Effects of altered expression and activity levels of casein kinase 1δ and ε on tumor growth and survival of colorectal cancer patients. Homo sapiens

Colorectal cancer (CRC) is the fourth leading cause of cancer-related death worldwide due to high apoptotic resistance and metastatic potential. Since mutations as well as deregulation of CK1 isoforms contribute to tumor development and progression, CK1 has become an interesting drug target. In this study, we show that CK1 isoforms are differently expressed in colon tumor cell lines and that growth of these cell lines can be inhibited by CK1-specific inhibitors. Furthermore, expression of CK1δ and ε is changed in colorectal tumors and high CK1ε expression levels significantly correlate with prolonged patients' survival. In addition to changes in CK1δ and ε expression, mutations within exon 3 of CK1δ were detected in colorectal tumors. These mutations influence ATP binding, leading to changes in the kinetic parameters. Overexpression of these mutants in HT29 cells alters their ability to grow anchorage independently. Consistent with these results, these CK1δ mutants lead to differences in proliferation rate and tumor size in xenografts due to changes in gene expression, especially in genes involved in regulation of cell proliferation, cell cycle, and apoptosis. In summary, our results provide evidence that changes in the expression levels of CK1 isoforms in colorectal tumors correlate with the survival of patients and that CK1δ mutations affect growth and proliferation of tumor cells and induced tumor growth in xenografts, leading to the assumption that CK1 isoforms provide interesting targets in new colorectal cancer therapy concepts. Overall design: To analyze the effects of the different exon 3 mutants of CK1δ on tumor cell growth and proliferation in vivo, HT29 cells stably expressing mtCK1δT67S, mtCK1δI68N, mtCK1δP66T,R69K, or the empty vector were subcutaneously injected into the hind flank of 6- to 8-week-old athymic nude mice to obtain xenografts. After 27 days, mice were sacrificed and the tumors were excised, measured, and weighed. Microarray analysis was performed to compare gene expression in the different groups (vector control group (ctrl), mtCK1δT67S, mtCK1δI68N, and mtCK1δP66T,R69K), using 200 ng total RNA as starting material and 5.5 µg ssDNA per hybridization (GeneChip Fluidics Station 450; Affymetrix, Santa Clara, CA).