SPOP downregulation promotes bladder cancer progression based on cancer cell-macrophage crosstalk via STAT3/CCL2/IL-6 axis and is regulated by VEZF1.

Cancer cells are intimately intertwined with tumor microenvironment (TME), fostering a symbiotic relationship propelling cancer progression. However, the interaction between cancer cells and tumor-associated macrophages (TAMs) in urothelial bladder cancer (UBC) remains poorly understood. UBC cell lines (5637, T24 and SW780), along with a monocytic cell line (U937) capable of differentiating into macrophage, were used in a co-culture system for cell proliferation and stemness by MTT, sphere formation assays. VEZF1/SPOP/STAT3/CCL2/ IL-6 axis was determined by luciferase reporter, ChIP, RNA-seq, co-IP, ubiquitination, RT-qPCR array and ELISA analyses. We observed the frequent downregulation of SPOP, an E3 ubiquitin ligase, was positively associated with tumor progression and TAM infiltration in UBC patients and T24 xenografts. Cancer cell-TAM crosstalk promoting tumor aggressiveness was demonstrated dependent on SPOP deficiency: 1) In UBC cells, STAT3 was identified as a novel substrate of SPOP, and SPOP deficiency increased STAT3 protein stability, elevated chemokine CCL2 secretion, which induced chemotaxis and M2 polarization of macrophage; 2) In co-cultured macrophages, IL-6 secretion enhanced UBC cell proliferation and stemness. Additionally, transcription factor VEZF1 could directly activate SPOP transcription, and its overexpression suppressed the above effects in UBC cells. A pivotal role of SPOP in maintaining UBC stemness and remodeling immunosuppressive TME was revealed. Both the intrinsic signaling (dysregulated VEZF1/SPOP/STAT3 axis) and the extrinsic cues from TME (CCL2-IL-6 axis based on macrophages) promoted UBC progression. Targeting this crosstalk may offer a promising therapeutic strategy for UBC patients with SPOP deficiency.