4087

SMAD2

JV18|JV18-1|MADH2|MADR2|hMAD-2|hSMAD2;SMAD family member 2;SMAD2;SMAD family member 2

MAD homolog 2|SMAD, mothers against DPP homolog 2|Sma- and Mad-related protein 2|mother against DPP homolog 2|mothers against decapentaplegic homolog 2

18q21.1

protein-coding

Count: SMAD2; 4087

BACKGROUND: pulmonary arterial hypertension (PAH) is a progressive disorder characterised by raised pulmonary artery pressures with pathological changes in small pulmonary arteries. Previous studies have shown that approximately 70% of familial PAH and also 11-40% of idiopathic PAH (IPAH) cases have mutations in the bone morphogenetic protein receptor type II (BMPR2) gene. In addition, mutations in the activin receptor-like kinase 1 (ALK1) gene have been reported in PAH patients. Since both the BMPR2 and ALK1 belonging to the transforming growth factor (TGF)-beta superfamily are known to predispose to PAH, mutations in other genes of the TGF-beta/BMP signalling pathways may also predispose to PAH. METHODS: We screened for mutations in ENDOGLIN(ENG), SMAD1, SMAD2, SMAD3, SMAD4, SMAD5, SMAD6 and SMAD8 genes, which are involved in the TGF-beta/BMP signallings, in 23 patients with IPAH who had no mutations in BMPR2 or ALK1. RESULTS: A nonsense mutation in SMAD8 designated c.606 C>A, p.C202X was identified in one patient. The father of this patient was also identified as having the same mutation. Functional analysis showed the truncated form of the SMAD8 C202X protein was not phosphorylated by constitutively active ALK3 and ALK1. The SMAD8 mutant was also unable to interact with SMAD4. The response to BMP was analysed using promoter-reporter activities with SMAD4 and/or ca-ALK3. The transcriptional activation of the SMAD8 mutant was inefficient compared with the SMAD8 wild type. CONCLUSION: We describe the first mutation in SMAD8 in a patient with IPAH. Our findings suggest the involvement of SMAD8 in the pathogenesis of PAH.

mutations in genes encoding members of the transforming growth factor (TGF)-beta superfamily have been identified in idiopathic forms of pulmonary arterial hypertension (PAH). The current study examined whether perturbations to the TGF-beta/Smad2,3 signalling axis occurred in a monocrotaline (MCT) rodent model of experimental PAH. expression of the TGF-beta signalling machinery was assessed in the lungs and kidneys of MCT-treated rodents with severe PAH by semi-quantitative reverse-transcription (RT)-PCR, real-time RT-PCR and immunoblotting. TGF-beta signalling was assessed in the lungs and in pulmonary artery smooth muscle cells (PASMC) from MCT-treated rodents by Smad2 phosphorylation, expression of the connective tissue growth factor gene, activation of the serpine promoter in a luciferase reporter system and by the induction of apoptosis. The expression of type1 TGF-beta receptor (TGFBR) activin-A receptor-like kinase1, TGFBR-2, TGFBR-3 (endoglin), Smad3 and Smad4; as well as TGF-beta signalling and TGF-beta-induced apoptosis, were dramatically reduced in the lungs and PASMC, but not the kidneys, of MCT-treated rodents that developed severe PAH. The current data indicate that the transforming growth factor-beta/Smad2,3 signalling axis is functionally impaired in monocrotaline-treated rodents with severe pulmonary arterial hypertension, underscoring the potential importance of transforming growth factor-beta/Smad2,3 signalling in the onset or development of pulmonary arterial hypertension.