Recent evidence suggests that histone deacetylase inhibitors (HDACi) may mediate part of their antitumor effects by interfering with tumor angiogenesis. As signalling via the vascular endothelial growth factor receptor-2 (VEGFR-2) pathway is critical for angiogenic responses during tumor progression, we explored whether established antitumor effects of HDACi are partly mediated through diminished endothelial VEGFR-2 expression. We therefore examined the potential impact of three different HDACi, trichostatin A (TSA), sodium butyrate (But) and valproic acid (VPA), on VEGFR-2 protein expression. TSA, VPA and But significantly inhibit VEGFR-2 protein expression in endothelial cells. Pertinent to these data, VEGFR-2 protein half-life is shown to be decreased in response to HDACi. Recently, it could be demonstrated that expression of VE-cadherin influences VEGFR-2 protein half-life. In our experiments, VEGFR-2 downregulation was accompanied by HDACi-induced VE-cadherin suppression. Interestingly, siRNA-mediated knockdown of VE-cadherin led to a pronounced loss of VEGFR-2 expression on the protein as well as on the mRNA level, implicating that VE-cadherin not only influences VEGFR-2 protein half-life but also the transcriptional level. To further distinguish which of the eight different histone deacetylases are responsible for the regulation of VEGFR-2 expression, specific HDAC genes were silenced by transfecting respective siRNAs. These studies revealed that HDACs 1, 4, 5 and 6 are preferentially involved in VEGFR-2 expression. Therefore, these results provide an explanation for the anti-angiogenic action of HDAC inhibitors via a VE-cadherin, HDAC 1 and HDACs 4-6-mediated suppression of VEGFR-2 expression and might be of importance in the development of new anti-angiogenic drugs.
Keywords: HDACs 1, 4, 5 and 6; VE-cadherin; VEGFR-2; angiogenesis; histone deacetylase inhibitors; protein half-life.
© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.