The nuclear retinoic acid (RA) receptor alpha (RARa) is a transcriptional transregulator that controls the expression of specific gene subsets through binding at response elements and dynamic interactions with coregulators, which are coordinated by the ligand. Here, we highlighted a novel paradigm in which the transcription of RARa target genes is controlled by phosphorylation cascades initiated by the rapid RA activation of the p38MAPK/MSK1 pathway. We demonstrate that MSK1 phosphorylates RARa at S369 located in the ligand-binding domain, allowing the binding of TFIIH and thereby phosphorylation of the N-terminal domain at S77 by cdk7/cyclin H. MSK1 also phosphorylates histone H3 at S10. Finally, the phosphorylation cascade initiated by MSK1 controls the recruitment of RARa/TFIIH complexes to response elements and subsequently RARa target gene activation. Cancer cells characterized by a deregulated p38MAPK/MSK1 pathway, do not respond to RA, outlining the essential contribution of the RA-triggered phosphorylation cascade in RA signalling.

The nuclear retinoic acid receptor RARγ2 undergoes proteasome‐dependent degradation upon ligand binding. Here we provide evidence that the domains that signal proteasome‐mediated degradation overlap with those that activate transcription, i.e. the activation domains AF‐1 and AF‐2. The AF‐1 domain signals RARγ2 degradation through its phosphorylation by p38MAPK in response to RA. The AF‐2 domain acts via the recruitment of SUG‐1, which belongs to the 19S regulatory subunit of the 26S proteasome. Blocking RARγ2 degradation through inhibition of either the p38MAPK pathway or the 26S proteasome function impairs its RA‐induced transactivation activity. Thus, the turnover of RARγ2 is linked to transactivation.

Nuclear retinoic acid receptors (RARs) are ligand-dependent transcription factors that regulate the expression of retinoic acid target genes. Although the importance of RAR phosphorylation in their N-terminal domain is clearly established, the underlying mechanism for the phosphorylation-dependent transcriptional activity of the receptors had not been elucidated yet. Here, using a yeast two-hybrid system, we report the isolation of vinexin ␤ as a new cofactor that interacts with the N-terminal A/B domain of the RAR␥ isotype. Vinexin ␤ is a multiple SH3 motif-containing protein associated with the cytoskeleton and also present in the nucleus. We demonstrate that vinexin ␤ colocalizes with RAR␥ in the nucleus and interacts with the non-phosphorylated form of the AF-1 domain of RAR␥. We also show that this interaction is prevented upon phosphorylation of the AF-1 domain. Using F9 cells stably overexpressing vinexin ␤ or vinexin knockdown by RNA interference, we demonstrate that vinexin ␤ is an inhibitor of RAR␥-mediated transcription. We propose a model in which phosphorylation of the AF-1 domain controls RAR␥-mediated transcription through triggering the dissociation of vinexin ␤.Retinoic acid (RA), 1 the most potent biologically active metabolite of vitamin A, influences the proliferation, differentiation, and apoptosis of a variety of cell types through modifications of expression of subsets of RA target genes (1-3). The effects of RA are mediated by two classes of nuclear receptors, the retinoic acid receptors (RAR␣, RAR␤, and RAR␥) and the retinoid X receptors (RXR␣, RXR␤, and RXR␥), which function as ligand-dependent heterodimeric RAR/RXR transcription activators (4 -6). RARs and RXRs exhibit a conserved modular structure (see Fig. 1A) with a central DNA-binding domain and two activation domains (AF-1 and AF-2) that synergize for the activation of RA target genes.Ligand-induced conformational changes in the AF-2 domain of RARs bound at cognate response elements (RA response elements) located in the promoter of target genes cause the dynamic, coordinated, and combinatorial recruitment of coactivators and large complexes with chromatin-modifying and chromatin-remodeling activity, which will decompact repressive chromatin to allow positioning of the transcription machinery at the promoter (2, 7). Other proteins are also recruited and serve as connections with the transcription machinery. In line with this, RARs interact with the general transcription factor TFIIH (8, 9). This results in the phosphorylation of one residue located in their N-terminal AF-1 domain (Ser 77 in RAR␣1, Ser 79 in RAR␥1, and Ser 68 in RAR␥2) (see Fig. 1A) by the Cdk7 subunit of TFIIH, which has cyclin H-dependent kinase activity. This phosphorylation process, which has been extensively studied especially in the case of RAR␣ (10), plays a critical role in the response to RA.However, in the particular case of the RAR␥ isotype, phosphorylation by TFIIH, although necessary, is not sufficient. Indeed, to be transcriptionally active, RAR␥ needs...

Nuclear retinoic acid receptors (RARs) work as ligand-dependent heterodimeric RAR͞retinoid X receptor transcription activators, which are targets for phosphorylations. The N-terminal activation function (AF)-1 domain of RAR␣ is phosphorylated by the cyclindependent kinase (cdk) 7͞cyclin H complex of the general transcription factor TFIIH and the C-terminal AF-2 domain by the cAMP-dependent protein kinase A (PKA). Here, we report the identification of a molecular pathway by which phosphorylation by PKA propagates cAMP signaling from the AF-2 domain to the AF-1 domain. The first step is the phosphorylation of S369, located in loop 9 -10 of the AF-2 domain. This signal is transferred to the cyclin H binding domain (at the N terminus of helix 9 and loop 8 -9), resulting in enhanced cyclin H interaction and, thereby, greater amounts of RAR␣ phosphorylated at S77 located in the AF-1 domain by the cdk7͞cyclin H complex. This molecular mechanism relies on the integrity of the ligand-binding domain and the cyclin H binding surface. Finally, it results in higher DNA-binding efficiency, providing an explanation for how cAMP synergizes with retinoic acid for transcription.cAMP͞nuclear retinoid receptors R etinoic acid (RA) has essential roles in cell growth and differentiation (1) and regulates the expression of specific networks of genes through two families of nuclear receptors, the RA receptors (RARs) (␣, ␤, and ␥) and the retinoid X receptors (RXRs) (␣, ␤, and ␥), which act as ligand-dependent heterodimeric RAR͞ RXR transcription activators (2-4). During the last decade, the molecular rationale for RAR and RXR action has been established by the determination of the crystal structure of the ligand-binding domain (LBD) (5) and by evidence that RAR and RXR are phosphoproteins (6).The LBD is composed of 11 ␣-helices (H1 and H3-H12) that form a compact structure. It is functionally complex, containing the ligand-binding pocket, the main dimerization domain, and activation function (AF)-2 (Fig. 1A). Ligand binding promotes allosteric effects, such as the propagation of signals across the heterodimerization surface (7,8). It also induces conformation changes, the most striking one being the swing of helix 12 (9-11), which leads to corepressor complex dissociation (12). It also generates a new interaction surface for coactivators, which then recruit a battery of chromatin remodelers and modifiers acting in a coordinated and͞or combinatorial manner to decompact chromatin and direct RNA polymerase II and the general transcription factors to the promoter (13-15), leading to transcription initiation.In the last several years, it has been demonstrated that RARs are also targeted for phosphorylation processes (Fig. 1 A), which regulate their transcriptional activity (6). The LBD of the RAR␣ isotype can be phosphorylated at S369, located in loop 9 -10 (16), by the cAMP-dependent protein kinase A (PKA), whereas the N-terminal AF-1 domain is phosphorylated at S77 (17) by the cyclin-dependent kinase (cdk)-activating kinase complex of th...

No abstract

Arsenite trioxide (As 2 O 3 ) induces apoptosis in several cell lines by disturbing key signal transduction pathways through its oxidative properties. Here, we report that As 2 O 3 also induces the phosphorylation of the retinoid receptor RXRa, subsequent to oxidative damages and the activation of the stress-activated protein kinases cascade (JNKs). We also report that RA amplifies both As 2 O 3 -induced phosphorylation of RXRa and apoptosis. Taking advantage of 'rescue' F9 cell lines expressing RXRa mutated at its phosphorylation sites, in an RXRa null background, we provide evidence that RXRa is a key element involved in that potentiating effect. Finally, we demonstrate that As 2 O 3 also abrogates the transactivation of RA-target genes.

The nuclear retinoic acid (RA) receptor alpha (RAR&x03B1;) is a transcriptional transregulator that controls the expression of specific gene subsets through binding at response elements and dynamic interactions with coregulators, which are coordinated by the ligand. Here, we highlighted a novel paradigm in which the transcription of RAR&x03B1;-target genes is controlled by phosphorylation cascades initiated by the rapid RA activation of the p38MAPK/MSK1 pathway. We demonstrate that MSK1 phosphorylates RAR&x03B1; at S369 located in the Ligand Binding Domain, allowing the binding of TFIIH and thereby phosphorylation of the N-terminal domain at S77 by cdk7/cyclin H. MSK1 also phosphorylates Histone H3 at S10. Finally, the phosphorylation cascade initiated by MSK1 is required for the recruitment of RAR&x03B1;/TFIIH complexes to response elements and subsequently for RAR&x03B1; target genes activation. Cancer cells characterized by a deregulated p38MAPK/MSK1 pathway, do not respond to RA, outlining the essential contribution of the RA-triggered phosphorylation cascade in RA signaling.

Diplômée d'études supérieures spécialisées en environnement, est chargée de mission à l'Ifrée depuis 20 ans, où elle développe la production de ressources à destination des praticiens de l'éducation à l'environnement ainsi que l'accompagnement de partenaires techniques pour la création de supports de sensibilisation et la formation dans différents domaines JEAN-ÉTIENNE BIDOU Géographe de formation, est chargé de la mission recherche à l'Ifrée Une recherche élémentaire pour les praticiens : les livrets de l'Ifrée