Tankyrase 1 (TNKS) and tankyrase 2 (TNKS2) belong to the poly(ADP-ribose) polymerase family of proteins, which use nicotinamide adenine dinucleotide to modify substrate proteins with ADP-ribose modifications. Emerging evidence has revealed the pathological relevance of TNKS and TNKS2, and identified these two enzymes as potential drug targets. However, the cellular functions and regulatory mechanisms of TNKS/2 are still largely unknown. Through a proteomic analysis, we defined the protein-protein interaction network for human TNKS/2 and revealed more than 100 high-confidence interacting proteins with numerous biological functions in this network. Finally, through functional validation, we uncovered a role for TNKS/2 in peroxisome homeostasis and determined that this function is independent of TNKS enzyme activities. Our proteomic study of the TNKS/2 protein interaction network provides a rich resource for further exploration of tankyrase functions in numerous cellular processes.

c-Myc (Myc) plays an important role in normal liver development and tumorigenesis. We show here that Myc is pathologically activated in and essential for promoting human hepatocellular carcinoma (HCC). Myc induces HCC through a novel, microRNA (miRNA)-mediated feedback loop comprised of miR-148a-5p, miR-363-3p, and ubiquitin-specific protease 28 (USP28). Myc directly binds to conserved regions in the promoters of the two miRNAs and represses their expression. miR-148a-5p directly targets and inhibits Myc, whereas miR-363-3p destabilizes Myc by directly targeting and inhibiting USP28. Inhibition of miR-148a-5p or miR-363-3p induces hepatocellular tumorigenesis by promoting G1 to S phase progression, whereas activation of them has the opposite effects. The Myc-miRNA feedback loop is dysregulated in human HCC. Conclusion: These results define miR-148a-5p and miR-363-3p as negative regulators of Myc, thus revealing their heretofore unappreciated roles in hepatocarcinogenesis.

MiRNAs are involved in many physiologic and disease processes by virtue of degrading specific mRNAs or inhibiting their translation. miR-148a has been implicated in the control of tumor growth and cholesterol and triglyceride homeostasis using in vitro or in vivo gene expression- and silencing-based approaches. Here miR-148a knockout (KO) mice were used to investigate the intrinsic role of miR-148a in liver physiology and hepatocarcinogenesis in mice. miR-148a downregulation was found to be correlated with poor clinical outcomes in hepatocellular carcinoma (HCC) patients. Under regular chow diet (RCD) or high fat diet (HFD), miR-148a deletion significantly accelerated DEN-induced hepatocarcinogenesis in mice. Mechanistically, miR-148a deletion promotes lipid metabolic disorders in mice. Moreover, restoration of miR-148a reversed these defects. Finally, miR-148a was found to directly inhibit several key regulators of hepatocarcinogenesis and lipid metabolism. These findings reveal crucial roles for miR-148a in the hepatic lipid metabolism and hepatocarcinogenesis. They further identify miR-148a as a potential therapeutic target for certain liver diseases, including cancer.