Elucidation of genetic abnormality and molecular pathogenesis of hereditary hemorrhagic telangiectasia

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Hereditary hemorrhagic telangiectasia(HHT) is an autosomal dominant disorder characterized by peripheral vascular dysplasia and recurrent hemorrhage from those lesions. Recent investigation has mapped one of the responsible genes for HHT to chromosome 9q33-q34 ; subsequently, nine different mutations have been identified in the endoglin gene, which encodes a transforming growth factor beta (TGF- beta) binding protein. We found a Japanese HHT family and identified a C to A mutation in exon 4 which changed an Ala^<160> codon(GCT) to an Asp^<160> codon(GAT). In order to reveal the mechanism by which vascular dysplasia was elicited in patients with having this mutation, TGF- beta signaling function was analyzed using recombinant normal and mutant endoglin proteins expressed in MCF7 cells. We confirmed that both normal and mutant endoglins were expressed on surface membranes of COS-1 cells at similar degrees by immunocytochemistry. Stable cell lines expressing normal or mutant endoglin were also established in MCF7 cells. When TGF- beta was added to these stable transformants, which were previously transfected with Smad2-flag plasmid, nuclear translocation of Smad2-flag protein was detected by immunofluoresense analysis in MCF7 cells expressing normal endoglin. Whereas, no immunofluoresense signal was observed in MCF7 cells expressing mutant endoglin. These results indicated several posibilities that mutant endoglin (1) lacks the binding actibity with TGF- beta, (2) can not present TGF- beta to type II receptor of TGF- beta or (3) fails to assemble to homodimer structure. These analyses are being undertaken now.