Caractérisation des mécanismes moléculaires impliqués dans l'activité anti-cancéreuse du Tamoxifène et de la Dendrogénine A

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

H2B monoubiquitination: t'ub or not t'ub for inducible enhancers

Recently, we reported the unexpected finding that the monoubiquitination of histone H2B (H2Bub1) regulates inducible enhancers. Here, we propose a conceptual framework to reconcile the apparently discrepant roles of H2Bub1 in transcription initiation and elongation, and we discuss how H2Bub1 could regulate cellular processes linked to non-coding transcription

Monoubiquitination of Histone H2B Blocks Eviction of Histone Variant H2A.Z from Inducible Enhancers

Covalent modifications of histones play a crucial role in the regulation of gene expression. Histone H2B monoubiquitination has mainly been described as a regulator of transcription elongation, but its role in transcription initiation is poorly documented. We investigated the role of this histone mark (H2Bub1) on different inducible enhancers, in particular those regulated by estrogen receptor a, by loss- and gain-of-function experiments with the specific E3-ubiquitin ligase complex of H2B: RNF20/RNF40. RNF20/RNF40 overexpression causes repression of the induced activity of these enhancers. Genome- wide profiles show that H2Bub1 levels are negatively correlated with the accessibility of enhancers to transcriptional activators. We found that the chromatin association of histone variant H2A.Z, which is evicted from enhancers for transcriptional activation, is stabilized by H2Bub1 by impairing access of the chromatin remodeler INO80. We propose that H2Bub1 acts as a gatekeeper of H2A.Z eviction and activation of inducible enhancers

Identification and pharmacological characterization of cholesterol-5,6-epoxide hydrolase as a target for tamoxifen and AEBS ligands.

International audienceThe microsomal antiestrogen binding site (AEBS) is a high-affinity target for the antitumor drug tamoxifen and its cognate ligands that mediate breast cancer cell differentiation and apoptosis. The AEBS, a hetero-oligomeric complex composed of 3beta-hydroxysterol-Delta8-Delta7-isomerase (D8D7I) and 3beta-hydroxysterol-Delta7-reductase (DHCR7), binds different structural classes of ligands, including ring B oxysterols. These oxysterols are inhibitors of cholesterol-5,6-epoxide hydrolase (ChEH), a microsomal epoxide hydrolase that has yet to be molecularly identified. We hypothesized that the AEBS and ChEH might be related entities. We show that the substrates of ChEH, cholestan-5alpha,6alpha-epoxy-3beta-ol (alpha-CE) and cholestan-5beta,6beta-epoxy-3beta-ol (beta-CE), and its product, cholestane-3beta,5alpha,6beta-triol (CT), are competitive ligands of tamoxifen binding to the AEBS. Conversely, we show that each AEBS ligand is an inhibitor of ChEH activity, and that there is a positive correlation between these ligands' affinity for the AEBS and their potency to inhibit ChEH (r2=0.95; n=39; P<0.0001). The single expression of D8D7I or DHCR7 in COS-7 cells slightly increased ChEH activity (1.8- and 2.6-fold), whereas their coexpression fully reconstituted ChEH, suggesting that the formation of a dimer is required for ChEH activity. Similarly, the single knockdown of D8D7I or DHCR7 using siRNA partially inhibited ChEH in MCF-7 cells, whereas the knockdown of both D8D7I and DHCR7 abolished ChEH activity by 92%. Taken together, our findings strongly suggest that the AEBS carries out ChEH activity and establish that ChEH is a new target for drugs of clinical interest, polyunsaturated fatty acids and ring B oxysterols

Vps11 and Vps18 of Vps-C membrane traffic complexes are E3 ubiquitin ligases and fine-tune signalling

In response to extracellular signals, many signalling proteins associated with the plasma membrane are sorted into endosomes. This involves endosomal fusion, which depends on the complexes HOPS and CORVET. Whether and how their subunits themselves modulate signal transduction is unknown. We show that Vps11 and Vps18 (Vps11/18), two common subunits of the HOPS/CORVET complexes, are E3 ubiquitin ligases. Upon overexpression of Vps11/Vps18, we find perturbations of ubiquitination in signal transduction pathways. We specifically demonstrate that Vps11/18 regulate several signalling factors and pathways, including Wnt, estrogen receptor α (ERα), and NFκB. For ERα, we demonstrate that the Vps11/18-mediated ubiquitination of the scaffold protein PELP1 impairs the activation of ERα by c-Src. Thus, proteins involved in membrane traffic, in addition to performing their well-described role in endosomal fusion, fine-tune signalling in several different ways, including through ubiquitination

Identification of a tumor-promoter cholesterol metabolite in human breast cancers acting through the glucocorticoid receptor

International audienceBreast cancer (BC) remains the primary cause of death from cancer among women worldwide. Cholesterol-5,6-epoxide (5,6-EC) metabolism is deregulated in BC but the molecular origin of this is unknown. Here, we have identified an oncometabolism downstream of 5,6-EC that promotes BC progression independently of estrogen receptor α expression. We show that cholesterol epoxide hydrolase (ChEH) metabolizes 5,6-EC into cholestane-3β,5α,6β-triol, which is transformed into the oncometabolite 6-oxo-cholestan-3β,5α-diol (OCDO) by 11β-hydroxysteroid-dehydrogenase-type-2 (11βHSD2). 11βHSD2 is known to regulate glucocorticoid metabolism by converting active cortisol into inactive cortisone. ChEH inhibition and 11βHSD2 silencing inhibited OCDO production and tumor growth. Patient BC samples showed significant increased OCDO levels and greater ChEH and 11βHSD2 protein expression compared with normal tissues. The analysis of several human BC mRNA databases indicated that 11βHSD2 and ChEH overexpression correlated with a higher risk of patient death, highlighting that the biosynthetic pathway producing OCDO is of major importance to BC pathology. OCDO stimulates BC cell growth by binding to the glucocorticoid receptor (GR), the nuclear receptor of endogenous cortisol. Interestingly, high GR expression or activation correlates with poor therapeutic response or prognosis in many solid tumors, including BC. Targeting the enzymes involved in cholesterol epoxide and glucocorticoid metabolism or GR may be novel strategies to prevent and treat BC