Interaction of the Mineralocorticoid Receptor With RACK1 and Its Role in Aldosterone Signaling

Abstract

The mineralocorticoid receptor (MR) is a member of the steroid-thyroid hormone receptor superfamily of ligand-dependent transcription factors with diverse functions including the biological actions of aldosterone. Identification of the various transcriptional coregulators of MR is essential for understanding the complexity of MR signaling pathways under physiological and pathological conditions. We used a yeast two-hybrid system to find proteins that interact with a full-length MR and found, among other proteins, that MR interacted specifically with receptor for activated C kinase 1 (RACK1), a scaffolding protein. Overexpression of RACK1 using a tetracycline-inducible lentivirus in mouse cortical collecting duct M1 cells stably expressing the rat MR and a Gaussia luciferase gene reporter under a hormone-response element promoter resulted in enhanced agonist-dependent MR transactivation. Knockdown of RACK1 protein expression by short hairpin RNAs led to a significant reduction in MR activation of the reporter gene and the endogenous genes Ctla2α and Psca. We also demonstrated that RACK1 regulation of MR action is mediated through phosphorylation by the PKC-β signaling pathway. MR and RACK1 were coimmunoprecipitated using an MR antibody in male Sprague-Dawley brain tissue and M1-rMR cells, and colocalization in M1-rMR cells and male rat brains was confirmed by immunofluorescence and immunohistochemistry. The scaffolding protein RACK1 is associated with MR under basal and agonist-stimulated conditions and facilitates agonist-stimulated MR actions through PKC-β. These findings indicate that RACK1 is a newly described coactivator of MR.

The role of WD40 repeat-containing proteins in endocrine (dys)function

“…RACK1 is thought to function as a coactivator of MR (see Table 1). It is associated with the MR under basal-and agonist-stimulated conditions and facilitates agonist-stimulated MR actions through PKC-β (Kuppusamy et al 2017).…”

“…Mifsud et al suggested that the MR is selectively involved in ciliogenesis in human fetal neuronal progenitor cells via binding to >50 ciliary genes (Mifsud et al 2021). Two WD40 proteins, RACK1 (Kuppusamy et al 2017) and Striatin (Pojoga et al 2012), were reported to play a role in MR activation. RACK1 regulates ciliated cell function through PKCepsilon (Slager et al 2008) and Striatin6 (one of the Striatin family members) is a cilia-related gene (Funfak et al 2015).…”

Urinary Exosomes and Their Cargo: Potential Biomarkers for Mineralocorticoid Arterial Hypertension?

“…Along with effects of aldosterone in AHT, different studies in cells, animal models, and human trials through the analysis of serum and urinary markers have confirmed the pathogenic role of aldosterone on inflammation, endothelial dysfunction, oxidative stress, and fibrosis ( 20 , 24 , 25 ). Other factors, as novel proteins associated to aldosterone have also been reported to independent activate or enhance the MR action, such as a small GTP-ase Rac1 ( 26 , 27 ), GPER ( 28 ), and the co-activator RACK1 ( 29 ). However, only Rac1 has been described as component of exosomes ( ).…”