Western blot analysis of activation of endogenous Smad2 in HL-60 cells.

Protein prepared from HL-60 cells untreated or treated with 10 ng/mL TGF-β1 or 10 nM ATRA (A) or treated with both (B) for the indicated times, as described in “Materials and methods,” were directly subjected to immunoblotting with antibodies against Smad2 (Total Smad2) or C–terminally phosphorylated Smad2 (P-Smad2).