Endocrine Abstracts

Obesity is emerging as a prevalent cause of chronic liver damage, which can lead to the development of metabolic-associated fatty liver disease (MAFLD), nonalcoholic steatohepatitis (NASH), or even hepatocellular carcinoma (HCC). Increasing evidence suggests a profound dysregulation of the splicing machinery (spliceosome and splicing factors) in these pathologies; however, the role of PRPF8, a pivotal spliceosome element, has not been described in chronic liver pathologies. Thus, we aimed to analyze the expression of PRPF8 in different liver cancer cohorts, and to characterize its putative role in tumor development/progression. PRPF8 expression (mRNA and protein) was analyzed in a retrospective cohort (n = 172 samples) and validated in two in silico cohorts (TCGA and CPTAC) of HCC samples with different aetiologies and their adjacent non-tumor control samples. Functional and molecular consequences of PRPF8 silencing (using specific siRNAs) were evaluated in liver-derived cell lines (HepG2, Hep3B and SNU-387) and in Hep3b-induced xenograft tumors. Moreover, RNAseq and eCLIP data generated in HepG2 cells were analyzed. This study shows that PRPF8 expression is elevated (at the mRNA/protein levels) in HCC samples from different aetiologies in all the cohorts analysed. PRPF8 levels were associated with: i) increased tumor aggressiveness (tumor size, patient survival, etc.), ii) the expression of HCC-related splicing variants and, iii) the alteration of critical genes related to cancer-associated pathways. PRPF8 silencing reduced in vitro aggressiveness of liver cancer cell lines (reducing proliferation, migration, tumorospheres-/colonies-formation, while increasing apoptosis), and decreased xenograft tumour growth in vivo. CLIPseq data in HepG2 demonstrated that PRPF8 binds preferentially to exons of protein-coding genes, and RNAseq analysis showed that PRPF8-silencing altered numerous splicing events, mainly exon skipping, of multiple genes. Integrated analysis of CLIPseq and RNAseq and in vitro experiments revealed that PRPF8-silencing modulates fibronectin (FN1) splicing, promoting the exclusion of exon 40.2, which is paramount for binding to integrins. Consistently, PRPF8 silencing reduced FAK/AKT phosphorylation and blunted stress-fibres formation. Finally, HepG2 cells exhibited lower invasive capacity in membranes treated with media from PRPF8-silenced cells compared to that observed with media from scramble-treated cells. Altogether, our data demonstrate that PRPF8 is overexpressed and associated with aggressiveness in alcoholic, viral and metabolic-associated HCC. Indeed, PRPF8 seems to play key roles in chronic liver disease progression and hepatocarcinogenesis by modulating FN1 splicing, which leads to FAK/AKT activation and stress-fibers formation.

Fundings

ISCIII (ERDF/ESF, ’Investing in your future’) (PI20/01301), JdA (BIO-0139) and CIBERobn.