Vascular Injury Triggers Krüppel-Like Factor 6 Mobilization and Cooperation With Specificity Protein 1 to Promote Endothelial Activation Through Upregulation of the Activin Receptor-Like Kinase 1 Gene

Abstract

Rationale Activin receptor-Like Kinase-1 (ALK1) is an endothelial TGF-β receptor involved in angiogenesis. ALK1 expression is high in the embryo vasculature, becoming less detectable in the quiescent endothelium of adult stages. However, ALK1 expression becomes rapidly increased after angiogenic stimuli such as vascular injury. Objective To characterize the molecular mechanisms underlying the regulation of ALK1 upon vascular injury. Methods and Results Alk1 becomes strongly upregulated in endothelial (EC) and vascular smooth muscle cells (vSMC) of mouse femoral arteries after wire-induced endothelial denudation. In vitro, denudation of monolayers of Human Umbilical Vein Endothelial Cells (HUVEC) also leads to an increase in ALK1. Interestingly, a key factor in tissue remodeling, Krüppel-like factor 6 (KLF6), translocates to the cell nucleus during wound healing, concomitantly with an increase in the ALK1 gene transcriptional rate. KLF6 knock down in HUVECs promotes ALK1 mRNA downregulation. Moreover, Klf6+/− mice have lower levels of Alk1 in their vasculature compared with their wild type siblings. Chromatin immunoprecipitation assays show that KLF6 interacts with ALK1 promoter in ECs, and this interaction is enhanced during wound healing. We demonstrate that KLF6 is transactivating ALK1 gene, and this transactivation occurs by a synergistic cooperative mechanism with Sp1. Finally, Alk1 levels in vSMCs are not directly upregulated in response to damage, but in response to soluble factors, such as IL-6, released from ECs after injury. Conclusions ALK1 is upregulated in ECs during vascular injury by a synergistic cooperative mechanism between KLF6 and Sp1, and in vSMCs by an EC-vSMC paracrine communication during vascular remodeling.

MiR-181a Regulates Blood-Tumor Barrier Permeability by Targeting Krüppel-Like Factor 6

“…More recently, KLF6 has been reported to be expressed in human umbilical vein ECs and can activate ALK1 gene after wire-induced endothelial denudation. 35 In response to vascular injury, KLF6 can also activate the endoglin and urokinase promoters in vascular repair. 22,36 Thus, these findings and our results of reduced KLF6 level in GECs have suggested that KLF6 might be involved in the regulation of vascular ECs.…”

Genome-wide analysis of the zebrafish Klf family identifies two genes important for erythroid maturation

“…Studies have shown that hepatocyte proliferation was decreased after klf6a (the zebrafish homolog of the mouse klf6) was knocked down in zebrafish (Zhao et al, 2010). klf6 is an important regulator of yolk sac hematopoiesis in mice (Matsumoto et al, 2006) and is also essential for the processes of nerve regeneration and vascular remodeling (Botella et al, 2002;Garrido-Martin et al, 2013;Veldman et al, 2007). However, whether klf6 functions in primitive erythropoiesis in other vertebrates remains unknown.…”

FBW7 regulates endothelial functions by targeting KLF2 for ubiquitination and degradation

“…The Krüppel-like factors (KLFs) are a family of zinc finger transcription factors with essential roles in cell growth, differentiation and tissue development [6]. Several KLFs, including KLF2, 4, 6, 10, and 15, have been reported to be involved in vascular functions [7][8][9][10][11]. Among them, KLF2 (also known as LKLF) is a central regulator of endothelial functions, including angiogenesis, inflammation, thrombosis and vascular tone [7,12].…”