The effect of S427F mutation on RXRα activity depends on its dimeric partner.

Ioannis Galdadas,Vangelis Bonis,Michail Papadourakis,Zoe Cournia,Panos Kakoulidis,Apostolos Klinakis,Paraskevi Vgenopoulou,Georgia Stergiou

doi:10.1039/d1sc04465f

Ioannis Galdadas, Vangelis Bonis + Show 6 more

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https://doi.org/10.1039/d1sc04465f

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Abstract

RXRs are nuclear receptors acting as transcription regulators that control key cellular processes in all tissues. All type II nuclear receptors require RXRs for transcriptional activity by forming heterodimeric complexes. Recent whole-exome sequencing studies have identified the RXRα S427F hotspot mutation in 5% of the bladder cancer patients, which is always located at the interface of RXRα with its obligatory dimerization partners. Here, we show that mutation of S427 deregulates transcriptional activity of RXRα dimers, albeit with diverse allosteric mechanisms of action depending on its dimeric partner. S427F acts by allosteric mechanisms, which range from inducing the collapse of the binding pocket to allosteric stabilization of active co-activator competent RXRα states. Unexpectedly, RXR S427F heterodimerization leads to either loss- or gain-of-function complexes, in both cases likely compromising its tumor suppressor activity. This is the first report of a cancer-associated single amino acid substitution that affects the function of the mutant protein variably depending on its dimerization partner.

Highlights

Bladder cancer is the second most common urogenital cancer with 550 000 new cases every year worldwide.[1]
The crystal structures of the full-length nuclear receptor complexes of RARb–retinoid X receptor a (RXRa) and peroxisome proliferator-activated receptor g (PPARg)–RXRa show that the DNA binding domain (DBD) and ligand-binding domain (LBD) regions of RARb and PPARg are physically connected through a DBD-LBD linker
A er we con rmed that the S427F mutation does not affect DNA binding of RXRa, we focused on the LBDs of RXRa complexed with retinoic acid receptor a (RARa) or PPARg and of the RXRa homodimer

Summary

Introduction

Bladder cancer is the second most common urogenital cancer with 550 000 new cases every year worldwide.[1]. RXRa is a nuclear receptor of the vitamin A metabolite 9-cis retinoic acid (9-cis RA), and serves as an obligate homo- and hetero-dimerization partner for many subfamily 1 nuclear receptors, including the retinoic acid receptor a (RARa) and peroxisome proliferator-activated receptor g (PPARg).[3] These protein dimers can bind to target response elements consisting of a direct repetition of a half-site motif (50-AGGTCA30) with an intervening spacer of 1–5 bp (DR1–5) leading to regulation of gene expression for various biological processes.[4] RXRa, as well as RARa and PPARg, function as ligandactivated transcriptional factors consisting of a ligand-binding domain (LBD) linked through a hinge region to a DNA binding domain (DBD). The LBD of these three receptors exhibits the canonical folding of nuclear receptors in which a single b-turn and 12 a-helices (H1–H12) enclose a hydrophobic binding pocket (Fig. S1†)

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