(f) TGF-2 increased the binding of TIAF1 with amyloid fibrils in L929 cells during treatment for 24h. protein (APP) at Thr668, followed by degradation and generation of APP intracellular domain (AICD), Aand amyloid fibrils. Polymerized TIAF1 physically interacts with amyloid fibrils, which would favorably support plaque formationin vivo. Keywords:TIAF1, amyloid beta, aggregation, plaque, TGF- Neurodegenerative diseases are frequently encountered in the aging populations in the human societies. The neuropathology of Alzheimer’s disease (AD) is characterized by extracellular accumulation of fibrillar amyloid(A) peptide and intracellular deposition of neurofibrillary tangles made of cytoskeletal protein tau.1These protein aggregates invoke neuronal death and block neurogenesis and learning and memory capabilities in AD patients. Role of transforming growth Uridine triphosphate factor beta (TGF-) in the pathogenesis Uridine triphosphate of AD is controversial.2,3,4,5Type II receptor for TGF-(TRII) is central to the TGF-/mothers against DPP homolog (Smad) signaling. Reduced levels of TRII are observed in human AD brains, and this correlates with age-dependent neurodegeneration and AD-like disease in a mouse model.2However, in a transgenic AD mouse model, TGF-1 is constitutively upregulated and neuronal apoptosis occurs.3Increased levels of TGF-in AD are associated with perivascular deposition of extracellular matrix, which hinders clearance of Aand allows the development of cerebral amyloid angiopathy.4Blockade of TGF-/Smad innate immune signaling mitigates Alzheimer-like pathology in transgenic TRII mouse model.5 Here, we identified TGF-1-induced antiapoptotic factor (TIAF1) protein aggregation, which may cause neuronal death. TIAF1, a 12-kDa TIAF1,6participates in TGF-signaling7and controls p53 activation.8TIAF1 is implicated in the activation of TH2 helper T lymphocytes in chronic organ rejection9and development of regulatory T cells,10as well as association with Hirschsprung’s disease.11TIAF1 tends to aggregate, and the protein aggregates are found in the hippocampi of postmortem nondemented humans and AD patients. Importantly, TIAF1 self-aggregation leads to generation of Aand amyloid fibrils from amyloid precursor protein (APP)in vitro. == Results == == TIAF1 binds and blocks Smad4-dependent promoter activation == TIAF1 is an effector of the TGF-signaling.6,7,8By yeast two-hybrid analysis,8,12,13,14we determined that TIAF1 physically interacted with Smad4 (Figure 1a). Stimulation of COS7 fibroblasts with TGF-1 for 30 min resulted in the binding of endogenous TIAF1 with Smad4, and the complex was accumulated in the nuclei (Figure 1b). == Figure 1. == TIAF1 physically binds Smad4 and blocks Smad4-regulated promoter activation. (a) By yeast two-hybrid library screening,8,12,13two Smad4 clones (No. 7 and 17), with an identical DNA sequence, were isolated as a TIAF1-binding protein. Both Smad4/TIAF1 interactions and positive control bindings for WOX1/p53 and MafB self-interaction are shown, as evidenced by the growth of yeast at 37 C using a selective galactose-containing agarose plate (six representative colonies). Empty pSos/pMyr vectors and p53/TIAF1 plasmid constructs8,12,13were regarded as negative controls. (b) COS7 cells were cultured in 10% FBS and treated with or without TGF-1 (5 Uridine triphosphate ng/ml) for 30 min, followed by isolating cytosolic and nuclear fractions for co-immunoprecipitation with anti-TIAF1 IgG. TGF-1 PIK3C3 increased the binding of TIAF1 with Smad4. Non-immune IgG was used as a negative control in co-immunoprecipitation. (c) COS7 cells were infected with retroviral TIAF1si or empty retrovirus and cultured for 48 h, followed by determining protein nuclear localization for Smad3 and 4 by immunofluorescence microscopy. TIAF1si knocked down endogenous TIAF1 protein by 70%.(d)COS7 cells were transfected with EGFP-Smad4 plasmid (using liposome) and infected with retroviral TIAF1si or empty retrovirus. The cells were grown for 48 h, fixed and immunostained with TIAF1. Nuclei were stained with DAPI. Knockdown of TIAF1 significantly induced nuclear accumulation of EGFP-Smad4. (eandf) Human monocytic U937 cells and mouse L929 fibroblasts were infected with TIAF1si or vacant retrovirus and cultured for 48 h, followed by isolating nuclear and cytosolic fractions. Spontaneous Uridine triphosphate build up of Smad3 and 4 in the nuclei was demonstrated in cells infected with TIAF1si. Reduction of endogenous TIAF1 protein by siRNA is definitely shown (6075% reduction; a representative set of data from two experiments).(g)COS7 cells were transfected with ECFP or ECFP-TIAF1 expression constructs, grown for 24 h, and treated with TGF-1 (5 ng/ml) for 18 h. The degree of build up of Smad2, 3 or 4 4 in the nuclei post TGF-1 treatment for 4 h is definitely demonstrated (n=3, 100 cells counted per Uridine triphosphate experiment), as determined by immunofluorescence microscopy. (h) COS7 cells were transfected having a SMAD-responsive element DNA construct (using GFP like a reporter), in the presence or absence of Smad4 and/or TIAF1 manifestation constructs. After 48 h, positive promoter activation in cells with green fluorescence was counted. Compared with Smad4 alone, TIAF1 significantly clogged the ectopic Smad4-induced activation of the promoter (*P<0.001 for the.