MST1R/Ron, a HGF Receptor/MET-type protein kinase, mediates the biological activities of macrophage-stimulating protein (MSP), a multifunctional cytokine that regulates cell adhesion, motility, growth, and survival. The protein is a membrane-spanning, disulfide-linked heterodimer, which results from cleavage of a glycosylated precursor into 35-kD (alpha) and 150-kD (beta) subunits. Ligand binding results in tyrosine phosphorylation of the beta chain. In knockout studies, MST1R/RON (-/-) mice failed to survive past the periimplantation period. The MST1R/RON gene has been mapped to 3p21, a region of frequent deletion or mutation in small cell lung and renal carcinoma, and has been implicated in the progression of several epithelial cancers. Ron expression has been documented in many normal human tissues. ESTs have been isolated from several tissue libraries, including normal colon, mouth, prostate, and testis and cancerous colon, prostate, stomach, and uterus.