INTRODUCTION: Breast cancer is one of the most common types of cancer in women. 
One of the genes that were found mutated in breast cancer is casein kinase 1 
epsilon (CK1epsilon). Because CK1epsilon is a crucial regulator of the Wnt 
signaling cascades, we determined how these CK1epsilon mutations interfere with 
the Wnt pathway and affect the behavior of epithelial breast cancer cell lines.
METHODS: We performed in silico modeling of various mutations and analyzed the 
kinase activity of the CK1epsilon mutants both in vitro and in vivo. 
Furthermore, we used reporter and small GTPase assays to identify how mutation 
of CK1epsilon affects different branches of the Wnt signaling pathway. Based on 
these results, we employed cell adhesion and cell migration assays in MCF7 cells 
to demonstrate a crucial role for CK1epsilon in these processes.
RESULTS: In silico modeling and in vivo data showed that autophosphorylation at 
Thr 44, a site adjacent to the breast cancer point mutations in the N-terminal 
lobe of human CK1epsilon, is involved in positive regulation of the CK1epsilon 
activity. Our data further demonstrate that, in mammalian cells, mutated forms 
of CK1epsilon failed to affect the intracellular localization and 
phosphorylation of Dvl2; we were able to demonstrate that CK1epsilon mutants 
were unable to enhance Dvl-induced TCF/LEF-mediated transcription, that 
CK1epsilon mutants acted as loss-of-function in the Wnt/beta-catenin pathway, 
and that CK1epsilon mutants activated the noncanonical Wnt/Rac-1 and NFAT 
pathways, similar to pharmacological inhibitors of CK1. In line with these 
findings, inhibition of CK1 promoted cell migration as well as decreased cell 
adhesion and E-cadherin expression in the breast cancer-derived cell line MCF7.
CONCLUSIONS: In summary, these data suggest that the mutations of CK1epsilon 
found in breast cancer can suppress Wnt/beta-catenin as well as promote the 
Wnt/Rac-1/JNK and Wnt/NFAT pathways, thus contributing to breast cancer 
development via effects on cell adhesion and migration. In terms of molecular 
mechanism, our data indicate that the breast cancer point mutations in the 
N-terminal lobe of CK1epsilon, which are correlated with decreased 
phosphorylation activities of mutated forms of CK1epsilon both in vitro and in 
vivo, interfere with positive autophosphorylation at Thr 44.