Abstract: Objective  Screening the differential expression of circular RNA (circRNA) in the triple negative breast cancer (TNBC) with its tumor-adjacent tissues and to analyze the potentially downstream miRNAs and target genes associated circRNA candidates by bioinformatics analysis,then predict the potential regulatory pathways of circRNA in TNBC.
Methods  One paired triple negative breast cancer sample and adjacent non-cancerous tissues for RNA-Seq was collected from a patient received surgery at department of the thyroid and galactophore in Peking University Shenzhen Hospital.We obtained differential expression of circRNA and a total of ten circRNAs the five most significant up-regulated and down-regulated circRNA were selected.The RegRNA 2.0 website was used to predict the potential miRNAs corresponding to circRNA candidates,and three bioinformatics websites (miRDB,TargetScan,and RNAInter) were further utilized to predict the downstream mRNA of miRNAs.Gene ontology (GO) and Kyoto Encylopedia of Genes and Genomes (KEGG) analysis were performed for these target genes.The protein-protein interaction (PPI) network of the predicted target genes was analyzed by STRING online tools,and the data were exported before we imported them into the Cytoscape software.The key genes were screened out by MCODE plug-ins.Kaplan-Meier Plotter online database was used to analyze the relationship between the expression level of key genes and the prognosis of TNBC.
Results  There were 6547 differentially expressed circRNAs in the triple negative breast cancer tissues with its tumor-adjacent tissues,2311 of which were up-regulated and 4326 were down-regulated；a total of 1161 mRNAs were predicted in the downstream of 5 up-regulated circRNAs and 5 down-regulated circRNAs most significantly;the results of GO and KEGG analysis showed that these mRNA were mainly involved in negative regulation of transcription from RNA polymerase Ⅱ promoter,covalent chromatin modification,regulation of transcription and they are mainly involved in endocytosis,oxytocin signaling pathway,Wnt signaling pathway and cGMP-PKG signaling pathway;five key genes were screened out (UBOX5,UBE2G2,DTX3L,FZR1,RNF19A) among which the low expression of UBE2G2 and DTX3L indicated the poor overall survival of triple negative breast cancer patients;the corresponding miRNA and circRNA for UBE2G2 are hsa_miR-93-3p and hsa_circ_0001361,and hsa_miR-2115-5p and hsa_circ_0002874 for DTX3L respectively.
Conclusion  Among the downstream target genes of miRNA probably binding to circRNA candidates expressed differentially in triple negative breast cancer,the key genes are may be UBOX5,UBE2G2,DTX3L,FZR1 and RNF19A.UBE2G2 and DTX3L are related to the prognosis of TNBC patients,and their corresponding regulatory axes in TNBC are hsa_circ_0001361/miR-93-3p/ UBE2G2 and hsa_circ_0002874/miR-2115-5p/DTX3L respectively,which suggest that these two axes may participate in the occurrence and development of triple negative breast cancer.

Key words: triple negative breast cancer, circRNA, bioinformatics