PARP-1 Regulates Estrogen-Dependent Gene Expression in Estrogen Receptor α-Positive Breast Cancer Cells

Poly(ADP-ribose) polymerase-1 (PARP-1) has gained considerable attention as a target for therapeutic inhibitors in breast cancers. Previously we showed that PARP-1 localizes to active gene promoters to regulate histone methylation and RNA polymerase II activity (Pol II), altering the expression of various tumor-related genes. Here we report a role for PARP-1 in estrogen-dependent transcription in estrogen receptor alpha (ERα)-positive (ER⁺) breast cancers. Global nuclear run-on and sequencing analyses functionally linked PARP-1 to the direct control of estrogen-regulated gene expression in ER⁺ MCF-7 breast cancer cells by promoting transcriptional elongation by Pol II. Furthermore, chromatin immunoprecipitation sequencing analyses revealed that PARP-1 regulates the estrogen-dependent binding of ERα and FoxA1 to a subset of genomic ERα binding sites, promoting active enhancer formation. Moreover, we found that the expression levels of the PARP-1- and estrogen-coregulated gene set are enriched in the luminal subtype of breast cancer, and high PARP-1 expression in ER⁺ cases correlates with poor survival. Finally, treatment with a PARP inhibitor or a transcriptional elongation inhibitor attenuated estrogen-dependent growth of multiple ER⁺ breast cancer cell lines. Taken together, our results show that PARP-1 regulates critical molecular pathways that control the estrogen-dependent gene expression program underlying the proliferation of ER⁺ breast cancer cells. IMPLICATIONS: PARP-1 regulates the estrogen-dependent genomic binding of ERα and FoxA1 to regulate critical gene expression programs by RNA Pol II that underlie the proliferation of ER⁺ breast cancers, providing a potential therapeutic opportunity for PARP inhibitors in estrogen-responsive breast cancers.