The mineralocorticoid receptor modulates timing and location of genomic binding by glucocorticoid receptor in response to synthetic glucocorticoids in keratinocytes

Glucocorticoids (GCs) exert potent antiproliferative and anti‐inflammatory properties, explaining their therapeutic efficacy for skin diseases. GCs act by binding to the GC receptor (GR) and the mineralocorticoid receptor (MR), co‐expressed in classical and non‐classical targets including keratinocytes. Using knockout mice, we previously demonstrated that GR and MR exert essential nonoverlapping functions in skin homeostasis. These closely related receptors may homo‐ or heterodimerize to regulate transcription, and theoretically bind identical GC‐response elements (GRE). We assessed the contribution of MR to GR genomic binding and the transcriptional response to the synthetic GC dexamethasone (Dex) using control (CO) and MR knockout (MREKO) keratinocytes. GR chromatin immunoprecipitation (ChIP)‐seq identified peaks common and unique to both genotypes upon Dex treatment (1 h). GREs, AP‐1, TEAD, and p53 motifs were enriched in CO and MREKO peaks. However, GR genomic binding was 35% reduced in MREKO, with significantly decreased GRE enrichment, and reduced nuclear GR. Surface plasmon resonance determined steady state affinity constants, suggesting preferred dimer formation as MR‐MR > GR‐MR ~ GR‐GR; however, kinetic studies demonstrated that GR‐containing dimers had the longest lifetimes. Despite GR‐binding differences, RNA‐seq identified largely similar subsets of differentially expressed genes in both genotypes upon Dex treatment (3 h). However, time‐course experiments showed gene‐dependent differences in the magnitude of expression, which correlated with earlier and more pronounced GR binding to GRE sites unique to CO including near Nr3c1. Our data show that endogenous MR has an impact on the kinetics and differential genomic binding of GR, affecting the time‐course, specificity, and magnitude of GC transcriptional responses in keratinocytes.