17β-Estradiol-induced interaction of ERα with NPPA regulates gene expression in cardiomyocytes

17-Oestradiol (E2) and its receptors (ER and ER) are important regulators of physiological and pathological processes in the cardiovascular system. ER act in concert with other regulatory factors mediating oestrogenic effects. However, the underlying mechanisms modulating ER transcriptional activity are not fully elucidated. To gain better understanding of E2-induced ER action in the human heart, we aimed to identify and functionally analyse interaction partners of ER. Using yeast two-hybrid assays with a human heart cDNA library, we identified atrial natriuretic peptide precursor A (NPPA), a well-known cardiac hypertrophy marker, as a novel ER interaction partner interacting in an E2-dependent manner. Mutation analyses and immunofluorescence data indicated that the LXXLL motif within NPPA is necessary for its E2-induced interaction with ER, its action as a co-repressor of ER, and its translocation into the nucleus of human and rat cardiomyocytes. Expression analysis and chromatin immunoprecipitation assays in a human left ventricular cardiomyocyte cell line, AC16, showed that NPPA interacts with E2/ER, suppressing the transcriptional activity of ER on E2-target genes, such as NPPA, connexin43, actinin-2, nuclear factor of activated T-cells, and collagens I and III. We characterize for the first time an E2-regulated interaction of NPPA with ER in cardiomyocytes, that may be crucial in physiological and/or pathological cardiac processes, thereby representing a potential therapeutic target.