FIGURE 6.

ErbB4 is not activated in the absence of EGFR. A, fetal type II cells isolated from EGFR knock-out mice were subjected to 5% cyclic stretch for the indicated periods of time. Samples were immunoprecipitated with ErbB4 antibody and immunoblotted with ErbB4 phosphospecific antibody and total ErbB4. Results are from three separate experiments. B, upper panel demonstrates overexpression of ErbB4 protein in cells transfected with ErbB4 as compared with no transfection or transfection with an empty vector (EV). In lower panel fetal type II cells isolated from wild-type mice were transfected with a plasmid encoding ErbB4 gene and then exposed to mechanical stretch or NRG. Samples were immunoprecipitated with ErbB4 antibody and immunoblotted with ErbB4 phosphospecific antibody and total ErbB4. Results are from three separate experiments. *, p < 0.05 versus control. C, EGFR (−/−) type II cells were transfected by electroporation with a plasmid encoding ErbB4 gene and then exposed to similar experimental conditions as described in A. Representative blot shows no phosphorylation of ErbB4 by stretch or neuregulin. D, EGFR (−/−) type II cells transfected with ErbB4 were exposed to 5% cyclic stretch for 16 h. Samples were processed to analyze SP-C mRNA by qRT-PCR. Results are from three independent experiments.