The effect of the proinflammatory cytokine interleukin (IL)-1b b on the cellular proliferation of human osteoblastic cells (SaM-1) and osteosarcoma-derived cells (SaOS-2, HOS, and MG-63) was examined. IL-1b b stimulated the proliferation of SaM-1 and MG-63 cells, but had no effect on that of SaOS-2 or HOS cells. Using reverse transcription-polymerase chain reaction (RT-PCR) analysis, the mRNA expression of IL-1 receptor type I (IL-1R1) was detected in SaM-1 and MG-63 cells consistently, but not in SaOS-2 or HOS cells in the proliferative stage. Neither the decoy inhibitory IL-1 receptor type II (IL-1R2) nor IL-1R antagonist mRNA was detected in any of the cell lines, suggesting that IL-1b b stimulated proliferation via IL-1R1. The IL-1b b-stimulated proliferation was inhibited by the MAPK kinase (MEK) inhibitor PD98059 but not by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 or the cyclooxygenase-2 specific inhibitor NS-398, suggesting that IL-1b b stimulated proliferation via MEK, without affecting prostaglandin E 2 synthesis. IL-1b b stimulated cellular proliferation but inhibited the synthesis of osteocalcin containing g g-carboxylated glutamic acid (Gla-OSCAL). Both the increased proliferation and decreased Gla-OSCAL synthesis were suppressed by vitamin K 2 (VK 2 ), which is a cofactor for g g-carboxylase. Furthermore, the inhibitory effect of VK 2 on IL-1b b-stimulated proliferation was suppressed by warfarin. However, rifampicin the nuclear receptor steroid and xenobiotic receptor (SXR) ligand had no effect of IL-b b, suggesting that IL-1b b is involved in VK 2 dependent g g-calboxylation but not SXR-activation. These results suggest that IL-1b b stimulated cellular proliferation via MEK and inhibited Gla-OSCAL synthesis, which were both inhibited by VK 2 via g g-carboxylation.

Glucocorticoids impair the proliferation, differentiation, and function of osteoblasts and induce apoptosis in mature osteoblasts. [1][2][3][4][5][6] In addition to their direct effects on osteoblasts, they have also been demonstrated to modify the synthesis of growth factors produced by osteoblastic cells. [7][8][9] These effects lead to the suppression of bone formation, a central feature in the pathogenesis of glucocorticoid induced osteoporosis. Hepatocyte growth factor (HGF), which was initially thought to be of mesodermal origin, and its receptor are expressed in osteoblasts and osteoclasts. [10][11][12] Previous studies have shown the inhibitory effects of glucocorticoids on HGF mRNA expression in rat calvarial osteoblasts 13) and human osteoblast-like cells, 14) and the stimulatory effects of HGF on thymidine incorporation in osteoblasts.11) These findings led us to investigate whether the effects of glucocorticoids on cellular proliferation are mediated by HGF in human osteoblastic cells. In this study, using osteoblastic cells (SaM-1) and osteogenic sarcoma cells (SaOS-2, HOS, and MG-63), we demonstrate that HGF functions in an autocrine and/or paracrine manner, resulting in mitogenesis. Furthermore, we show that the inhibitory effects of glucocorticoid on the proliferation of human osteoblastic cells can probably be explained by the concomitant glucocorticoidinduced inhibition of HGF production. MATERIALS AND METHODS MaterialsHydrocortisone was obtained from Sigma (St. Louis, MO, U.S.A.), and recombinant human HGF protein and a human HGF enzyme-linked immunosorbent assay (ELISA) system were obtained from R&D systems (Minneapolis, MN, U.S.A.). The bromodeoxyuridine (BrdU) cell proliferation ELISA was from Roche (Penzberg, Germany). QIAzol lysis reagent was obtained from Qiagen (Hilden,was obtained from CalBiochem (San Diego, CA, U.S.A.). Normal human osteoblasts (SaM-1 cells) were kindly provided by Dr. Koshihara (Tokyo Metropolitan Institute of Gerontology), who prepared them from an explant of ulnar periosteum obtained from a 20-year-old male patient undergoing curative surgery who gave his informed consent for its experimental use. SaM-1 cells have a mitotic life span of 34 population doubling levels (PDL), 15) and we used them at 23-24 PDL in our experiments. HOS and SaOS-2 human osteogenic sarcoma cells were obtained from the RIKEN Cell Bank (Tsukuba, Japan). MG-63 human osteogenic sarcoma cells were from the American Type Culture Collection (Rockville, MD, U.S.A.). Alpha-modified minimum essential medium (a-MEM) was purchased from Gibco BRL (Grand Island, NY, U.S.A.), and fetal calf serum (FCS) was obtained from Cell Culture Laboratories (Cleveland, OH, U.S.A.) and Irvine Scientific (Santa Ana, California, U.S.A.). All other chemicals used were of reagent grade.Cell Culture The medium used for all cell lines was a-MEM containing 10% fetal calf serum (FCS), and the cells were incubated in a humidified incubator at 37°C in 95% air and 5% CO 2 . In an analysis of proliferation, SaM-1 cells were seed...