Macrophage-derived CTSZ promotes prostate cancer progression via αVβ3 integrin-mediated activation of the AKT/FOXO1/JUNB signaling axis

BACKGROUND: The tumor microenvironment (TME), especially tumor-associated macrophages (TAMs), plays a critical role in prostate cancer (PCa) progression. Cathepsin Z (CTSZ) is a lysosomal protease implicated in various malignancies, but its specific function and mechanism within the PCa-associated TAMs remain largely unexplored. METHODS: We analyzed single-cell RNA sequencing data (GSE141445, GSE137829) to identify CTSZ expression patterns. Its role in macrophage polarization was validated by immunofluorescence co-localization in human PCa tissues and in vitro experiments (qPCR, Western blot, flow cytometry) using THP-1-derived macrophages overexpressing CTSZ. The effects of CTSZ-polarized macrophages on PCa cell (PC3) malignant behaviors (proliferation, migration, and invasion) were evaluated in vitro using EdU, CCK-8, colony formation, scratch, and Transwell assays, and their functions were assessed in vivo through orthotopic and lung metastasis models. RNA sequencing of treated tumor cells was conducted to identify downstream pathways. Mechanistic insights were obtained using CTSZ-neutralizing antibodies, recombinant CTSZ protein, and the αVβ3 integrin inhibitor Cilengitide (Cyclo), followed by western blot, co-immunoprecipitation, and dual-luciferase reporter assays. RESULTS: CTSZ was predominantly highly expressed in macrophages of PCa tissues. Overexpression of CTSZ in macrophages promoted M2 polarization, as evidenced by increased CD163 and decreased CD86/iNOS expression. Conditioned medium from OE-CTSZ macrophages significantly enhanced PCa cell proliferation, migration, and invasion, and promoted tumor growth and metastasis in mouse models. RNA sequencing revealed significant enrichment in the TNF signaling pathway and marked downregulation of JUNB. Mechanistically, macrophage-derived CTSZ bound to the αVβ3 integrin receptor on tumor cells, activating the AKT/FOXO1 signaling axis, leading to phosphorylation of FOXO1 and subsequent transcriptional repression of JUNB. These pro-tumorigenic effects were effectively reversed by either a CTSZ-neutralizing antibody or the αVβ3 inhibitor. CONCLUSION: Our study identifies a novel pathway in which macrophage-derived CTSZ promotes PCa progression by driving M2 macrophage polarization and directly activating the αVβ3/AKT/FOXO1 axis in tumor cells, ultimately leading to JUNB downregulation. Targeting the CTSZ/αVβ3 axis may represent a promising therapeutic strategy for PCa treatment.