F-box/WD Repeat-Containing Protein 5 Mediates the Ubiquitination of Apoptosis Signal-Regulating Kinase 1 and Exacerbates Nonalcoholic Steatohepatitis in Mice.

Inhibition of apoptosis signal-regulating kinase 1 (ASK1) activation has emerged as a promising target for the treatment of nonalcoholic steatohepatitis (NASH). Multiple forms of posttranslational modifications determine the activity of ASK1. In addition to phosphorylation, recent studies revealed that ubiquitination is essential for ASK1 activation. However, the endogenous factor that regulates ASK1 ubiquitination and activation remains poorly defined. In this study, we identified the E3 ligase Skp1-Cul1-F-box (SCF) protein F-box/WD repeat-containing protein 5 (FBXW5) as a key endogenous activator of ASK1 ubiquitination. FBXW5 is the central component of the SCF complex (SCFFbxw5 ) that directly interacts with and ubiquitinates ASK1 in hepatocytes during NASH development. An in vivo study showed that hepatocyte-specific overexpression of FBXW5 exacerbated diet-induced systemic and hepatic metabolic disorders, as well as the activation of ASK1-related mitogen-activated protein kinase (MAPK) signaling in the liver. Conversely, hepatocyte-specific deletion of FBXW5 significantly prevented the progression of these abnormalities. Mechanically, FBXW5 facilitated the addition of Lys63-linked ubiquitin to ASK1 and thus exacerbated ASK1-c-Jun N-terminal kinase/p38 MAPK signaling, inflammation, and lipid accumulation. Furthermore, we demonstrated that the N-terminus (S1) and C-terminus (S3) of FBXW5 respectively and competitively ablate the function of FBXW5 on ASK1 activation and served as effective inhibitors of NASH progression. Conclusion: This evidence strongly suggests that SCFFbxw5 is an important activator of ASK1 ubiquitination in the context of NASH. The development of FBXW5(S1) or FBXW5(S3)-mimicking drugs and screening of small-molecular inhibitors specifically abrogating ASK1 ubiquitination-dependent activation are viable approaches for NASH treatment.

Induction of apoptosis in hormone-resistant human prostate cancer PC3 cells by inactivated Sendai virus.

OBJECTIVE: Inactivated Sendai virus particle [hemagglutinating virus of Japan envelope (HVJ-E)] has a potential oncolytic effect due to its ability to induce apoptosis in tumor cells. However, the molecular mechanism of apoptosis induction in cancer cells mediated by HVJ-E has not been fully elucidated. This paper aims to investigate the underlying mechanism of apoptosis induction by HVJ-E in prostate cancer cells (PC3). METHODS: PC3 cells were treated with HVJ-E at various MOI, and then interferon-ß (IFN-ß) production, and the cell viability and apoptosis were detected by ELISA, MTT-based assay and flow cytometry, respectively. Next, the roles of Jak-Stat, MAPK and Akt pathways played in HVJ-E-induced apoptosis in PC3 cells were analyzed by immunoblot assay. To further evaluate the cytotoxic effect of HVJ-E on PC3 cells, HVJ-E was intratumorally injected into prostate cancers on BALB/c-nude mice, and the tumor volume was monitored for 36 days. RESULTS: HVJ-E induced IFN-ß production and activated Jak-Stat signaling pathway, which resulted in the activation of caspase-8, caspase-3, and PARP in PC3 prostate cancer cells post HVJ-E treatment. Furthermore, we observed for the first time that p38 and Jnk MAPKs in PC3 cells contributed to HVJ-E-induced apoptosis. In addition, intratumoral HVJ-E treatment displayed a direct inhibitory effect in an in vivo BALB/c nude mouse prostate cancer model. CONCLUSION: Our findings have provided novel insights into the underlying mechanisms by which HVJ-E induces apoptosis in tumor cells.