Fig. 1

ErbB3 is expressed on macrophages and neuregulin (NRG1) is expressed by tumor cells. a BAC macrophages, MDA-MB 231 breast cancer cells (231), and human umbilical vein endothelial cells (HUVEC) were analyzed using fluorescence-activated cell sorting (top) to determine surface ErbB3 expression. Cells were labeled with an ErbB3 blocking antibody reactive to both mouse and human ErbB3, with the corresponding IgG isotype and secondary antibody only as the experimental controls. Quantitation (bottom) is shown as the mean and SEM for the ErbB3 blocking antibody minus the mean signal of the isotype control from three independent experiments: ***p < 0.001, t test. b Quantitation of NRG1 mRNA expression by qRT-PCR. Values calculated as: (20-Delta cycle threshold (CT)). N = 3; ***p < 0.001, t test. c Detection of NRG1 protein expression by western blot, showing a doublet of bands at 32–34 kiloDalton (kDa) most strongly in MDA-MB 231 and BT549 cells