MEK5-ERK5 pathway mediates mitophagy by regulating Nur77 to promote tumorigenesis of osteosarcoma cells

Objectives To investigate the influence of MEK5/ERK5 pathway on mitophagy in osteosarcoma (OS), as well as the involved molecular mechanisms. Methods The overlapped genes of mitophagy-related genes from MSigDB database and DEGs between metastatic and primary OS groups from GSE32981 were identified. GSVA of mitophagy-related pathways between the metastatic and primary groups were analyzed. The relationships between Nur77 and mitophagy-related pathways, prognosis, immune infiltrating cells, immune response gene sets were investigated. Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blotting were utilized to assess the expression levels of MEK5, ERK5, Nur77, PINK1, and Parkin. Cellular behaviors and mitochondrial potential were evaluated via CCK-8, Transwell assay and JC-1 staining. Results Total 4 overlapped genes were obtained as mitophagy-related DEGs, including GABARAPL1, HIF1A, PINK1, and RB1CC1. The activity scores of 3 mitophagy-related pathways exhibited significant differences between metastatic and primary groups. Importantly, Nur77 was significantly negatively correlated with a mitophagy-related pathway (GOBP MITOPHAGY: R = - 0.48, P = 0.02). The Nur77 expression in metastatic group was remarkedly higher than that in the primary group (P < 0.001). Patients with high Nur77 expression had poor prognosis, with AUC values all above 0.615 in predicting 1-, 3-, and 5-year survival. In addition, Nur77 was closely related to numerous immune cells, including activated dendritic cells, activated mast cells and M0 macrophages, and immune response gene sets chemokines and cytokines (all P < 0.05). In addition, MEK5/ERK5 pathway is activated in OS, and Nur77 is overexpressed in OS, and MEK5/ERK pathway promotes Nur77 expression, tumorigenesis and mitochondrial function in U2OS cells. Cytosporone B implement significantly increased the tumorigenesis of U2OS cells in sh-MEK5 group, and inhibited the weaken in mitochondrial membrane potential caused by MEK5 downregulation, and reversed the protein levels of mitophagy markers PINK1 and Parkin in sh-MEK5 group. Conclusions MEK5-ERK5 pathway mediates mitophagy by regulating Nur77 to promote tumorigenesis of OS cells. These findings offered promising therapeutic targets for OS.