PARATHYROID-HORMONE-(1-34) - MEDIATED INTERLEUKIN-6 INDUCTION

Parathyroid hormone (PTH) functions in part by regulating osteoblast c ytokine expression. We recently demonstrated that PTH induced a rapid and transient increase in interleukin-6 (IL-6) mRNA expression in rat bones in vivo. To determine the molecular basis of this effect, we ana lyzed the human IL-6 promoter fused (-1,179 to +9) with the chloramphe nicol acetyltransferase (CAT) reporter gene in stable transfections in to human osteoblast-like osteosarcoma SaOS-2 cells. We compared the ef fects of PTH on IL-6 expression with adenylate cyclase activator forsk olin, PKC activator phorbol 12-myristate 13-acetate (PMA), calcium ion ophore A23187, interleukin-1 alpha (IL-1 alpha), prostaglandin E-2 (PG E-2), RS-66271 (a parathyroid hormone-related peptide analog), and pla telet-derived growth factor-BE (PDGF-BB). Analyses of cell clones show ed that IL-6 promoter expression was extremely low in the unstimulated state. Exposure to PTH (0.001-100 nM) for 12 h stimulated CAT express ion in a dose-dependent manner (200-500% of control). Treatment with I L-1 alpha was more potent than PTH in inducing transcription of the IL -6 promoter (900-1,000%). Activation of the cAMP-PKA pathway by treatm ent with forskolin induced a comparable level of induction with PTH. T ogether, the effects of PTH and forskolin were additive. RS-66271, pre viously shown to have PTH-like effects, induced a comparable level of IL-6 promoter expression. When examined together, PTH + RS-66271 effec ts were comparable to PTH effects alone. Exposure to PGE-2, PMA, PDGF- BB, or A23187 for 12 h did not significantly alter IL-6 promoter expre ssion. These results demonstrate PTH, forskolin, the PTHrP analog RS-6 6271, and IL-1 alpha stimulate IL-6 expression by stimulating gene tra nscription. The response to forskolin suggests that the messenger syst em mediated by PKA is sufficient to induce IL-6 expression. (C) 1997 W iley-Liss, Inc.