonogenicity, apoptosis and metabolism were measured.

Result: PRRX1 is frequently upregulated in human HCC. Patients with high PRRX1 show elevated expression of TGFBR1. The genes positively correlated with PRRX1 display enrichment in crucial features of cancer, including stroma remodeling, signal transduction, downregulated metabolic pathways, focal adhesion and EMT. I could identify two EMT-related transcription factors, ZEB1 and ZEB2, as novel PRRX1-related genes in HCC. PRRX1 in combination with ZEBs significantly predicted survival outcome in HCC patient cohorts investigated. In HCC cell lines, TGF-β1 treatment increases expression of PRRX1. PRRX1 influences cell migration and modulates expression of EMT markers in a cell type dependent-manner. PRRX1 knockdown increases cell proliferation and clonogenicity. Further, knock down of PRRX1 promotes glucose consumption (Warburg effect), regulates core metabolic genes and levels of TCA cycle metabolites and amino acids. Moreover, depleting PRRX1 causes upregulation of genes regulating fatty acid biosynthesis and oxidation with influence on fatty acid levels.

Conclusion: The findings of my study provide evidence for a functional role of PRRX1 in HCC, including a master control on pathways that facilitate tumor progression, including modulation of cell metabolism. The new findings on PRRX1 functions suggest further in-depth mechanistic studies on the relevance of PRRX1 in human liver cancer.