Interferon-gamma inhibits macrophage insulin-like growth factor-I synthesis at the transcriptional level.

Abstract

Spontaneous production of insulin-like growth factor-I (IGF-I) by inflammatory macrophages contributes to aberrant wound healing, but little is known about regulation of IGF-I synthesis in myeloid cells. The T cell-derived cytokine interferon-gamma (IFN gamma) inhibits several fibrogenic and angiogenic components of the wound-healing response. We have used metabolic labeling of primary colony stimulating factor-1 (CSF-1)-derived macrophages and a transformed macrophage cell line (PU5-1R) followed by immunoprecipitation to demonstrate that synthesis of the 17 kilodalton (kDa) prepro-IGF-I protein by these cells is substantially inhibited by IFN gamma. An exon 4 IGF-I/beta-actin riboprobe expression cassette was used in RNase protection assays to show that IFN gamma also reduces steady state levels of IGF-I mRNA in three different populations of macrophages in a time- and dose-dependent manner. This effect is specific for IFN gamma because neither the IFNs-alpha/beta nor lipopolysaccharide (LPS) affects expression of steady state IGF-I transcripts. Down-regulation of IGF-I mRNA by IFN gamma is dependent on de novo protein synthesis and is abrogated by coculture with cycloheximide. Nuclear run-on assays revealed that elongation of IGF-I transcripts is absent in fresh bone marrow cells but is induced several-fold after cells are cultured for 6 days with CSF-1. Treatment of these CSF-1-derived macrophages with IFN gamma for 6 h substantially inhibits synthesis of IGF-I mRNA. Studies on the decay of IGF-I mRNA in PU5-1R macrophages treated with an RNA polymerase inhibitor confirmed that the decline in IGF-I steady state mRNA in IFN gamma-treated cultures arises from an inhibition of transcription rather than from a reduction in mRNA stability. Since a variety of inflammatory mediators can induce expression of IGF-I in macrophages, inhibition of macrophage IGF-I synthesis by IFN gamma provides a mechanism by which leukocytes regulate levels of this growth factor in their microenvironment.

Transcriptional Regulation of Insulin-like Growth Factor-I by Interferon-γ Requires STAT-5b

“…With IFN-␥ treatment, the increase in IGF-I mRNA was time-dependent but transient, with a 6 Ϯ 1.0-fold induction observed by 3 h post-treatment and a further increase to 8 Ϯ 1.7-fold 5 h after treatment. This is contrary to that observed in rodent macrophages (11), most likely reflecting cell type and/or species differences. The -fold induction was significantly higher than that observed when the dermal fibroblasts were treated with GH (1.8 Ϯ 0.6-fold, 3 h post-treatment (9)).…”

“…The majority of such studies, however, have employed rodent cell models, where cytokines appear to have inhibitory effects on IGF-I mRNA expression (11, 13, 14, 20 -22). For example, IFN-␥ significantly inhibited IGF-I mRNA transcription in a timeand dose-dependent manner in mouse macrophages (11,12), and in rat glioma cells, IFN-␣/␤ also down-regulated IGF-I mRNA expression (13). In contrast, no alterations in IGF-I mRNA were observed in IFN-␥-treated rat aortic vascular smooth muscle cells (21) or C2C12 cells (14,22).…”

The interactions and essential effects of intrinsic insulin‐like growth factor‐I on Leishmania (Leishmania) major growth within macrophages

“…We evaluated the localization of IGF‐I and its association with the parasite using confocal microscopy and analysed whether modulation of IGF‐I expression might affect intracellular parasite growth. Knowing that Th1 cytokines inhibit IGF‐I expression in macrophages , we used interferon‐gamma (IFN‐γ) as a stimulus to reduce IGF‐I expression and to evaluate the consequential effects on parasitism in L. major –infected macrophages. For these experiments, RAW 264·7 cells (macrophage cell line, ATCC) were grown in DMEM medium (Sigma, St. Louis, MO, USA) that was supplemented with 0·5% bovine serum albumin (BSA; Sigma).…”

Expression of insulin-like growth factor-I in lesional and non-lesional skin of patients with morphoea

“…Growth hormone (GH) induces the production of IGF‐I by the liver, which is the major source of IGF‐I in the circulation, and in tissues, whereby it mediates the effects of GH on the different body organs and tissues 6 . Other cytokines that stimulate IGF‐I production include tumour necrosis factor‐α, 7 colony stimulating factors 8 and interferon‐γ 9 …”

“…5 Growth hormone (GH) induces the production of IGF-I by the liver, which is the major source of IGF-I in the circulation, and in tissues, whereby it mediates the effects of GH on the different body organs and tissues. 6 Other cytokines that stimulate IGF-I production include tumour necrosis factor-a, 7 colony stimulating factors 8 and interferon-c. 9 Actions of IGF-I occur via binding to IGF-I receptor, a tetrameric, type I surface receptor that is composed of two a-chains and two b-chains that are joined by disulphide linkages. IGF-I is involved in cellular growth, division, differentiation, migration, inhibition of apoptosis, metabolism, and regulation of gene transcription.…”