HSP90 inhibitors potentiate PGF2α-induced IL-6 synthesis via p38 MAP kinase in osteoblastsReport as inadecuate




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Heat shock protein 90 HSP90 that is ubiquitously expressed in various tissues, is recognized to be a major molecular chaperone. We have previously reported that prostaglandin F2α PGF2α, a potent bone remodeling mediator, stimulates the synthesis of interleukin-6 IL-6 through p44-p42 mitogen-activated protein MAP kinase and p38 MAP kinase in osteoblast-like MC3T3-E1 cells, and that Rho-kinase acts at a point upstream of p38 MAP kinase. In the present study, we investigated the involvement of HSP90 in the PGF2α-stimulated IL-6 synthesis and the underlying mechanism in MC3T3-E1 cells. Geldanamycin, an inhibitor of HSP90, significantly amplified both the PGF2α-stimulated IL-6 release and the mRNA expression levels. In addition, other HSP90 inhibitors, 17-allylamino-17demethoxy-geldanamycin 17-AAG and 17-dimethylamino-ethylamino-17-demethoxy-geldanamycin 17-DMAG and onalespib, enhanced the PGF2α-stimulated IL-6 release. Geldanamycin, 17-AAG and onalespib markedly strengthened the PGF2α-induced phosphorylation of p38 MAP kinase. Geldanamycin and 17-AAG did not affect the PGF2α-induced phosphorylation of p44-p42 MAP kinase and myosin phosphatase targeting subunit MYPT-1, a substrate of Rho-kinase, and the protein levels of RhoA and Rho-kinase. In addition, HSP90-siRNA enhanced the PGF2α-induced phosphorylation of p38 MAP kinase. Furthermore, SB203580, an inhibitor of p38 MAP kinase, significantly suppressed the amplification by geldanamycin, 17-AAG or 17-DMAG of the PGF2α-stimulated IL-6 release. Our results strongly suggest that HSP90 negatively regulates the PGF2α-stimulated IL-6 synthesis in osteoblasts, and that the effect of HSP90 is exerted through regulating p38 MAP kinase activation.



Author: Kazuhiko Fujita, Haruhiko Tokuda, Gen Kuroyanagi, Naohiro Yamamoto, Shingo Kainuma, Tetsu Kawabata, Go Sakai, Rie Matsushima-Nish

Source: http://plos.srce.hr/



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