DDR1a Promotes Tumor Invasion and Metastasis via the ZEB1/COL4 Axis in Bladder Cancer

Background: Although discoidin domain receptor 1 (DDR1) can enhance cell invasion in bladder cancer by regulating the ex-pression of epithelial-mesenchymal transition (EMT)-related molecules, the isoforms responsible for the phenomenon are still unknown. The purpose of our research was to identify the DDR1 isoform responsible for promoting bladder cancer progression, and potential mechanisms. Methods: The expression of DDR1a, DDR1b, COL4 (type IV collagen), MMP2 (matrix metalloproteinase-2), and EMT-related genes in bladder cancer cells or tissues was evaluated using western blotting, quantitative reverse transcription PCR (polymerase chain reaction), as well as immunohistochemistry. T24 cells (human bladder cancer cells) were transfected independently with DDR1 inhibitor, DDR1 overexpressed plasmid, and siRNA-ZEB1 (zinc-finger E-box binding homeobox 1). Then, the cell prolif-eration, as well as migration and invasion were examined by cell counting kit-8, and Transwell assays, respectively. Finally, an in vivo tumorigenic experiment was carried out to explore the actions of DDR1a in tumor invasion and metastasis. Results: In comparison with the SV-HUC-1 cells (human ureteral epithelial immortalized cells), DDR1a, COL4, vimentin, E-cadherin, and ZEB1 were overexpressed in T24 cells, while DDR1b expression was not significantly different between the two cell lines. Immunohistochemistry revealed that COL4 was significantly overexpressed in tumor tissues. In the background of DDR1 inhibition, the expression of COL4, MMP2, E-cadherin, Slug, and ZEB1 decreased significantly. DDR1a overexpression promoted bladder cancer cell proliferation. Meanwhile, ZEB1 silencing reversed the effect of DDR1a overexpression with respect to cell growth. The in vivo tumorigenic assay yielded results similar to those obtained in in vitro experiments. Conclusions: DDR1a promotes invasion and metastasis in bladder cancer via regulating the ZEB1/COL4 axis.