Cathepsin B as a potential prognostic and therapeutic marker for human lung squamous cell carcinoma

Background: The lung squamous cell carcinoma survival rate is very poor despite multimodal treatment. It is urgent to discover novel candidate biomarkers for prognostic assessment and therapeutic targets to lung squamous cell carcinoma (SCC). Results: Herein a two-dimensional gel electrophoresis and ESI-Q-TOF MS/MS-based proteomic approach was used to identify differentially expressed proteins between lung SCC and adjacent normal tissues. 31 proteins with significant alteration were identified. These proteins were mainly involved in metabolism, calcium ion binding, signal transduction and so on. Cathepsin B (CTSB) was one of the most significantly altered proteins and was confirmed by western blotting. Immunohistochemistry showed the correlation between higher CTSB expression and lower survival rate. No statistically significant difference between CTSB-shRNA treated group and the controls was observed in tumor volume, tumor weight, proliferation and apoptosis. However, the CTSB-shRNA significantly inhibited tumor metastases and prolonged survival in LL/2 metastatic model. Moreover, CTSB, Shh and Ptch were up-regulated in patients with metastatic lung SCC, suggesting that hedgehog signaling might be activated in metastatic lung SCC which could affect the expression of CTSB that influence the invasive activity of lung SCC. Conclusions: These data suggested that CTSB might serve as a prognostic and therapeutic marker for lung SCC.