The Localisation of IL-1α and IL-1β in Colon Cancer Microenvironment Affects Tumor Progression

IL-1 is one of the major pro-inflammatory and immunostimulatory pleiotropic cytokines, acting mainly by inducing a local cascade of pro-inflammatory molecules and by promoting cell infiltration. IL-1α and IL-1β are the major agonistic molecules. IL-1 expression in the inflamed colon was demonstrated in IBD patients and in experimental colitis in mice, along with other pro-inflammatory cytokines. Very little is known about the differential functions of IL-1α and IL-1β and their interaction patterns in chronic colon inflammation and carcinogenesis.

In this study, we used the surgical orthotopic implantation model with the mouse colon cancer line MC38. We found more pronounced tumor growth in mice deficient in IL-1Ra. There was no difference in tumor growth in IL-1α deficient mice compared to control mice, but in mice deficient in IL-1β, significant retardation of tumor growth was observed. Liver metastases were found only in IL-1Ra KO mice.

To study the effects of IL-1 agonistic molecules in the development of CRC, we analyzed their expression in the tumor microenvironment.

MC38 cells were injected into mice together with Matrigel plugs, or orthotopically into the cecum of control mice. After different time intervals, Matrigel plugs and colon tumors were extracted and analyzed by FACS.

These two models allow us to analyze the role of IL-1 in early (Matrigel) and late stages of tumor development.

The expression of IL-1 molecules was determined by intracellular staining of extracted tumors and infiltrating immune cells. Infiltrating cells were isolated by magnetic beads (Miltenyi), using anti-CD45 antibodies and o myeloid cell composition was analyzed by FACS, using specific antibodies. A fraction of CD45-negative cells was also collected and analyzed for expression of CD44 and EpCAM molecules, markers of malignant colon cells and epithelial cells, respectively.

Whereas most myeloid cells express both IL-1α and IL-1β molecules, we found higher levels ofIL-1α. On the contrary, tumor cells mainly produce IL-1α and only a very small amount of IL-1β. These results were consistent in both systems used in our study. Therefore, IL-1α is seen to be a key molecule involved in tumor progression. IL-1α is produced by both malignant and microenvironment cells and thus is involved in early stages of tumor progression. In contrast, IL-1β expression by infiltrating cells supports tumor progression, mostly during later stages of the malignant process.

These results show the importance of both IL-1 molecules in the development of CRC.