Fusion transcripts landscape in hepatocellular carcinoma and potential impact on the expression of fusion partners

Fusion transcripts (FTs) are RNA molecules, also known as chimeric transcripts, formed through chromosomal rearrangements or transcriptional processes, contributing to tumorigenesis. This study systematically examined tumour-specific FTs in hepatocellular carcinoma (HCC) using high-throughput RNA sequencing data from independent datasets and The Cancer Genome Atlas (TCGA). Our meta cohort analysis included 328 HCC samples. Using STAR-Fusion, we identified 15 novel tumour-specific FTs, with SERPINA1-H19 as the most recurrent fusion event. Comparative expression analysis of fusion partner genes revealed significant downregulation in HCC tumours relative to normal adjacent liver tissues (NAT). We validated the expression levels of the key partner genes with 436 TCGA samples serving as an in silico validation cohort and in wet lab validation cohorts with 42 samples. ALB, APOA2, IGF2, MT2A, SERPINA1, and H19, which are key liver-associated genes, were frequently involved in tumour-specific fusion events suggesting either a loss of tumour suppressor property or gaining a novel function playing a role in hepatocarcinogenesis. Detailed characterization of SERPINA1-H19 identified 16 transcript variants with distinct structural modifications that may impact its functional output. Furthermore, low expression of SERPINA1 and H19 was associated with more aggressive HCC phenotypes. Overall, this study established a comprehensive repository of FTs for the first time, offering valuable insights into their role in HCC and their potential to serve as diagnostic and prognostic biomarkers for HCC.