T G Fb Superfamily培训课件.ppt

TGF-b activation The 3 TGF-b isoforms are synthesized and homodimeric pro-TGF-b = TGF covalently linked to latency associated protein (LAP) Intracellularly cleaved by furin-type enzymes-- mature TGF-b , remains non-covalently associated with LAP= SLC Few cells produce and secrete diffusible SLC. Majority secrete TGF as part of the LLC, formed within secretory vesicles: covalent disulfide bond between the SLC and a member of the LTBP family LTBP-1,-3,-4 bind TGF-bs. LTBPs belong to the superfamily of fibrillin-like ECM proteins Bind a series of ECM proteins TGF-b is synthesized in excess, and bioavailability depends on activation Latent TGF-b activation Activation of TGF-b varies according to cell type and physiological context Heat, acid, reactive oxygen species, glycosidases, thrombospondin, proteolysis and integrin- mediated activation Proteases: Plasmin, thrombin, elastase, MT-MMP,MMP-2, MMP3, MMP-9, MMP13 etc.. in vitro. In vivo, however, simple proteolysis has not been shown. No supporting genetic evidence.. Predominantly non-proteolytic mechanism for TGF-b activation in vivo: Integrin (av, b6, b8) and TGF-b KO mice have overlapping phenotypes. The TGF-b1 RGD-RGE mutation phenocopies the TGF-b1 KO. Integrins shown to bind and possibly activate latent TGF-b1 avb1: binding yes, activation not known. avb3: binding yes, activation yes. avb5: binding yes, activation yes. avb6: binding yes, activation yes. avb8: binding yes, activation yes. a8b1: binding yes, activation no xb1: binding yes, activation yes. Latent TGF-b activation Integrins bind to the RGD sequence at the N-term of LAP. Mutation to RGE abolishes binding and activation in epithelial cells RGD peptides reduce TGF-b activation in myofibroblasts The TGF-b1 RGD-RGE mutation phenocopies the TGF-b1 KO. avb6 has a higher affinity for the RGD in LAP than in FN due to a DLXXL motif. Some LTBPs also have an RGD, but it has not been shown to be an integrin ligand. Why do not all integrins that bind