Effects of environmental stress factors on colon cancer and its microenvironment

Over the last decade, cancer-associated fibroblasts (CAFs) have risen to increased prominence as one of the key drivers in the pro-tumorigenic tumor microenvironment (TME). Their incredible heterogeneity means, however, that detailed analysis of these cells remains elusive and requires the usage of complex technologies such as single-cell sequencing. Using these approaches, numerous subtypes of cancer-associated fibroblasts have been identified, mainly based on their gene expression profiles.
In this thesis, we highlight the IL1-family, especially IL1B and IL1R1, as an important driver in the pro-tumorigenic nature of fibroblast. We show how IL1B and IL1R1 are upregulated in CRC CAFs when contrasted to normal, non-tumor-associated, fibroblasts and how IL1R1 expression is strongly elevated in one of the CAF subtypes we identified using single-cell sequencing – cyCAF2. We also identified that IL1R1 correlates strongly with two of the markers characteristic of this subtype, FAP and CXCL12, and that it shows elevated signs of IL1β-derived signaling, based on gene signature analysis.
From a functional perspective, we show that IL1β-activated fibroblasts induce the secretion of pro-inflammatory cytokines such as IL6, CXCL8, CXCL5, and CXCL1 and act in a pro-tumorigenic manner on tumor cells in three-dimensional co-culture systems. Furthermore, we show that IL1B can be upregulated in CAFs by, at the moment, unknown secreted factors from tumor spheroids. We also found that inhibition of basal IL1 cross-talk between CAFs and tumor spheres via IL1-inhibition results in lowered pro-tumorigenic activity of CAFs and that this can be recapitulated in vivo using ColVIcre+ IL1R1fl/fl conditional knockout mice. Finally, we highlight how IL1β stimulation in primary CAFs can modulate immune cell proliferation and the upregulation of immunomodulatory proteins such as PD-L1 and PD-L2 and may, therefore, alter the effectiveness of immune checkpoint therapy. Altogether, the results presented in this thesis suggest that inhibition of IL1β-signaling in CAFs may be a promising therapeutic option in CRC patients.