Abstract 2574: Curcumin either stimulates or inhibits expression of short isoform of stem-cell-marker DCLK1 (DCLK1-S) in non-transformed vs transformed cells, resulting in stabilization/inhibition of growth, respectively.
Authors: Sarkar Shubhashish , Connell1 Malaney O’ , Moya Stephanie M. , Singh Pomila 
Published: August 2014

Inhibitory effects of curcumin are well documented on colon cancer cells, with minimal side effects on normal cells. Mechanisms mediating opposite effects of curcumin on normal vs cancer cells, remain unknown. We examined possible differential effects of curcumin on stem-cell-marker, DCLK1 in non-transformed (HEK-C, NCM460) vs transformed/cancer (HEKmGAS, HCT-116) cells. Curcumin (10-25μM) significantly inhibited growth of HEKmGAS/HCT-116 cells in a dose-dependent manner, with no significant effects on HEK-C cells. Surprisingly, transcript levels of DCLK1-S were increased by 3-10 fold in non-transformed cells, but decreased by 50-80% in transformed cells, which correlated with activation/inhibition of transiently transfected intron V promoter-reporter constructs in response to curcumin. Several cis elements, including NFκB binding sites, identified in intron V promoter, may play a role in transcribing DCLK1-S. Significant down-regulation of DCLK1-S by curcumin correlated with significant inhibition of NFκBp65 binding to intron V promoter in a ChIP assay. L-isoform of DCLK1 (DCLK1-L) was mainly expressed by non-transformed/normal cells, due to possible epigenetic silencing of DCLK1-L 5’promoter in cancer cells. The 5’ promoter was positive for several cis elements including TCF/β-catenin binding sites. Since Wnt/β-catenin pathway is up-regulated in many cancer cells, transiently transfected 5’ promoter-reporter constructs were activated by several fold in HEKmGAS/HCT-116 cells compared to that in non-transformed cells; curcumin significantly inhibited TCF expression and β-catenin binding to the 5’ promoter in a ChIP assay. However, since 5’ promoter is silenced in many cancer cells, significant effects of curcumin were not measured on DCLK1-L transcript in cancer cells. Curcumin did not inhibit DCLK1-L transcript in non-transformed cells, suggesting that pathways other than Wnt/β-catenin likely up-regulate DCLK1-L expression in normal cells, which may not be inhibited by curcumin. Role of other transcriptional factors in differential expression of S and L forms in non-transformed vs transformed cells remains unknown, which likely contributes to stimulatory vs inhibitory effects of curcumin on non-transformed vs transformed cells. It is speculated that significant differences in inhibitory effects of curcumin on transformed vs non-transformed cells may be due to significant differences in pathways inducing transcriptional activation of the promoters transcribing DCLK1-S/L isoforms. These differences may allow us to develop promoter-specific inhibitors for targeting cancer stem cells while sparing normal stem cells.

This work was supported by NIH Grant to PS (R01CA09795909).

Citation Format: Shubhashish Sarkar, Malaney O’ Connell1, Stephanie M. Moya, Pomila Singh. Curcumin either stimulates or inhibits expression of short isoform of stem-cell-marker DCLK1 (DCLK1-S) in non-transformed vs transformed cells, resulting in stabilization/inhibition of growth, respectively. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2574. doi:10.1158/1538-7445.AM2013-2574