Long non-coding RNA (lncRNA), highly up-regulated in liver cancer (HULC) plays an important role in tumorigenesis. Depletion of HULC resulted in a significant deregulation of several genes involved in liver cancer. Although up-regulation of HULC expression in hepatocellular carcinoma has been reported, the molecular mechanisms remain unknown. In this study, we used in vivo and in vitro approaches to characterize cancer-dependent alterations in the chromatin organization and find a CREB binding site (encompassing from −67 to −53 nt) in the core promoter. Besides, we also provided evidence that PKA pathway may involved in up-regulation of HULC. Furthermore, we demonstrated HULC may act as an endogenous ‘sponge’, which down-regulates a series of microRNAs (miRNAs) activities, including miR-372. Inhibition of miR-372 leads to reducing translational repression of its target gene, PRKACB, which in turn induces phosphorylation of CREB. Over-expression of miR-372 decreases the association of CREB with the proximal promoter, followed by the dissociation of P300, resulting in a change of the histone ‘code’, such as in deacetylation and methylation. The study elucidates that fine tuning of HULC expression is part of an auto-regulatory loop in which it’s inhibitory to expression and activity of miR-372 allows lncRNA up-regulated expression in liver cancer.

O-GlcNAcylation has been implicated in the tumorigenesis of various tissue origins, but its function in liver tumorigenesis is not clear. Here, we demonstrate that O-GlcNAcylation can enhance the expression, stability and function of Yes-associated protein (YAP), the downstream transcriptional regulator of the Hippo pathway and a potent oncogenic factor in liver cancer. O-GlcNAcylation induces transformative phenotypes of liver cancer cells in a YAP-dependent manner. An O-GlcNAc site of YAP was identified at Thr241, and mutating this site decreased the O-GlcNAcylation, stability, and pro-tumorigenic capacities of YAP, while increasing YAP phosphorylation. Importantly, we found via in vitro cell-based and in vivo mouse model experiments that O-GlcNAcylation of YAP was required for high-glucose-induced liver tumorigenesis. Interestingly, a positive feedback between YAP and global cellular O-GlcNAcylation is also uncovered. We conclude that YAP O-GlcNAcylation is a potential therapeutic intervention point for treating liver cancer associated with high blood glucose levels and possibly diabetes.

Ferroptosis is an outcome of metabolic disorders and closely linked to liver cancer. However, the mechanism underlying the fine regulation of ferroptosis in liver cancer remains unclear. Here, we have identified two categories of genes: ferroptosis up-regulated factors (FUF) and ferroptosis down-regulated factors (FDF), which stimulate and suppress ferroptosis by affecting the synthesis of GSH. Furthermore, FUF are controlled by one transcription factor HIC1, while FDF controlled by another transcription factor HNF4A. Occurrence of ferroptosis might depend on the histone acetyltransferase KAT2B. Upon stimulation of ferroptosis, dissociation of KAT2B prevents HNF4A from binding to the FDF promoter. This effect happens prior to the recruitment of KAT2B to the FUF promoter, which facilitates HIC1 binding to transcribe FUF. Clinically, HIC1 and HNF4A conversely correlate with tumor stage in liver cancer. Patients with lower HIC1 and higher HNF4A exhibit poorer prognostic outcomes. Disrupting the balance between HIC1 and HNF4A might be helpful in treating liver cancer.

Yes-associated protein (YAP), the downstream effecter of the Hippo-signaling pathway as well as cyclic adenosine monophosphate response element-binding protein (CREB), has been linked to hepatocarcinogenesis. However, little is known about whether and how YAP and CREB interact with each other. In this study, we found that YAP-CREB interaction is critical for liver cancer cell survival and maintenance of transformative phenotypes, both in vitro and in vivo. Moreover, both CREB and YAP proteins are highly expressed in a subset of human liver cancer samples and are closely correlated. Mechanistically, CREB promotes YAP transcriptional output through binding to −608/−439, a novel region from the YAP promoter. By contrast, YAP promotes protein stabilization of CREB through interaction with mitogen-activated protein kinase 14 (MAPK14/p38) and beta-transducin repeat containing E3 ubiquitin protein ligase (BTRC). Gain-of-function and loss-of-function studies demonstrated that phosphorylation of CREB by MAPK14/p38 at ser133 ultimately leads to its degradation. Such effects can be enhanced by BTRC through phosphorylation of MAPK14/p38 at Thr180/Tyr182. However, YAP negatively controls phosphorylation of MAPK14/p38 through inhibition of BTRC expression. Conclusion: There is a novel positive autoregulatory feedback loop underlying the interaction between YAP and CREB in liver cancer, suggesting that YAP and CREB form a nexus to integrate the protein kinase A, Hippo/YAP, and MAPK14/p38 pathways in cancer cells and thus may be helpful in the development of effective diagnosis and treatment strategies against liver cancer. (Hepatology 2013;53:1011–1020)