Heparin inhibits the expression of interleukin-11 and granulocyte- macrophage colony-stimulating factor in primate bone marrow stromal fibroblasts through mRNA destabilization

Interactions between different cytokines, extracellular matrix components, and various cell types inside the bone marrow microenvironment are believed to play important roles in the regulation of hematopoiesis. We observed that both interleukin-1 (IL-1) and 12-O- tetradecanoylphorbol-13-acetate (TPA) can stimulate the expression of IL-11 and granulocyte-macrophage colony-stimulating factor (GM-CSF) genes in a primate bone marrow stromal fibroblast cell line, PU-34. We also found that IL-1 or TPA-stimulated IL-11 and GM-CSF expression in PU-34 cells can be abolished by heparin, a class of molecules related to extracellular matrix components, glycosaminoglycans. Because the growth inhibitory signals provided by extracellular factors were less understood, the mechanisms of heparin inhibition of IL-11 and GM-CSF gene expression were further investigated. Our data demonstrate for the first time that heparin did not alter the transcription of endogenous IL-11 and GM-CSF genes or an exogenous IL-11 promoter construct containing an AP-1 sequence. Instead, heparin facilitated the degradation of the corresponding mRNAs. Through RNA gel shift assays, heparin-mediated mRNA destabilization was tentatively linked to its competition for mRNA binding proteins both in the cell-free system and in intact cells. Collectively, our findings suggest that varying degrees of heparin inhibition may provide a novel mechanism for the regulation of cytokine expression during the growth and differentiation of different lineages of hematopoietic cells.