Fig. 5. SRF interacts with Smad2. (A) 293T cells were transfected with HA-tagged SRF and Flag-tagged Smad2 with or without constitutively active Activin type-I receptor (ALK4^*). Cell lysates were immunoprecipitated (IP) with anti-Flag antibody, followed by immunoblotting (IB) with anti-HA antibody to detect Smad-bound SRF. (B,C) Interaction of endogenous SRF and Smad2 was examined in Mv1Lu and HeLa cells. (B) Mv1Lu cells were left untreated or treated with Activin A for 1 hour. Cell lysates were subjected to IP with anti-SRF rabbit polyclonal antibody, followed by IB with an anti-Smad2 mouse monoclonal antibody. (C) HeLa cell lysates were subjected to IP with anti-SRF antibody, followed by IB with anti-Smad2 antibody. This was repeated in reverse order. (D) Schematic of Smad2 truncation mutants. (E) Flag-tagged Smad2 deletion mutants were transfected into 293T cells together with GST-SRF. Cell lysates were pulled down by glutathione-agarose beads and then immunoblotted with antiFlag antibody.