Structure and Functional Analysis of Bone Morphogenetic Protein Receptor

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We have isolated several novel receptor Ser/Thr kinase cDNAs from a mouse MC3T3-E1 cells cDNA using oligonucleotide primers designed in the conserved sequence among TGF-beta family receoptors such as activin and TGF-beta type II receptors. One of them designated as mTFR11turned out to be a type I class of receptor that binds both BMP-2 and BMP-4. We constructed a mutantreceptor cDNA that predicts a truncated receptor lacking entire Ser/Thr kinase and confirmed that the dominant negative receptor inhibited both BMP-2 and BMP-4 in cultured osteoblastic cells and in early embryos. Moreover, we generated constitutively active form ofthe BMP receptor by a point mutation Gln to Asp in GS domain, which is believed to be essential for BMP signaling. We further confirmed that the mutant receptor transmits BMP-like signals independent of BMP ligands.Our effort is now focused on the identification of downstream factor that mediates BMP signaling. Therefore, we have screened a human cDNA library by yeast two-hybrid method using a cytoplasmic region of the BMP receptor as a bait. Successfully, we have isolated three cDNAs that encodes proteins that binds BMP receptor and function of the proteins in the signal transduction is currently investigated.