Cyclin K Interacts with β-catenin to Induce Cyclin D1 Expression and Facilitates Tumorigenesis and Radioresistance in Lung Cancer

Radioresistance remains the major cause of local relapse and distant metastasis in lung cancer. However, the underlying molecular mechanisms remain poorly defined. This study aimed to investigate the role and regulatory mechanism of Cyclin K in lung cancer radioresistance. Expression levels of Cyclin K were measured by immunohistochemistry in human lung cancer tissues and adjacent normal lung tissues. Cell growth and proliferation, neutral comet and foci formation assays, G2/M checkpoint and a xenograft mouse model were used for functional analyses. Gene expression was examined by RNA sequencing and quantitative real-time PCR. Protein-protein interaction was assessed by immunoprecipitation and GST pull-down assays. We report that Cyclin K is frequently overexpressed and correlates with poor prognosis in lung cancer patients. Functionally, we demonstrate that Cyclin K depletion results in reduced proliferation, defective G2/M checkpoint and enhanced radiosensitivity in lung cancer. Mechanistically, we reveal that Cyclin K interacts with and promotes the stabilization of β-catenin protein, thereby upregulating the expression of Cyclin D1. More importantly, we show that Cyclin D1 is the major effector that mediates the biological functions of Cyclin K in lung cancer. These findings suggest that Cyclin K positively modulates the β-catenin/Cyclin D1 axis to promote tumorigenesis and radioresistance in lung cancer, indicating that Cyclin K may represent a novel attractive biomarker for lung cancer radiotherapy.