Inducible resistance to Fas—mediated apoptosis in B cells

Apoptosis produced in B cells through Fas(APO-1,CD95) triggering is regulated by signals derived from other surface receptors:CD40 engagement produces upregulation of Fas expression and marked susceptibility to Fas-induced cell death,whereas antigen receptor engagement,or IL-4R engagement,inhibits Fas killing and in so doing induces a state of Fas-resistance,even in otherwise sensitive,CD40-stimulated targets.Surface immunoglobulin and IL-4R utilize at least partially distinct path ways to produce Fas-resistance that differentially depend on PKC and STAT6,respectively.Further,surface immunoglobulin signaling for inducible Fas-resistance bypasses Btk,requires NF-κB,and entails new macromolecular synthesis.Terminal effectors of B cell Fas-resistance include the known anti-apoptotic gene products,Bcl-XL and FLIP,and a novel anti-apoptotic gene that encodes FAIM (Fas Apoptosis Inhibitory Molecule).faim was identified by differential display and exists in two alternatively spliced forms;faim-S is broadly expressed,but faim-L expression is tissue-specific.The FAIM sequence is highly evolu tionarily conserved,suggesting an important role for this molecule throughout phylogeny.Inducible resistance to Fas killing is hypothesized to protect foreign antigen-specific B cells during potentially hazardous interactions with FasL-bearing T cells,whereas autoreactive B cells fail to become Fas-resistant and are deleted via Fas-dependent cytotoxicity.Inadvertent or aberrant acquisition of Fas-resistance may permit autoreactive B cells to escape Fas deletion,and malignant lymphocytes to impede anti-tumor immunity.     

Towards Multiparametric Fluorescent Imaging of Amyloid Formation: Studies of a YFP Model of α-Synuclein Aggregation

Misfolding and aggregation of proteins are characteristics of a range of increasingly prevalent neurodegenerative disorders including Alzheimer's and Parkinson's diseases. In Parkinson's disease and several closely related syndromes, the protein α-synuclein (AS) aggregates and forms amyloid-like deposits in specific regions of the brain. Fluorescence microscopy using fluorescent proteins, for instance the yellow fluorescent protein (YFP), is the method of choice to image molecular events such as protein aggregation in living organisms. The presence of a bulky fluorescent protein tag, however, may potentially affect significantly the properties of the protein of interest; for AS in particular, its relative small size and, as an intrinsically unfolded protein, its lack of defined secondary structure could challenge the usefulness of fluorescent-protein-based derivatives. Here, we subject a YFP fusion of AS to exhaustive studies in vitro designed to determine its potential as a means of probing amyloid formation in vivo. By employing a combination of biophysical and biochemical studies, we demonstrate that the conjugation of YFP does not significantly perturb the structure of AS in solution and find that the AS-YFP protein forms amyloid deposits in vitro that are essentially identical with those observed for wild-type AS, except that they are fluorescent. Of the several fluorescent properties of the YFP chimera that were assayed, we find that fluorescence anisotropy is a particularly useful parameter to follow the aggregation of AS-YFP, because of energy migration Förster resonance energy transfer (emFRET or homoFRET) between closely positioned YFP moieties occurring as a result of the high density of the fluorophore within the amyloid species. Fluorescence anisotropy imaging microscopy further demonstrates the ability of homoFRET to distinguish between soluble, pre-fibrillar aggregates and amyloid fibrils of AS-YFP. Our results validate the use of fluorescent protein chimeras of AS as representative models for studying protein aggregation and offer new opportunities for the investigation of amyloid aggregation in vivo using YFP-tagged proteins.     

Fas Apoptosis Inhibitory Molecule Contains a Novel β-Sandwich in Contact with a Partially Ordered Domain

Fas apoptosis inhibitory molecule (FAIM) is a soluble cytosolic protein inhibitor of programmed cell death and is found in organisms throughout the animal kingdom. A short isoform of FAIM is expressed in all tissue types, while an alternatively spliced long isoform is specifically expressed in the brain. Here, the short isoform is shown to consist of two independently folding domains in contact with each other. The NMR solution structure of the C-terminal domain of murine FAIM is solved in isolation and revealed to be a novel protein fold, a noninterleaved seven-stranded β-sandwich. The structure and sequence reveal several residues that are likely to be involved in functionally significant interactions with the N-terminal domain or other binding partners. Chemical shift perturbation is used to elucidate contacts made between the N-terminal domain and the C-terminal domain.     

PACAP ameliorates hepatic metabolism and inflammation through up‐regulating FAIM in obesity

Obesity is considered a chronic inflammatory disease, the inflammatory factors, such as interleukin 6 (IL‐6), monocyte chemoattractant protein 1 (MCP‐1) and small inducible cytokine A5 (RANTES), are elevated in obese individuals. Pituitary adenylate cyclase‐activating polypeptide (PACAP) suppresses anti‐inflammatory cytokines and ameliorates glucose and lipid metabolism. Our previous study showed that Fas apoptosis inhibitory molecule (FAIM) is a new mediator of Akt2 signalling, increases the insulin signalling pathway and lipid metabolism. In this study, we found that PACAP promoted the expression of FAIM protein in a human hepatocyte cell line (L02). Overexpression of FAIM with lentivirus suppressed the expression of the inflammatory factor interleukin 6 (IL‐6), monocyte chemoattractant protein 1 (MCP‐1) and tumour necrosis factor alpha (TNF‐α). Following treatment of obese mice with FAIM or PACAP for 2 weeks, inflammation was alleviated and the bodyweight and blood glucose levels were decreased. Overexpression of FAIM down‐regulated the expression of adipogenesis proteins, including SREBP1, SCD1, FAS, SREBP2 and HMGCR, and up‐regulated glycogen synthesis proteins, including Akt2 (Ser474) phosphorylation, GLUT2 and GSK‐3β, in the liver of obese mice. However, down‐regulation of FAIM with shRNA promotes obesity. Altogether, our data identified that FAIM mediates the function of PACAP in anti‐inflammation, glucose regulation and lipid metabolism in obese liver.     

Fas凋亡抑制分子FAIM 1表达缺失诱发单纯性肥胖的初步研究

利用肥胖患者血液和肥胖动物模型研究Fas凋亡抑制分子FAIM 1与单纯性肥胖的关系,为揭示单纯性肥胖发生的分子机理和诊治肥胖提供新的实验基础。检测40例单纯性肥胖患者和17例正常者血液白细胞的FAIM 1蛋白的表达量,分析FAIM 1与单纯性肥胖的相关性。为进一步揭示FAIM 1与单纯性肥胖发生、发展的内在关系,利用高脂饲料建立肥胖模型,并测定肥胖组和对照组大鼠的体重和血糖水平;造模成功的肥胖组大鼠和对照组大鼠禁食12h,麻醉心脏取血,分析血脂中总胆固醇(TC)、甘油三酯(TG)、高密度脂蛋白-胆固醇(HDL-C)和低密度脂蛋白-胆固醇(LDL-C)的变化;取肥胖组和对照组大鼠的附睾脂肪垫和肾周脂肪,分析重量变化;取肥胖组和对照组大鼠,利用Western-blot检测FAIM 1及胰岛素受体β(IRβ)的表达变化。实验结果表明:与正常者相比,单纯性肥胖患者血液白细胞的FAIM 1表达量平均减少36.4%;与对照组相比,肥胖组大鼠血清TC、TG和LDL-C分别增加37.1%、25.6%和39.1%,而HDL-C则降低33.3%;肥胖组大鼠附睾脂肪垫和肾周脂肪分别是对照组的1.85倍和2.24倍;与对照组相比,肥胖组大鼠肝脏FAIM 1、IRβ的表达量分别降低45.9%和32.6%,与临床血液样本的检测结果一致。研究表明,FAIM 1表达与单纯性肥胖发生具有显著的负相关性,FAIM 1可成为单纯性肥胖诊断和治疗的新靶点。