hPMC2 is required for recruiting an ERβ coactivator complex to mediate transcriptional upregulation of NQO1 and protection against oxidative DNA damage by tamoxifen

In the presence of ERβ, trans-hydroxytamoxifen (TOT) protects cells against 17β-estradiol (E₂)-induced oxidative DNA damage (ODD) and this correlates with increased expression of the antioxidative enzyme quinone reductase (QR). Here, we investigate the molecular mechanism responsible for ERβ-mediated protection against ODD. We observe constitutive interaction between ERβ and the novel protein hPMC2. Using a combination of breast epithelial cell lines that are either positive or negative for ERα, we demonstrate TOT-dependent recruitment of both ERβ and hPMC2 to the EpRE (electrophile response element)-regulated antioxidative enzyme QR. We further demonstrate TOT-dependent corecruitment of the coactivators Nrf2, PARP-1 (poly (ADP-ribose) polymerase 1) and topoisomerase IIβ, both in the presence and absence of ERα. However, absence of either ERβ or hPMC2 results in nonrecruitment of PARP-1 and topoisomerase IIβ, loss of antioxidative enzyme induction and attenuated protection against ODD by TOT even in the presence of Nrf2 and ERα. These findings indicate minor role for Nrf2 and ERα in TOT-dependent antioxidative gene regulation. However, downregulation of PARP-1 attenuates TOT-dependent antioxidative gene induction. We conclude that ERβ and hPMC2 are required for TOT-dependent recruitment of coactivators such as PARP-1 to the EpRE resulting in the induction of antioxidative enzymes and subsequent protection against ODD.