Abstract
Marrow stromal cells are thought to regulate hematopoiesis by producing colony-stimulating factors (CSFs) and other cytokines, either constitutively or in response to mediators such as interleukin-1 alpha (IL-1 alpha) or tumor necrosis factor-alpha (TNF alpha). The mechanisms by which these inflammatory cytokines induce CSF expression in stromal cells are not fully defined. In this study, we used human marrow stromal cells transformed by simian virus 40 (SV-MSCs) to study growth factor and cytokine gene regulation in response to IL-1 alpha and TNF alpha. IL-1 alpha induced significant and prolonged increases in steady- state mRNA levels for interleukin-6 (IL-6), interleukin-1 beta (IL-1 beta), granulocyte-macrophage CSF (GM-CSF), and, to a lesser extent, granulocyte-CSF (G-CSF); this induction was not dependent on new protein synthesis. Nuclear run-on analyses showed that IL-1 alpha transcriptionally activated the genes for IL-6, GM-CSF, and IL-1 beta, while TNF alpha transcriptionally induced expression of IL-6 and IL-1 beta. Furthermore, mRNA for IL-6 and IL-1 beta was dramatically superinduced by the combination of cycloheximide and TNF alpha. When SV- MSCs were cultured in semisolid medium, they formed colonies of blast- like cells that, when replated on plastic, resumed adherent growth. These “colony-derived” cell lines, unlike the parental SV-MSCs from which they were derived, constitutively expressed colony-stimulating activity and mRNA for GM-CSF, G-CSF, IL-6, and IL-1 beta. In this report, we show that the expression of IL-6 and IL-1 beta mRNA in the colony-derived cell lines was due, at least in part, to constitutive transcriptional activation of these genes (similar to the findings in IL-1 alpha- and/or TNF alpha-stimulated parental SV-MSCs). However, in contrast to the transcriptional activation of the GM-CSF gene seen in cytokine-induced parental SV-MSCs, GM-CSF transcripts accumulated in the colony-derived cell lines by a posttranscriptional mechanism.
