Isolation and characterization of a transforming growth factor-β Type II receptor cDNA from Xenopus laevis

Abstract

Transforming Growth Factor-β (TGF-β) and their receptors have been characterized from many organisms. Two TGF-β signaling receptors called Type I and II have been described for various ligands of the superfamily from organisms ranging from Drosophila to humans. In Xenopus laevis, TGF-β2 and 5 have been reported and presumably, play important roles during early development. Several Type I and type II receptors for many ligands of the TGF-β superfamily except TGF-β type II receptor (TβIIR), have been characterized in Xenopus laevis. A chemical cross linking experiment using iodinated TGF-β1 and -β5, revealed four specific binding proteins on XTC cells. In order to understand the TGF-β involvement during Xenopus development, a TGF-β type II receptor (XTβIIR) has been isolated from a XTC cDNA library. XTβIIR was a partial cDNA lacking a portion of the signal peptide. The sequence analysis and homology comparison with the human TβIIR revealed 67% amino acid similarity in the extra cellular domain, 60% similarity in the transmembrane domain and 87% similarity in the cytoplasmic kinase domain, suggesting that XTβIIR is a putative TGF-β type II receptor. In addition, the consensus amino acid motif for serine threonine receptor kinases was also present. Further, a dominant negative expression construct lacking the cytoplasmic kinase domain (engineered with the signal peptide from human TGF-β type II receptor), was able to abolish TGF-β mediated induction of a luciferase reporter plasmid, in a transient cell transfection assay. This substantiates the notion that XTβIIR cDNA can act as a receptor for TGF-β. RT-PCR analysis using RNA isolated from various developmental stages of Xenopus laevis revealed expression of this gene in all the early stages of development and in the adult organs, except in stages 46/48.