Abstract: Background and purpose: The transmembrane adaptor Csk-binding protein (CBP), a recently identified tyrosine kinase of the Src family, is implicated in various aspects of cancer cell biology. This study aimed to investigate the effect of the transmembrane protein CBP on the proliferation and apoptosis ability of A431 cells of human cutaneous squamous cell carcinoma and the implicated molecular mechanism. Methods: The CBP-EGFP lentiviral vector was constructed. A431 cells were transfected with CBP-EGFP lentiviral vector or negative-EGFP lentiviral vector, or remained untransfected. The transfection efficiency was detected by laser confocal microscope. After additional culture, the proliferation potential of A431 cells was assayed with CCK-8, and the apoptotic rate was assessed by flow cytometry (FCM). Lck, Csk and Fyn mRNA levels were detected by real-time fluorescence quantitative polymerase chain reaction (RTFQ-PCR) and their protein levels by Western blot. Results: The A431 cell line with overexpression of PAG was constructed successfully. CCK-8 results suggested that overexpression of CBP markedly inhibited cell growth, with statistically significant differences at 2-6 days between the groups (P<0.05). FCM showed that both the apoptotic rate and the death rate of the cells transfected with CBP-EGFP lentiviral vector were increased significantly compared to those of the cells transfected with negative-EGFP lentiviral vector or untransfected cells (P<0.001). RTFQ-PCR results showed that the Lck mRNA relative expression level of the cells transfected with CBP-EGFP lentiviral vector was significantly reduced (P<0.001), but Csk and Fyn mRNA expression levels were 1.6 times and 3.8 times as high as the untransfected cells, respectively (P<0.001). Western blot results showed that the Lck protein level was significantly decreased after transfection with CBP-EGFP lentiviral vector (P<0.001), whereas the Csk and Fyn protein levels were significantly increased (P<0.001). Conclusion: The ectopic expression of CBP might inhibit the proliferation or growth of A431 cells, induce cell apoptosis and accelerate cell death, which may be related to down-regulation of Lck and up-regulation of Csk and Fyn expression.

Key words: cutaneous squamous cell carcinoma, Csk-binding protein, proliferation, apoptosis