Regulatory Mechanisms Of Tumor Exosome Secretion And Selective Package Of MicroRNAs Into Exosome

Exosomes are a class of nanoparticles with diameters ranging from 50-100 nm that are secreted by cells transmitting information from cell to cell.Exosomes can shuttle bioactive molecules including lipids,proteins,as well as nucleic acids from one cell to another,leading to the exchange of genetic information and reprogramming of the recipient cells,which exhibit pleiotropic biological functions.MicroRNAs(miRNAs)are a class of non-coding RNAs with length of about 22 nucleotides which regulate target gene expression at the post-transcriptional level.They can be delivered by exosomes into recipient cells regulating multiple target genes or signaling events.Under different physiological conditions,cells can sort specific intracellular miRNAs into exosomes and further secret those exosomes to modulate biological activities.Though the importance of exosomes and their packaged miRNAs in a variety of cellular processes has been recognized widely.The molecular mechanisms of exosome secretion and sorting of miRNAs into exosomes are poorly understood.We start with the phenomenon that tumor cells release excessive amount of exosomes than normal ones and find PKM2,the rate-limiting enzyme of tumor aerobic glycolysis has a strong relationship with tumor exosome secretion.By a systematic biochemistry study,we find PKM2 dimer is an active protein kinase,which can phosphorylate SNAP-23 and promote exosome secretion.A further study of miRNA selective packaged mechanism show the Karyopherin protein family mediate the transport of miRNAs into exosomes.A bioinformatics analysis show that special motifs with sequentially arrayed nucleotides on the stem-loop structure of pre-miRNAs can determine the identification and sorting of miRNAs into exosomes.The study reports the first regulatory mechanism of tumor exosome secretion.PKM2 not only plays a role as pyruvate kinase elevating aerobic glycolysis in tumor cells,but also works as protein kinase promoting exocytosis through phosphorylation of SNAP-23.Besides,we first report the Karyopherin protein family is the shuttle transporting miRNAs in cells.They can recognize motifs localized on the stem-loop structure of pre-miRNAs and sort them into exosomes,providing a new sight into mechanism of exosome selective packaged miRNAs.