Function of Rho-kinase in prostaglandin D 2-induced interleukin-6 synthesis in osteoblasts

Abstract

We have previously reported that prostaglandin D 2 (PGD 2) stimulates interleukin-6 (IL-6), a potent bone resorptive agent, in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether Rho-kinase is implicated in the PGD 2-stimulated IL-6 synthesis in MC3T3-E1 cells. PGD 2 time-dependently induced the phosphorylation of myosin phosphatase targeting subunit (MYPT-1), a Rho-kinase substrate. Y27632, a specific Rho-kinase inhibitor, significantly reduced the PGD 2-stimulated IL-6 synthesis as well as the MYPT-1 phosphorylation. Fasudil, another inhibitor of Rho-kinase, suppressed the PGD 2-stimulated IL-6 synthesis. The PGD 2-stimulated IL-6 synthesis was reduced by PD98059, a MEK inhibitor, and SB203580, an inhibitor of p38 mitogen-activated protein (MAP) kinase, but not SP600125, an inhibitor of stress-activated protein kinase/c – Jun N-terminal kinase (SAPK/JNK). However, Y27632 and fasudil failed to affect the PGD 2-induced phosphorylation of p44/p42 MAP kinase. On the other hand, Y27632 as well as fasudil markedly attenuated the PGD 2-induced phosphorylation of p38 MAP kinase. In addition, PGD 2 additively induced IL-6 synthesis in combination with endothelin-1 which induces IL-6 synthesis through p38 MAP kinase regulated by Rho-kinase. These results strongly suggest that Rho-kinase regulates PGD 2-stimulated IL-6 synthesis via p38 MAP kinase activation in osteoblasts.