Targeting Cyclin Y Inhibits STAT3 Activation to Enhance Radiosensitivity via Down-regulation of RRM2 in Lung Cancer

Purpose: Radioresistance is a main reason for the recurrence and metastasis of lung cancer. Cyclin Y is involved in normal physiological processes such as cell proliferation, growth and metabolism, as well as in the development of certain cancers. However, the function and mechanism of Cyclin Y in lung cancer are still unclear.Methods: Lung cancer cell lines were subjected to Cyclin Y knockdown using small interfering RNA (siRNA), and their growth and proliferation were assessed in vitro. Comet assay, γH2AX/Rad51 foci formation assay and clonogenic cell survival assay were performed to assess DNA damage and the DNA repair capacity. SgRNA transfection was applied to construct cell lines with stable Cyclin Y knockdown. Xenograft mouse models were used to validate the findings in vivo. RNA sequencing (RNA-seq) analysis was conducted to clarify the downstream target genes of Cyclin Y. Western blotting was employed to measure protein expression.Results: Cyclin Y was overexpressed in lung cancer, correlating with poor prognosis. Cyclin Y knockdown inhibited cell growth and proliferation, increased DNA damage, inhibited DNA damage repair and increased radiosensitivity in vitro and in vivo. RNA-seq analysis was used to reveal RRM2 as a downstream target gene of Cyclin Y. Cyclin Y depletion down-regulated the protein and mRNA levels of RRM2, leading to reduced STAT3 phosphorylation. Rescue experiments demonstrated that the effect of Cyclin Y on lung cancer was mediated partially by RRM2.Conclusions: We revealed for the first time that targeting Cyclin Y inhibits tumorigenesis and promotes radiosensitivity in lung cancer partially through the RRM2-STAT3 signaling pathway.