Investigation of heterotypic interactions between cancer cells and cancer-associated fibroblasts

This thesis addresses heterotypic physical interactions between cancer cells and cancerassociated fibroblasts (CAFs) with different experimental approaches including timelapse movies, microarray and mass spectrometry analysis. Low-light and confocal imaging demonstrated the existence of direct physical interactions between cancer cells and fibroblasts. By combining light and SEM microscopy with siRNA methods it was shown that cancer cell and fibroblast contacts undergo a maturation process starting from filopodia to stable cadherin based interaction sites in which a stable cytoskeleton arrangement in fibroblasts plays an essential role. ROCK kinases stabilise cancer cell fibroblast interactions by stabilising the localisation of beta and p120-catenins at the interaction site. In addition, Src has a destabilising role on cancer cell-fibroblast interactions, independent of its ability to antagonise ROCK. Further it could be shown by analysing gene expression data of cancer cell-fibroblast co-cultures that atypical cadherins, protocadherin-7 (PCDH7) and protocadherin-9 (PCDH9), are expressed by both cell types. Cell migration assays using imprinted fibronectin chips and 3D spheroid assays of A431 and VCAF co-cultures showed that a stable expression of PCDH7 and PCDH9 seem to be important for cancer cells to move efficiently in certain environments in which they need the connection to fibroblasts. To understand the downstream signalling consequences of direct cancer cell fibroblast interactions additional experimental approaches as mass spectrometry and microarray were performed. Mass spectrometry analysis demonstrated that ERK kinase activity is up regulated in fibroblasts upon direct interaction with cancer cells. In addition to information including pathways activation and cell adhesion molecules and the better understanding of the nature of direct cancer cell-fibroblasts interactions, we obtained data by gene expression analysis. These data revealed a link of direct cancer cellfibroblast interactions to strong activation of interferon-regulated genes in both cell types, which gives an interesting link of cancer and inflammation