| Summary: | <p>Myofibroblasts are an important cellular component of the tumour microenvironment and play an essential role in facilitating carcinogenesis through bidirectional communications with epithelial cells. Accumulation of myofibroblasts is associated with poor prognosis in colorectal cancers. Myofibroblasts are distinguished from skin fibroblasts by positive expression of amine oxidase, copper containing 3 (AOC3) and NKX2-3. The current project aims to study the in vitro interactions between myofibroblasts and colorectal cancer (CRC) epithelial cell lines and their effects on gene expression in myofibroblasts, primarily AOC3 and NKX2-3. </p> <p>In vitro interactions between myofibroblasts and CRC cell lines were analysed using various assays. An increase in cancer cell growth, myofibroblast migration and formation of bigger lumens in CRC cell lines was found in co-culture as compared to monoculture (Chapter 3). The results show high expression of NKX2-3 in all myofibroblasts, while AOC3 expression was more heterogeneous. These data suggest NKX2-3 to be a key mediator for maintaining the myofibroblast phenotype, while AOC3 serves as a negative indicator for their activation state. Knockdown experiments indicated NKX2-3 to be a regulator for AOC3 and ACTA2 expression in myofibroblasts. AOC3 expression in myofibroblasts is downregulated by TGFβ1, EGF, PDGF-AA and CC. Our data indicate that PDGF-AA and CC are significant players for the interactions between myofibroblasts and CRC cell lines. The fibroblast activation protein (FAP) was shown to be an indicator of myofibroblast activation whose regulation by PDGF-AA differed between normal and cancer-derived myofibroblasts (Chapter 4). Lastly, we established a serum free chemically defined (NEW) medium which supports the growth of myofibroblasts but not CRC cell lines (Chapter 5). </p> <p>In conclusion, our results illustrate in vitro cross-communication between myofibroblasts and CRC epithelial cell lines with a significant role for the PDGF-A and C/PDGFRA signalling pathway in the interactions between those two cell types.</p>
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