HIF1A and breast cancer: Under hypoxia, CLDN6 is transcriptionally upregulated by HIF-1α and inhibits breast cancer cells migration and invasion by combining and decreasing β-catenin in the cytoplasm, then reducing the transcriptional regulation of SENP1 by β-catenin, which prevents the deSUMOylation of HIF-1α and leads to HIF-1α degradation, suggesting there is a negative feedback loop between HIF-1α and CLDN6 [22].