DCAMKL1 is associated with the malignant status and poor outcome in bladder cancer

DCLK1 and its oncogenic functions: A promising therapeutic target for cancers

Doublecortin-like kinase 1 (DCLK1), a significant constituent of the protein kinase superfamily and the doublecortin family, has been recognized as a prooncogenic factor that exhibits a strong association with the malignant progression and clinical prognosis of various cancers. DCLK1 serves as a stem cell marker that governs tumorigenesis, tumor cell reprogramming, and epithelial-mesenchymal transition. Multiple studies have indicated the capable of DCLK1 in regulating the DNA damage response and facilitating DNA damage repair. Additionally, DCLK1 is involved in the regulation of the immune microenvironment and the promotion of tumor immune evasion. Recently, DCLK1 has emerged as a promising therapeutic target for a multitude of cancers. Several small-molecule inhibitors of DCLK1 have been identified. Nevertheless, the biological roles of DCLK1 are mainly ambiguous, particularly with the disparities between its α- and β-form transcripts in the malignant progression of cancers, which impedes the development of more precisely targeted drugs. This article focuses on tumor stem cells, tumor epithelial-mesenchymal transition, the DNA damage response, and the tumor microenvironment to provide a comprehensive overview of the association between DCLK1 and tumor malignant progression, address unsolved questions and current challenges, and project future directions for targeting DCLK1 for the diagnosis and treatment of cancers.

DCLK1 autoinhibition and activation in tumorigenesis

Doublecortin-like kinase 1 (DCLK1) is upregulated in many tumors and is a marker for tumor stem cells. Accumulating evidence suggests DCLK1 constitutes a promising drug target for cancer therapy. However, the regulation of DCLK1 kinase activity is poorly understood, particularly the function of its autoinhibitory domain (AID), and, moreover, no physiological activators of DCLK1 have presently been reported. Here we determined the first DCLK1 kinase structure in the autoinhibited state and identified the neuronal calcium sensor HPCAL1 as an activator of DCLK1. The C-terminal AID functions to block the ATP-binding site and is competitive with ATP. HPCAL1 binds directly to the AID in a Ca²⁺-dependent manner, which releases the autoinhibition. We also analyzed cancer-associated mutations occurring in the AID and elucidate how these mutations disrupt DCLK1 autoinhibition to elicit kinase activity upregulation. Our results present a molecular mechanism for autoinhibition and activation of DCLK1 kinase activity and provide insights into DCLK1-associated tumorigenesis.

Cytoplasmic expression of DCLK1-S, a novel DCLK1 isoform, is associated with tumor aggressiveness and worse disease-specific survival in colorectal cancer

BACKGROUND: Isoform-specific function of doublecortin-like kinase 1 (DCLK1) has highlighted the key role of the DCLK1-S (short isoform) in the maintenance, progression, and invasion of the tumor. OBJECTIVE: This study was designed to produce an anti-DCLK1-S polyclonal antibody to evaluate DCLK1-S in human colorectal cancer (CRC) specifically. METHODS: The expression pattern and clinical significance of DCLK1-S were assessed in a well-defined tissue microarray (TMA) series of 348 CRC and 51 adjacent normal tissues during a follow-up period of 108 months. RESULTS: Expression of DCLK1-S was significantly higher in CRC samples compared to adjacent normal samples (P< 0.001). Cytoplasmic expression of DCLK1-S was significantly higher in the tumors at the advanced stage of cancer and with poorer differentiation (P< 0.001, P= 0.02). 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 rates (P= 0.01). Additionally, an improved prognostic value was observed in the patients with CRC with high DCLK1-S expression vs. its moderate expression (HR: 2.70, 95% CI: 0.98–7.38; p= 0.04) by multivariate analysis. CONCLUSIONS: Our findings strongly supported that high cytoplasmic expression of DCLK1-S compared to its moderate expression could be considered an independent prognostic factor influencing DSS.

Autoregulatory control of microtubule binding in doublecortin-like kinase 1

The microtubule-associated protein, doublecortin-like kinase 1 (DCLK1), is highly expressed in a range of cancers and is a prominent therapeutic target for kinase inhibitors. The physiological roles of DCLK1 kinase activity and how it is regulated remain elusive. Here, we analyze the role of mammalian DCLK1 kinase activity in regulating microtubule binding. We found that DCLK1 autophosphorylates a residue within its C-terminal tail to restrict its kinase activity and prevent aberrant hyperphosphorylation within its microtubule-binding domain. Removal of the C-terminal tail or mutation of this residue causes an increase in phosphorylation within the doublecortin domains, which abolishes microtubule binding. Therefore, autophosphorylation at specific sites within DCLK1 has diametric effects on the molecule's association with microtubules. Our results suggest a mechanism by which DCLK1 modulates its kinase activity to tune its microtubule-binding affinity. These results provide molecular insights for future therapeutic efforts related to DCLK1's role in cancer development and progression.

Increased DCLK1 correlates with the malignant status and poor outcome in malignant tumors: a meta-analysis

Doublecortin-like kinase 1 (DCLK1) has been found to be involved in malignant biological behavior of cancers and poor prognosis of cancer patients. The aim of this meta-analysis was to systematically clarify the relationships between expression level of DCLK1 and clinicopathological characteristics in tumors and assess its clinical value in cancer diagnosis and prognosis. 18 eligible studies with a total of 2660 patients were identified by searching the electronic bibliographic databases. Pooled results showed that DCLK1 was highly expressed in tissues from cancer patients compared to normal tissues (OR, 10.00), and overexpression of DCLK1 was significantly correlated with advanced clinical stage (OR, 2.48), positive lymph node metastasis (OR, 2.18), poorly differentiated cancers (OR, 1.83) and poor overall survival (HR, 2.15). The overall combined sensitivity and specificity for DCLK1 in distinguishing malignant tumors were 0.58 and 0.90, respectively. The mean diagnostic odds ratio was 12.70, and the corresponding area under the summary receiver operating characteristic curve was 0.78. In summary, our study indicated that DCLK1 could be a risk factor for development of malignant tumors and may serve as a promising diagnostic and prognostic biomarker for malignant tumors.