MMP9 and breast carcinoma: Interestingly, the MMP-9 luciferase reporter gene and chromatin immunoprecipitation (ChIP) assays carried out on breast cancer MDA-MB-231 cells under hypoxic conditions, showed that HIF-1 forms a complex with p300 that increases MMP-9 promoter activity, including H3 and H4 acetylation [83].