Identification of Mesenchymal stem cells Functions in the development of osteosarcoma：A bioinformatics analysis 

Background: ： Mesenchymal stem cells can promote osteosarcoma cell proliferation and migration, while the underlying mechanism remains unknown. The aim of the study was to identify the crucial genes between mesenchymal stem cells (MSC) and osteosarcoma cells (OS) to investigate the potential molecular mechanism of osteosarcoma. Methods: ： GSE42352 and GSE39262 were downloaded from Gene Expression Omnibus (GEO) database. The GEO2R calculation method was used to analyze these two gene profiles. Differentially expressed genes (DEGs) were identified between mesenchymal stem cells and osteosarcoma cells. Moreover, FunRich was utilized to conduct functional enrichment analysis. These DEGs were mapped to STRING database to construct a protein-protein interaction (PPI) network, and hub genes were identified by Cytoscape plug-in CytoHubba and CytoNCA. Furthermore, the expression of identified hub genes was validated by the GEPIA database. The correlations between microRNA (miRNA) and hub genes were analyzed by the online website StarBase. The correlation among microRNA (miRNA), transcription factors (TFs) and hub genes were analyzed by Cytoscape plug-in iRegulon and TRRUST database. Cytoscape was used to establish a regulatory network of TF‐miRNA‐target gene. Finally, the TCGA clinical data was used to verify the clinical pathological features of CCNA2. Results: : A total of 225 markedly robust DEGs were identified (101 upregulated and 124 downregulated). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that these DEGs were related to various cancer-related biological pathways and functions. A PPI network was constructed including 225 nodes and 1695 edges, and 9 hub genes were found in the PPI networks. Re-analysing a PPI network of all cell cycle genes showed CCNA2 is the most important node in biological networks. Analysis of human samples confirmed that miR-381 and CCNA2 exhibited an inverse pattern of expression in human osteosarcomas. Analysis of the original patients data from TCGA Website confirmed that CCNA2 expression increased in patients was associated with metastatic. Investigating the relationship between CCNA2 and tumour immunity showed CCNA2 was involved in the infiltration of CD4+ T cells in SARC and had a significant coexpression relationship with CD274 and TOX. Conclusions: : CCNA2 is a promising prognostic biomarker and potential therapeutic target for OS patients. In particular, miR-381 may inhibit the proliferation of OS by specifically targeting CCNA2.