Role of doublecortin-like kinase 1 and leucine-rich repeat-containing G-protein-coupled receptor 5 in patients with stage II/III colorectal cancer: Cancer progression and prognosis

Clinical Implications and Prognostic Value of Leucine-Rich G Protein-Coupled Receptor 5 Expression as A Cancer Stem Cell Marker in Malignancies: A Systematic Review and Meta-Analysis

Leucine-rich G protein-coupled receptor 5 (LGR5) is a marker of cancer stem cells (CSCs) in various cancers. Based on different studies, conflicting reports exist on correlation between LGR5 expression and poor prognosis/ clinicopathological parameters in cancer patients. Therefore, our purpose in conducting this study was to investigate correlation between LGR5 expression and outcomes of cancer patients under study through a systematic review and meta-analysis. Relevant articles were searched and collected using EMBASE, PubMed, Science Direct, and Scopus databases until December 21, 2022. This study was conducted to examine correlation between LGR5 expression and different clinical outcomes, such as recurrence-free survival (RFS), disease-free survival (DFS), overall survival (OS), and clinicopathological characteristics of the included cancer patients. To achieve this, hazard ratios (HRs) with 95% confidence intervals (CIs) and odds ratios (ORs) with 95% CIs were used as statistical measures. A meta-analysis was conducted using STATA 12.0 software. Finally, 53 studies including 9523 patients met the inclusion criteria. Significantly, high-level expression of LGR5 was related to poor prognosis in terms of OS, higher tumor stage, presence of distant metastasis, and presence of lymph node metastasis. It was discovered through subgroup analysis that several factors, including the study area, evaluation method, and type of cancer, can influence the correlation between LGR5 expression and negative prognosis in cancer patients. According to the results of our study, LGR5 overexpression was related to poor OS in cancer patients. In addition, clinicopathological data indicated an unfavorable prognosis in cancer patients with high LGR5 expression. In conclusion, LGR5 may serve as a potential prognostic marker for predicting survival in certain cancer types.

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.

Pleiotropic effects of DCLK1 in cancer and cancer stem cells

Doublecortin-like kinase 1 (DCLK1), a protein molecule, has been identified as a tumor stem cell marker in the cancer cells of gastrointestinal, pancreas, and human colon. DCLK1 expression in cancers, such as breast carcinoma, lung carcinoma, hepatic cell carcinoma, tuft cells, and human cholangiocarcinoma, has shown a way to target the DCLK1 gene and downregulate its expression. Several studies have discussed the inhibition of tumor cell proliferation along with neoplastic cell arrest when the DCLK1 gene, which is expressed in both cancer and normal cells, was targeted successfully. In addition, previous studies have shown that DCLK1 plays a vital role in various cancer metastases. The correlation of DCLK1 with numerous stem cell receptors, signaling pathways, and genes suggests its direct or an indirect role in promoting tumorigenesis. Moreover, the impact of DCLK1 was found to be related to the functioning of an oncogene. The downregulation of DCLK1 expression by using targeted strategies, such as embracing the use of siRNA, miRNA, CRISPR/Cas9 technology, nanomolecules, specific monoclonal antibodies, and silencing the pathways regulated by DCLK1, has shown promising results in both in vitro and in vivo studies on gastrointestinal (GI) cancers. In this review, we will discuss about the present understanding of DCLK1 and its role in the progression of GI cancer and metastasis.

Targeting DCLK1 overcomes 5-fluorouracil resistance in colorectal cancer through inhibiting CCAR1/β-catenin pathway-mediated cancer stemness

Background

To date, 5‐fluorouracil‐based chemotherapy is very important for locally advanced or metastatic colorectal cancer (CRC). However, chemotherapy resistance results in tumor recurrence and metastasis, which is a major obstacle for treatment of CRC.

Methods

In the current research, we establish 5‐fluorouracil resistant cell lines and explore the potential targets associated with 5‐fluorouracil resistance in CRC. Moreover, we perform clinical specimen research, in vitro and in vivo experiments and molecular mechanism research, to reveal the biological effects and the mechanism of DCLK1 promoting 5‐fluorouracil resistance, and to clarify the potential clinical value of DCLK1 as a target of 5‐fluorouracil resistance in CRC.

Results

We discover that doublecortin‐like kinase 1 (DCLK1), a cancer stem cell maker, is correlated with 5‐fluorouracil resistance, and functionally promotes cancer stemness and 5‐fluorouracil resistance in CRC. Mechanistically, we elucidate that DCLK1 interacts with cell cycle and apoptosis regulator 1 (CCAR1) through the C‐terminal domain, and phosphorylates CCAR1 at the Ser343 site, which is essential for CCAR1 stabilisation. Moreover, we find that DCLK1 positively regulates β‐catenin signalling via CCAR1, which is responsible for maintaining cancer stemness. Subsequently, we prove that blocking β‐catenin inhibits DCLK1‐mediated 5‐fluorouracil resistance in CRC cells. Importantly, we demonstrate that DCLK1 inhibitor could block CCAR1/β‐catenin pathway‐mediated cancer stemness and consequently suppresses 5‐fluorouracil resistant CRC cells in vitro and in vivo.

Conclusions

Collectively, our findings reveal that DCLK1 promotes 5‐fluorouracil resistance in CRC by CCAR1/β‐catenin pathway‐mediated cancer stemness, and suggest that targeting DCLK1 might be a promising method to eliminate cancer stem cells for overcoming 5‐fluorouracil resistance in CRC.

SPINOPHILIN: a multiplayer tumor suppressor

SPINOPHILIN (SPN, PPP1R9B or NEURABIN-2) is a multifunctional protein that regulates protein-protein interactions in different cell signaling pathways. SPN is also one of the regulatory subunits of protein phosphatase 1 (PP1), implicated in the dephosphorylation of retinoblastoma protein (pRB) during cell cycle. The SPN gene has been described as a tumor suppressor in different human tumor contexts, in which low levels of SPN are correlated with a higher grade and worse prognosis. In addition, mutations of the SPN protein have been reported in human tumors. Recently, an oncogenic mutation of SPN, A566V, was described, which affects both the SPN-PP1 interaction and the phosphatase activity of the holoenzyme, and promotes p53-dependent tumorigenesis by increasing the cancer stem cell (CSC) pool in breast tumors. Thus, the loss or mutation of SPN could be late events that promotes tumor progression by increasing the CSC pool and, eventually, the malignant behavior of the tumor.

Prognostic Impact of LGR5, Prox1, and Notch1 Biomarkers in Stage II to III Colon Cancer

The potentiation and activation of Wnt signaling pathways are now assumed to mediate the self-renewal and proliferation of colon cancer stem cells that are responsible for therapeutic resistance, tumor relapse, and metastasis. We aimed to evaluate LGR5, Prox1, and Notch1 immunohistochemical expression in stage II to III colon cancer. Their predictive role of tumor relapse, overall survival, and disease-free survival was statistically analyzed. Our results revealed that high LGR5 expression was identified in 56.7% of the patients, LGR5 expression was significantly associated with left-sided tumors (P<0.001). Moreover, its expression was significantly associated with the unfavorable tumor characteristics including high grade, deep invasion (pT), lymph node metastasis, and advanced tumor stage (P<0.001 for each). High Prox1 expression was observed in 65% of the cases, and its expression was significantly associated with tumor grade, lymph node metastasis, and the advanced tumor stage (P=0.004, 0.009, 0.016, respectively). Positive Notch1 expression was identified in 35% of patients, and it was inversely associated with high grade lymph node metastasis, deep invasion (pT), and advanced tumor stage (P<0.001 for each). During the follow-up period, the tumor relapse was significantly associated with high LGR5, high Prox1, and negative Notch1 expression. Shorter overall survival and disease-free survival were significantly associated with high LGR5, high Prox1, and negative Notch1 expression. High LGR5, high Prox1, and negative Notch1 expression are unfavorable prognostic factors in colon cancer. Prox1 is a crucial regulator of Notch-independent LGR5+ stem cells that is mostly responsible for relapse and therapeutic resistance in stage II to III colon cancer.