Background: NOX4 is highly expressed in breast cancer and is closely associated with cell invasion and metastasis. The involvement of NOX4 in glycolysis in breast cancer remains unclear. The aim of this study was to investigate the role and mechanism of NOX4 in glycolysis in breast cancer. Methods: NOX4 expression in breast cancer cells was detected by qRT-PCR and western blotting. siRNAs and plasmids were used to silence or enhance the expression of NOX4. The mRNA and protein expression of HK2, GLUT1, PKM2, LDHA, and YAP was detected by qRT-PCR and western blotting, and the ¹⁸F-FDG uptake rate was detected by γ-radiometer. Detection of reactive oxygen species (ROS) in cells was performed using a commercial ROS kit. After transfection, CCK8, EDU and Transwell experiments were conducted to detect cell proliferation and migration ability. MicroPET imaging was used to detect the effects of NOX4 on tumor metabolism. Immunohistochemistry was used to detect the expression of NOX4, glycolytic enzymes HK2, GLUT1, PKM2, LDHA, the proliferation index KI67, and the activation of YAP pathway molecule. Results: In this study, the expression of NOX4 in MDA-MB-231 and MDA-MB-453 was higher than in MCF10A. qRT-PCR and western blotting experiments showed that NOX4 downregulation decreased the expression of glycolytic enzymes HK2, GLUT1, PKM2, LDHA, and 18F-FDG uptake. Conversely, the overexpression of NOX4 enhanced the expression of HK2, GLUT1, PKM2, LDHA, and 18F-FDG uptake. Proliferation and migration experiments showed that after down-regulation of NOX4, cell proliferation and migration ability decreased, while NOX4 overexpression promoted cell proliferation and migration ability. Additionally, ROS content and YAP expression decreased after NOX4 down-regulation, while ROS content and YAP expression increased following NOX4 overexpression, which was reversed by N-acetyl cysteine (NAC), a ROS inhibitor. Furthermore, exposure to NAC and Peptide17, a YAP inhibitor, blocked the increase in glycolytic enzyme expression, and the enhancement of proliferation and migration caused by NOX4 overexpression. In addition, in animal experiments, the results of the MicroPET imaging showed that the glucose metabolism rate of the NOX4 inhibitor group was significantly lower than that of the control group. ROS levels in the NOX4 inhibitor group was lower than that in the control group. Immunohistochemistry showed that the expression of HK2, GLUT1, PKM2, LDHA, KI67, and YAP in the NOX4 knock-down group were decreased. Conclusions: NOX4 affects breast cancer glycolysis through ROS-induced activation of the YAP pathway, further promoting the proliferation and migration of breast cancer cells.

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