Project Summary

The Wnt pathway is highly active in the basal-like subgroup of breast cancer. Additionally, genes of the Wnt pathway are overrepresented in the expression profiles of all subtypes of breast cancer which later develop brain metastases. However, previous studies of breast cancer primaries could neither identify a Wnt ligand nor the specific Wnt sub-pathway mediating these signals. Own hierarchical cluster analysis of external gene expression datasets (GEO) yielded a close relation between basal-like cancers and brain metastases of all subtypes. This indicates that the brain metastasis cluster is more closely related to basal-like breast cancers than to the respective original subtype.    To further clarify the Wnt activity in breast cancer, we comparatively investigated human breast cancer brain metastases as well as MDA MB 231 and MCF 7 cells as paradigms for the basal-like and the luminal A subtype. Wnt 5a and b and their putative receptors ROR1/2 were found overexpressed in MDA-MB-231 cells and brain metastases of all subtypes. Invasiveness of MDA MB-231 was reduced by Wnt inhibitors, whereas MCF-7 invasion was enhanced by recombinant Wnt 5b and abolished by JNK antagonists. Neither the basal-like MDA MB 231 nor brain metastases showed nuclear β-catenin, while there was strong nuclear c Jun staining. Further gene set enrichment analyses demonstrated that the Wnt pathway is enriched among the genes responsible for distant metastasis, in particular when using the KEGG derived gene set, which comprises genes of β-catenin-dependent and independent Wnt signaling. This implicates the Wnt pathway not only in the dissemination into the brain but also in metastasis formation in general. This also suggests that the Wnt/β-catenin pathway may not represent the critical Wnt cascade in breast cancer metastasis.              
Currently there is no Wnt gene set available, which distinguishes between the different Wnt sub-pathways and links to sub-pathway activation. Therefore the central aim of the project is the establishment of a new bioinformatics model of the Wnt pathway in breast cancer. The model will be described as a directed graph containing important signaling molecules and directly or indirectly regulated targets as nodes and the different types of molecular interactions or regulation mechanisms as vertices. To establish the new Wnt model own biological data need to be generated. For this we will manipulate the described paradig-matic cell lines through stimulation with Wnt ligands, gene silencing and overexpression of pathway com-ponents. To gain information on Wnt signaling in cerebral metastasis cell lines of metastases will be es-tablished and subjected to the same studies. This will be complemented by external datasets. The result-ing model will consider the different sub-pathways of Wnt signaling as well as dependencies.