FIGURE 4.

ErbB receptors phosphorylation and dimerization in response to mechanical stretch in normal fetal type II cells. A and B, fetal type II cells were exposed to 5% cyclic stretch for the indicated periods of time. Collected proteins were immunoprecipitated with ErbB2 or ErbB3 receptor antibodies and immunoblotted with anti-phosphotyrosine antibody (Ptyr) to detect activation. Blots were reprobed with total ErbB receptor to control for protein loading. NRG (40 nm) added for 5 min was used as a positive control for receptor stimulation. Blots are representative of three independent experiments. *, p < 0.01 versus control. C, samples were processed as described above except that activation levels of ErbB4 were analyzed using an ErbB4 phosphospecific antibody. Blots were reprobed with total ErbB4 to control for protein loading and with EGFR antibody to investigate their interactions. NRG was used as a positive control. Results are from three independent experiments. *, p < 0.01 versus control; **, p < 0.001 versus control.