TOPK Inhibition Enhances the Sensitivity of Colorectal Cancer Cells to Radiotherapy by Reducing the DNA Damage Response.

OBJECTIVE: Abnormal expression of T-lymphokine-activated killer cell-originated protein kinase (TOPK) was reported to be closely related to the resistance of prostate cancer to radiotherapy and to targeted drug resistance in lung cancer. However, the role of TOPK inhibition in enhancing radiosensitivity of colorectal cancer (CRC) cells is unclear. This study aimed to evaluate the radiosensitization of TOPK knockdown in CRC cells. METHODS: The expression of TOPK was detected in CRC tissues by immunohistochemistry, and the effect of TOPK knockdown was detected in CRC cells by Western blotting. CCK-8 and clonogenic assays were used to detect the growth and clonogenic ability of CRC cells after TOPK knockdown combined with radiotherapy in CRC cells. Furthermore, proteomic analysis showed that the phosphorylation of TOPK downstream proteins changed after radiotherapy. DNA damage was detected by the comet assay. Changes in the DNA damage response signaling pathway were analyzed by Western blotting, and apoptosis was detected by flow cytometry. RESULTS: The expression of TOPK was significantly greater in CRC tissues at grades 2-4 than in those at grade 1. After irradiation, CRC cells with genetically silenced TOPK had shorter comet tails and reduced expression levels of DNA damage response-associated proteins, including phospho-cyclin-dependent kinase 1 (p-CDK1), phospho-ataxia telangiectasia-mutated (p-ATM), poly ADP-ribose polymerase (PARP), and meiotic recombination 11 homolog 1 (MRE11). CONCLUSIONS: TOPK was overexpressed in patients with moderately to poorly differentiated CRC. Moreover, TOPK knockdown significantly enhanced the radiosensitivity of CRC cells by reducing the DNA damage response.

MARK3 kinase: Regulation and physiologic roles.

Microtubule affinity-regulating kinase 3 (MARK3), a member of the MARK family, regulates several essential pathways, including the cell cycle, ciliated cell differentiation, and osteoclast differentiation. It is important to understand the control of their activities as MARK3 contains an N-terminal serine/threonine kinase domain, ubiquitin-associated domain, and C-terminal kinase-associated domain, which perform multiple regulatory functions. These functions include post-translational modification (e.g., phosphorylation) and interaction with scaffolding and other proteins. Differences in the amino acid sequence and domain position result in different three-dimensional protein structures and affect the function of MARK3, which distinguish it from the other MARK family members. Recent data indicate a potential role of MARK3 in several pathological conditions, including congenital blepharophimosis syndrome, osteoporosis, and tumorigenesis. The present review focuses on the physiological and pathological role of MARK3, its regulation, and recent developments in the small molecule inhibitors of the MARK3 signalling cascade.

Inhibiting ALK-TOPK signaling pathway promotes cell apoptosis of ALK-positive NSCLC.

T-LAK cell-oriented protein kinase (TOPK) is a potential therapeutic target in tumors. However, its role in anaplastic lymphoma kinase (ALK)-positive non-small cell lung cancer (NSCLC) has not been reported. Here, we found that TOPK was highly expressed in ALK-positive NSCLC. Additionally, ALK was identified as another upstream kinase of TOPK by in vitro kinase assay screening. Then, it was proven that ALK phosphorylated TOPK at Y74 in vitro and ex vivo, and the pathways downstream of ALK-TOPK were explored by phosphoproteomic analysis. Subsequently, we demonstrated that inhibiting TOPK enhanced tumor sensitivity to alectinib (an ALK inhibitor). The combination of alectinib and HI-032 (a TOPK inhibitor) suppressed the growth and promoted the apoptosis of ALK-positive NSCLC cells ex vivo and in vivo. Our findings reveal a novel ALK-TOPK signaling pathway in ALK-positive NSCLC. The combination of alectinib and HI-032 might be a promising therapeutic strategy for improving the sensitivity of ALK-positive NSCLC to targeted therapy.