Activation of apoptosis signal‐regulating kinase 1 (ASK1) is a key driving force of the progression of nonalcoholic steatohepatitis (NASH) and represents an attractive therapeutic target for NASH treatment. However, the molecular and cellular mechanisms underlying ASK1 activation in the pathogenesis of NASH remain incompletely understood. In this study, our data unequivocally indicated that hyperactivated ASK1 in hepatocytes is a potent inducer of hepatic stellate cell (HSC) activation by promoting the production of hepatocyte‐derived factors. Our previous serial studies have shown that the ubiquitination system plays a key role in regulating ASK1 activity during NASH progression. Here, we further demonstrated that tumor necrosis factor receptor–associated factor 6 (TRAF6) promotes lysine 6 (Lys6)‐linked polyubiquitination and subsequent activation of ASK1 to trigger the release of robust proinflammatory and profibrotic factors in hepatocytes, which, in turn, drive HSC activation and hepatic fibrosis. Consistent with the in vitro findings, diet‐induced liver inflammation and fibrosis were substantially attenuated in Traf6+/– mice, whereas hepatic TRAF6 overexpression exacerbated these abnormalities. Mechanistically, Lys6‐linked ubiquitination of ASK1 by TRAF6 facilitates the dissociation of thioredoxin from ASK1 and N‐terminal dimerization of ASK1, resulting in the boosted activation of ASK1‐c‐Jun N‐terminal kinase 1/2 (JNK1/2)‐mitogen‐activated protein kinase 14(p38) signaling cascade in hepatocytes. Conclusion: These results suggest that Lys6‐linked polyubiquitination of ASK1 by TRAF6 represents a mechanism underlying ASK1 activation in hepatocytes and a key driving force of proinflammatory and profibrogenic responses in NASH. Thus, inhibiting Lys6‐linked polyubiquitination of ASK1 may serve as a potential therapeutic target for NASH treatment.

Background and Aims Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease, which has no specific pharmacological treatments partially because of the unclear pathophysiological mechanisms. Regulator of G protein signaling (RGSs) proteins are proteins that negatively regulate G protein–coupled receptor (GPCR) signaling. The members of the R4/B subfamily are the smallest RGS proteins in size, and RGS5 belongs to this family, which mediates pluripotent biological functions through canonical G protein–mediated pathways and non‐GPCR pathways. This study combined a genetically engineered rodent model and a transcriptomics‐sequencing approach to investigate the role and regulatory mechanism of RGS5 in the development of NAFLD. Approach and Results This study found that RGS5 protects against NAFLD and nonalcoholic steatohepatitis. Using RNA sequencing and an unbiased systematic investigative approach, this study found that the activation of mitogen‐activated protein kinase signaling cascades in response to metabolic challenge is negatively associated with hepatic RGS5 expression. Mechanistically, we found that the 64‐181 amino‐acid‐sequence (aa) fragment of RGS5 directly interacts with transforming growth factor beta–activated kinase 1 (TAK1) through the 1‐300aa fragment and inhibits TAK1 phosphorylation and the subsequent c‐Jun‐N‐terminal kinase (JNK)/p38 pathway activation. Conclusions In hepatocytes, RGS5 is an essential molecule that protects against the progression of NAFLD. RGS5 directly binds to TAK1, preventing its hyperphosphorylation and the activation of the downstream JNK/p38 signaling cascade. RGS5 is a promising target molecule for fine‐tuning the activity of TAK1 and for the treatment of NAFLD.

Activation of the stimulator of interferon gene (STING)-mediated innate immune response has been suggested as a promising therapeutic strategy for cancers. However, the effects of STING agonist on natural killer (NK) cell-mediated anti-tumor responses in pancreatic cancer remains unknown. Herein, we evaluated the effects of a classical STING agonist cyclic GMP-AMP (cGAMP) on NK cells in pancreatic cancer. We found that cGAMP could directly activate NK cells and enhance the sensitivity of pancreatic cancer cells to NK cell cytotoxicity, suggesting that cGAMP may become a potential adjuvant for NK cell therapy. In addition, combination of CAR-NK-92 cells targeting mesothelin and cGAMP displayed greater antitumor efficacy by inhibiting tumor growth and prolonging survival of the mouse model of pancreatic cancer. These results suggest that the combination of a STING agonist and NK cells may become a novel immunotherapy strategy for pancreatic cancer.