Retinoic Acid Receptors Inhibit AP1 Activation by Regulating Extracellular Signal-Regulated Kinase and CBP Recruitment to an AP1-Responsive Promoter

Abstract

Retinoids exhibit antineoplastic activities that may be linked to retinoid receptor-mediated transrepression of activating protein 1 (AP1), a heterodimeric transcription factor composed of fos-and jun-related proteins. Here we show that transcriptional activation of an AP1-regulated gene through the mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (ERK) pathway (MAPK ERK ) is characterized, in intact cells, by a switch from a fra2-junD dimer to a junD-fosB dimer loading on its promoter and by simultaneous recruitment of ERKs, CREB-binding protein (CBP), and RNA polymerase II. All-trans-retinoic acid (atRA) receptor (RAR) was tethered constitutively to the AP1 promoter. AP1 transrepression by retinoic acid was concomitant to glycogen synthase kinase 3 activation, negative regulation of junD hyperphosphorylation, and to decreased RNA polymerase II recruitment. Under these conditions, fra1 loading to the AP1 response element was strongly increased. Importantly, CBP and ERKs were excluded from the promoter in the presence of atRA. AP1 transrepression by retinoids was RAR and ligand dependent, but none of the functions required for RAR-mediated transactivation was necessary for AP1 transrepression. These results indicate that transrepressive effects of retinoids are mediated through a mechanism unrelated to transcriptional activation, involving the RAR-dependent control of transcription factors and cofactor assembly on AP1-regulated promoters.

Extracellular Signals Regulate Rapid Coactivator Recruitment at AP-1 Sites by Altered Phosphorylation of both CREB Binding Protein and c-jun

“…7). Coactivators such as CBP were required for activation of RA-responsive genes, and inhibition of AP-1 activity by RA was attributed to RAR competition for limiting amounts of CBP (4,11). In the case of retinoic acid signaling, the displacement of coactivator binding occurs with faster kinetics than repressor dissociation from RAR␣.…”

MAP kinases as structural adaptors and enzymatic activators in transcription complexes

“…This is accompanied by an increase in JunD-FosB binding and a decrease in JunD-Fra2 binding at the AP1 site (Benkoussa et al, 2002). Constitutively tethering RAR (all-trans retinoic acid receptor) to the promoter, together with treatment with atRA (all-trans retinoic acid) and TPA, led to decreased recruitment of ERKs, CBP and pol II (Benkoussa et al, 2002). It was therefore suggested that RAR might regulate ERK access to the AP1 complex and hence modulate phosphorylation of its substrate and CBP association (Benkoussa et al, 2002).…”

“…Using ChIP assays, Benkoussa et al found that activation of ERKs by 12-O-tetradecanoylphorbol-13-acetate (TPA) leads to recruitment of ERK1 and ERK2, CREB-binding protein (CBP) and pol II to an AP1-responsive reporter gene in vivo (Benkoussa et al, 2002). This is accompanied by an increase in JunD-FosB binding and a decrease in JunD-Fra2 binding at the AP1 site (Benkoussa et al, 2002).…”

“…Constitutively tethering RAR (all-trans retinoic acid receptor) to the promoter, together with treatment with atRA (all-trans retinoic acid) and TPA, led to decreased recruitment of ERKs, CBP and pol II (Benkoussa et al, 2002). It was therefore suggested that RAR might regulate ERK access to the AP1 complex and hence modulate phosphorylation of its substrate and CBP association (Benkoussa et al, 2002). It is conceivable that the loss of TPAinduced pol II recruitment upon atRA treatment is partly due to lack of interactions with ERK1/ERK2 that is excluded from the AP1 complex by ligand-bound RAR.…”

“…Using ChIP assays, Benkoussa et al found that activation of ERKs by 12-O-tetradecanoylphorbol-13-acetate (TPA) leads to recruitment of ERK1 and ERK2, CREB-binding protein (CBP) and pol II to an AP1-responsive reporter gene in vivo (Benkoussa et al, 2002). This is accompanied by an increase in JunD-FosB binding and a decrease in JunD-Fra2 binding at the AP1 site (Benkoussa et al, 2002). Constitutively tethering RAR (all-trans retinoic acid receptor) to the promoter, together with treatment with atRA (all-trans retinoic acid) and TPA, led to decreased recruitment of ERKs, CBP and pol II (Benkoussa et al, 2002).…”