β-Trcp ubiquitin ligase and RSK2 kinase-mediated degradation of FOXN2 promotes tumorigenesis and radioresistance in lung cancer

Aberrant expression of FOXN2, a member of the Forkhead box transcription factors, has been found in several types of cancer. However, the underlying mechanisms of FOXN2 deregulation in tumorigenesis remain largely unknown. Here, we find that FOXN2 binds to and is ubiquitinated by beta-Trcp ubiquitin ligase and RSK2 kinase for degradation. Furthermore, we demonstrate that the Ser365 and Ser369 sites in a conserved DSGYAS motif are critical for the degradation of FOXN2 by beta-Trcp and RSK2. Moreover, gain-of-function and loss-of-function studies show that FOXN2 impairs cell proliferation in vitro and in vivo and enhances the radiosensitivity of lung cancer. Importantly, beta-Trcp-mediated and RSK2-mediated degradation of FOXN2 promotes tumorigenesis and radioresistance in lung cancer cells. Collectively, our study reveals a novel post-translational modification of FOXN2 and suggests that FOXN2 may be a potential therapeutic and radiosensitization target for lung cancer.