RON forms a complex with the EpoR and is a substrate of Jak2. (A-B) COS cells were transfected with pSG5-based expression constructs encoding RONwt (A) or RONkd (B), together with Lyn, Tec, and Jak2. Cells were harvested without factor stimulation. (C) COS cells were transfected with RONwt, together with EpoR and Jak2, and were stimulated with EPO (5 U/mL) 10 minutes before cell harvest. (A-C) Two days after transfection, COS cells were lysed, and RON (A-B) or EpoR (C) was immunoprecipitated. Immunoprecipitated proteins were subjected to SDS-PAGE and immunoblotting. Size markers are indicated in kDa. Upper panels represent blots stained with antiphosphotyrosine antibodies (PY99), and lower panels represent blots stained with anti-RON, anti-EpoR, or both, when appropriate. Arrows indicate the positions of the expressed proteins.