Doublecotin-like kinase 1 increases chemoresistance of colorectal cancer cells through the anti-apoptosis pathway

Colorectal cancer (CRC) is the third most common cancer diagnosed and the second leading cause of cancer-related deaths in the United States. About 50% of CRC patients relapsed after surgical resection and ultimately died of metastatic disease. Cancer stem cells (CSCs) are believed to be the primary reason for the recurrence of CRC. Specific stem cell marker, doublecortin-like kinase 1 (DCLK1) plays critical roles in initiating tumorigenesis, facilitating tumor progression, and promoting metastasis of CRC. It is up-regulated in CRC and up-regulation of DCLK1 indicates poor prognosis. Whether DCLK1 is correlated with enhanced chemoresistance of CRC cells is unclear. Our research aims to reveal association of DCLK1 with chemoresistance of CRC cells and the underlying molecular mechanisms. In order to achieve our goal, we established stable DCLK1 over-expression cells (DCLK1+) using the HCT116 cells (WT). DCLK1+ and WT cells were treated with 5-Fluorouracil (5-Fu) at different doses for 24 or 48 hours. MTT assay was used to evaluate cell viability and IC50 of 5-Fu was determined. Quantitative real time PCR was applied to determine gene expression of caspase-3 (casp-3), caspase-4 (casp-4), and caspase-10 (casp-10). Cleaved casp-3 expression was investigated using Western blot and immunofluorescence. Our results demonstrated that IC50 of 5-Fu for the DCLK1+ cells was significantly higher than that of the WT cells for both 24 and 48-hour treatment (P=0.002 and 0.048 respectively), indicating increased chemoresistance of the DCLK1+ cells. Gene expression of casp-3, casp-4, and casp-10 were significantly inhibited in the DCLK1+ cells after 5-Fu treatment compared to the WT cells (P=7.616e-08, 1.575e-05 and 5.307e-08, respectively). Cleaved casp-3 amount and casp-3 positive cells were significantly decreased in the DCLK1+ cells after 5-Fu treatment compared to the WT cells (P=0.015). In conclusion, our results demonstrated that DCLK1 overexpression enhanced the chemoresistance of CRC cells to 5-Fu treatment by suppressing gene expression of key caspases in the apoptosis pathway and activation of apoptosis pathway. DCLK1 can be an intriguing therapeutic target for the effective treatment of CRC patients.