The Mechanism Study Of Splicing Factor NONO In Mediating Glioblastoma Progression

Glioblastoma multiforme(GBM)is the most malignant tumor of the central nervous system.The current treatment options include surgical resection and temozolomide combined with adjuvant radiotherapy and chemotherapy,while the prognosis of patients is still only 14 months.Therefore,it is urgent to explore new treatment options and strategy to improve the prognosis of GBM patients.Process of precursor mRNA(pre-mRNA)by splicing factor is a critical step in cancer progression,which demonstrates the proteins with splicing function may be potential molecular targets for cancer therapy.The hyperactivation of transcription is a common feature of various cancers producing an increase in nascent mRNA which requires processing.PremRNA splicing is a post-transcriptional process used to generate multiple mRNA isoforms from a single gene.As the mRNA determines the protein sequence and function,the splicing process has the potential to expand the variety of encoded proteins.Pre-mRNA expression is regulated by transcription,and the relative abundance of specific mRNA depends on the splicing context.RNA sequencing has indicated that greater than 90%of human genes encoding proteins undergo pre-mRNA splicing to remove introns,and intron retention is a common type of abnormal splicing.Recent studies have reported numerous aberrant splicing events that influence cancer progression,including glioblastoma multiforme(GBM).It is indicated that splicing factors are potential therapeutic target in the treatment of GBM.Previous studies have reported that certain RNA binding proteins(RBPs)with splicing functions are dysregulated and promote the development of cancer.Non-POU domaincontaining octamer-binding protein(NONO)is an RBP and belongs to the Drosophila behavior human splicing(DBHS)family.Other members of the DBHS family include the paralogs splicing factor,proline-and glutamine-rich(SFPQ)and paraspeckle component 1(PSPC1).These predominantly nuclear proteins have two RNA-recognition motifs(RRM)and are components of subnuclear body-paraspeckles.The paraspeckle complex is known to regulate DNA repair and RNA metabolism,including splicing,stabilization and export.Similar to many RBPs,NONO exerts its various functions through multiple mechanisms,and participates in different physiological and pathological conditions.For example,NONO is essential for cGAS-mediated innate immune activation and directly binds the viral capsid in the immunity pathway.The protein is also recruited to repair DNA damage and suppresses telomere instability.Apart from these roles,NONO is required in transcriptional and posttranscriptional regulation at different stages.The Drosophila ortholog of NONO,NonA,facilitates pre-mRNA splicing and upregulates cpx expression.NONO deficiency interferes with TET1-associated transcription through epigenetic mechanisms in mice.NONO also coordinates pre-mRNA processing of metabolic genes,especially the removal of introns.However,the function of NONO requires further elaboration in RNA splicing and the development of cancer,especially in GBM,which has been until now largely unexplored.In this study,we found the mRNA splicing protein NONO to be overexpressed in human gliomas based on analysis of expression data from publicly available databases,The Cancer Genome Atlas(TCGA)and the Chinese Glioma Genome Atlas(CGGA).In vitro and in vivo NONO promoted GBM progression including growth and invasion,and inhibited cell apoptosis.We further demonstrated that NONO promotes GBM proliferation and invasion through splicing of specific pre-mRNAs such as GPX1.Splicing of the GPX1 pre-mRNA required a specific functional domain of NONO and interaction with other DBHS protein family members.Through the function of downstream molecular GPX1,knockdown of NONO altered the state of GBM redox homeostasis which was rescued with ectopic expression of GPX1.Finally,to explore the underlying mechanisms and the potential for future clinical translation,we tested Auranofin,a small molecule inhibitor previously reported to target NONO,in a xenograft model for GBM.Auranofin thus provides a promising candidate molecule for the treatment of GBM.