title: Investigating the role of the Wnt signalling antagonist DKK1 in Cholangiocarcinoma
Creators: name: Tsokkou, Panagiota
Publisher: name: The University of Edinburgh
Year: 2020
Subjects: subject: Cholangiocarcinoma
subject: DKK1
subject: Wnt signalling pathway
subject: lipoprotein receptor-related protein
subject: LRP5/6)
subject: Wnt antagonist

description: Cholangiocarcinoma (CCA) is an aggressive and highly invasive malignancy that emerges along the ducts of the biliary tree. Due to its asymptomatic nature, CCA has poor prognosis and the majority of patients are diagnosed at an advanced stage where therapeutic options are limited. Although several risk factors have been associated with CCA, the molecular mechanisms underlying its pathogenesis remain largely unknown. Consequently, there is an urgent need to better understand initiation and progression of CCA towards the development of effective targeted therapies. DKK1 is a secreted glycoprotein that antagonises the canonical Wnt signalling pathway by binding to the Wnt co-receptors low-density lipoprotein receptor-related protein 5 or 6 (LRP5/6). Aberrant activation of canonical Wnt signalling has been well documented in many malignancies, including CCA where hyperactivation of this pathway drives cancer cell proliferation. Despite acting as a Wnt antagonist, DKK1 is frequently overexpressed in CCA and this has been associated with worse prognosis and lymphatic metastasis in CCA patients. According to these clinical studies, we hypothesised that DKK1 contributes to CCA progression through the regulation of LRP5/6-independent signalling pathways. One such signalling pathway that has been recently identified is the CKAP4/PI3K/AKT signalling pathway with CKAP4 being a novel DKK1 receptor. However, whether this pathway is activated in CCA is still elusive. To investigate the functional role of DKK1 in CCA we utilised a mouse CCA model and human CCA cell lines in which DKK1 was overexpressed. Using these systems, we have demonstrated that DKK1 overexpression is sufficient to promote tumour growth and the recruitment of macrophages into the tumours. To elucidate whether these DKK1-mediated changes occur through interaction with CKAP4 we initially assessed CKAP4 expression in DKK1 overexpressing CCA tumours. Interestingly, we found that CKAP4 is highly expressed in a subset of tumour-associated macrophages and myofibroblasts. According to these findings we hypothesised that DKK1 may exerts direct effects on these cells by binding to CKAP4 on their cell surface in order to regulate the CCA microenvironment and thereby, promoting tumour growth. To functionally evaluate this, we used bone marrow-derived macrophages and hepatic myofibroblasts isolated from healthy mice and assessed their response to DKK1 in cell growth and motility assays. This has provided novel evidence that DKK1 may promote CCA progression through interactions with CKAP4 expressing macrophages and myofibroblasts. Moreover, using human CCA cell lines we have demonstrated that DKK1 overexpression promotes cell growth and migration. Collectively, our data suggest that high levels of DKK1 promote CCA growth and this might be through the regulation of the CCA microenvironment.