The Hinge-Helix 1 Region of Peroxisome Proliferator-Activated Receptor γ1 (PPARγ1) Mediates Interaction with Extracellular Signal-Regulated Kinase 5 and PPARγ1 Transcriptional Activation: Involvement in Flow-Induced PPARγ Activation in Endothelial Cells

Abstract

Peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors that form a subfamily of the nuclear receptor gene family. Since both flow and PPAR␥ have atheroprotective effects and extracellular signal-regulated kinase 5 (ERK5) kinase activity is significantly increased by flow, we investigated whether ERK5 kinase regulates PPAR␥ activity. We found that activation of ERK5 induced PPAR␥1 activation in endothelial cells (ECs). However, we could not detect PPAR␥ phosphorylation by incubation with activated ERK5 in vitro, in contrast to ERK1/2 and JNK, suggesting a role for ERK5 as a scaffold. Endogenous PPAR␥1 was coimmunoprecipitated with endogenous ERK5 in ECs. By mammalian two-hybrid analysis, we found that PPAR␥1 associated with ERK5a at the hinge-helix 1 region of PPAR␥1. Expressing a hinge-helix 1 region PPAR␥1 fragment disrupted the ERK5a-PPAR␥1 interaction, suggesting a critical role for hinge-helix 1 region of PPAR␥ in the ERK5-PPAR␥ interaction. Flow increased ERK5 and PPAR␥1 activation, and the hinge-helix 1 region of the PPAR␥1 fragment and dominant negative MEK5␤ significantly reduced flow-induced PPAR␥ activation. The dominant negative MEK5␤ also prevented flow-mediated inhibition of tumor necrosis factor alpha-mediated NF-B activation and adhesion molecule expression, including vascular cellular adhesion molecule 1 and E-selectin, indicating a physiological role for ERK5 and PPAR␥ activation in flow-mediated antiinflammatory effects. We also found that ERK5 kinase activation was required, likely by inducing a conformational change in the NH 2 -terminal region of ERK5 that prevented association of ERK5 and PPAR␥1. Furthermore, association of ERK5a and PPAR␥1 disrupted the interaction of SMRT and PPAR␥1, thereby inducing PPAR␥ activation. These data suggest that ERK5 mediates flow-and ligand-induced PPAR␥ activation via the interaction of ERK5 with the hinge-helix 1 region of PPAR␥.Peroxisome proliferator-activated receptors (PPAR) are ligand-activated transcription factors that form a subfamily of the nuclear receptor gene family. Among PPAR family members, the expression of PPAR␣ and PPAR␥ has been reported in endothelial cells (ECs). Recently, Pasceri et al. reported that PPAR␥ activators inhibit expression of vascular cellular adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) in activated ECs and significantly reduce monocyte/macrophage homing to atherosclerotic plaques (23). Mitogen-activated protein (MAP) kinase signaling pathways have been shown to phosphorylate PPAR␥ and to decrease PPAR␥ transcriptional activity (7, 13). The NH 2 -terminal domain of PPAR␥ contains a consensus MAP kinase site in a region conserved between PPAR␥1 and PPAR␥2 isoforms (7, 13). Phosphorylation of PPAR␥2 Ser112 (13) and PPAR␥1 Ser82 (7) significantly inhibits both ligand-independent and ligand-dependent transcriptional activation by PPAR␥. Phosphorylation-mediated transcriptional repression is due to a diminished ability of PPAR␥ to become transcriptionally a...

Big Mitogen-Activated Protein Kinase 1 (BMK1)/Extracellular Signal Regulated Kinase 5 (ERK5) Is Involved in Platelet-Derived Growth Factor (PDGF)-Induced Vascular Smooth Muscle Cell Migration

“…In contrast to our hypothesis, several recent studies have proposed a protective role for BMK1 activation in cardiovascular injury (11,45). With regard to such a model, it seems undeniable that the activation of BMK1 in the cuff-injured artery was the result of a compensatory response to the injury.…”

Fluid shear stress inhibits TNF-mediated JNK activation via MEK5–BMK1 in endothelial cells

“…In EC, laminar flow activates PPARγ activity and activation of PPARγ exerts anti-inflammatory effects since PPARγ ligands reduce TNF induced VCAM-1 expression [29]. We have shown previously that flow-induced PPARγ activation is dependent upon ERK5, and is functionally important because expression of dominant negative PPARγ decreased the ability of ERK5 to decrease VCAM-1 expression [30].…”

Erk5 Activation Elicits a Vasoprotective Endothelial Phenotype via Induction of Krüppel-like Factor 4 (KLF4)

“…Recent knock-out studies revealed an indispensable role of the MEK5/Erk5 cascade in embryonic vascular development and maintenance of vascular integrity in mature blood vessels (2, 8 -10). Erk5 further was shown to mediate shear stress-dependent repression of inflammatory responses via interaction with PPAR␥1 (11) and regulates flow-mediated expression of KLF2 (12), a mechano-activated transcription factor that controls various vasoprotective, anti-thrombotic, and anti-inflammatory responses to laminar flow (12)(13)(14)(15). However, Erk5 is * This work was funded by Deutsche Forschungsgemeinschaft Grants GO 811/1-5 (to M. G.) and GRK880/3 (International Research Training Group Vascular Medicine, Graduiertenkolleg 880/3 (to M. S. and M. G.)).…”