The endothelial ETS transcription factor Erg plays an important role in homeostasis and angiogenesis by regulating many endothelial functions including survival and junction stability. Here we show that Erg regulates endothelial cell (EC) migration. Transcriptome profiling of Ergdeficient ECs identified ϳ 80 genes involved in cell migration as candidate Erg targets, including many regulators of RhoGTPases. Inhibition of Erg expression in HUVECs resulted in decreased migration in vitro, while Erg overexpression using adenovirus caused increased migration. Live-cell imaging of Erg-deficient HUVECs showed a reduction in lamellipodia, in line with decreased motility. Both actin and tubulin cytoskeletons were disrupted in Erg-deficient ECs, with a dramatic increase in tubulin acetylation. Among the most significant microarray hits was the cytosolic histone deacetylase 6 (HDAC6), a regulator of cell migration. Chromatin immunoprecipitation (ChIP) and transactivation studies demonstrated that Erg regulates HDAC6 expres-
IntroductionAngiogenesis is a tightly controlled process that involves a cascade of events. A breakthrough in understanding the cellular and molecular mechanisms underlying angiogenesis has been the identification of highly motile, polarized endothelial cells (ECs), named tip cells, which lead the growth of the developing sprout. 1 Dynamic reorganization of the cytoskeleton in tip cells supports the projection of lamellipodia and filopodia, which allow the cell to sense the microenvironment for migration cues and guide the sprouting vessel toward an angiogenic stimulus. The functional cross-talk between the actin and tubulin cytoskeletal systems is essential for cell motility. 2 Several families of intracellular regulators control these pathways. Among the most studied are the small GTPases of the Rho family, with Rac as the main regulator of lamellipodia and CDC42 as the regulator of filopodia; both of these GTPases have been shown to be involved in angiogenesis. 3 The class II histone deacetylase 6 (HDAC6), a known regulator of cell motility, 4 has been recently shown to be involved in EC migration and to support angiogenesis. 5 HDAC6 is expressed in many cells (including ECs) and localizes predominantly to the cytoplasm, binding to microtubules and deacetylating several cytosolic proteins, including ␣-tubulin 4,6 and cortactin. 7 Acetylation of tubulin, characteristic of stabilized microtubules, is thought to contribute to regulating microtubule dynamics, 8 while acetylation of cortactin is thought to modulate actin dynamics by regulating the interaction of cortactin with F-actin. 7 HDAC6 modulation of both cytoskeletons mediates its role in regulating endothelial migration, cytoskeletal dynamics, and angiogenesis. 4,8 We have been interested in the transcriptional regulation of endothelial gene expression and angiogenesis, and have focused on the ETS transcription factor Erg (ETS-related gene). Erg is the most abundantly expressed ETS factor in resting ECs and its expression, although not uniquely ...