Search

Objective Diet-induced obesity is often associated with nonalcoholic fatty liver disease (NAFLD), which instigates severe metabolic disorders, including cirrhosis, hepatocellular carcinoma, and type 2 diabetes. We have shown that hepatic depletion of CREB regulated transcription co-activator (CRTC) 2 protects mice from the progression of diet-induced fatty liver phenotype, although the exact mechanism by which CRTC2 modulates this process is elusive to date. Here, we investigated the role of hepatic CRTC2 in the instigation of NAFLD in mammals. Methods Crtc2 liver-specific knockout (Crtc2 LKO) mice and Crtc2 flox/flox (Crtc2 f/f) mice were fed a high fat diet (HFD) for 7–8 weeks. Body weight, liver weight, hepatic lipid contents, and plasma triacylglycerol (TG) levels were determined. Western blot analysis was performed to determine Sirtuin (SIRT) 1, tuberous sclerosis complex (TSC) 2, and mammalian target of rapamycin complex (mTORC) 1 activity in the liver. Effects of Crtc2 depletion on lipogenesis was determined by measuring lipogenic gene expression (western blot analysis and qRT-PCR) in the liver as well as Oil red O staining in hepatocytes. Effects of miR-34a on mTORC1 activity and hepatic lipid accumulation was assessed by AAV-miR-34a virus in mice and Ad-miR-34a virus and Ad-anti-miR-34a virus in hepatocytes. Autophagic flux was assessed by western blot analysis after leupeptin injection in mice and bafilomycin treatment in hepatocytes. Lipophagy was assessed by transmission electron microscopy and confocal microscopy. Expression of CRTC2 and p-S6K1 in livers of human NAFLD patients was assessed by immunohistochemistry. Results We found that expression of CRTC2 in the liver is highly induced upon HFD-feeding in mice. Hepatic depletion of Crtc2 ameliorated HFD-induced fatty liver disease phenotypes, with a pronounced inhibition of the mTORC1 pathway in the liver. Mechanistically, we found that expression of TSC2, a potent mTORC1 inhibitor, was enhanced in Crtc2 LKO mice due to the decreased expression of miR-34a and the subsequent increase in SIRT1-mediated deacetylation processes. We showed that ectopic expression of miR-34a led to the induction of mTORC1 pathway, leading to the hepatic lipid accumulation in part by limiting lipophagy and enhanced lipogenesis. Finally, we found a strong association of CRTC2, miR-34a and mTORC1 activity in the NAFLD patients in humans, demonstrating a conservation of signaling pathways among species. Conclusions These data collectively suggest that diet-induced activation of CRTC2 instigates the progression of NAFLD by activating miR-34a-mediated lipid accumulation in the liver via the simultaneous induction of lipogenesis and inhibition of lipid catabolism. Therapeutic approach to specifically inhibit CRTC2 activity in the liver could be beneficial in combating NAFLD in the future., Graphical abstract Image 1, Highlights • CRTC2 expression is elevated in livers of HFD-fed mice. • Liver-specific depletion of Crtc2 ameliorated HFD-induced fatty liver phenotype in mice. • Crtc2 knockout dampened miR-34a-mTORC1 pathway, leading to the inhibition of lipogenesis and the activation of lipophagy. • Close association of CRTC2 with mTORC1 activity was also demonstrated in the human NAFLD patients. • Diet-induced activation of CRTC2 instigates the progression of NAFLD by activating the miR-34a-mTORC1 pathway.

Ubiquitin-specific proteases (USPs) play an important role in fundamental cellular processes. Among these, USP10 is known for its association with tumor development and progression of multiple cancers. We aimed to investigate the clinical significance of USP10 expression in colorectal cancer and examined the potential link between USP10 and p14ARF in patients with colorectal cancer. USP10 and p14ARF protein expression was assessed via immunohistochemistry (IHC) on a tissue microarray from 280 colorectal cancer cases. IHC scores were evaluated by digital image analysis and compared with patients' outcomes. In addition, we examined DNA hypermethylation in colorectal cancer cell lines and tissues, which were matched with adjacent normal colon samples. USP10 expression was lost (USP10loss) in 18.6% of samples (52/280 cases), which was linked to lymphovascular invasion (p = 0.019) and distant metastases (p < 0.001). Similarly, loss of p14ARF expression (p14ARFloss) was associated with more advanced tumors. USP10 expression correlated positively with p14ARF expression (r = 0.617, p < 0.001). USP10loss, p14ARFloss, and dual loss of USP10 and p14ARF were significantly associated with shorter disease-free survival and overall survival in comparison to USP10intact, p14ARFintact, and dual loss of USP10 and p14ARF, respectively. Multivariate analysis revealed that USP10loss (p = 0.030) and dual loss of USP10 and p14ARF (p = 0.014) are independent prognostic factors for poor disease-free survival in colorectal cancer patients. Furthermore, aberrant hypermethylation of the USP10 promoter region was found in colorectal cancer cell lines and tissues. The present results suggest that USP10loss is a potential prognostic marker for colorectal cancer.