Coordinated functions of Akt/PKB and ETS1 in tubule formation

Abstract

We investigated the inter-relationship between two downstream effectors of vascular endothelial growth factor (VEGF), the serine-threonine kinase Akt (or protein kinase B) and the transcription factor ETS1, in tubulogenesis. We show that VEGF upregulates ETS1 transcription through an Aktdependent pathway in primary endothelial cells. Activation of Akt also results in tubule formation in vitro, a process requiring ETS1 activity. In vivo, the Drosophila ETS1 is required for cell motility per se while Akt is responsible for organized cell movement. Thus, ETS1 and Akt control different aspects of cell migration that are integrated in the regulation of vascular tubule formation. KeywordsAkt; ETS1; angiogenesis; Drosophila; tubulogenesis; tracheal development Angiogenesis is the mechanism by which new blood vessels are formed from the pre-existing vascular network (Shiojima and Walsh 2002). It is widely accepted that vascular endothelial growth factor (VEGF) is the main activator of angiogenesis, inducing basement membrane degradation, endothelial cell proliferation and cell motility (Merenmies et al. 1997). Among the cellular mechanisms that underlie angiogenesis, cell motility is the least understood. Angiogenic tubulogenesis requires, a priori, migratory potential of the vascular cells. However, the cell migration events that lead to blood vessel formation needs to be both organized and directional. In other words, simple mobilization of vascular cells does not necessarily lead to tubule formation. How organized cell movement is regulated remains unresolved. Since VEGF is sufficient for inducing tube-like structures in three dimensional cell culture systems (Nehls and Drenckhahn 1995;Papapetropoulos et al. 1997), this model provides a good approximation for dissecting the complex mechanisms involved in organized cell migration. VEGF can activate many different signaling pathways, depending on cellular context and environmental cues (Veikkola et al. 2000). Among the various responses VEGF can elicit, Akt and ETS1 have emerged as two important down-stream regulators of angiogenic cell movement.Upon growth factor stimulation, phosphatidylinositol-3-kinase (PI3K) is activated which leads to recruitment of Akt to the plasma membrane where it binds phosphoinositol lipids via its pleckstrin homology domain (Chan et al. 1999). PI3K-Akt-mediated signaling has been implicated in many aspects of cellular functions, including cell survival and cell size control, which are regulated by other growth factors such as EGF and the insulin family of proteins (Brazil et al. 2002). These Akt functions are evolutionarily conserved at least in Drosophila (Scanga et al. 2000;Potter et al. 2002;Radimerski et al. 2002). Recently PI3K and by extension, Akt, have been implicated in upregulation of angiogenesis in vivo and tubule formation in vitro (Jiang et al. 2000;Morales-Ruiz et al. 2000). Although the inductive effect of PI3K on angiogenesis has been ascribed to promoting cell migration, no studies have clearly On the other hand, ...

Ets proteins in biological control and cancer

“…Ets can also mediate similar communication across different tumor and stroma compartments. VEGF, produced by tumor cells and fibroblasts, can induce Ets1 expression in endothelial cells [Lavenburg et al, 2003]. Concomitantly, Ets1, in cooperation with Hif-2a, activates the transcription of VEGF receptor 2 [Elvert et al, 2002].…”

H-Ras, R-Ras, and TC21 Differentially Regulate Ureteric Bud Cell Branching Morphogenesis

“…Activation of the Rho GTPases (Maru et al, 1998;Rogers et al, 2003;Wozniak et al, 2003), PI3-K (Lavenburg et al, 2003), and the MAPK family members (Khwaja et al, 1998;Ishibe et al, 2003Ishibe et al, , 2004O'Brien et al, 2004) has been shown to play a 3 ) were plated in collagen I/MG gels as described in Materials and Methods. In the top three panels, the gels were fixed 2, 4, and 6 d after plating, stained with rhodamine-phalloidin, and subjected to confocal microscopy as described in Materials and Methods.…”

Poly-N-Acetyl Glucosamine Nanofibers Regulate Endothelial Cell Movement and Angiogenesis: Dependency on Integrin Activation of Ets1

“…However, activation of the Ets1 transcription factor has emerged as an important downstream regulator of angiogenic cell movement. Endothelial cell (EC) growth factors, such as vascular endothelial growth factor (VEGF) and fibroblast growth factor, specifically upregulate the activity of Ets1 in primary EC [2, 3] resulting in the activation of downstream target genes, such as metalloproteinases and vimentin [4] that are important for matrix degradation and cell migration [5]. In addition, antisense Ets1 can block the proangiogenic function of VEGF in cultured EC [2, 6, 7].…”

“…Endothelial cell (EC) growth factors, such as vascular endothelial growth factor (VEGF) and fibroblast growth factor, specifically upregulate the activity of Ets1 in primary EC [2, 3] resulting in the activation of downstream target genes, such as metalloproteinases and vimentin [4] that are important for matrix degradation and cell migration [5]. In addition, antisense Ets1 can block the proangiogenic function of VEGF in cultured EC [2, 6, 7]. Thus, Ets1 appears to be a major regulator of migratory potential in response to chemotactic growth factors, a function that is also evolutionarily conserved [2, 8].…”

“…In addition, antisense Ets1 can block the proangiogenic function of VEGF in cultured EC [2, 6, 7]. Thus, Ets1 appears to be a major regulator of migratory potential in response to chemotactic growth factors, a function that is also evolutionarily conserved [2, 8]. …”