Differential transcriptional and posttranscriptional regulation of gene expression of the colony-stimulating factors by interleukin-1 and fetal bovine serum in murine fibroblasts

Abstract

Colony-stimulating factors (CSF) are important factors in the proliferation and differentiation of hematopoietic progenitor cells (HPC), and in the survival and activation of mature blood cells. Interleukin-1 (IL-1) combined with fetal bovine serum (FBS) strongly induces the expression of macrophage-CSF (M-CSF), granulocyte-CSF (G- CSF), and granulocyte-macrophage-CSF (GM-CSF) in fibroblasts. Here, we report on the regulation of CSF gene expression in murine fibroblasts following IL-1 and FBS stimulation. We demonstrate that 10T1/2 murine fibroblasts induced by FBS or IL-1 accumulate M-CSF messenger RNA (mRNA). G-CSF mRNA expression was induced by IL-1, and not by FBS. For GM-CSF expression, induction with both FBS and IL-1 was required. Blocking studies with actinomycin-D showed that active transcription is essential for accumulation of all three CSF mRNAs. After blocking protein synthesis with cycloheximide, IL-1- or FBS-induced M-CSF expression and IL-1 plus FBS-induced GM-CSF expression still occurred and was increased. IL-1-induced G-CSF expression was completely prevented in these cells by pretreatment with cycloheximide, illustrating that, for this effect, intermediate protein synthesis was required. The half-lives of M-CSF transcripts were not substantially altered by addition of IL-1, FBS, or FBS plus IL-1. Using nuclear run- on assays, we demonstrated that the transcription rate of M-CSF was increased up to 20-fold by the addition of FBS, IL-1, or FBS plus IL-1. After blocking protein synthesis with cycloheximide, IL-1-or FBS- induced increase in M-CSF transcription rate was also observed. GM-CSF transcription increased up to fourfold after induction with FBS or IL- 1. G-CSF transcription rate was not altered by FBS or IL-1. Our results indicate that M-CSF expression induced by FBS or IL-1 in these fibroblasts is primarily regulated at the transcriptional level. GM-CSF expression appears to be regulated both transcriptionally and posttranscriptionally, and G-CSF expression is regulated mainly at the posttranscriptional level.

Transcriptional regulation of the mouse CSF-1 gene

“…3B). In summary, these studies, along with others (Falkenburg et al, , 1991Harrington et al, 1990) demonstrated that proliferating fibroblasts express the CSF-1 gene, and in response to growth arrest, the steady-state level of the CSF-1 mRNA decreases. CSF-1 gene transcription is activated when growth-arrested cells are restimulated with either IL-1 or serum.…”

“…Based upon sequence identity, this region contains a putative binding site for the transcription factor NF-IL6 (also known as C/EBPb) . NF-IL6 was originally identified as a transcription factor that bound to the IL-6 promoter in response to IL-1 treatment (Isshiki et al, 1990), and the CSF-1 gene is transcriptionally activated in fibroblasts treated with IL-1 (Falkenburg et al, 1991). However, antibodies to C/EBPb did not cross-react with the binding activity, so we are in the process of trying to identify the binding activity.…”

“…When we initiated our studies (Falkenburg et al, , 1991 the CSF-1 gene was thought to be constitutively expressed in fibroblasts and subject to little if any regulation. Our hypothesis predicted that under basal conditions (with nonproliferating or quiescent fibroblasts) there would be a minimal amount of CSF-1 gene expression, and in response to tissue damage or in response to interleukin-1 (IL-1) produced as a consequence of an infection, CSF-1 gene expression in fibroblasts would increase.…”

Rapamycin inhibits lipopolysaccharide induction of granulocyte‐colony stimulating factor and inducible nitric oxide synthase expression in macrophages by reducing the levels of octamer‐binding factor‐2

“…Although recombinant G-CSF is routinely used to treat neutropenia and to mobilize hematopoietic stem cells from the bone marrow into the peripheral blood before transplantation [31], it is also expressed endogenously in a variety of cell types in response to treatment with LPS, tumor necrosis factor-a, interleukin-1b, PMA or interferon-c [32]. Expression of G-CSF can be regulated at both the transcriptional and posttranscriptional levels [33]; however, the regulatory mechanisms are poorly understood. To our knowledge, this is the first study showing that rapamycin reduces the LPS-induced expression of G-CSF at the transcriptional level in macrophages by blocking mTOR activity.…”

Is interleukin 17, an inducible cytokine that stimulates production of other cytokines, merely a redundant player in a sea of other biomolecules?

“…These effects can be direct on the stem or progenitor cells them-selves, actions which are most rigorously determined in vitro with an initial culture of a single isolated stem or progenitor cell (14)(15)(16), or the effects can be indirectly mediated. This latter effect involves accessory cells which can be induced by a number of stimuli, including cytokines, to produce and release a single, but more likely a group of cytokines (1)(2)(3)(4)(5)(6)(7)(17)(18)(19)(20)(21)(22)(23) which can then directly act on stem or progenitor cells or have a cascading effect on induction of the production or release of additional cytokines or other biologically active molecules.…”