Structure and Dynamics of Nucleoproteic and Membrane Assemblies

Theme 1 : Nuclear Receptors and Coregulators

A. le Maire, P. Germain, W. Bourguet

The precise regulation of gene expression requires activation and repression of DNA transcription. A number of diseases, including some cancers, originate from dysfunctional repression. The overall goal of this project is to gain mechanistic insights into the general principles governing the (de)regulation of gene repression by nuclear receptors.

Team5 Fig1Association and dissociation of coregulators from RAR upon ligand binding (CoA, coactivator ; CoR, corepressor).


Some nuclear receptors including retinoic acid (RAR) and thyroid hormone (TR) receptors act as transcriptional repressors by recruiting corepressor complexes to target genes. However, knowledge of the precise role of gene silencing still lags behind that of gene activation, and several diseases (e.g. acute promyelocytic leukemia and renal carcinomas) have been linked to aberrant interactions between modified forms of nuclear receptors and corepressors. The goals of this project are (i) to uncover the mechanistic aspects of the transcriptional repression mediated by wild-type and mutant RARs and TRs, (ii) to decipher how this silencing activity could be modulated by natural and pharmacological ligands, and (iii) to provide molecular tools to probe the importance of this repression in physiological, developmental and pathological processes. The strength of our project resides in the synergism that emerges from the combination of biophysical, structural, cell biology, functional genomics and in vivo studies.

Main collaborators : G. Benoit (ENS Lyon), F. Flamant (IGFL Lyon), N. Ghyselinck (IGBMC Illkirch), P. Veber (LBBE Lyon), M. Privalsky (UC Davis USA), AC. Figueira (CNPEM Brasil), A. Yunes (Boldrini Brasil).

References : le Maire et al., Nat. Struct. Mol. Biol., 2010 ; Germain et al., Chem. Biol., 2009 ; Nadendla et al., Plos One, 2015 ; Sharman et al., NAR, 2011

Theme 2 : Nuclear Receptors as Targets of Environmental Contaminants

W. Bourguet, V. Delfosse

Many chemicals released into the environment bind to nuclear receptors and activate or inhibit their action in an inappropriate spatio-temporal fashion. Referred to as endocrine disruptors (EDs), these compounds cause a wide range of developmental, reproductive, neurological or metabolic defects. The goal of this project is to provide mechanistic insights into the endocrine disrupting action of environmental pollutants.

TeamA5 pxr entier surf

Structure of the receptor PXR bound to the contraceptive ethinylestradiol and the pesticide trans-nonachlor.

The group of molecules acting as EDs is highly heterogeneous and comprises compounds that are often distantly related to endogenous ligands in terms of size or chemical structure. This group contains substances as chemically different as bisphenols, phthalates, parabens, dioxins, alkylphenols, organotins, benzophenones, or natural compounds such as the phytoestrogen genistein. This large structural diversity renders the interaction of EDs with their biological targets poorly understood and barely predictable. Our correlative analysis of structural, biophysical, cell-based and in vivo data allows revealing a variety of, sometimes unforeseen, mechanisms of action. Characterization of the interactions between nuclear receptors and environmental compounds at the structural and functional levels is important for the assessment of the harmful hormonal activity of a large number of chemicals, the rational design of safer substitutes, and the development of robust in silico screening methods.

Main collaborators : P. Balaguer (IRCM Montpellier), B. Demeneix (MNHN Paris), V. Laudet (OOB Banyuls/Mer)

References : Delfosse et al., Nat Commun., 2015 ; Delfosse et al., PNAS, 2012 ; le Maire et al., EMBO Rep., 2009

Theme 3 : Lipid Transport by Osh/ORP Proteins

W. Bourguet, V. Delfosse

Lipids, a group of more than 1000 subspecies, play critical roles in numerous cellular functions as precursors of a number of nuclear receptor ligands or as key components of cell membranes. Decrypting how cellular lipid homeostasis arises is essential to the understanding of many physio(patho)logical mechanisms.

TeamA5 osh4 pi4p ball

Crystal structure of Osh4p bound to PI(4)P.

The endoplasmic reticulum (ER) is the major place of lipid synthesis. Newly made lipids are then transported to other subcellular compartments (Golgi apparatus, plasma membrane (PM), nucleus, etc.) by dedicated carriers, including the Osh/ORP family of proteins. In close collaboration with the team of Guillaume Drin, we discovered that Osh4p and Osh6p transport sterol and phosphatidylserine, respectively, from the ER to their site of action by exchanging them with phosphatidylinositol-4-phosphate [PI(4) P]. As PI(4)P is prominent in the trans-Golgi and the PM but absent from the ER, we proposed a general mechanism by which Osh/ORP proteins use this unbalance to transport key lipids vectorially between organelles. Indeed, our structural and sequence analyzes suggest that all ORP/Osh proteins bind PI(4)P that can exchange with a second lipid, which is specific of each family member. Our current work aims at addressing key questions regarding the general scope of this mechanism and the nature of the lipids recognized by other Osh/ORP proteins.

Main Collaborators : G. Drin (IPMC Valbonne Sophia-Antipolis), A. Copic (IJM Paris)

References : de Saint-Jean et al., J. Cell Biol., 2011 ; Moser von Filseck et al., Science, 2015