High APEX1 Expression Facilitates Osteosarcoma Cell Proliferation

Osteosarcoma (OS) is a serious malignancy affecting children and young adults; however, there is limited improvement in the survival of patients with OS over the past four decades. Molecular targeted therapy is a promising treatment strategy for OS. Apurinic/apyrimidinic exonuclease 1 (APEX1)-a key factor for DNA damage repair-is associated with OS proliferation, but the underlying molecular mechanism remains unclear. APEX1 expression in OS tissues and paired paracancerous tissues and in human osteoblast cell line hFOB1.19 and OS cell lines was determined using real-time quantitative PCR (RT-qPCR). APEX1-shRNA and NC-shRNA lentiviral vectors were constructed and transfected into MG-63 cells. The effects of APEX1 knockdown on MG-63 cell proliferation and apoptosis were assessed using MTT, xenograft tumor growth, and terminal deoxynucleotidyl transferase dUTP nick end labeling assays. Expression changes of apoptosis- and angiogenesis-related genes due to APEX1 knockdown were detected using RT-qPCR and immunohistochemistry. To preliminarily determine the mechanism by which APEX1 affects OS cell proliferation, transcription factors were predicted using three databases, and construction of protein-protein interaction network, gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed. APEX1 expression was higher in OS tissues than in paracancerous tissues. APEX1 expression was also higher in OS cell lines than in hFOB1.19 cells, with the highest APEX1 expression observed in MG-63 cells. APEX1 knockdown mediated by APEX1-shRNA lentivirus markedly suppressed MG-63 cell proliferation both in vitro and in vivo and induced their apoptosis. APEX1 knockdown downregulated CD31 expression but had no effect on the expression of P53 and Caspase3. Bioinformatics analyses suggested that USF1 or SP1 regulates APEX1 transcription and its recruitment in DNA damage response pathways, affecting OS cell proliferation. Thus, high APEX1 expression in OS facilitates cell proliferation likely via CD31, and USF1 or SP1 may regulate APEX1 transcription and its recruitment in DNA damage response pathways.