HSP70 inhibitor amplifies the bFGF‑induced release of IL‑6 in osteoblasts.

Heat shock protein 70 (HSP70) functions as an ATP‑dependent molecular chaperone under stress and is involved in protein homeostasis, folding and degradation. HSP70 inhibitors amplify TGF‑β‑stimulated VEGF synthesis in the mouse osteoblastic MC3T3‑E1 cell line. Basic fibroblast growth factor (bFGF) stimulates IL‑6 release via p38 MAPK in MC3T3‑E1 osteoblast‑like cells. In the present study, the effects of HSP70 on the bFGF‑stimulated release of IL‑6 was evaluated using MC3T3‑E1 osteoblast‑like cells. IL‑6 release and mRNA expression levels were analyzed using ELISA and reverse transcription‑quantitative PCR, respectively. Phosphorylation of p38 MAPK and HSP70 was assessed using western blotting. HSP70 inhibitor VER‑155008 significantly increased the bFGF‑stimulated release of IL‑6 in both MC3T3‑E1 osteoblastic cells and normal human osteoblasts. Furthermore, VER‑155008 significantly enhanced the mRNA expression levels of IL‑6 stimulated by bFGF. Western blotting demonstrated a significant increase in the bFGF‑stimulated phosphorylation of p38 MAPK in VER‑155008‑treated MC3T3‑E1 cells. A significant increase in the bFGF‑stimulated phosphorylation of p38 MAPK was also demonstrated in MC3T3‑E1 cells treated with YM‑08, another HSP70 inhibitor. VER‑155008 or YM‑08 did not significantly affect the expression of HSP70 with or without bFGF stimulation. Finally, the specific p38 MAPK inhibitor SB203580 markedly suppressed the enhancing effects of VER‑155008 on bFGF‑stimulated release of IL‑6. Taken together, these results indicated that HSP70 inhibitor amplified bFGF‑stimulated release of IL‑6 through p38 MAPK activation in the osteoblastic MC3T3‑E1 cell line.