Small tRNA-derived RNAs are increased and more abundant than microRNAs in chronic hepatitis B and C. Homo sapiens

Small, non-coding RNAs control gene expression post-transcriptionally and play important roles in virus-host interactions. Within the liver, the microRNA (miRNA) miR-122 is essential for replication of hepatitis C virus (HCV), while repression of miR-148a by hepatitis B virus (HBV) may enhance tumorigenesis. Despite their importance to the outcome of these infections, few previous studies have described unbiased profiling of small RNAs in the liver during chronic viral hepatitis. Here, we sequenced small (14-40 nts) RNAs in liver from subjects with chronic hepatitis B and C. We found that small RNAs derived from tRNAs, specifically 5’ tRNA-halves (“5’ tRHs”, ~31-34 nts), are abundant in liver and significantly increased during chronic viral infection in humans and also chimpanzees. In most infected livers, 5’ tRH abundance exceeded that of miRNAs. In contrast, in hepatocellular carcinoma (HCC) tissue from these subjects, tRH abundance was reduced concomitant with decreased expression of the tRNA-cleaving ribonuclease, angiogenin. Although tRHs have been identified in mice, our results show they are abundantly expressed in human tissue, increased in chronic viral infection, and decreased in liver cancer. Our findings highlight the potential biological and clinical relevance of these small non-coding RNAs. Overall design: Small RNA-seq of liver samples from control subjects (n=4), subjects with chronic hepatitis B (n=4) and hepatitis B associated hepatocellular carcinoma (n=4, 3 out of 4 matched with non-tumor tissue) and subjects with chronic hepatitis C (n=4) and tissue from hepatocellular carcinoma of the same patients. Also, small RNA-seq of AGO2 and IgG pulldown in FT3-7 cells. Sequenced AGO2 pulldown (n=3), IgG pulldown (n=2) and total small RNA from FT3-7 cells (n=3).