ESR1 and breast cancer: Prx1 enhances p65-mediated cyclooxygenase (COX)-2 gene expression in estrogen receptor (ER) deficient human breast cancer cells (MDA-MB-231), and knockdown of Prx-I can attenuate COX-2 expression by reducing the occupancy of NF-κB at its upstream promoter element, indicating that Prx-I acts as a chaperone to enhance the transactivation potential of NF-kappaB in ER-deficient-breast cancer cells [39].