p68RacGAP Is a Novel GTPase-activating Protein That Interacts with Vascular Endothelial Zinc Finger-1 and Modulates Endothelial Cell Capillary Formation

Abstract

The endothelium is required for maintenance of vascular integrity and homeostasis during vascular development and in adulthood. However, little is known about the coordinated interplay between transcription factors and signaling molecules that regulate endothelial cell-dependent transcriptional events. Vascular endothelial zinc finger-1 (Vezf1) is a zinc finger-containing transcription factor that is specifically expressed within the endothelium during vascular development. We have previously shown that Vezf1 potently activates transcription of the endothelin-1 promoter. We now report the identification of p68RacGAP, a novel Vezf1-interacting 68-kDa RhoGAP domain-containing protein. p68RacGAP mRNA is highly expressed in vascular endothelial cells by Northern blot analysis, and immunohistochemical staining of adult mouse tissues identified p68RacGAP in endothelial cells, vascular smooth muscle cells, and epithelial cells in vivo. Rac1 and Vezf1 both bind avidly to p68RacGAP, suggesting that p68RacGAP is not only a GTPase-activating protein for Rac1 but that p68RacGAP may also be part of the protein complex that binds to and modulates Vezf1 transcriptional activity. Functionally p68RacGAP specifically activates the GTPase activity of Rac1 in vivo but not Cdc42 or RhoA. In addition, p68RacGAP potently inhibits Vezf1/DB1-mediated transcriptional activation of the human endothelin-1 promoter and modulates endothelial cell capillary tube formation. Taken together, these data suggest that p68RacGAP is a multifunctional regulatory protein that has a Rac1-specific GTPase-activating activity, regulates transcriptional activity of the endothelin-1 promoter, and is involved in the signal transduction pathway that regulates endothelial cell capillary tube formation during angiogenesis.

Vezf1 regulates genomic DNA methylation through its effects on expression of DNA methyltransferase Dnmt3b

“…Lemons and H. Stuhlmann, in prep.). However, transcriptional activation of at least some of the target gene promoters appears to be dependent on interactions between VEZF1 and components of the Rho GTPase machinery, including p68RacGAP (Aitsebaomo et al 2004) and RhoB (Lebowitz and Prendergast 1998;Kuhnert and Stuhlmann 2007). The homologous protein in chicken, BGP1, has known binding sites in the chicken ␤-globin promoter (Lewis et al 1988); and in the insulator at the 5Ј end of the ␤-globin locus (A.…”

Rho-GTPase signaling drives melanoma cell plasticity

“…As such, phosphorylation of CDGAP by the ERK MAPK inhibits its GAP activity towards Rac1 both in vitro and in vivo. 28 The ARHGAP24 isoforms RC-GAP72 and p73RhoGAP, and the ARHGAP22 isoform p68RacGAP, which are derived by mRNA splice variation and which lack PH domains, have been characterized as endothelial-cell-restricted proteins that contribute to angiogenesis [29][30][31] indicating an important role of these family of proteins in migratory processes during vascularization and angiogenesis.…”

Identification of RhoGAP22 as an Akt-Dependent Regulator of Cell Motility in Response to Insulin

“…One of the proteins we identified was RhoGAP22, a product of the ARHGAP22 gene. RhoGAP22 is a GTPase-activating protein (GAP) for Rac1 and an inhibitor of VEZF1-dependent transcriptional activity (3). In a large-scale siRNA screen, knockdown of RhoGAP22 caused a defect in the transition from the ameboid to mesenchymal mode of cell movement, suggesting that ARHGAP22 has an important role in controlling cell motility (27).…”

“…The generation of PI (3,4,5)P3 by phosphatidylinositol 3 kinase (PI3K) at the leading edge of a migrating cell is necessary for directed migration (16) and for lamellipodium formation in response to an attractant during chemotaxis (4). The presence of PI (3,4,5)P3 at the leading edge recruits and activates guanine nucleotide exchange factors (GEFs), such as Vav (1,14), that promote the GTP loading and activation of Rac and CDC42.…”

“…The generation of PI (3,4,5)P3 by phosphatidylinositol 3 kinase (PI3K) at the leading edge of a migrating cell is necessary for directed migration (16) and for lamellipodium formation in response to an attractant during chemotaxis (4). The presence of PI (3,4,5)P3 at the leading edge recruits and activates guanine nucleotide exchange factors (GEFs), such as Vav (1,14), that promote the GTP loading and activation of Rac and CDC42. Akt binds PI (3,4,5)P3 and may localize to the leading edge of the cell to regulate the activity of substrates that coordinate changes in cell motility, such as the actinbinding protein girdin (11) and PAKa (10).…”