TrkB is highly expressed in NSCLC and mediates BDNF-induced the activation of Pyk2 signaling and the invasion of A549 cells.
BACKGROUND
Aberrant regulation in the invasion of cancer cells is closely associated with their metastatic potentials. TrkB functions as a receptor tyrosine kinase and is considered to facilitate tumor metastasis. Pyk2 is a non-receptor tyrosine kinase and integrates signals in cell invasion. However, little is known about the expression of TrkB in NSCLC and whether Pyk2 is involved in TrkB-mediated invasion of A549 cells.


METHODS
The expression of TrkB was investigated in NSCLC by immunohistochemical staining. Both HBE and A549 cells were treated with BDNF. The expression of TrkB, Pyk2 and ERK phosphorylations were assessed by western blot. Besides, A549 cells were transfected with TrkB-siRNA or Pyk2-siRNA, or treated with ERK inhibitor where indicated. Transwell assay was performed to evaluate cell invasion.


RESULTS
40 cases (66.7%) of NSCLC were found higher expression of TrkB and patients with more TrkB expression had significant metastatic lymph nodes (p = 0.028). BDNF facilitated the invasion of A549 cells and the activations of Pyk2 in Tyr402 and ERK. However, the effects of BDNF were not observed in HBE cells with lower expression of TrkB. In addition, the increased Pyk2 and ERK activities induced by BDNF were significantly inhibited by blocking TrkB expression, so was the invasion of A549 cells. Knockdown studies revealed the essential role of Pyk2 for BDNF-induced cell invasion, since the invasion of A549 cells was abolished by Pyk2-siRNA. The application of ERK inhibitor also showed the suppressed ERK phosphorylation and cell invasion.


CONCLUSIONS
These data indicated that higher expression of TrkB in NSCLC was closely correlated with lymph node metastasis, and BDNF probably via TrkB/Pyk2/ERK promoted the invasion of A549 cells.
Center of Laboratory Technology and Experimental Medicine, China Medical University, Shenyang, China. labczs@mail.cmu.edu.cn
Siyang
S
Zhang
Dawei
D
Guo
Wenting
W
Luo
Qingfu
Q
Zhang
Ying
Y
Zhang
Chunyan
C
Li
Yao
Y
Lu
Zeshi
Z
Cui
Xueshan
X
Qiu
D019208:Brain-Derived Neurotrophic Factor / Q000096:biosynthesis*; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism*; D045744:Cell Line, Tumor; D020690:GTPase-Activating Proteins / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism*; D008207:Lymphatic Metastasis; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D034741:RNA, Small Interfering / Q000378:metabolism; D020813:Receptor, trkB / Q000096:biosynthesis*; D015398:Signal Transduction
D019208:Brain-Derived Neurotrophic Factor; D020690:GTPase-Activating Proteins; D034741:RNA, Small Interfering; D020813:Receptor, trkB; C410332:ASAP2 protein, human