Cytoplasmic Expression of DCLK1-S, a Novel DCLK1 Isoform, Is Associated with Tumor Aggressiveness and Worse Disease-Specific Survival in Colorectal Cancer

Abstract

Background: Oncogenic role of doublecortin-like kinase 1 (DCLK1) as a putative cancer stem cell (CSC) marker has been clarified in colorectal cancer (CRC). Isoform-specific function of DCLK1 has highlighted key role of the DCLK1-S (short isoform) in tumor maintenance, progression, and invasion. Considering the lack of commercial anti-DCLK1-S antibody suitable for immunohistochemical (IHC) application, this study was conducted to produce and validate an anti-DCLK1-S polyclonal antibody in order to specifically evaluate expression pattern and clinical significance of short isoform of DCLK1 in colorectal cancer tissues.Methods: Rabbit immunization was performed against a synthetic peptide corresponding to the published six specific amino acid sequences of DCLK1-S, and production of antibody was evaluated by enzyme-linked immunosorbent assay (ELISA). After IHC assessment of the purified anti-DCLK1-S polyclonal antibody, it was used to undertake a definitive study for determining prognostic significance of DCLK1-S expression in a well-defined tissue microarray (TMA) series including 348 CRC and 51 adjacent normal tissues with a follow-up period of 108 months. Results: Positive immunoreactivity of DCLK1-S was found in 84.2% of CRC samples. Cytoplasmic expression was the main localization of DCLK1-S compared to nuclear and membranous area of tumor cells. Expression of DCLK1-S in CRC samples was significantly higher compared to adjacent normal samples (P <0.001). A positive significant association was found between high cytoplasmic expression of DCLK1-S and advanced tumor, nodes, and metastases (TNM) stage (P<0.001) as well as the increased tumor differentiation (P= 0.02). Moreover, the patients with CRC whose tumors showed higher cytoplasmic expression of DCLK1-S had worse disease-specific survival (DSS) (log-rank test, P = 0.03) and 5-year DSS rate (P= 0.01). Additionally, the improved prognostic value was seen in the patients with CRC with high DCLK1-S expression versus moderate expression (HR: 2.70, 95% CI: 0.98-7.38; p =0.04) by multivariate analysis.Conclusions: Our findings strongly supported that DCLK1-S isoform may play a crucial role in invasion, tumor aggressive behavior, and worsened DSS of the patients with CRC. Importantly, high cytoplasmic expression of DCLK1-S compared to moderate expression could be considered as an independent prognostic factor influencing DSS. Taken together, DCLK1-S can be a candidate as a promising prognostic and targeted-therapeutic indicator for effective treatment of CRC.

Oncogenic functions and clinical significances of DCLK1 isoforms in colorectal cancer: a systematic review and meta-analysis

“…Most articles (n = 9) applied the IHC detection method for analyzing tissue. Among the 10 clinical studies, 8 experiments reported the cytoplasmic localization of DCLK1-L and DCLK1-L/S expression, and one study detected DCLK1-S in the cytoplasmic area of tumor cells [ 52 ] by immunohistochemical assay. Another study detected the cytoplasmic, membranous, and nucleus expression of DCLK1-S by immune-electron-microscopy (IEM) [ 30 ].…”