Correction: Functional specific roles of FADD: comparative proteomic analyses from knockout cell lines.

Correction for 'Functional specific roles of FADD: comparative proteomic analyses from knockout cell lines' by Hongqin Zhuang et al., Mol. BioSyst., 2013, 9, 2063-2078.

FADD is a key regulator of lipid metabolism.

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.

Comparative proteomics analysis reveals roles for FADD in the regulation of energy metabolism and proteolysis pathway in mouse embryonic fibroblast.

Fas-associated death domain-containing protein (FADD) is a classical apoptotic pathway adaptor. Further studies revealed that it also plays essential roles in nonapoptotic processes, which is assumed to be regulated by its phosphorylation. However, the exact mechanisms are still poorly understood. To study the nonapoptotic effects of FADD, a comprehensive strategy of proteomics identification combined with bioinformatic analysis was undertaken to identify proteins differentially expressed in three cell lines containing FADD and its mutant, FADD-A and FADD-D. The cell lines were thought to bear wild-type FADD, unphosphorylated FADD mimic and constitutive phosphorylated FADD mimic, respectively. A total of 47 proteins were identified to be significantly changed due to FADD phosphorylation. Network analysis using MetaCore™ identified a number of changed proteins that were involved in cellular metabolic process, including lipid metabolism, fatty acid metabolism, glycolysis, and oxidative phosphorylation. The finding that FADD-D cell line showed an increase in fatty acid oxidation argues that it could contribute to the leaner phenotype of FADD-D mice as reported previously. In addition, six proteins related to the ubiquitin-proteasome pathway were also specifically overexpressed in FADD-D cell line. Finally, the c-Myc gene represents a convergent hub lying at the center of dysregulated pathways, and was upregulated in FADD-D cells. Taken together, these studies allowed us to conclude that impaired mitochondrial function and proteolysis might play pivotal roles in the dysfunction associated with FADD phosphorylation-induced disorders.

Functional specific roles of FADD: comparative proteomic analyses from knockout cell lines.

Fas-associated death domain (FADD) is a classical adaptor protein involved in tumor necrosis factor receptor family-mediated apoptosis. Besides being an essential instrument in cell death, it also plays key roles in cell proliferation and survival. The current study shows for the first time that FADD is probably associated with energy metabolism and proteolysis. It has been reported that embryonic death caused by FADD deficiency in mice was not attributable to impaired apoptosis. Furthermore, mice bearing the substitution in FADD of serine 191 to aspartic acid exhibited leaner body size than both wild-type control and serine 191 to alanine mutant mice, indicating metabolic disorders. To study these non-apoptotic effects of FADD, a comprehensive strategy of proteomics identification combined with bioinformatic analyses and further cell biology validation was utilized to identify differentially-expressed proteins in FADD-deficient mouse embryonic fibroblasts (MEFs). A total of 45 unique proteins were determined to be significantly changing due to FADD deficiency. Network analysis of these proteins using MetaCore™ suggested induction of transcriptional factors that are too low to be detected by two-dimensional gels and identified an enriched cluster of changed proteins that are involved in cellular metabolic processes, including lipid metabolism, fatty acids metabolism, glycolysis, tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. Fatty acids ß-oxidation was found to be enhanced in FADD-deficient cells. In addition, five proteins related to the ubiquitin-proteasome (UP) pathway were also specifically up-regulated in the FADD(-/-) MEFs. Finally, the c-Myc gene represents a convergent hub lying at the center of dysregulated pathways, and was up-regulated in FADD knockout cells. Taken together, these studies show that impaired mitochondrial function and proteolysis may play pivotal roles in the dysfunction associated with FADD deficiency-induced disorders, probably including embryonic lethality. The link between FADD and cell metabolism may provide us new insight for understanding the crosstalk of independent cell signaling pathways.

Suppression of HSP70 expression sensitizes NSCLC cell lines to TRAIL-induced apoptosis by upregulating DR4 and DR5 and downregulating c-FLIP-L expressions.

Many cancer cell types are resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Here, we examined whether HSP70 suppression by small interfering RNA (siRNA) sensitized non-small cell lung cancer (NSCLC) cells to TRAIL-induced apoptosis and the underlying mechanisms. We demonstrated that HSP70 suppression by siRNA sensitized NSCLC cells to TRAIL-induced apoptosis by upregulating the expressions of death receptor 4 (DR4) and death receptor 5 (DR5) through activating NF-κB, JNK, and, subsequently, p53, consequently significantly amplifying TRAIL-mediated caspase-8 processing and activity, cytosolic translocation of cytochrome c, and cell death. Consistently, the pro-apoptotic proteins Bad and Bax were upregulated, while the anti-apoptotic protein Bcl-2 was downregulated. The luciferase activity of the DR4 promoter was blocked by a NF-κB pathway inhibitor BAY11-7082, suggesting that NF-κB activation plays an important role in the transcriptional upregulation of DR4. Additionally, HSP70 suppression inhibited the phosphorylation of ERK, AKT, and PKC, thereby downregulating c-FLIP-L. A549 xenografts in mice receiving HSP70 siRNA showed TRAIL-induced cell death and increased DR4/DR5 levels and reduced tumor growth. The combination of psiHSP70 gene therapy with TRAIL also significantly increased the survival benefits induced by TRAIL therapy alone. Interestingly, HSP27 siRNA and TRAIL together could not suppress tumor growth or prolong the survival of tumor-bearing mice significantly, although the combination could efficiently induce the apoptosis of A549 cells in vitro. Our findings suggest that HSP70 suppression or downregulation might be promising to overcome TRAIL resistance in cancer.