The Role Of Ribosomal Protein RPS27L In DNA Damage Repair Of Lung Cancer Cells

Ribosomal proteins（RPs）,important components of the ribosome,play prime roles in protein synthesis.In addition,many ribosomal proteins have been shown to activate the tumor suppressor p53 and its downstream pathways in response to ribosomal stress.Ribosomal protein S27-like（RPS27L）is an evolutionarily conserved ribosomal protein.Recent studies showed that RPS27L is a direct p53 target and plays an important role in maintenance of genome integrity,regulation of cell cycle,apoptosis and many other physiological activities.Our previous studies have shown that Rps27l knockout triggered genomic instability,resulting in loss of heterozygosity in the p53 allele,eventually leading to lymphomagenesis in p53^+/-mice.Moreover,we also found that Rps27l disruption inhibited DNA damage response via p53-MDM2 and MDM2-MRN-ATM axes,sensitizing p53^+/-mice to radiation.However,whether and how RPS27L regulates DNA repair is still unknown.In this study,we found that RPS27L interacts with FANCD2 and FANCI,two proteins functioning in FA pathway,the major pathway to rapir DNA interstrand crosslinks,ICLs.FANCD2 and FANCI bind to each other to form a heterodimer,named ID2 complex,the key complex in FA pathway.RPS27L knockdown in lung cancer cell promotes the degradation of FANCD2 and FANCI via p62-mediated autophagy-lysosome pathway.Treatment with chloroquine（CQ）,a lysosomal inhibitor,or silencing of Beclin 1,the key autophagy protein,reverses the reduction of FANCD2and FANCI by RPS27L disruption.Biologically,RPS27L knockdown impaires DNA damage repair upon ICL-inducing agent mitomycin C（MMC）treatment,leading to sensitization of lung cancer cells to MMC,which can be partially reversed by CQ treatment.Finally,RPS27L m RNA levels were lower in different types of non-small cell lung cancer（NSCLC）（including lung adenocarcinoma,large cell lung cancer,and squamous cell lung cancer）tissues,as compared to normal lung tissues.Moreover,RPS27L m RNA level is correlated with tumor differentiation.Immunohistochemical staining of the lung cancer tissuse microarray containing 117 tumor tissues using RPS27L antibody reveals that low RPS27L protein level is significantly associated with the poor survival of NSCLC patients.Collectively,these results showed that RPS27L positively regulates ICL repair by binding with FANCD2 and FANCI to prevent their degradation via the autophagy-lysosome pathway.Moreover,RPS27L expression correlates with lung cancer progression and patient survival,suggesting that RPS27L might be served as a biomarker for prognosis of NSCLC patients.