Becker B., Multhoff G., Farkas B., Wild P. of HSP90 without affecting Ca2+ oscillations observed with EGF. Extracellular HSP90 induced EGFR phosphorylation at Tyr-1068, and this event was prevented by both the protein kinase C inhibitor, rottlerin, and the c-Src inhibitor, PP2. Altogether, our results suggest that extracellular HSP90 transactivates EGFR/ErbB1 through TLR4 and a PKC/c-Src pathway, which induces ATP release and cytosolic Ca2+ 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. and values 0.05 were significant. RESULTS Extracellular HSP90 Accelerates Glioblastoma Cell Migration in Vitro Immunofluorescence analyses detected the HSP90 isoform at the cell surface of glioblastoma U87 cells (Fig. 1in the range from 60 ng/ml to 6 g/ml). This resulted in higher rates of gap closure observed as early as the first hour of cell incubation and confirmed in the following hours, 6 and 12 h (Fig. 1= 6 experiments). The extracellular localization of HSP90 was confirmed by flow cytometry analysis using anti-HSP90 or anti-HSP70 (= 3). = 2; *, values 0.05 control). = 3; *, values 0.05 control). Extracellular HSP90 Increases [Ca2+]i in U87 Cells To determine the role of Ca2+ store in U87 response to HSP90, we measured [Ca2+]within 1C3 min (Fig. 2in the absence of external Ca2+, demonstrating that HSP90 did not deplete completely internal stores. In Ca2+-free conditions, the amplitude of Ca2+ peak induced by EGF remained unchanged, but the duration of the plateau phase was decreased, and Ca2+ readdition to the bath medium resulted in a transient Ca2+ influx through plasma membrane channels due to capacitative Barnidipine Ca2+ entry (Fig. 2with a frequency of three spikes per 5 min; 98%, = 50), which were rapidly abolished by the removal of HSP90 (Fig. 2(average of 10 cells; = 10). = 10). The shows the contribution of ATP-mediated Barnidipine pathways to HSP90-induced Ca2+ signaling in superimposed traces obtained from cells preincubated with apyrase (40 units/ml) or suramin (10 m) for 10 min, before the addition Barnidipine of HSP90 plus EGF (= 10). total EGFR proteins (not shown). Both EGF and HSP90 induced EGFR phosphorylation at Tyr-1068 within 15 min, which was attenuated by cell pretreatment with the PKC inhibitor, rottlerin (Fig. 4are isotype IgG controls. panel indicates co-localization of EGFR and BSA (= 3). = 3). Open in a separate window FIGURE 4. Tyrosine phosphorylation of EGFR Rabbit Polyclonal to AK5 and partial co-localization of TLR4 and EGFR in glioblastoma cells. ErbB1 analyzed Barnidipine by densitometry (mean S.D., = 2). are isotype IgG controls (= 3). panel, indicates co-localization of both receptors. Confocal optical sections of 0.4 m thickness are shown (= 3). = 4). panel, indicates co-localization of clathrin and P-EGFR. Confocal optical sections of 0.4 m thickness are shown (= 3). EGFR was mainly located at the cell periphery, whereas TLR4 was found throughout the cell (Fig. 4(Fig. 5increase in U87 cells. The contribution of TLR4 and EGFR (ErB1) to HSP90-mediated cell invasion is shown in Fig. 5(Fig. 6and the cell migration induced by HSP90 (Fig. 6, = 3) as performed. in TLR4 shRNA (= 3). = 2; *, values 0.05 control). The following cells were used as control in this specific experiment; cultures of U87 cells and normal human astrocytes (Lonza Walkersville, Inc.) were grown to confluency in DMEM plus 10% fetal bovine serum (Lonza). For lentiviral transduction particles Barnidipine and transfections, human TLR4 shRNA, EGFR (ErbB) shRNA and control lentiviral particles were used according to the manufacturer’s recommendations (Santa Cruz Biotechnology). Open in a separate window FIGURE 6. The HSP90-induced cell migration and Ca2+ signaling are slightly reduced by an endotoxin-binding.