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.

Colorectal cancer (CRC) is characterized by a pro-inflammatory microenvironment and features high energy supply molecules that assure tumor growth. A still underestimated macromolecule is the Inorganic Polyphosphate (iPolyP), a high-energy linear polymer that is ubiquitous in all forms of life. Made up of hundreds of repeated orthophosphate units, iPolyP is essential for a wide variety of functions in mammalian cells, including the regulation of proliferative signaling pathways. Some evidence has suggested its involvement in carcinogenesis, although more studies need to be pursued. In this study, we tested the role of iPolyP on CRC proliferation, using in-vitro and ex-vivo approaches, in order to evaluate its effect on tumor growth. We found that iPolyP is significantly increased in tumor tissues compared to the corresponding peritumoral counterparts. In addition, iPolyP signaling occurs through the TRPM8 receptor, promoting CRC cell proliferation. Pharmacological inhibition of TRPM8 or RNA interference experiments showed that the involvement of TRPM8 is essential, greater than that of the other two known iPolyP receptors, P2Y1 and RAGE. The presence of iPolyP drives cancer cells towards the mitotic phase of the cell cycle by enhancing the expression of ccnb1, which encodes for the Cyclin B protein. In-vitro 2D and 3D data reflected the ex-vivo results, obtained by the generation of CRC-derived organoids, which increased in size. These results indicate that iPolyP may be considered a novel and unexpected early biomarker supporting colorectal cancer cell proliferation.