Background: PKC is extremely important for a wide array of cellular processes. However, its inactivation is poorly understood. Results: FADD deficiency or phosphoryl-mimicking mutation (FADD-D) leads to accumulation of phosphorylated PKC and sustained signaling. Conclusion:The apoptotic adapter FADD is required for PKC dephosphorylation, degradation and signaling inactivation and may be regulated by its phosphorylation. Significance: FADD is critical for PKC dephosphorylation, stability, and signaling termination.

2,4,6-trinitrotoluene (TNT) has been reported to cause numerous adverse effects. However, the detailed molecular mechanisms underlying TNT-induced liver toxicity need to be elucidated. In this study, we used HepG2 (p53wt) and Hep3B (p53null) cell lines to investigate the cytotoxic effects of TNT. At first, we found that TNT significantly decreased cell viability and induced DNA damage. Thereafter, through transcriptomic analysis, we observed that the diverse biological functions affected included mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Mitochondrial dysfunction was evidenced by the loss of mitochondrial membrane potential, increased expression of cleaved-caspase-9&-3 and increased caspase-3/7 activity, indicating that apoptosis had occurred. In addition, the expressions of some ER stress-related proteins had increased. Next, we investigated the role of reactive oxygen species (ROS) in TNT-induced cellular toxicity. The levels of DNA damage, mitochondrial dysfunction, ER stress and apoptosis were alleviated when the cells were pretreated with N-acetyl-cysteine (NAC). These results indicated that TNT caused the ROS dependent apoptosis via ER stress and mitochondrial dysfunction. Finally, the cells transfected with CHOP siRNA significantly reversed the TNT-induced apoptosis, which indicated that ER stress led to apoptosis. Overall, we examined TNT-induced apoptosis via ROS dependent mitochondrial dysfunction and ER stress in HepG2 and Hep3B cells.

FADD, a classical apoptotic signaling adaptor, was recently reported to have non‐apoptotic functions. Here, we report the discovery that FADD regulates lipid metabolism. PPAR‐α is a dietary lipid sensor, whose activation results in hypolipidemic effects. We show that FADD interacts with RIP140, which is a corepressor for PPAR‐α, and FADD phosphorylation‐mimic mutation (FADD‐D) or FADD deficiency abolishes RIP140‐mediated transcriptional repression, leading to the activation of PPAR‐α. FADD‐D‐mutant mice exhibit significantly decreased adipose tissue mass and triglyceride accumulation. Also, they exhibit increased energy expenditure with enhanced fatty acid oxidation in adipocytes due to the activation of PPAR‐α. Similar metabolic phenotypes, such as reduced fat formation, insulin resistance, and resistance to HFD‐induced obesity, are shown in adipose‐specific FADD knockout mice. Additionally, FADD‐D mutation can reverse the severe genetic obesity phenotype of ob/ob mice, with elevated fatty acid oxidation and oxygen consumption in adipose tissue, improved insulin resistance, and decreased triglyceride storage. We conclude that FADD is a master regulator of glucose and fat metabolism with potential applications for treatment of insulin resistance and obesity.

Background:The balance between self-renewal and differentiation in muscle stem cells is critical for tissue homeostasis. Results: Fas-associated death domain (FADD) phosphorylation mutation regulates muscle satellite cell cycle progression, inhibits muscle stem cell differentiation, and promotes muscle stem cell self-renewal. Conclusion: FADD regulates muscle stem cell fate decisions. Significance: The characterization of proteins involved in fate decisions in muscle stem cells is crucial for muscle stem cell biology.

Notch signaling plays critical roles during myogenesis by promoting the proliferation and inhibiting the differentiation of myogenic progenitors. However, the mechanism of the temporal regulation of Notch signaling during the myogenic lineage progression remains elusive. In the present study, we show that a constitutively phosphoryl-mimicking mutation of Fas-associated death domain (FADD-D) enhances Notch-1 signaling and compromises Wnt signaling in both cultured myoblasts and regenerating muscles, which results in inhibited myogenic differentiation and muscle regeneration. Inhibition of Notch signaling recovers the regeneration ability in injured FADD-D muscles through rescuing Wnt signaling. Furthermore, we found that protein kinase Cα mediates FADD-D-induced Notch-1 signaling by stabilizing Notch-1. Collectively, these data identify a novel mechanism for the temporal regulation of Notch signaling during myogenic lineage progression and muscle regeneration.