The Potential Role And Mechanism Of Cathepsin K In Non-small Cell Lung Cancer

Background: Lung cancer is the most common primary malignant tumor in the lungs.Because of its high incidence,late detection and poor prognosis,lung cancer has become one of the malignant tumors with the fastest increasing mortality rate and the greatest threat to human life health.Non-small cell lung cancer(NSCLC)is the most common type of lung cancer,accounting for 80 %-85 % of lung cancer.In the past few years,the use of immunotherapy has significantly improved the survival rate of NSCLC patients.However,the overall cure rate and survival rate for NSCLC patients remain very low,especially for those in the metastatic stage.Therefore,inhibiting the metastasis of NSCLC to hinder its development has become an important measure in the clinical treatment of lung cancer.Cathepsin K is a cysteine protease belonging to the papain family,mainly found in lysosomes,and is the most potent proteolytic enzyme in mammals.Cathepsin K is associated with a variety of human diseases,and has been thoroughly studied in osteoporosis.In addition,it is closely related to the occurrence and development of tumors.Studies have shown that Cathepsin K has a significant correlation with lung cancer postoperative survival,but there are few studies on its specific role in NSCLC.Therefore,through exploring the effect and mechanism of Cathepsin K on the proliferation,migration and invasion of NSCLC cells,in order to provide a reference for the targeted therapy of NSCLC.Methods: 1.Human embryonic lung fibroblasts MRC-5,NSCLC cells A549 and H1299 were cultured.Total proteins were extracted and the gray values of Cathepsin K and Tubulin/GAPDH in each group of cells were detected by Western Blot(WB).Expression levels of Cathepsin K in each group of cells were analyzed and calculated.2.Immunofluorescence(IF)was used to detect the localization and expression of Cathepsin K in MRC-5 and A549 cells.3.The A549 cells were transfected by liposome transfection,and the A549 group,the vector group,the Cathepsin K-over expression(CTSK-OE)group,the scramble group and the Cathepsin K-knockdown(CTSK-KD)group were set up for biobehavioral test: CCK-8 method was used to detect cell proliferation ability.Cell migrationability was detected by cell scratch repair experiment.Cell invasion ability was detected by Transwell invasion assay.4.WB assay was used to detect mTOR signaling pathway related proteins to explore the possible mechanism of Cathepsin K in NSCLC cells.Results: 1.Compared with human embryo lung fibroblasts MRC-5,the expression level of Cathepsin K protein in human NSCLC cells A549 was increased with statistical differences(p < 0.05),and the expression of Cathepsin K protein in H1299 was increased without statistical difference.2.In MRC-5 cells,Cathepsin K was discretely distributed in the cytoplasm,while in A549 cells Cathepsin K was expressed in large amounts and diffused throughout the cytoplasm.3.Compared with the A549 group and the vector group,the level of Cathepsin K mRNA was significantly increased(p < 0.001),and the protein in the CTSK-OE group was increased with statistical differences(p < 0.05).The proliferation,migration and invasion ability were enhanced with statistical differences(p < 0.05);Compared with the A549 group and the scramble group,the level of Cathepsin K protein in the CTSK-KD group was significantly reduced(p < 0.01).Reduced proliferation,migration and invasion ability with statistical differences(p < 0.05).4.Compared with the A549 group and the vector group,the p-mTOR/mTOR ratio increased with statistical differences in the CTSK-OE group(p < 0.05);Compared with the A549 group and the scramble group,the p-mTOR/mTOR ratio decreased in the CTSK-KD group with statistical differences(p <0.05).Conclusions: 1.Cathepsin K is highly expressed and diffuses cytoplasm in NSCLC cells.2.CTSK-OE promotes the proliferation,migration and invasion of NSCLC cells;CTSK-KD inhibits the proliferation,migration and invasion of NSCLC cells.3.CTSK-OE promotes the activation of the mTOR signaling pathway;CTSK-KD inhibits the activation of the mTOR signaling pathway.It is predicted that Cathepsin K participates in accelerating the progression of NSCLC by mediating the mTOR signaling pathway.The above shows that Cathepsin K may be a new target for NSCLC treatment.