hnRNP Q/SYNCRIP interacts with LIN28B and modulates the LIN28B/let-7 axis in human hepatoma cells.

The RNA-binding protein LIN28B represses the biogenesis of the tumor suppressor let-7. The LIN28B/let-7 axis regulates cell differentiation and is associated with various cancers. The RNA-binding protein Q (hnRNP Q) or SYNCRIP (Synaptotagmin Binding Cytoplasmic RNA Interacting Protein) has been implicated in mRNA splicing, mRNA transport, translation, and miRNAs biogenesis as well as metabolism in cancer. To determine whether hnRNP Q plays a role in the LIN28B/let-7 axis, we tested for interactions between hnRNP Q and LIN28B. We demonstrated that hnRNP Q interacts with LIN28B in an RNA-dependent manner. Knockdown of hnRNP Q caused reduced expression of a well-known let-7 target TRIM71, an E3 ubiquitin ligase that belongs to the RBCC/TRIM family, and also LIN28B, whose mRNA itself is down-regulated by let-7. In addition, hnRNP Q knockdown increased let-7 family miRNA levels and reduced the activity of luciferase reporters fused with the TRIM71 3'UTR or a synthetic 3'UTR carrying 8X let-7 complementary sites. Finally, depletion of hnRNP Q inhibited the proliferation of a hepatocellular carcinoma cell line, Huh7. This observation is consistent with the survival curve for liver cancer patients from the TCGA database, which indicates that high expression of hnRNP Q is a prognostic marker for a poor outcome in individuals afflicted with hepatocellular carcinoma. Together, our findings suggest that hnRNP Q interacts with LIN28B and modulates the LIN28B/let-7 axis in hepatocellular carcinoma.