JUN and breast cancer: At the molecular level, NCOA1 upregulates VEGFa expression in both mouse mammary tumors and cultured breast cancer cells, and it does so by associating with both c-Fos, which is recruited to the AP-1 site at bp −938 of the VEGFa promoter, and HIF1α, which is recruited to the HIF1α-binding element at bp −979 of the VEGFa promoter, to enhance VEGFa transcription.