Characterization of two monoclonal antibodies against the RON tyrosine kinase receptor.

RON is a receptor protein tyrosine kinase belonging to the hepatocyte growth factor (HGF) receptor family. Using Récepteur d'Origine Nantais (RON) transfected cell lines, Macrophage Stimulating Protein (MSP) was identified as the ligand of RON. RON is synthesized as a single chain precursor, which subsequently is cleaved to yield a disulfide-linked heterodimer, with a 40-kDa alpha chain and a 150-kDa beta chain. Activation of RON by MSP results in cell migration, shape change, and proliferation. The present work centers on the production and characterization of two monoclonal antibodies (MAbs) to RON called ID-1 and ID-2. Antibodies were generated by immunization of mice with Madin-Darby Canine Kidney (MDCK) cells expressing human RON (clone RE7). Both antibodies recognized the mature and precursor form of RON. The specificity of the anti-RON antibodies was confirmed using a hepatocarcinoma cell line HepG2 expressing both task MET and RON receptors. Specific immunoprecipitation with ID-1 and ID-2 or anti-MET antibody followed by Western blotting under reducing conditions with rabbit polyclonal antibodies against RON and MET showed that our anti-RON antibodies recognize specifically the RON receptor. Ligand binding experiments showed that both antibodies are able to block the binding of radiolabeled MSP to RON and showed also that the antibodies recognize two different epitopes in the molecule. The blocking of MSP binding to RON by the anti-RON antibodies was confirmed by inhibition of cell migration induced by MSP in HT-29-D4 cells. Significant immunostaining was not observed in any subpopulation of whole blood with either ID-1 or ID-2. We analyzed the expression of RON receptor in a number of human hematopoietic and nonhematopoietic cells lines by flow cytometry. We found a strong mean of fluorescence intensity (MFI) in colon adenocarcinoma cells SW620 and HT-29-D4, low MFI in SVK14 and HepG2 cells, and no immunostaining in melanoma, lymphoma, and leukemia cells. Immunohistochemistry revealed that RON was expressed in germinal centers of tonsil, in skin, small intestine, and colon. These antibodies defined RON as CDw136 during the last leucocyte typing VI.