Role of heat shock protein 27 in transforming growth factor-β-stimulated vascular endothelial growth factor release in osteoblasts

We have previously reported that transforming growth factor-beta (TGF-beta) stimulates heat shock protein 27 (HSP27) induction via p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase in osteoblast-like MC3T3-E1 cells, and that the release of vascular endothelial growth factor (VEGF) is induced by TGF-beta in these cells. In the present study, we investigated the effect of HSP27 knockdown on the TGF-beta-stimulated VEGF release in these cells. Gene silencing using short interfering RNA against HSP27 (HSP27-siRNA) significantly suppressed the TGF-beta-induced VEGF release. Immunofluorescence microscopy also revealed that HSP27-siRNA suppressed the TGF-beta-stimulated VEGF induction as well as the reduction of HSP27 induction in these cells. However, the mRNA expression of VEGF stimulated by TGF-beta was not reduced even in cells transfected with HSP27-siRNA. These results strongly suggest that HSP27 induction is critical for TGF-beta-induced VEGF release in osteoblasts.