Accumulation of unfolded proteins can disturb the functions of the endoplasmic reticulum (ER), leading to ER-stress or unfolded protein response (UPR). Recent data have shown that activation of UPR can be found in postmortem brains of Alzheimer's disease (AD) patients; and biological markers for activation of UPR are abundant in neurons with diffuse phosphorylated tau. Although these observations suggest a linkage between ER-stress and tau pathology, little is known of their relationship. In this study, we found that high levels of phosphorylated PKR-like ER-resident kinase (p-PERK) and phosphorylated eukaryotic initiation factor 2 alpha (p-eIF2α) as markers for activation of UPR in the hippocampus of aged P301L mutant tau transgenic mice. The immunoreactivity of p-PERK was found to co-localize with that of phosphorylated tau. We then hypothesized that phosphorylation of tau could induce ER-stress and vice versa in promoting AD-like pathogenesis. By using the protein phosphatase 2A inhibitor okadaic acid (OA) as an inducer for phosphorylation of tau, we found that primary cultures of rat cortical neurons treated with OA triggered UPR as indicated by increased levels of p-PERK and p-eIF2α, splicing of mRNA for xbp-1 and elevated levels of mRNA for GADD153. On the other hand, thapsigargin as an ER-stress inducer stimulated phosphorylation of tau at Thr231, Ser262 and Ser396. Thapsigargin also induced activation of caspase-3 and cleavage of tau. These findings suggested that ER-stress and hyperphosphorylation of tau could be induced by each other to form a vicious cycle to propagate AD-like neurodegeneration.

Liver cancer, primarily hepatocellular carcinoma (HCC), is the fifth most common cancers and the third leading cause of cancer mortality worldwide. In recent years, deregulated epigenetic mechanisms were found important in a wide range of human carcinogenesis, including HCC. The epigenetic changes elicited by various environmental factors and lifestyles (such as hepatitis B virus (HBV) and hepatitis C virus (HCV) infection, chronic alcohol intake) were suspected to promote HCC development. However, the underlying mechanism and specific gene targets are still unknown. Our previous study suggested that deregulation of epigenetic regulators was a common event in human HCC. Among 90 epigenetic modifiers analyzed in human HCC, Euchromatic histone-lysine N-methyltransferase 2 (EHMT2/G9a) was the most significantly up-regulated one. G9a is a SET domain containing histone methyltransferase specific for histone H3 lysine 9 mono- and di-methylation. Previous work had revealed that G9a is important for embryonic development and adipocyte differentiation. However, little is known about functional roles of G9a in human HCC. We hypothesize that deregulation of G9a may led to aberrant epigenetic changes and contribute to initiation and progression of human HCC. In this study, we found that G9a mRNA expression in primary HCC was 3 folder than their corresponding non-tumor liver and 10 fold higher than normal livers. The up-regulation of G9a was detected in 63% (24/38) of primary HCC samples and was significantly associated with the presence of venous invasion (P = 0.006). The frequent G9a up-regulation in HCC was attributed to gene amplification and microRNA deregulation. We showed that 53% of HCC samples have 3 or more copies of G9a gene. In addition, we identified that miR-1 was a post-transcriptional regulator of G9a. Ectopic expression of miR-1 suppressed G9a 3′-untranslated-region-coupled luciferase activity. Functionally, knockdown of G9a significantly suppressed HCC cell proliferation, migration and colony formation. We also demonstrated that UNC0638, as a G9a specific inhibitor, could effectively inhibit HCC cell growth and cause cell morphology changes. By utilizing nude mice model, we showed that depletion of G9a drastically inhibited in vivo tumorigenicity. Our finding suggested that up-regulation of G9a contributed to the liver carcinogenesis and could be a therapeutic target for HCC treatment. Citation Format: Lai Wei, Felice Ho-Ching Tsang, Jeffery Chi-Fai Lau, Sandy Leung-Kuen Au, Joyce Man-Fong Lee, Carmen Chak-Lui Wong, Irene Oi-Lin Ng, Chun-Ming Wong. Deregulation of G9a and its functional roles in liver cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5147. doi:10.1158/1538-7445.AM2014-5147