Interferon-gamma inhibits macrophage insulin-like growth factor-I synthesis at the transcriptional level.
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.
Arkins
S
S
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.
Rebeiz
N
N
Brunke-Reese
D L
DL
Biragyn
A
A
Kelley
K W
KW
D000818:Animals; D002461:Cell Line, Transformed; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D007163:Immunosorbent Techniques; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D007371:Interferon-gamma / Q000494:pharmacology*; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D008264:Macrophages / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011920:Rats, Inbred WF; D011994:Recombinant Proteins; D014158:Transcription, Genetic
D012333:RNA, Messenger; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D016173:Macrophage Colony-Stimulating Factor; D007371:Interferon-gamma; D003513:Cycloheximide