Smad2 transduces common signals from receptor serine–threonine and tyrosine kinases

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Abstract
SMAD proteins mediate signals from receptor serine–threonine kinases (RSKs) of the TGF-β superfamily. We demonstrate here that HGF and EGF, which signal through RTKs, can also mediate SMAD-dependent reporter gene activation and induce rapid phosphorylation of endogenous SMAD proteins by kinase(s) downstream of MEK1. HGF induces phosphorylation and nuclear translocation of epitope-tagged Smad2 and a mutation that blocks TGF-β signaling also blocks HGF signal transduction. Smad2 may thus act as a common positive effector of TGF-β- and HGF-induced signals and serve to modulate cross talk between RTK and RSK signaling pathways.