A Short Isoform Of Dclk1, Transcribed From An Alternate Promoter In Human Colon Cancers, Represents A Novel Biomarker And Target For Diagnostic And Treatment Purposes

DCLK1 is a specific marker of colon and pancreatic cancers in mice, and is expressed by human colon adenocarcinomas (hCRCs). A sub-set of DCLK1 +ve colon cancer-stem-cells, are resistant to chemopreventive/chemotherapeutic reagents and undergo autophagic survival, resulting in the relapse of colon-cancer disease. However, down-regulation of DCLK1, along with chemopreventive agents, inhibits spheroidal/xenograft growths from hCRC cells, and eliminates both colon-cancer-stem cells and relapse of the disease. We now know that the 5′-promoter of DCLK1 gene is hypermethylated in hCRCs, but not in mouse colon-tumors, resulting in the loss of expression of DCLK1 long-transcripts (DCLK1-L), from the 5′promoter of DCLK1-gene in humans, but not in mice. We hypothesized that elevated levels of DCLK1 protein, detected in hCRCs, are likely transcribed from an alternate-promoter in humans. We used several in silico and molecular biology approaches to test our hypothesis, and report for the first time that hCRCs express short-transcripts of DCLK1 (DCLK1-S) from an alternate promoter in IntronV of the gene, while normal human colons express the long transcript (DCLK1-L) from 5′-promoter. We additionally report an important role of β-catenin and TCF4/LEF binding-sites for activating 5′-promoter, while NF-κBp65 binding to NF-κB cis element, activates the TATA box containing IntronV-promoter in cancer cells. DCLK1-S expression was examined in a cohort of 92 CRC patients, in relation to overall survival and clinicopathological parameters. High expressors had significantly worse overall-survival compared to low expressors, and DCLK1-S expression was found to be an independent prognostic factor. Conclusions. Our novel findings regarding alternate promoter usage by normal colons vs hCRCs suggest that we can develop strategies for specifically targeting DCLK1-S to eliminate colon cancer-stem-cells, while sparing DCLK1-L functions in neurons and normal cells. Our findings further suggest prognostic/diagnostic value of measuring DCLK1-S in CRC patients. Loss of DCLK1-L expression can also be used as a diagnostic marker for indicating the on-set of epigenetic changes associated with colon carcinogenesis in humans, as an early marker. Citation Format: Malaney R. O9Connell, Shubhashish Sarkar, Gurinder Luthra, Yoshinaga Okugawa, Yuji Toiyama, Ajay Goel, Aakash Gajjar, Suimin Qiu, Lawrence Sowers, Pomila Singh. A short isoform of DCLK1, transcribed from an alternate promoter in human colon cancers, represents a novel biomarker and target for diagnostic and treatment purposes. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 543. doi:10.1158/1538-7445.AM2015-543