GPX1 and breast carcinoma: For example, differences in CpG island methylation between ERα-positive and ERα-negative breast cancer cells led to different accessibility of the ERα promoter for AP-2γ binding.[44] Similarly, glutathione peroxidase 1, a key factor influencing the oxidative stress response in breast cancer, is mainly controlled by AP-2γ and the methylation status of the promoter.