Alveolar macrophages release an insulin-like growth factor I-type molecule.
Human alveolar macrophages, when activated, release a progression-type growth factor for fibroblasts that signals "competent" fibroblasts to replicate. The present study demonstrates that this growth activity is an insulin-like growth factor I (IGF-I)-type molecule. Partial purification of medium conditioned by activated alveolar macrophages using ion exchange and gel filtration chromatography revealed an IGF-I molecule as detected by an anti-IGF-I polyclonal antibody and that the specific activity of the progression-type growth activity tracked with the amount of IGF-I present. In a serum-free complementation test, the increase in fibroblast proliferation by alveolar macrophage IGF-I was reduced in a dose-response manner with an anti-IGF-I monoclonal antibody. The alveolar macrophage IGF-I displaced 125I-IGF-I from its receptor in a binding assay utilizing human lung fibroblasts and it stimulated type I IGF receptors purified from human lung fibroblasts to phosphorylate a tyrosine-containing artificial substrate. In contrast to the 7.6-kD serum IGF-I, gel chromatography revealed that the alveolar macrophage IGF-I had an apparent molecular mass of 26 kD, similar to other tissue IGF-Is. Alveolar macrophages expressed IGF-I mRNA transcripts as detected by solution hybridization using a 32P-labeled riboprobe complementary to exons I-II-III of the IGF-I gene. In the context of the known functions of the family of IGF-I molecules in cell growth, IGF-I released by activated alveolar macrophages may play a role in acute and chronic inflammatory disorders.
Rom
W N
WN
Pulmonary Branch, National Heart, Lung and Blood Institute, Bethesda, Maryland 20892.
Basset
P
P
Fells
G A
GA
Nukiwa
T
T
Trapnell
B C
BC
Crysal
R G
RG
D001667:Binding, Competitive; D002852:Chromatography, Ion Exchange; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000378:metabolism*; D008262:Macrophage Activation; D008264:Macrophages / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology*; D012333:RNA, Messenger / Q000032:analysis; D013002:Somatomedins / Q000378:metabolism*
D012333:RNA, Messenger; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I