Abstract
Angiogenesis is an essential physiological process and an important factor in disease pathogenesis. However, its exploitation as a clinical target has achieved limited success and novel molecular targets are required. Although heme oxygenase-1 (HO-1) acts downstream of vascular endothelial growth factor (VEGF) to modulate angiogenesis, knowledge of the mechanisms involved remains limited. We set out identify novel HO-1 targets involved in angiogenesis. HO-1 depletion attenuated VEGF-induced human endothelial cell (EC) proliferation and tube formation. The latter response suggested a role for HO-1 in EC migration, and indeed HO-1 siRNA negatively affected directional migration of EC towards VEGF; a phenotype reversed by HO-1 over-expression. EC from Hmox1−/− mice behaved similarly. Microarray analysis of HO-1-depleted and control EC exposed to VEGF identified cyclins A1 and E1 as HO-1 targets. Migrating HO-1-deficient EC showed increased p27, reduced cyclin A1 and attenuated cyclin-dependent kinase 2 activity. In vivo, cyclin A1 siRNA inhibited VEGF-driven angiogenesis, a response reversed by Ad-HO-1. Proteomics identified structural protein vimentin as an additional VEGF-HO-1 target. HO-1 depletion inhibited VEGF-induced calpain activity and vimentin cleavage, while vimentin silencing attenuated HO-1-driven proliferation. Thus, vimentin and cyclins A1 and E1 represent VEGF-activated HO-1-dependent targets important for VEGF-driven angiogenesis.
Highlights
Revealed the importance of heme oxygenase-1 (HO-1) activity in growth-factor driven EC cell cycle progression, proliferation and capillary formation[5,14,15]
HO-1 plays a central role in angiogenesis driven by VEGF and SDF1-α.Both cytokines increase HO-1 expression and activity[5,16,20,22], with the induction of HO-1 dependent upon nuclear translocation of Nrf[224]
Using gain and loss of function approaches we have identified cyclin A1, cyclin E1 and vimentin as downstream targets of HO-1 during VEGF-driven angiogenic responses in the vascular endothelium (Fig. 9)
Summary
Revealed the importance of HO-1 activity in growth-factor driven EC cell cycle progression, proliferation and capillary formation[5,14,15]. VEGF is able to increase HO-1 expression and activity[5,22], suggesting the presence of a positive feedback pathway and endogenous amplification[6,23] These data have been reinforced and extended by two recent studies. Context-dependent, cell-type specific actions have been reported, with HO-1 and CO able to either enhance or inhibit angiogenesis under specific circumstances[14,20,26,27], in the tumour microvasculature[28] These findings, which likely reflect differences in the local microenvironment, including the presence or absence of individual growth factors and pro-inflammatory responses, serve to further emphasise the dual role of HO-1 in different settings[6], and the need for improved understanding of molecular mechanisms. The data generated demonstrate that cyclins A1 and E1, and the structural protein vimentin, are HO-1-dependent proteins that play an important role in VEGF-driven angiogenic responses including cell proliferation and migration
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
