MicroRNA-499a-5p inhibits osteosarcoma cell proliferation and differentiation by targeting protein phosphatase 1D through protein kinase B/glycogen synthase kinase 3β signaling

A number of studies have attempted to elucidate the association between mircoRNAs (miRNAs/miRs) and cancer-associated processes. The aim of the present study was to determine how miR-499a-5p intervenes in human osteosarcoma cell proliferation and differentiation. The cancerous tissues and adjacent non-cancerous tissues of 62 patients with osteosarcoma (OS) were collected. miRNA microarray analysis revealed that 29 miRNAs were upregulated while 26 were downregulated, among which miR-499a-5p expression was the most decreased. Western blot analysis and reverse transcription-quantitative polymerase chain reaction demonstrated that the mRNA and protein expression of miR-499a-5p was lower, while that of protein phosphatase 1D (PPM1D) was higher in OS tissues compared with expression levels in normal tissues. Furthermore, miR-499a-5p expression was markedly decreased in the metastatic tumors and in those at stage III+IV compared with the non-metastatic tumors and those at stage I, respectively. In addition, following transfection of the human OS MG-63 cell line with an miR-499a-5p mimic, the expression of miR-499a-5p was elevated while the protein and mRNA expression of PPM1D was decreased. When combining these findings with the information obtained from the Targetscan predictive software, it was confirmed that PPM1D was targeted by miR-499a-5p. In MG-63 cells transfected with an miR-499a-5p mimic, PPM1D-associated downstream proteins phosphorylated protein kinase B (p-Akt) and phosphorylated glycogen synthase kinase 3β (p-GSK-3β) were significantly downregulated compared with the negative control (NC) group, while the expression of p-Akt and p-GSK-3β were significantly elevated in the tumor tissues compared with the adjacent non-tumor tissues. Simultaneously, the growth and proliferation activity of MG-63 cells were notably reduced when transfected with the miR-499a-5p mimic, compared with the NC group. Therefore, it may be concluded that miR-499a-5p suppresses OS cell proliferation and differentiation by targeting PPM1D through modulation of Akt/GSK-3β signaling.