title: Unidirectional crosstalk between Bcl-xL and Bcl-2 enhances the angiogenic phenotype of endothelial cells.
abstract: Expression of Bcl-x(L) correlates with the clinical outcomes of patients with cancer. While the role of Bcl-2 in angiogenesis is becoming increasingly evident, the function of Bcl-x(L) in angiogenesis is unclear. Here, we showed that epidermal growth factor (EGF) induces in vitro capillary sprouting and Bcl-x(L) expression in primary endothelial cells. Bcl-x(L)-transduced human dermal microvascular endothelial cells (HDMEC-Bcl-x(L)), but not empty vector control cells, spontaneously organize into capillary-like sprouts. Searching for a mechanism to explain these responses, we observed that Bcl-x(L) induced expression of the pro-angiogenic chemokines CXC ligand-1 (CXCL1) and CXC ligand-8 (CXCL8), and that blockade of CXC receptor-2 (CXCR2) signaling inhibited spontaneous sprouting of HDMEC-Bcl-x(L). Bcl-x(L) led to Bcl-2 upregulation, but Bcl-2 did not upregulate Bcl-x(L), suggesting the existence of a unidirectional crosstalk from Bcl-x(L) to Bcl-2. EGF and Bcl-x(L) activate the mitogen-activated protein kinase/ERK pathway resulting in upregulation of vascular endothelial growth factor (VEGF), a known inducer of Bcl-2 in endothelial cells. Inhibition of VEGF receptor signaling in HDMEC-Bcl-x(L) prevented Bcl-2 upregulation and demonstrated the function of a VEGF-mediated autocrine loop. Bcl-2 downregulation by RNAi blocked CXCL1 and CXCL8 expression downstream of Bcl-x(L), and markedly decreased angiogenesis in vivo. We conclude that Bcl-x(L) functions as a pro-angiogenic signaling molecule controlling Bcl-2 and VEGF expression. These results emphasize a complex interplay between Bcl-2 family members beyond their classical roles in apoptosis.
authors.affiliation: Angiogenesis Research Laboratory, Department of Restorative Sciences, University of Michigan School of Dentistry, Ann Arbor, MI 48109-1078, USA.
authors.forename: E
authors.initials: E
authors.lastname: Karl
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: Z
authors.initials: Z
authors.lastname: Dong
authors.forename: K G
authors.initials: KG
authors.lastname: Neiva
authors.forename: M S
authors.initials: MS
authors.lastname: Soengas
authors.forename: A E
authors.initials: AE
authors.lastname: Koch
authors.forename: P J
authors.initials: PJ
authors.lastname: Polverini
authors.forename: G
authors.initials: G
authors.lastname: Núñez
authors.forename: J E
authors.initials: JE
authors.lastname: Nör
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D054360:Chemokine CXCL1 / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000378:metabolism*; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D051379:Mice; D016513:Mice, SCID; D018919:Neovascularization, Physiologic; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D014161:Transduction, Genetic; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D051020:bcl-X Protein / Q000378:metabolism*
chemical_list: C475829:CXCL1 protein, human; C508606:CXCL8 protein, human; D054360:Chemokine CXCL1; D016209:Interleukin-8; D019253:Proto-Oncogene Proteins c-bcl-2; D042461:Vascular Endothelial Growth Factor A; D051020:bcl-X Protein; D004815:Epidermal Growth Factor