Extracellular HSP70 blocks CD40L-induced apoptosis and tubular formation in endothelial cells

Abstract

Background: Recent studies have shown that CD40, a key player in angiogenesis and tubular formation, is an extracellular receptor of the heat shock protein 70 (HSP70)-peptide complex in endothelial cells. The aim of the present study was to determine the effect of extracellular HSP70 treatment on CD40L-suppressed apoptosis and CD40L-induced tubular formation in human umbilical vein endothelial cells (HUVEC). Methods: The apoptotic index of CD40L-stimulated HUVEC with or without recombinant human HSP70 was evaluated using terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling assay analysis. Binding of HSP70-peptide complex to CD40 on HUVEC was determined by double-labeling immunofluorescence methods. To evaluate the biological activity of CD40 engagement pretreated with rhHSP70 (0.5, 1 and 3 ng/mL), the extent of new capillary-like networking structure (tubular formation) formation in HUVEC was counted using an Olympus digital camera. Vascular invasion into MNK-28 cell clusters was assessed by counting the number of tubular structures extending from the HUVEC into growth factor-depleted Matrigel. Scores for CD34, HSP70 and CD40L expression levels in gastric cancer tissues were determined by immunostaining. Results: CD40L stimulation inhibited vincristine-induced apoptosis of HUVEC in a dose-dependent manner. Extracellular HSP70 treatment significantly blocked the inhibition of apoptosis by CD40L in HUVEC exposed to vincristine. HSP70-peptide complex bound to CD40 on HUVEC. Extracellular HSP70 treatment also significantly reduced CD40L-induced tubular formation in a dose-dependent manner. HSP70 treatment also suppressed invasive tubular formation into MKN-28 cells clusters by CD40L-activated HUVEC. There was a significant relationship between CD40L expression levels and microvessel density; however, the relationship between HSP70 expression level and microvessel density in gastric cancer tissues was not significant. Conclusions: Extracellular HSP70 treatment blocks CD40L inhibition of apoptosis and CD40L induction of tubular formation in HUVEC. © 2008 The Authors.