The heat‐shock protein 27 (HSP27) is up‐regulated in tumor cells and released in their microenvironment. Here, we show that extracellular HSP27 has a proangiogenic effect evidenced on chick chorioallantoic membrane. To explore this effect, we test the recombinant human protein (rhHSP27) at physiopathological doses (0.1–10 μg/ml) onto human microvascular endothelial cells (HMECs) grown as monolayers or spheroids. When added onto HMECs, rhHSP27 dose‐dependently accelerates cell migration (with a peak at 5 (μg/ml) and favors spheroid sprouting within 12‐24 h. rhHSP27 increases VEGF gene transcription and promotes secretion of VEGF‐activating VEGF receptor type 2. Increased VEGF transcription is related to NF‐κB activation in 30 min. All of these effects are initiated by rhHSP27 interaction with Toll‐like receptor 3 (TLR3). Such an interaction can be detected by immunoprecipitation but does not seem to be direct, as we failed to detect an interaction between rhHSP27 and monomeric TLR3 by SPR analysis. rhHSP27 is rapidly internalized with a pool of TLR3 to the endosomal compartment (within 15–30 min), which is required for NF‐κB activation in a cytosolic Ca ²⁺ ‐dependent manner. The HSP27/TLR3 interaction induces NF‐κB activation, leading to VEGF‐mediated cell migration and angiogenesis. Such a pathway provides alternative targets for antiangiogenic cancer therapy.—Thuringer, D., Jego, G., Wettstein, G., Terrier, O., Cronier, L., Yousfi, N., Hébrard, S., Bouchot, A., Hazoumé, A., Joly, A‐L., Gleave, M., Rosa‐Calatrava, M., Solary, E., and Garrido, C., Extracellular HSP27 mediates angiogenesis through Toll‐like receptor 3. FASEB J. 27, 4169–4183 (2013). www.fasebj.org

Extracellular heat shock protein HSP90α was reported to participate in tumor cell growth, invasion, and metastasis formation through poorly understood signaling pathways. Herein, we show that extracellular HSP90α favors cell migration of glioblastoma U87 cells. More specifically, externally applied HSP90α rapidly induced endocytosis of EGFR. This response was accompanied by a transient increase in cytosolic Ca(2+) appearing after 1-3 min of treatment. In the presence of EGF, U87 cells showed HSP90α-induced Ca(2+) oscillations, which were reduced by the ATP/ADPase, apyrase, and inhibited by the purinergic P(2) inhibitor, suramin, suggesting that ATP release is requested. Disruption of lipid rafts with methyl β-cyclodextrin impaired the Ca(2+) rise induced by extracellular HSP90α combined with EGF. Specific inhibition of TLR4 expression by blocking antibodies suppressed extracellular HSP90α-induced Ca(2+) signaling and the associated cell migration. HSPs are known to bind lipopolysaccharides (LPSs). Preincubating cells with Polymyxin B, a potent LPS inhibitor, partially abrogated the effects of HSP90α without affecting Ca(2+) oscillations observed with EGF. Extracellular HSP90α induced EGFR phosphorylation at Tyr-1068, and this event was prevented by both the protein kinase Cδ inhibitor, rottlerin, and the c-Src inhibitor, PP2. Altogether, our results suggest that extracellular HSP90α transactivates EGFR/ErbB1 through TLR4 and a PKCδ/c-Src pathway, which induces ATP release and cytosolic Ca(2+) increase and finally favors cell migration. This mechanism could account for the deleterious effects of HSPs on high grade glioma when released into the tumor cell microenvironment.

Gap junction-mediated transfer of miR-145-5p from microvascular endothelial cells to colon cancer cells inhibits angiogenesis

Modulation of the inwardly rectifying potassium channel Kir4.1 by the pro-invasive miR-5096 in glioblastoma cells

Transfer of functional microRNAs between glioblastoma and microvascular endothelial cells through gap junctions

Primary tumor- and metastasis-derived colon cancer cells differently modulate connexin expression and function in human capillary endothelial cells