The KIF5B-RET Fusion Kinase Promotes Cell Proliferation By Multilevel Activation Of STAT3in Lung Cancer

Background:Lung cancer in nonsmokers tends to be driven by a single somatic mutation or a gene fusion.KIF5B-RET fusion is an oncogene identified in non-small cell lung cancers,but it is unclear how KIF5B-RET activates the specific signaling pathways for cellular transformation.STAT3 mediates a variety of biological processes including cell survival and cell proliferation,and it is often activated in lung cancer.In this study,we investigated the oncogenic activity of KIF5B-RET fusion and explored the hypothesis that STAT3 may be involved in the signaling triggered by KIF5B-RET.We aimed to provide a basis for the further development of RET-targeted therapy inKIF5B-RETpositive lung cancer patients.Methods:RT-PCR was used to screen for KIF5B-RET fusions in Chinese lung cancer patients.To further explore the oncogenic activity ofKIF5B-RET kinase in lung cancer cells we manipulated its expression genetically followed by colony formation and tumor formation assays.The mechanism of KIF5B-RET kinase inducing cell proliferation was investigated by western blot,co-immunoprecipitation,and use of RET,MAPK and STAT3 inhibitors.Results:KIF5B-RET fusion gene was identified in a Chinese lung adenocarcinoma patient(about 1.0%).When the KIF5B-RETwere exogenously expressed in lung cancer cells,the fusion kinase was constitutively active in the absence of serum or ligand stimulation,and KIF5B-RET transfected cells showed a significantly increasing proliferation rate and colony-forming ability.Consistently,suppression of KIF5B-RET kinase activity by its inhibitor reduced the proliferation of positive cells.Unexpectedly,we found that the expression of KIF5B-RET fusion kinase increased STAT3 phosphorylation,indicating that STAT3 signaling likely mediated these effects triggered by KIF5B-RET.In particular,we observed that KIF5B-RET fusion kinase could directly induce STAT3 phosphorylation on Tyr705 and phosphorylated Ser727 partially through the MAPK-ERK pathway.Conclusions:Our findings demonstrate an important role of KIF5B-RET in promoting the cell growth and tumorigenicity of non-small cell lung cancer through sustained activation of STAT3 signaling.