ARTICLE IN PRESS

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LUNG-3075; No. of Pages 6 

ARTICLE IN PRESS 

Lung Cancer xxx (2008) xxx–xxx 

Contents lists available at ScienceDirect 

Lung Cancer 

journal homepage: www.elsevier.com/locate/lungcan 

Up-regulation of proline-rich tyrosine kinase 2 in non-small 

cell lung cancer 

Siyang Zhang, Xueshan Qiu ∗ , Yumei Gu, Enhua Wang 

Department of Pathology, College of Basic Medical Sciences, China Medical University, and Department of Pathology, 

the First Affiliated Hospital of China Medical University, Shenyang, China 

article info 

Article history: 

Received 11 October 2007 

Received in revised form 6 April 2008 

Accepted 5 May 2008 

Keywords: 

PYK2 

Expression and activation 

NSCLC 

Metastasis 

ERK1/2 

1. Introduction 

abstract 

Lung cancer is the leading cause of death among the malignant 

tumors worldwide, and the incidence of lung cancer is increasing. 

Non-small cell lung cancer (NSCLC) is the primary histological classification 

of lung cancer, and the prognosis of patients with NSCLC 

principally correlates with tumor metastasis, which is regulated by 

associated gene expression. More information should be gathered 

on the research of prometastatic genes. 

Proline-rich tyrosine kinase 2 (PYK2) is a member of FAK family, 

functions as an effector of multiple cytokines involved in the 

regulation of fundamental cellular activities, such as cell proliferation 

[1], differentiation [2], and motility [3]. PYK2 is up-regulated 

∗ Corresponding author at: Department of Pathology, College of Basic Medical 

Sciences, China Medical University, and Department of Pathology, the First Affiliated 

Hospital of China Medical University, Heping Ward, North 2nd Road 92, Shenyang, 

China. Tel.: +86 2423261638; fax: +86 2423265539. 

E-mail address: qiuxueshan pathology@126.com (X. Qiu). 

0169-5002/$ – see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. 

doi:10.1016/j.lungcan.2008.05.008 

Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor tyrosine kinase, plays different roles in intracellular 

signaling pathways, that regulates a number of biological processes, such as cell proliferation, 

differentiation, adhesion and migration, which have been shown to correlate with tumor development 

and aggression. However, the involvement of PYK2 in human non-small cell lung cancer (NSCLC) has not 

yet been determined. 

In the present study, 90 patients with NSCLC (represented by adenocarcinoma and squamous cell 

carcinoma) were included retrospectively. NSCLC tissues were detected for the expression of PYK2 by 

immunohistochemistry. Correlation between the expression of PYK2 with the clinicopathological characteristics 

was analyzed. There were 64% (58 out of 90) of NSCLC patients with higher level of PYK2. Higher 

expression of PYK2 was significantly correlated with lymph node metastasis (node positive versus node 

negative, p = 0.007). Patients with higher expression of PYK2 had advanced stage of NSCLCs (I + II versus 

III + IV, p = 0.012). Protein level of PYK2 was also examined in 30 of these tumorous samples and matched 

non-tumorous counterparts by western blotting. PYK2 was apparently up-regulated in NSCLC tissues 

(tumor versus non-tumor, p = 0.000). In the cell studies, extensive expression and activation of PYK2 were 

both found in higher metastatic BE1 cells. The activity of ERK1/2 in BE1 cells appeared extremely high 

as well. In conclusion, our results demonstrated that PYK2 is up-regulated in NSCLCs, and the higher 

expression and activation of PYK2 may play a role in modulating the activity of ERK1/2, and lead to the 

progression of NSCLC. 

© 2008 Elsevier Ireland Ltd. All rights reserved. 

in different primary human tumors, including brain [4] and liver 

[5] tumors. Hepatocellular carcinoma patients with higher level of 

PYK2 had larger tumor size and advanced Edmonson grading [5], 

and PYK2 overexpression was found in invasive tumor cells and 

lung metastatic nodules by animal studies. The overexpression of 

PYK2 might play an important role in the progression of malignant 

tumors. 

PYK2 is a non-receptor tyrosine kinase, and also an integrator 

for the signaling events that regulate tumorous processes of 

anti-apoptosis [6], adhesion [7] and especially migration [8]. PYK2 

mediated biological functions are performed mainly by phosphorylation. 

PYK2 is rapidly tyrosine phosphorylated in response to 

various extracellular signals acting via different post-receptor pathways 

[9]. The tyrosine 402 (Tyr402) of PYK2 serves as the primary 

autophosphorylation site that is essential for PYK2 activation and 

function [10,11]. When activated by a number of cytokines, PYK2 

leads to the activation of various downstream signaling molecules, 

such as ERK/MAPK [12–14], which results in the differential regulation 

of cell characteristics in different cell lines. The activity of 

PYK2 in Tyr402 may play an important role in up-regulating the 

Please cite this article in press as: Zhang S, et al., Up-regulation of proline-rich tyrosine kinase 2 in non-small cell lung cancer, Lung Cancer (2008), 

doi:10.1016/j.lungcan.2008.05.008

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2 S. Zhang et al. / Lung Cancer xxx (2008) xxx–xxx 

Table 1 

Clinicopathological characteristics of 90 NSCLC tumors and PYK2 expression by 

immunohistochemistry 

Clinicopathological characteristics Cases 

(n = 90) 

Higher 

expression 

(n = 58) 

Lower 

expression 

(n = 32) 

p-Value 

Tumor size and invasiveness 

T1+T2 47 34 13 0.102 

T3+T4 

Histological type 

43 24 19 

Sq 48 27 21 0.083 

Ad 

Differentiation 

42 31 11 

Well 37 25 12 0.605 

Poor–moderate 

Stage 

53 33 20 

I + II 35 17 18 0.012 * 

III + IV 

Lymph node status 

55 41 14 

+ 48 37 11 0.007 ** 

− 42 21 21 

PYK2 expression: * significant difference between early (I + II) and advanced (III + IV) 

stage of NSCLCs; ** significant difference between tumors with positive (+) and negative 

(−) nodes. 

migratory ability of tumor cells, which is supported by the high 

activity of Tyr402 found in the progression of breast tumor cells to 

have invasive and metastatic phenotype [15]. 

However, despite the increasing emphasis on PYK2 in human 

tumors, whether it positively participates in primary human nonsmall 

cell lung cancer has not yet been determined. The aim of 

this study is to investigate the expression and clinical significance 

of PYK2 in 90 surgically resected NSCLCs with different clinicopathological 

features, and the association of PYK2 expression and 

activation with ERK1/2 activity and metastatic potential of NSCLC 

cell lines. 

2. Materials and methods 

2.1. Tissue samples and patients 

A total of 90 cases of non-small cell lung tumors were retrospective 

database from the Pathology Department of China 

Medical University. All of the enrolled patients underwent curative 

surgical resection without having chemotherapy or radiation therapy. 

Formalin-fixed paraffin-embedded sections of tumor obtained 

from surgical samples were stained routinely with hematoxylin and 

eosin (H&E), and reviewed by two senior pathologists in order to 

determine the histological type and stage, according to the WHO 

classification of lung and pleural tumors (2004) and the TNM staging 

system (1997). 30 cases (included in the 90 cases) of tumor 

and paired non-tumorous portion (distant from the primary tumor) 

of the same case were quickly frozen in deep freeze refrigerator 

until protein extraction. Lymph node status was determined by 

routine pathological examination of dissected pulmonary hilar and 

mediastinal and intrapulmonary lymph nodes. Clinicopathological 

information of the patients about tumor size, histological type, differentiation, 

stage and lymph node metastasis was obtained from 

patient records, and summarized in Table 1. 

2.2. Immunohistochemistry 

90 paraffin sections of tumor were deparaffinized and rehydrated 

routinely. The slides were then heated in an autoclave 

sterilizer for 2 min in 0.1 mol/L Tris–HCl buffer at pH 10. The sections 

were incubated overnight with primary rabbit polyclonal antibody 

detecting PYK2 (1:100 dilution, sc-9019) (Santa Cruz Biotechnology), 

following 3% H 2O 2 and 5% rabbit serum treatment at 37 ◦ C 

for 1 h. After which they were incubated with second antibody and 

SP complex for 30 min (SP kit-9710), lastly they were visualized 

with DAB (DAB kit-0031) (both from Maixin Biotechnology). Hepatocellular 

carcinoma tissues were used as positive controls for 

PYK2, and negative controls were prepared by non-immune rabbit 

IgG at the same dilution as for the primary antibody. All the 

immunoreactions were separately evaluated by two senior pathologists. 

Brown particles appearing in cytoplasm was as regarded 

as positive cells. The intensity of PYK2 immunostaining (1 = weak, 

2 = moderate, and 3 = intense) and the percentage of positive tumor 

cells (0% = negative, 1–50% = 1, 51–75% = 2, ≥76% = 3) were assessed 

in at least 5 high power fields (×400 magnification). The scores of 

each tumorous sample were multiplied to give a final score of 0, 1, 

2, 3, 4, 6 or 9, and the tumors were finally determined as negative: 

score 0; lower expression: score ≤4; or higher expression: score 

≥6. 

2.3. Western blotting 

Frozen tissues (including tumor and non-tumorous portion) 

or cells were washed twice with ice-cold phosphate-buffered 

saline (PBS), homogenized on ice in 10 volumes (w/v) of lysis 

buffer containing 20 mM Tris–HCl, 1 mM EDTA, 50 mM NaCl, 

50 mM NaF, 1 mM Na 3VO 4, 1% Triton-X100, 1 mM PMSF and phosphatase 

inhibitor using a homogenizer (Heidoph, DLA × 900). The 

homogenate was centrifuged at 15000 rpm for 30 min at 4 ◦ C. The 

supernatant was collected and stored at −70 ◦ C. Protein content 

was determined by the BCA assay (BCA protein assay kit-23227, 

Pierce Biotechnology). From each sample preparation, 80 �goftotal 

protein was separated by 8% SDS-PAGE and then transferred to 

PVDF blotting membranes. The total protein extracts were analyzed 

by immunoblotting with indicated antibodies following SDS-PAGE 

analysis. Immunoblots were performed using rabbit polyclonal 

primary antibodies specific for PYK2, p-Tyr402 and �-actin (a 

housekeeping protein used as a loading control to assure equal 

amounts of protein in all lanes), and mouse monoclonal antibody 

for p-ERK1/2. After blocking nonspecific binding with 5% 

BSA in TBS (pH 7.5) containing 0.05% Tween-20 (TBST), primary 

antibodies were incubated on the membranes for PYK2 (1:300, 

sc-9019), p-Tyr402 (1:200, sc-9023), p-ERK1/2 (1:200, sc-7383) 

and �-actin (1:200, sc-1616-R) (all from Santa Cruz Biotechnology) 

overnight at 4 ◦ C in TBST. Following three times washes 

in TBST, the membranes were incubated for 2 h at 37 ◦ C with 

secondary goat anti-rabbit IgG antibodies (1:2000, ZDR-5306) 

and goat anti-mouse IgG antibody (1:2000, ZDR-5307) labeled 

with horseradish peroxidase (all from Zhongshan Biotechnology). 

Immunoreactive straps were identified using the DAB system (DAB 

kit-0031, Maixin Biotechnology), as directed by the manufacturer. 

Specific bands for PYK2, p-Tyr402, p-ERK1/2 and �-actin were identified 

by prestained protein molecular weight marker (SM0441, 

MBI Fermentas). The EC3 Imaging System (UVP Inc.) was used 

to catch up the specific bands, and the optical density of each 

band was measured using an Image J software. The ratio between 

the optical density of interest proteins and �-actin of the same 

sample was calculated as relative content and expressed graphically. 

2.4. Cell lines and culture 

Lung PG (pulmonary giant) cell lines including the higher 

metastatic BE1 cells and the lower metastatic LH7 cells [16] were 


doi:10.1016/j.lungcan.2008.05.008

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S. Zhang et al. / Lung Cancer xxx (2008) xxx–xxx 3 

Fig. 1. PYK2 expression by immunohistochemistry. (A) PYK2 immunostaining in the ciliated epithelial cells of bronchus. (B) PYK2 expression in the alveolar cells. (C) PYK2 

immunoreactivity in the cytoplasm of serous cells. (D) PYK2 expression in the endothelial cells of neoplastic stroma. PYK2 immunostaining in lung squamous cell carcinoma 

with (E) and without (F) positive nodes. PYK2 expression in lung adenocarcinoma with (G) and without (H) node metastasis. It was shown that PYK2 expression was correlated 

with lymph node status, but not with histological type. Negative controls were prepared by non-immune rabbit IgG at the same dilution as for the primary antibody in normal 

(I) and tumor sample (J), respectively. Original magnification: all ×400. 

kind gifts from Prof. Jie Zheng (Department of Pathology, Peking 

University, China). Human bronchial epithelial cells (HBE) and 

lung adenocarcinoma A549 cells were conserved in our department. 

BE1, LH7 and HBE cells were cultured in RPMI1640 and 

A549 was in DMEM (both from Gibco, Invitrogen Corporation) 

supplemented with 10% FCS, 100 U/ml penicillin, 100 U/ml streptomycin, 

glutamine, and NaHCO 3, in incubator with 5% CO 2. 

Cells were cultured to subconfluence until protein extraction. 

The experiments for each cell line were repeated at least three 

times. 

Statistical analysis. SPSS for windows 13.0 statistical analysis 

soft was applied to complete data processing. 2 -Test was 

applied to analyze the correlation between the expression of PYK2 

and clinicopathological characteristics for the results of immunohistochemistry, 

paired-samples t-test was used to analyze the 

significant difference of PYK2 expression between tumor and normal, 

and independent-samples t-test was used to evaluate the 

difference of optical density in the neoplastic tissues with different 

node status as well as the lung cell lines with different 

metastatic potentials. Results were considered statistically significant 

at p < 0.05. 

3. Results 

3.1. PYK2 expression and localization in NSCLCs by 

immunohistochemistry 

PYK2 immunoreactivity was detected in both normal and 

tumorous lung cells. In normal lung tissues, PYK2 expression was 

observed in ciliated epithelial cells, serous cells of the submucosal 

glands and alveolar cells, as shown in Fig. 1A–C. 

PYK2 immunostaining was observed in every neoplastic tissue. 

We considered that 58 of the NSCLCs (64%) were higher expression 

(scores of 6 or 9); 32 cases (36%) were lower expression (scores 

of 0, 1, 2, 3 or 4), as described above in Materials and methods. 

PYK2 was also detected in the endothelial cells of vessels within 

the neoplastic stroma (Fig. 1D). 

In addition, as shown in Table 1, no significant difference of PYK2 

expression was found between the two most represented histological 

types of lung cancer (Ad versus Sq, p = 0.083). Examples of PYK2 

immunostaining in adenocarcinoma and squamous cell carcinoma 

are shown in Fig. 1E–H. The negative controls were prepared by 

non-immune rabbit IgG at the same dilution as for the primary 

Fig. 2. (A) Expression of PYPK2 by western blotting in matched tumorous (T) and non-tumorous (N) tissues from 8 of 30 NSCLC patients, and 4 of which were accompanied 

with lymph node metastasis (the lower panel). Band intensities indicate significant PYK2 up-regulation in tumorous in comparison with the non-tumorous tissue of the same 

patient. Furthermore, patients with positive nodes expressed higher level of PYK2 in tumor. �-Actin was used as a loading control to assure equal amounts of protein in all 

lanes. (B) The ratio between the optical density of PYK2 and �-actin of the same patient was calculated and expressed graphically. The significant difference of PYK2 expression 

between tumorous (T) and non-tumorous (N) tissues as well as neoplastic samples with positive and negative nodes were analyzed statistically. PYK2 immunoreactivity is 

greater in neoplastic tissues (p = 0.000) and cases with positive nodes (p = 0.018). 


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Fig. 3. PYK2, p-Tyr402, p-ERK1/2 level in lung cell lines with different metastatic potentials by Western blotting analysis. The ratio between the optical density of specific 

bands and �-actin of the same cells was calculated (i.e. O.D.P/a, O.D.p-Y/a and O.D.p-E/a) and expressed graphically. (A) Human bronchial epithelial (HBE) cells expressed 

the minimal level of PYK2, and the higher metastatic BE1 cells showed much higher level of PYK2 compared with the lower metastatic LH7 and A549 cells. (B) p-Tyr402 is 

scarcely detected in HBE cells, and BE1 cells showed higher level of p-Tyr402 compared with LH7 and A549 cells. (C) HBE cells showed a basal level of p-ERK1/2, and BE1 

cells exhibited higher level of p-ERK1/2 than LH7 and A549 cells. �-Actin was used as a loading control to assure equal amounts of protein in all lanes. The experiments for 

each cell line were repeated at least three times. The results are represented as mean ± S.D. of three independent experiments. 

antibody, and results for normal and tumor samples were shown 

in Fig. 1I and J. 

3.2. Comparative analysis and clinicopathological correlation 

As shown in Table 1, no statistical difference was found between 

the higher PYK2 expression and the characteristics of tumor size 

(T1 + T2 versus T3 + T4, p = 0.102) as well as differentiation (high 

versus low, p = 0.605). However, patients with higher PYK2 expression 

had advanced stage of NSCLC (I + II versus III + IV, p = 0.012). 

In addition to promotion of cell proliferation, PYK2 also increased 

the tumor cells invasiveness and migration [20]. Therefore, the 

association between PYK2 expression revealed by immunohistochemistry 

and the presence of lymph node metastasis at the 

time of resection was analyzed statistically. Comparison of PYK2 

expression was made between the NSCLCs with different lymph 

node status. PYK2 immunoreactivity was stronger in the NSCLCs 

with lymph node metastasis compared with the node negative 

cases, with moderate–strong immunostaining. Immunohistochemistry 

showed a statistically significant correlation between higher 

protein expression and a positive node (p = 0.007). 

3.3. PYK2 expression in NSCLCs by Western blotting 

Western blotting was used to evaluate PYK2 expression in 30 

NSCLCs and paired non-tumorous lung tissues distant from the 

primary tumor of the same case. The increased PYK2 expression 

was found in 27 NSCLC samples in comparison with the nontumorous 

counterparts. The western blotting of eight samples is 

shown in Fig. 2A, and the optical density of the tumorous (T) and 

non-tumorous (N) tissues of the same patient was measured and 

expressed graphically (Fig. 2B). Previous researches have demonstrated 

that PYK2 overexpression enhanced cell mobility [8], thus 

comparison of PYK2 expression was made between NSCLCs with 

and without lymph node metastasis statistically. PYK2 expression 

was significant higher in node-positive NSCLCs (Fig. 2B). 

3.4. PYK2 expression and activity in lung cell lines 

As we expected, expression of PYK2 was found quite weak 

in human bronchial epithelial (HBE) cells, and higher metastatic 

BE1 cells have intense PYK2 expression compared with the lower 

metastatic LH7 and A549 cells (Fig. 3A). PYK2 activity is regulated by 

tyrosine phosphorylation [17], especially the autophosphorylation 

site Tyr402, so the phosphorylation status of Tyr402 measured by 

western blotting was examined to evaluate the activation and possible 

function of PYK2 in different lung cell lines. The p-Tyr402 was 

detected in all lung tumor cell lines examined, however scarcely in 

HBE cells. Moreover, the level of p-Tyr402 in the NSCLC cell lines 

was also various, with a significant difference between BE1 and LH7 

or A549 cells, and much stronger p-Tyr402 was observed in BE1 

cells, as shown in Fig. 3B. These results suggest that up-regulation 

of PYK2 and increased activity are correlated with the metastatic 

potential of NSCLC cell lines. 

3.5. ERK1/2 activation in lung cell lines 

ERK1/2 activity linked to the phosphorylated PYK2 has been 

demonstrated previously [7], thus to further investigate the correlation 

between the activation of ERK1/2 and metastatic potential 

of lung tumor, we examined the p-ERK1/2 in various lung cell lines. 

Elevated p-ERK1/2 was associated with the higher metastatic BE1 

cells, similar to the intense p-Tyr402, while the p-ERK1/2 was also 

quite low in PYK2-inactive HBE cells, as shown in Fig. 3C. These 

findings provide a possibility that PYK2/ERK signaling plays a role 

in promoting tumor cells more aggressive in NSCLC. 

4. Discussion 

PYK2 is a non-receptor tyrosine kinase, mediates various biological 

processes, such as cell proliferation [18] and migration [19], 

all of which are critical to tumorigenesis, invasion and metastasis, 

and suggest a significant role of PYK2 in the development and 

progression of cancer [20]. PYK2 expression is up-regulated in a 

variety of human tumors including liver and brain tumors. Aiming 

at interfering PYK2 expression or blocking PYK2 activation may be 

helpful in the progression of effective anticancer therapies. Recent 

researches have been shown that inhibited PYK2 activity was correlated 

with the inactivation of ERK1/2, and reduced the adhesive 

ability of prostate cancer cells [7]. 

This study evaluated PYK2 expression in NSCLCs, with regard 

to the tumor size, histological type, differentiation, stage and 

lymph node status of NSCLCs, to determine the clinical significance 

of PYK2 for the advanced NSCLCs. We examined 90 tumors 

by means of immunohistochemistry, 30 of which were also analyzed 

by western blotting, and found a statistical evidence of 

PYK2 up-regulation in NSCLCs. Weak–moderate PYK2 immunostaining 

was observed in ciliated epithelial cells in bronchus, the 

serous cells of the submucosal glands, as well as normal alveoli. 

While PYK2 immunoreactivity was detected extensively in every 

neoplastic tissue, supporting the potential role in tumorigenesis, 

promoting proliferation and survival of tumor cells [5]. We also 

found that PYK2 overexpression was common in NSCLCs, regardless 

of the histological type and differentiation. However, patients 

with higher PYK2 expression had a significant metastatic phenotype. 

The immunohistochemical observations may be further supported 

by our semi-quantitative western blotting evaluations of 


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PYK2 expression in 30 tumorous and paired non-tumorous counterparts. 

PYK2 expression were significantly higher in the neoplastic 

than the non-neoplastic tissues, which was consistent with previous 

studies of PYK2 overexpression in human malignant tumors [4]. 

Moreover, tumorous samples in which PYK2 higher expression was 

determined by western blotting came from patients with lymph 

node metastasis at the time of resection. Taken together, these findings 

suggest that PYK2 up-regulation stimulated cell proliferation, 

and migration as well, possibly by attenuating the adhesive ability 

of tumor cells in NSCLCs [6]. Despite that further research is 

required, these results suggest a crucial role of PYK2 in affecting 

tumorigenesis and aggression of NSCLC. 

Studies have been reported that PYK2 activity especially in 

Tyr402 in human malignant tumors has been correlated with 

outgrowth and invasiveness of breast cancer cells [9], and active 

ERK1/2 was included in LPA-induced PC12 cell migration mediated 

by PYK2 [3]. So we also examined the expression and p-Tyr402 

of PYK2 and the p-ERK1/2 in the human bronchial epithelial cells 

(HBE) and different NSCLC cell lines. HBE cells as normal control, 

lower metastatic A549 cells as we confirmed previously, as 

well as lower metastatic LH7 cells and higher metastatic BE1 cells 

were included in this study. We found that the expression of PYK2 

was quite weak in HBE cells, while the higher metastatic BE1 

cells expressed the maximal level of PYK2, compared with the 

lower metastatic LH7 and A549 cells. So it is acceptable that PYK2 

overexpression stimulated cell proliferation and more aggressive. 

Furthermore, PYK2 up-regulation was accompanied by the increasing 

PYK2 activity as evaluated by the level of p-Tyr402 [21], and 

ERK1/2 also proved to be more activated in higher metastatic BE1 

cells. However, HBE cells expressed a low level of PYK2 with a 

scarcely detectable p-Tyr402 and a low p-ERK1/2. It was further 

indicated that PYK2 expression and activation might play a role in 

promoting a more malignant phenotype by regulating the activity 

of ERK1/2 in NSCLC. 

Previous studies have been shown that PYK2 was essential for 

the pulmonary vascular endothelial cell spreading and migration 

[22], besides PYK2 kinase activity enhanced migration of endothelial 

cells [23], which resulted in vasculogenesis and angiogenesis. 

We also found PYK2 immunostaining in the endothelial cells of neoplastic 

stroma in several cases of NSCLCs, which showed lymph 

node positive. This pattern of PYK2 expression may indicate the 

invasive and metastatic malignant phenotype of NSCLCs. 

Therefore, the PYK2 mediated signaling pathway may become a 

promising target for tumor inhibition. It has recently been shown 

that inhibiting PYK2 activity by the expression of kinase inactive 

PYK2 mutant attenuated the adhesive ability of prostate cancer 

cells [7]. The similar report has been found in glioma cells, in 

which the suppression of PYK2 activity within the FERM domain 

reduced the capacity of PYK2 to stimulate glioma cell migration 

[24]. As far as lung cancer is concerned, PYK2 appears to be the key 

interactive effector of Src in mediating the survival signals in lung 

adenocarcinoma cells upon detachment, which may contribute to 

the metastasis of malignant lung tumors [6]. Moreover, inhibition 

of PYK2 expression by siRNA, attenuated anchorage-independent 

survival and proliferation of SCLC cells [25]. 

In conclusion, our study demonstrates the facts that upregulation 

of PYK2 is common in NSCLC tissues, increased 

expression and activity of PYK2 in lung cell lines are correlated 

with higher metastatic potential, possibly by the activation of 

ERK1/2. The detection of higher PYK2 expression by western blotting 

in 27 of the 30 NSCLCs examined suggests that PYK2 may 

play a role in promoting malignant transformation, which is crucial 

to the tumorigenesis of NSCLC. The suppression of PYK2 expression 

and phosphorylation in Tyr402 may provide a helpful target 

for inhibitory therapies of metastasis in NSCLC. The regulatory 


S. Zhang et al. / Lung Cancer xxx (2008) xxx–xxx 5 

significance of PYK2 in NSCLC therefore requires further investigation. 

Conflict of interest 

None declared. 

Acknowledgements 

We are grateful to Prof. Jie Zheng for offering the cell lines used 

in this study. We also thank teacher Chengyao Xie and Nan Liu for 

technical assistance, and the members of our department for useful 

suggestions. 

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