Knockdown of ErbB3 suppresses HRG-β1-induced EMT in SK-BR-3 cells. The cells were transfected with control (Ctrl) or ErbB3 siRNAs and treated with 25 ng/ml of HRG-β1 for 24 h. The expressions of ErbB3, E-cadherin, fibronectin, phospho-Smad2, and Snail were analyzed by western blotting. β-actin was reprobed as a loading control. Data represent the means ± SD of three independent experiments. *P < 0.05, **P < 0.01, significant difference.