Inhibition of Rac1 GTPase downregulates vascular endothelial growth factor receptor‐2 expression by suppressing Sp1‐dependent DNA binding in human endothelial cells

Abstract

RhoA, Rac1 and CDC42 are small GTP-binding proteins of the Rho family that play a crucial role in regulation of the actin-based cytoskeleton. In addition to cell growth regulation, they are implicated in transcriptional activation, oncogenic transformation and angiogenesis. The small Rho-GTPases have been linked to vascular endothelial growth factor (VEGF)-induced signalling pathways, but their role has not yet been elucidated. As signalling via the VEGF receptor-2 (VEGFR2) pathway is critical for angiogenic responses in cancer, wound repair and ischaemic and inflammatory diseases, we investigated whether the small Rho-GTPase Rac1 influences VEGFR2 expression in human endothelial cells. In this study, we show that a dominant negative Rac1 expression vector led to a pronounced decrease in VEGFR2 mRNA and protein expression. To identify minimal promoter requirements and potential applications of the small Rho-GTPases, we used VEGFR2 promoter-reporter gene constructs containing various deletions. The inhibitory effects of dominant negative Rac1 on the transcriptional activity of the VEGFR2 promoter localized to an element between -77 and -60 that contains an Sp1 transcription factor binding site. Electrophoretic mobility shift assays demonstrated that constitutive Sp1-dependent DNA binding decreased with Rac1 inhibition. Hence, repression of the small Rho GTPase Rac1 seems to be an additional critical molecular mechanism in the regulation of VEGFR2 expression.

Epileptiform Activity Induces Vascular Remodeling and Zonula Occludens 1 Downregulation in Organotypic Hippocampal Cultures: Role of VEGF Signaling Pathways

“…VEGF is known to be rapidly induced in hypoxic or inflammatory conditions, via transcription factors such as HIF-1 (hypoxia-inducible factor 1), AP-1 (activator protein 1), Sp-1, and STAT 3 (signal transducer and activator of transcription 3), which are also activated by seizures (Feng et al, 1997(Feng et al, , 1999Choi et al, 2003). Similarly, VEGFR-2 synthesis was shown to depend on the same transcription factors (HIF-1 and Sp-1) in hypoxic or inflammatory conditions and after seizures (Gerber et al, 1997;Meissner et al, 2009). Nevertheless, in OHCs, VEGFR-2 activation occurred early after seizure induction (2 h post-KA) and not at later time points when VEGF and VEGFR-2 were over- expressed.…”

Hyaluronic Acid Promotes Angiogenesis by Inducing RHAMM-TGFβ Receptor Interaction via CD44-PKCδ

“…Rac1 is required for activation of hypoxia inducible factor 1 (Hirota et al, 2001). Rac1 is also necessary for the induction of VEGFR-2 in vascular endothelial cells (Meissner et al, 2009) and is necessary for endothelial cell migration (Lee et al, 2007). VEGF activates Rac1 via vav-2 (Garrett et al, 2007) and activation of Rac1 is involved in the hypoxia-induced production of angiogenesis-promoting factors (Xue et al, 2006).…”

Vascular endothelial growth factor receptor-2 in breast cancer

“…In contrast, another report showed that basal and shear stress-induced activation of VEGFR-2 promoter constructs in HUVECs was primarily dependent on two more proximal GC-rich sites at −58 and −44 bp [101]. Sp1-dependent DNA binding within −77 and −60 region of VEGFR-2 promoter seems to be essential for the regulation of both mRNA and protein in human EC by Rac-1 (a small Rho-GTPase) [102]. Consensus or nonconsensus estrogen receptor element (ERE motifs) has not been found in 5′ VEGFR-2 promoter region [96].…”