Comparison of TrkB expression in HBE and A549 cells by western blot. HBE cells exhibited a minimal amount of TrkB and much higher level of TrkB was found in A549 cells (A). In the presence of BDNF, the phosphorylations of Pyk2 in Tyr402 and ERK were promoted in TrkB-positive A549 cells, which were not observed in TrkB-null HBE cells (A). Simultaneously, the invasive number of A549 cells was increased after BDNF treatment, while the invasion of HBE cells was not affected (B). Original magnification, all ×400. The experiments for cells were repeated at least three times.