Inorganic Polyphosphate Activates the NLRP3 Inflammasome Signaling Pathway via TRPM8 and Promotes the Epithelial to Mesenchymal Transition in Colorectal Cancer

Background: During normal development, epithelial cells can experience alterations at transcriptional and morphological levels, which can trigger a process named the epithelial-mesenchymal transition (EMT). The EMT underpins changes in cytoskeleton dynamics that are characteristic of neoplastic transformation. Described in many tumors, including colorectal cancer (CRC), over the past ten years, although it is an essential process in cancer development it is still poorly understood. Once initiated, the EMT regulates metastasis, the microenvironment and immune system resistance in CRC. Overexpression of the pro-inflammatory molecule inorganic polyphosphate (iPolyP) has been shown to play important role in CRC progression, alongside its binding receptor called transient receptor potential cation channel subfamily M (melastatin) member 8 (TRPM8). In this study we tested whether iPolyP/TRPM8 axis regulates EMT changes as well as NLRP3 inflammasome activation within the tumor microenvironment (TME) of CRC. Methods: To investigate these issues, western blotting, fixed and live cells immunofluorescence, 2D and 3D cell culture on CRC-patient derived biopsies, ELISA and wound healing assays were performed. Results: iPolyP triggers the expression of several EMT markers in CRC cell lines compared to control. Pharmacological inhibition of TRPM8 receptor restricts the migratory effects of cancer cells due to the presence of iPolyP. Moreover, the iPolyP/TRPM8 axis also displays an indirect pro-tumorigenic performance through shaping the immune microenvironment. By triggering NLRP3 inflammasome activation, iPolyP ensures high levels of the pro-inflammatory cytokine IL-1, which foster CRC carcinogenesis. Conclusion: This study suggests that the iPolyP/TRPM8 signaling axis is a promising target for impeding CRC progression and spread.