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

Abstract

The MEK5/Erk5 MAPK cascade has recently been implicated in the regulation of endothelial integrity and represents a candidate pathway mediating the beneficial effects of laminar flow, a major factor preventing vascular dysfunction and disease. Here we expressed a constitutively active mutant of MEK5 (MEK5D) to study the transcriptional and functional responses to Erk5 activation in human primary endothelial cells. We provide evidence that constitutive Erk5 activation elicits an overall protective phenotype characterized by increased apoptosis resistance and a decreased angiogenic, migratory, and inflammatory potential. This is supported by bioinformatic microarray analysis, which uncovered a statistical overrepresentation of corresponding functional clusters as well as a significant induction of anti-thrombotic, hemostatic, and vasodilatory genes. We identify KLF4 as a novel Erk5 target and demonstrate a critical role of this transcription factor downstream of Erk5. We show that KLF4 expression largely reproduces the protective phenotype in endothelial cells, whereas KLF4 siRNA suppresses expression of various Erk5 targets. Additionally, we show that vasoprotective statins potently induce KLF4 and KLF4-dependent gene expression via activation of Erk5. Our data underscore a major protective function of the MEK5/Erk5/KLF4 module in ECs and implicate agonistic Erk5 activation as potential strategy for treatment of vascular diseases.The vascular endothelium, located at the interface between blood and tissue, fulfills a plethora of important functions, including the supply of nutrients and oxygen to the surrounding tissues as well as regulation of hemostasis and inflammatory responses. Endothelial dysfunction contributes to several diseases including chronic inflammation, hemophilia, thrombosis, and atherosclerosis. Thus, elucidation of the factors and molecular mechanisms that influence endothelial function is essential for the development of novel prophylactic and therapeutic strategies against diseases involving the vascular system. A major determinant influencing endothelial integrity is the hemodynamic force exerted by steady pulsatile blood flow. This force generates a continuous shear stress on the endothelial cells (ECs) 3 in the vessel wall, resulting in gene expression changes that protect the vessel from excessive inflammatory responses and thrombosis and provides an essential survival and quiescence signal for the vascular endothelium (1).Various signaling pathways and transcription factors are involved in perception and mediation of shear stress responses. These include the MEK5/Erk5 mitogen-activated protein kinase (MAPK) pathway (2), which is activated by laminar shear stress in ECs (3). In analogy to the related Erk1/2 MAPK, Erk5 activation is triggered by dual phosphorylation at a TEY consensus motif by a mitogen-activated protein kinase kinase (MAPKK or MEK), which in turn is activated via phosphorylation by a MEK kinase (MEKK or MAP3K) (4). In the case of Erk5, the activating phosphorylation is e...

Endothelial Krüppel-Like Factor 4 Mediates the Protective Effect of Statins against Ischemic AKI

“…These results are consistent with those from previous studies showing simvastatin induced KLF4 expression and a shift to vasoprotective phenotype via the activation of the MEK5/ Erk5 cascade in human primary ECs. 31 Moreover, Maejima et al 32 also showed that pitavastatin induced KLF4 expression, accompanied by the chromatin structure changes in the promoterenhancer region of the KLF4 gene in HUVECs. Further studies on the mechanism by which statins induce KLF4 expression may shed light on novel therapeutic targets for treating and preventing ischemic AKI and other vascular diseases.…”

ERK5/KLF4 signaling as a common mediator of the neuroprotective effects of both nerve growth factor and hydrogen peroxide preconditioning

“…Since ERK5 has been a focus of interests in cardiovascular diseases, we searched the literature in the vascular system and found that KLF4 has been reported to be an important mediator for ERK5 (Ohnesorge et al 2010;Clark et al 2011;Sunadome et al 2011). Importantly, NGF has been reported to transiently up-regulate KLF4 mRNA level in PC12 cells (Dijkmans et al 2009).…”

“…While there is considerable information regarding ERK5's upstream activators, little is known regarding the downstream effectors of ERK5, especially in the CNS. In a recent report by Ohnesorge et al, transcription factor Krüppel-like factor 4 (KLF4) was identified as a novel executioner of MEK5/ERK5 pathway to elicit an antiapoptotic and anti-inflammatory phenotype in human endothelial cells (Ohnesorge et al 2010). KLF4 is well known for its role in stem cell biology (Takahashi and Yamanaka 2006), cardiovascular disease (Dong and Huang 2009) and cancer (Cho et al 2007;Akaogi et al 2009).…”

“…In Dijkmans' report, the authors found that the NGFinduced increase in KLF4 expression was partially abolished by U0126 (inhibitor against MEK1/2 and MEK5), suggesting an involvement of the ERKs (Dijkmans et al 2009). Given that ERK5 signaling induces KLF4 expression in peripheral cells to counteract apoptosis (Ohnesorge et al 2010), and that NGF activates ERK5 in PC12 cells (Obara et al 2009), we hypothesized that NGF and/or PC protects neuronal cells from apoptosis via activation of an ERK5/KLF4 pathway. By using both PC12 cells and mouse primary hippocampal neurons as the complimentary models, we examined (1) the effect of blocking ERK signaling on KLF4 induction by NGF and PC, and (2) whether depletion of ERK5 or KLF4 by RNAi can attenuate the neuroprotection elicited by NGF and PC against an H 2 O 2 insult.…”

Laminar Flow Activation of ERK5 Protein in Vascular Endothelium Leads to Atheroprotective Effect via NF-E2-related Factor 2 (Nrf2) Activation

“…Transcriptional activation of KLF2 triggers induction of anti-inflammatory genes including eNOS and reduction of proinflammatory genes including cytokines (13,14). In addition to KLF2, ERK5 activation induces the expression of KLF4-dependent genes, which are also important in flow-mediated EC-protective responses (15,16). Taken together, a growing body of evidence suggests ERK5 as an emerging upstream signaling molecule in flow-mediated atheroprotective responses.…”