HoxB5 induces endothelial sprouting in vitro and modifies intussusceptive angiogenesis in vivo involving angiopoietin-2.
OBJECTIVE
Homeobox (Hox) proteins are transcriptional regulators in embryonic patterning, cell differentiation, proliferation, and migration in vertebrates and invertebrates. A growing body of evidence suggests that Hox proteins are involved in endothelial cell regulation. We have shown earlier that HoxB5 upregulates vascular endothelial growth factor receptor-2 and thereby contributes to enhanced endothelial precursor cell differentiation. Here we aim to elucidate the role of HoxB5 in angiogenesis.


RESULTS
Endothelial cell sprouting was investigated in the human umbilical vein endothelial cell spheroid assay. We investigated in vivo angiogenesis in the chick (Gallus gallus) chorioallantoic membrane assay. Expression profiling of proangiogenic factors was done by quantitative PCR. The angiopoietin-2 (Ang2) promoter and deletion fragments thereof were cloned into the pGL3 reporter system for analysis of transcriptional activity. We observed that HoxB5 enhances endothelial cell sprouting and modulates the expression of adhesion molecules in vitro. Accordingly, we observed a modification of vascular growth by HoxB5 in vivo. The HoxB5 effect is reminiscent of the effects of angiopoietins. We demonstrate that Ang2 is upregulated upon HoxB5 overexpression and that the HoxB5 effect is abolished by the angiopoietin antagonist soluble Tie-2.


CONCLUSIONS
HoxB5 has an activating effect on Ang2 that is essential for endothelial cell sprouting and coordinated vascular growth.
Winnik
Stephan
S
Department of Cardiology, University of Freiburg, Hugstetter Strasse 55, Freiburg 79106, Germany.
Klinkert
Mei
M
Kurz
Haymo
H
Zoeller
Christoph
C
Heinke
Jennifer
J
Wu
Yaxu
Y
Bode
Christoph
C
Patterson
Cam
C
Moser
Martin
M
D042702:Angiopoietin-2 / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D049033:Chorioallantoic Membrane / Q000098:blood supply*; D053595:Embryonic Stem Cells / Q000378:metabolism; D042783:Endothelial Cells / Q000378:metabolism*; D020869:Gene Expression Profiling / Q000379:methods; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D018919:Neovascularization, Physiologic / Q000235:genetics; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D042787:Receptor, TIE-2 / Q000378:metabolism; D014161:Transduction, Genetic; D015854:Up-Regulation
D042702:Angiopoietin-2; D015815:Cell Adhesion Molecules; D018398:Homeodomain Proteins; D042787:Receptor, TIE-2