SOD2 and breast cancer: In addition, β-carotene was demonstrated to be involved in the downregulation, at the protein level, of the antioxidant enzyme superoxide dismutase 2, SOD-2, of its transactivation factor (Nrf-2), and of XBP-1, the endoplasmic reticulum (ER) stress marker, further supporting the anticancer activity of β-carotene in the MCF-7 breast cancer cell line [90].