ETS‐dependent enhancers for endothelial‐specific expression of serum/glucocorticoid‐regulated kinase 1 during mouse embryo development

Abstract

Serum/glucocorticoid‐regulated kinase 1 (SGK1) is predominantly expressed in endothelial cells of mouse embryos, and Sgk1 null mice show embryonic lethality due to impaired vascular formation. However, how the SGK1 expression is controlled in developing vasculature remains unknown. In this study, we first identified a proximal endothelial enhancer through lacZ reporter mouse analyses. The mouse Sgk1 proximal enhancer was narrowed down to the 5’ region of the major transcription initiation site, while a human corresponding region possessed relatively weak activity. We then searched for distal enhancer candidates using in silico analyses of publicly available databases for DNase accessibility, RNA polymerase association and chromatin modification. A region approximately 500 kb distant from the human SGK1 gene was conserved in the mouse, and the mouse and human genomic fragments drove transcription restricted to embryonic endothelial cells. Minimal fragments of both proximal and distal enhancers had consensus binding elements for the ETS transcription factors, which were essential for the responsiveness to ERG, FLI1 and ETS1 proteins in luciferase assays and the endothelial lacZ reporter expression in mouse embryos. These results suggest that endothelial SGK1 expression in embryonic vasculature is maintained through at least two ETS‐regulated enhancers located in the proximal and distal regions.

The role of serum-glucocorticoid regulated kinase 1 in reproductive viability: implications from prenatal programming and senescence

“…Interestingly, merging evidence reveals that SGK1 is pivotal to the early vasculogenesis [ 51 , 75 , 76 ]. As early as embryonic day 8.5 (E8.5), SGK1 was already observed throughout mouse embryo, especially higher in the yolk sac [ 77 ], a primary tissue where angioblasts differentiate into endothelial cells in the blood islands to form the earliest cardiovascular system [ 75 ].…”

“…As early as embryonic day 8.5 (E8.5), SGK1 was already observed throughout mouse embryo, especially higher in the yolk sac [ 77 ], a primary tissue where angioblasts differentiate into endothelial cells in the blood islands to form the earliest cardiovascular system [ 75 ]. Ablation of SGK1 results in early cardiovascular failure and embryonic lethality at E10.5–E11.5 due to defective angiogenic remodeling and to impaired myocardial trabeculation [ 75 , 76 ]. The lethal effects of SGK1 absence are accompanied by decreased expression levels of Notch signaling components [ 75 ].…”

“…Moreover, phosphorylation of NDRG1 by SGK1 alters NF-κB signaling and the expression of the downstream target VEGF-A, a pivotal growth factor plays a pivotal role in mediating the differentiation of endothelial cells [ 51 ]. The disruption of SGK1 leads to defective endothelial cell migration and tube formation, while increased apoptosis of vascular smooth muscle cells and endothelial cells, thus suggesting a pro-survival role for SGK1 during angiogenesis in the cardiac neo-angiogenesis and the endocardium-myocardium crosstalk during trabeculation [ 51 , 75 , 76 , 78 ].…”