Conversely, accumulated damaged mitochondria that suffer excessive oxidative stress show m decreases, mitochondrial permeability transition (MPT) pore opening and mitochondrial depolarization, which lead to Cyt c release to cytosol, and trigger Caspase-3 activation and cell apoptosis. 1% O2 environment. Results: MRPL52 expression was upregulated in human breast cancer and was significantly associated with aggressive clinicopathological characteristics and a higher metastatic risk of breast cancer patients. We found that the overexpression of MRPL52 in breast cancer is induced by hypoxia-inducible factor-1 in response to hypoxic exposure. The role of MRPL52 in suppressing apoptosis and promoting migration and invasion of hypoxic breast cancer cells was demonstrated by our experimental evidence. Mechanistically, MRPL52 promoted PTEN-induced putative kinase 1 /Parkin-dependent mitophagy to remove oxidatively damaged mitochondria and prevent uncontrolled reactive oxygen species (ROS) generation, thus repressing activation of the mitochondrial apoptotic cascade. Additionally, MRPL52 augmented epithelial-mesenchymal transition, migration and invasion of hypoxic breast cancer cells by activating the ROS-Notch1-Snail signaling pathway. Benefited from this bidirectional regulatory mechanism, MRPL52 is responsible for maintaining ROS GTS-21 (DMBX-A) levels in a window that can induce tumorigenic signal transduction without causing cytotoxicity in hypoxic breast cancer cells. Conclusions: This work elucidates the molecular mechanism by which MRPL52 mediates hypoxia-induced apoptotic resistance and metastatic initiation of breast cancer, and provides new insights into the interplay between cancer and the tumor microenvironment. orthotopic xenograft implantation assay, female BALB/c mice (6 weeks old, weighing 16-20 g, acquired from Charles River, Beijing) were randomly divided into 4 groups (n = 5 per group); the MRPL52 overexpressed group, the MRPL52 knockdown group and the control groups. The stably-transfected 4T1 cells were validated by RT-qPCR, suspended in 100 L of PBS plus 100 L of Matrigel substrate and injected into the 4th coupled mammary fat pad of mice GTS-21 (DMBX-A) at a density of 5 105 cells. Tumor volumes were measured every 3 SCKL days using the following formula: length width2 0.5 (cm3). Mice were sacrificed on the 24th day post-injection, and tumors were removed and weighed. The volume of the tumor was calculated and a tumor growth curve was then plotted. Then the xenografts were imaged, fixed in 4% paraformaldehyde, and embedded in paraffin. The green fluorescein-based TUNEL assay of the tissues was performed by an Cell Death Detection Kit (Roche, Germany). The lungs and livers of mice were collected, fixed in 4% paraformaldehyde, embedded in paraffin and stained by hematoxylin and eosin (H&E). The animal experimental procedures were approved by the China Medical University Institutional Ethics Committee and followed the Guide for the Care and Use of Laboratory Animals (US National Institutes of Health publication, Doc. 2011-11490). Statistical analyses All data analyses were performed using GraphPad Prism software (version 8.0), with results expressed as the mean standard deviation. Chi-Square test and Pearson’s 2 test were used to analyze patient data. Student’s t test was used to compare two groups, while one way analysis of variance (ANOVA) was used for multiple data groups. All experiments were repeated in least triplicate. A P value 0.05 was considered statistically significant. Results MRPL52 upregulation is negatively related to the clinical outcomes of human BC To screen for significant genes in BC that are potentially associated with BC metastasis, we performed RNA-seq assays of our clinical BC samples, and the screening rationale is shown in Figure ?Figure1A.1A. Gene Set Enrichment Analysis (GSEA) was performed on differential genes between BC tissues from metastatic (TM) and non-metastatic (TnM) patient cohorts. The pathways with a significant enrichment (P 0.05) are listed in Figure ?Figure1B,1B, among which two mitochondria-related pathways (mitochondrial transport and mitochondrial gene expression) draw our attention. Interestingly, we noted GTS-21 (DMBX-A) that the MRP family genes account for more than half of total genes enriched in the two pathways. Therefore, six MRP family candidate genes that were enriched and upregulated in RNA-seq (P 0.01) have been screened out. The expression of these genes were further verified in clinical samples, which demonstrated that MRPL52 exhibited the highest expression in BC tissues compared with ANTs (Figure ?(Figure1C).1C). As indicated, the correlated genes of MRPL52 were enriched in GO terms closely related to mitochondria, including mitochondrial gene translation, ETC complex assembly and electron transfer activity (Figure S1A-B). Consistent with the transcriptome sequencing results, MRPL52 was differentially overexpressed in our clinical samples from 102 BC patients (Figure ?(Figure1D-E).1D-E). The TM displayed higher MRPL52 expression than TnM in a 5-year follow-up period (Figure ?(Figure1F).1F). MRPL52 overexpression was strongly correlated with more advanced.