Cytokine-cytokine synergy and protein kinase C in the regulation of lung fibroblast leukemia inhibitory factor

Studies were undertaken to characterize the cytokines and cytokine- cytokine interactions that stimulate human lung fibroblast leukemia inhibitory factor (LIF) production and the mechanisms of these regulatory effects were investigated. Unstimulated fibroblasts did not produce significant amounts of LIF, whereas recombinant interleukin-1α (rIL-1α), transforming growth factor-β (TGF-β), and recombinant tumor necrosis factor (rTNF) were dose-dependent stimulators of LIF production. TGF-β and rIL-1α also interacted in a synergistic fashion to further increase LIF elaboration. Under all conditions alterations in LIF production were associated with comparable alterations in LIF mRNA accumulation. The kinetics of mRNA induction, however, differed with rIL-1-induced LIF mRNA being readily detected after 2 h, TGF-β1 induction peaking after 16-24 h, and the induction caused by rIL-1α plus TGF-β1 being most prominent after 2-4 h and decreasing with additional incubation. Protein synthesis was not required for LIF induction. In addition, even though A23187 was an effective stimulator of LIF production, the calmodulin antagonists W-7 and trifluoperazone dichoride (TFP) did not significantly alter the LIF-stimulatory effects of IL-1 and TGF-β. PKC did appear to play an important role in this induction, however, since LIF was induced by PMA and cytokine induction of LIF production was markedly diminished by chronic phorbol ester preincubation, staurosporine, and H-7, but not by HA1004. These studies demonstrate that 1) rIL-1, TGF-β, TNF, agents that increase intracellular calcium and agents that activate PKC, stimulate lung fibroblast LIF production; 2) rIL-1 and TGF-β interact in a synergistic fashion to further increase fibroblast LIF production; and 3) rIL-1 and TGF-β stimulate lung fibroblast LIF production via a pretranslational activation pathway that is largely PKC-dependent and protein synthesis-, cyclic nucleotide-, and calmodulin-independent. Cytokine- stimulated LIF production may play an important role in homeostasis and repair in the human lung.