Molecular cloning of a mouse counterpart for human TGF-beta type I receptor

TGF-beta is a multifunctional polypeptide which is involved in the regulation of cell growth, differentiation, and immunomodulation. Its signaling receptors on the cell surface are postulated to be the type I (TGF beta RI) and type II receptors (TGF beta RII). Previously, TGF beta RII has been cloned and was found to be a receptor type serine/threonine kinase (RSK). In an attempt to isolate novel RSKs expressed in mouse ES cells, we obtained a clone designated as ESK2, which was very closely related to human TGF beta RI. The amino acid sequence of the intracellular domain is completely identical and the transmembrane domain is identical except for one residue. The extracellular domain is 90% homologous with a deletion and an insertion of four amino acid residues. ESK2 also binds to TGF-beta in the presence of TGF beta RII, indicating that ESK2 is the mouse counterpart for human TGF beta RI.