Investigation of the role of interleukin-1 family members, IL-33 and IL-36, in the pathogenesis of colon cancer

The importance of inflammation in cancer is well established, with cytokines/chemokines playing an important role in carcinogenesis. IL-33 was recently identified as the ligand for ST2. ST2 is a member of the toll-like receptor/IL-1 receptor family. Three isoforms of ST2 exist: a trans-membrane receptor (ST2L), a secreted soluble form (sST2), and a variant form (ST2V). The IL-33/ST2 pathway has been implicated in inflammatory bowel disease, a major risk factor for colon cancer. The aim of the first part of my thesis was to investigate the role of IL-33 and ST2 in colon cancer. CT26 and HT29 colon cancer cells were found to express ST2 and IL-33 in vitro, with expression increased by inflammatory mediators (LPS, TNF-α and PGE2). Stimulation with IL-33 increased the migration, but not proliferation, of colon tumour cells. Functional analyses showed that stimulation with IL-33 induced the expression of CXCL-1 by CT26 and CCL2 expression by HT29 cells. To investigate the role of ST2 in vivo, ST2 knockdown cells were generated using ST2-specific shRNA (CT26 ST2shRNA) and injected subcutaneously into BALB/C mice. Knockdown of ST2 in colon tumours resulted in enhanced tumour growth (2.3 fold increase compared to CT26 scrshRNA) in vivo. This was associated with alterations in immune cell infiltration, including an increase in macrophage infiltration. In contrast, characterisation of human colon tumours revealed that ST2L expression was increased in tumour cells relative to adjacent non-tumour cells, with no change in expression of total ST2. These results indicate that the IL-33/ST2 signalling axis may play an important role in colon carcinogenesis and merits further investigation. The role of the IL-36R, a second IL-1R family member, in colon cancer was investigated in the second part of my thesis. Characterization of human colon tumours ex vivo showed significantly increased expression of the IL-36 ligands, IL-36α and IL-36γ, compared to adjacent non-tumour tissue. In vitro colon cancer cell lines HT29 and SW480 were shown to express the IL-36R and IL-36 ligands. IL-36α and IL-36γ stimulation of HT29 cells also increased the expression of the chemokines CXCL-1, CCL2, CCL20, and IL-8. This suggests that IL-36 signalling may promote tumour-derived immune cell recruitment. This field requires further study to determine if the recruitment of immune cells by IL-36 signalling could be utilised to break tolerance against tumour antigens. This thesis has laid the basis for further studies to explore the role of IL-36 signalling in colon cancer