Bioinformatics analysis reveals CTSF suppresses tumor cell malignant phenotype and CD8 + T cell exhaustion by downregulating Bcl- 2 protein in the microenvironment of bladder cancer.

The tumor microenvironment (TME) plays an important role in tumor progression. However, the underlying mechanism of TME on bladder cancer (BLCA) progression remains largely unknown. Here, we obtained the BLCA-related gene expression motifs and the fraction of immune cells in TME of BLCA from GSE166947 dataset and TCGA database. Overlapping differentially expressed genes (DEGs) were screened, and the Spearman correlation coefficient between DEGs and the fraction of CD8 + T cell infiltration was calculated. Cathepsin F (CTSF) was screened as a key regulator of tumor cell malignant proliferation and CD8 + T cell infiltration in TME of BLCA. Moreover, CTSF was downregulated in BLCA tissues and cells. BLCA cells were transfected with CTSF shRNA (sh-CTSF) or CTSF lentiviral vector (LV-CTSF), and the supernatants were isolated as conditioned medium (CM) to culture CD8 + T cells. The results showed that overexpression of CTSF inhibited proliferation and induced apoptosis of BLCA cells, silencing CTSF decreased the levels of Granzyme B, TNF-α, IFN-γ, IL-2, and increased the percentage of PD-1 + Tim3 + CD8 + cells. Next, the interaction between CTSF and B-cell lymphoma-2 (Bcl-2) was predicted by STRING and verified by Co-IP analysis. Silencing Bcl-2 reversed CD8 + T cell exhaustion; overexpression of Bcl-2 counteracted CTSF-induced apoptosis of BLCA cells. Finally, T24 cells transfected with recombinant protein (rh-CTSF) were subcutaneously injected into mice to construct xenograft tumor models, and found that overexpression of CTSF inhibited BLCA tumor growth in vivo. In conclusion, CTSF inhibited CD8 + T cell exhaustion and tumor cell malignant proliferation by downregulating Bcl-2 protein level, thus inhibiting the progression of BLCA.