OR07-4 Regulation of Mineralocorticoid Receptor Transactivation By Circadian Protein Timeless

The mineralocorticoid receptor (MR) is a ligand activated transcription factor that plays an important role in cardiovascular physiology and disease. MR transactivation is regulated by ligand-dependent conformational change in the MR and recruitment of coregulator binding partners to form a unique DNA-binding complex at the hormone response element in target gene promoters. Differences in the recruitment of coregulatory proteins can promote tissue-, ligand- or gene-specific transcriptional outputs. The goal of this study was to evaluate a candidate MR coregulator, the circadian gene timeless for ligand and cell-selective regulation of MR transactivation. While timeless is not essential for mammalian clock function and does not bind DNA, timeless RNA and protein levels oscillate over 24hr. Co-expression of timeless dose-dependently down-regulated MR transactivation of an MR-responsive reporter in HEK293 cells, yet enhanced transactivation mediated by other steroid receptors. Timeless also inhibited MR transactivation of synthetic and native gene promoters, and expression of endogenous MR target genes, in H9c2 cardiac myoblasts. Immunofluorescence staining of timeless, and MR showed colocalization to the nucleus in the presence of aldosterone and co-immunoprecipitation which suggested an interaction, although a direct interaction was not confirmed. Taken together, these data suggest timeless is a novel MR coregulatory protein that may contribute to time-of-day-dependent MR transcriptional outputs and suggest new opportunities for the development of MR antagonists with selective actions. Presentation: Saturday, June 11, 2022 12:15 p.m. - 12:30 p.m.