Parp7 And Mono-Adp-Ribosylation Negatively Regulate Estrogen Receptor Alpha Signaling In Human Breast Cancer Cells

ADP-ribosylation is a post-translational protein modification catalyzed by a family of proteins known as poly-ADP-ribose polymerases. PARP7 (TIPARP; ARTD14) is a mono-ADP-ribosyltransferase involved in several cellular processes, including responses to hypoxia, innate immunity and regulation of nuclear receptors. Since previous studies suggested that PARP7 was regulated by 17 beta-estradiol, we investigated whether PARP7 regulates estrogen receptor alpha signaling. We confirmed the 17 beta-estradiol-dependent increases of PARP7 mRNA and protein levels in MCF-7 cells, and observed recruitment of estrogen receptor alpha to the promoter of PARP7. Overexpression of PARP7 decreased ligand-dependent estrogen receptor alpha signaling, while treatment of PARP7 knockout MCF-7 cells with 17 beta-estradiol resulted in increased expression of and recruitment to estrogen receptor alpha target genes, in addition to increased proliferation. Co-immunoprecipitation assays revealed that PARP7 mono-ADP-ribosylated estrogen receptor alpha, and mass spectrometry mapped the modified peptides to the receptor's ligand-independent transactivation domain. Co-immunoprecipitation with truncated estrogen receptor alpha variants identified that the hinge region of the receptor is required for PARP7-dependent mono-ADP-ribosylation. These results imply that PARP7-mediated mono-ADP-ribosylation may play an important role in estrogen receptor positive breast cancer.