In dermal fibroblasts, 5-FU antagonized TGF–driven COL1A2 transcription and inhibited formation of Smad3/4 DNA complexes in a JNK-dependent manner, providing a molecular explanation to the observed clinical benefits of 5-FU as an antifibrotic agent (Wendling 2003). A new class of water-soluble small molecule inhibitors, related to imidazole inhibitors of p38, CGP60474 have recently been shown to inhibit the kinase activity of TGF- Type I receptors ALK4 and ALK5. of EMT and genes for collagens, plasminogen activator inhibitor-1 and the tissue inhibitor of metalloprotease-1. Smad3 null mice are resistant to radiation-induced cutaneous fibrosis, bleomycin-induced pulmonary fibrosis, carbon tetrachloride-induced hepatic fibrosis as well as glomerular fibrosis induced by induction of type 1 diabetes with streptozotocin. In fibrotic conditions that are induced by EMT, such as proliferative vitreoretinopathy, ocular capsule injury and glomerulosclerosis resulting from unilateral ureteral obstruction, Smad3 null mice also show an abrogated CGP60474 fibrotic response. Animal models of scleroderma, cystic fibrosis and cirrhosis implicate involvement of Smad3 in the observed fibrosis. Additionally, inhibition of Smad3 by overexpression of the inhibitory Smad7 protein or by treatment with the small molecule, halofuginone, dramatically reduces responses in animal INHBB models of kidney, lung, liver and radiation-induced fibrosis. Small moleucule inhibitors of Smad3 may have tremendous clinical potential in the treatment of pathological fibrotic diseases. (Mad) and (Sma). The eight mammalian Smads are grouped into three subfamilies, the five receptor-activated Smads (R-Smads), the one common mediator Smad (Co-Smad) and the two inhibitory Smads (I-Smads) (Moustakas 2001; Derynck & Zhang 2003; Shi & Massague 2003). Of the R-Smads, Smads 2 and 3 signal for TGF- and activin, while Smads 1, 5 and 8 transduce signals from BMP ligands (Figure 1). For TGF- signalling, ligand binding to the constitutively active ser/thr kinase Type II receptor recruits the Type I receptor into the complex where it is phosphorylated by the Type II receptor resulting in its activation. Smads 2 and 3 are recruited to the activated Type I receptor by SARA (Smad anchor for receptor activation) and are directly phosphorylated by the Type I TGF- receptor kinase on the last two serines of a conserved SSXS motif located at the extreme carboxyl terminus of the R-Smads. The phosphorylated R-Smad is released from the receptor complex to form a heteromeric complex of two R-Smads and the co-Smad (Smad4), and this complex translocates to the nucleus where it can interact with various transcription factors and affect transcriptional responses. The I-Smads (Smad 6 for the BMP pathway and Smad7 for the TGF-/activin pathway) function by binding to the Type I receptor and preventing recruitment and phosphorylation of R-Smads. The I-Smads also bring the E3 ubiquitin ligases Smurfs 1 and 2 (Smad ubiquitination regulatory factors 1 and 2) to the Type I receptor which CGP60474 subsequently ubiquitinate and degrade the receptor. Open in a separate window Figure CGP60474 1 Overview of the transforming growth factor- (TGF-)/Smad-signalling pathway. At the cell surface, binding of TGF- ligand to the constitutively active Type II receptor recruits the Type I receptor into the complex where it is phosphorylated. The activated Type I receptor then phosphorylates Smad 2 or 3 3 which are recruited there by SARA (Smad anchor for receptor activation) at the C-terminal serines. Activin also phosphorylates Smads 2/3, while BMPs phosphorylate Smads 1/5/8. The receptor-activated Smads then complex with the common mediator Smad4 and this complex translocates to the nucleus where it regulates transcription of target genes and binds to a variety of transcription factors (TFs). Activation of R-Smads by Type I receptor kinases is inhibited by Smad6 for the BMP pathway and Smad7 for the TGF-/activin pathway. The E3 ubiquitin ligases Smurfs 1 and 2 which degrade the R-Smads also interact with Smads 6/7 and ubiquitinate the Type I receptors. The structural domains of the three Smad subfamilies are shown in Figure 2. R-Smads and the co-Smad contain conserved amino- and carboxyl-terminal MH (mad homology) 1 and 2 domains, respectively, which flank a more divergent proline-rich middle linker region. In I-Smads, the MH1 domain is replaced by a more divergent amino-terminus which does not bind to DNA. The MH1 domain mediates autoinhibition by its interaction with the MH2 domain preventing its phosphorylation in the absence of ligand. The MH1 domain can bind directly to DNA except in the case of the normal splice variant of Smad2 where a 30 amino acid insertion in this domain prevents DNA binding. The minimal Smad-binding element (SBE) contains only four base pairs, 5-AGAC-3, but there are reports of binding to other G/C-rich sequences. Protein kinase C phosphorylation of Smads 2 or 3 3 in this domain abrogates its DNA-binding activity. A nuclear localization signal which.
- Numbers 1BC1E demonstrate dramatic effect of heterogeneous relationships on clonal destiny: enhanced synergy, caused by substitution of an individual Ab, is enough to save an unfit lineage from extinction
- Shown are the proportions (%) of splenocyte-derived CD4+ (A), CD8+ (B), CD69+ (C) and CD4+/CD25+ (D) T cells in recipient C57BL/6 mice treated with the indicated immunosuppressive regimens
- No upsurge in QTc was observed, but just low dosages (3 relatively,4-DAP 10 mg or 20 mg) were administered
- Positive and negative signaling through SLAM receptors regulate synapse organization and thresholds of cytolysis
- Kandel R, Hartshorn KL