Involvement of Rho-kinase in TGF-β-stimulated heat shock protein 27 induction in osteoblasts.

We previously reported that transforming growth factor-β (TGF-β) stimulates heat shock protein 27 (HSP27) induction through p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase and stress-activated protein kinase/ c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. In addition, we recently reported that the Rho-kinase inhibitors Y27632 and fasudil suppressed the TGF-β-induced phosphorylation of SAPK/JNK, but not p44/p42 MAP kinase, p38 MAP kinase or Smad2. In the present study, to investigate whether Rho-kinase is involved in TGF-β-stimulated HSP27 induction in MC3T3-E1 cells, we examined the effects of Rho-kinase inhibitors on HSP27 induction. Y27632 and fasudil significantly suppressed the HSP27 induction stimulated by TGF-β in a dose-dependent manner, without affecting the protein levels of HSP70 or HSP90. Immunofluorescence microscopy also revealed that TGF-β clearly stimulated, while Y27632 and fasudil markedly suppressed, HSP27 induction in the cytosol of these cells. Taken together, these findings indicate that Rho-kinase regulates TGF-β-stimulated HSP27 induction via SAPK/JNK activation in osteoblasts.