Abstract: Background and purpose: Colorectal cancer is one of the most common gastrointestinal malignancies in China. Tissue kallikrein-related peptidase 8 (KLK8) is a serine protease. Its abnormal expression plays an important role in the occurrence and development of a variety of tumors, but its effect on apoptosis of colorectal cancer cells has rarely been reported. Epidermal growth factor (EGF) can inhibit cell apoptosis through a variety of mechanisms, and plays an important role in the occurrence and development of tumor. This study aimed to investigate the effect of KLK8 on apoptosis of colorectal cancer cells by regulating EGF and its mechanism. Methods: This study explored the relationship between KLK8 and clinicopathological features of colorectal cancer based on GEO public databases. KLK8 plasmid and KLK8 siRNA were used to construct stable KLK8 overexpression transfected and KLK8 knockdown cell lines using colorectal cancer cell lines RKO and SW480. Annexin Ⅴ-FITC/PI double staining was used to detect the apoptosis of colorectal cancer cells before and after KLK8 overexpression. Based on The Cancer Genome Atlas (TCGA) database, the “GO” gene set of gene set enrichment analysis (GSEA) was used to analyze the gene expression of KLK8 in colorectal cancer tissues with high and low expression. The effect of KLK8 overexpression on EGF protein level was detected by enzyme-linked immunosorbent assay (ELISA). siRNA of epidermal growth factor receptor (EGFR) was used to detect the apoptosis of RKO and SW480 cells before and after EGFR knockdown. Results: Using GEO microarray data sets GSE21815, GSE37182 and GSE71187, this study found that KLK8 expression was increased in colorectal cancer. Annexin Ⅴ-FITC/PI double staining flow cytometry showed that the apoptosis of RKO and SW480 cells with KLK8 overexpression decreased, while the apoptosis of KLK8 knockdown colorectal cancer cells increased. GSEA analysis showed that the high expression of KLK8 was closely related to the decomposition of extracellular matrix (ECM) and epidermal development. ELISA showed that the expression of EGF was significantly increased in the supernatant of RKO and SW480 cells overexpressing KLK8. Subsequently, knockdown of EGFR in RKO and SW480 cells overexpressing KLK8 resulted in increased apoptosis. Conclusion: KLK8 can inhibit the apoptosis of colorectal cancer cells. It may regulate the apoptosis of colorectal cancer cells by promoting the expression of EGF protein, so as to promote the progression of colorectal cancer.

Key words: Colorectal cancer, Tissue kallikrein-related peptidase 8, Epidermal growth factor, Apoptosis