TAL-1/SCL and Its Partners E47 and LMO2 Up-Regulate VE-Cadherin Expression in Endothelial Cells

Abstract

The basic helix-loop-helix TAL-1/SCL essential for hematopoietic development is also required during vascular development for embryonic angiogenesis. We reported that TAL-1 acts positively on postnatal angiogenesis by stimulating endothelial morphogenesis. Here, we investigated the functional consequences of TAL-1 silencing in human primary endothelial cells. We found that TAL-1 knockdown caused the inhibition of in vitro tubulomorphogenesis, which was associated with a dramatic reduction in vascular endothelial cadherin (VE-cadherin) at intercellular junctions. Consistently, silencing of TAL-1 as well as of its cofactors E47 and LMO2 down-regulated VE-cadherin at both the mRNA and the protein level. Endogenous VE-cadherin transcription could be activated in nonendothelial HEK-293 cells by the sole concomitant ectopic expression of TAL-1, E47, and LMO2. Transient transfections in human primary endothelial cells derived from umbilical vein (HUVECs) demonstrated that VE-cadherin promoter activity was dependent on the integrity of a specialized E-box associated with a GATA motif and was maximal with the coexpression of the different components of the TAL-1 complex. Finally, chromatin immunoprecipitation assays showed that TAL-1 and its cofactors occupied the VE-cadherin promoter in HUVECs. Together, these data identify VE-cadherin as a bona fide target gene of the TAL-1 complex in the endothelial lineage, providing a first clue to TAL-1 function in angiogenesis.

SUPPLEMENTAL MATERIAL

We are indebted to Valérie Pinet and Philippe Couttet for helpful discussions and to Robert Hipskind for critical reading of the manuscript. We acknowledge Olivier Bernard, Trang Hoang, and Catherine Porcher for providing us with cDNA reagents and Gerlinde Layh-Schmitt for the anti-LMO2 antibody. We are grateful to Ignacio A. Romero and Babette Wekler for the hCMEC/D3 endothelial cell line. We thank Pierre Travo and Julien Cau (RIO Platform, Montpellier, France) for their constant help with imaging studies.

V.D. was a fellowship recipient of the Ligue Nationale Contre le Cancer (France) and is now funded by the Institut National du Cancer (INCa, France). E.C. was a recipient of the Association pour la Recherche sur le Cancer (ARC, France). R.E.-H. is supported by the Ligue Régionale contre le Cancer (Hérault, France) and D.M. by the Institut National de la Santé et de la Recherche Médicale (INSERM, France). This work was supported in part by grants from ARC and Cancéropôle Grand Sud-Ouest (France).