Soluble IL-6 receptor induces calcium flux and selectively modulates chemokine expression in human dermal fibroblasts.

Truncated forms of cytokine receptors have been regarded as modulators of the activity of their cognate ligands. In addition to inhibiting effects of their respective ligands, soluble receptors can also facilitate ligand-mediated signaling. Several studies have demonstrated that exogenous IL-6 in association with the soluble IL-6 receptor alpha (sIL-6Ralpha) can activate cells expressing the gp130 signal transducer lacking the specific, membrane-bound IL-6Ralpha. Since cell cultures of human dermal fibroblasts express high amounts of IL-6, we examined whether the addition of sIL-6Ralpha in association with endogenous IL-6 would be sufficient to stimulate these cells via gp130. As an early rapid signal we analyzed changes in intracellular free calcium concentrations (Ca2+]i). Addition of sIL-6Ralpha induced an acute and transient increase in cytosolic free calcium concentrations in a dose-dependent fashion. This Ca2+-signal was abolished when cells were pretreated with anti-IL-6 or anti-gp130 antibodies. Using flow cytometric analysis we could demonstrate membrane-associated IL-6 and gp130, but not IL-6Ralpha on fibroblasts. We also analyzed MCP-1 and IL-8 expression as a response involved in the more recently recognized chemoattractant functions of fibroblasts, and found MCP-1 to be up-regulated, but not IL-8. These data suggest that sIL-6Ralpha binds to cell-associated, endogenous IL-6 produced by fibroblasts and this complex then activates the cells via gp130. This pathway of fibroblast activation by sIL-6Ralpha adds another dimension to the role of fibroblasts in the cytokine network.