Rat C6 glial cells synthesize insulin-like growth factor I (IGF-I) and express IGF-I receptors and IGF-II/mannose 6-phosphate receptors.
We have used the rat C6 glial cell line as a model system to study the role of insulin-like growth factors (IGF) in neuroglial cells of the central nervous system (CNS). Northern blot analysis of C6 RNA demonstrated the presence of IGF-I mRNA and undetectable IGF-II mRNA. IGF-I and IGF-binding protein(s), but not IGF-II, were detected in C6 glial cell-conditioned medium. The level of IGF-I was 1-4 ng/ml in conditioned medium based on a human IGF-I standard. The immunoreactive IGF-I inhibited [125I]IGF-I binding to the IGF-I receptor on chick embryo fibroblasts and stimulated [3H]thymidine incorporation into chick embryo fibroblast DNA. Competitive binding and affinity cross-linking experiments using [125]IGF-I and [125I]IGF-II demonstrated the presence of IGF-I receptors (type I) and IGF-II/mannose 6-phosphate receptors (type II) on C6 glial cell membranes. An immunoglobulin (no. 3637) directed against the rat IGF-II receptor blocked the degradation of [125I]IGF-II added to C6 glial cells, presumably by blocking receptor-mediated internalization. We were unable to demonstrate an autocrine role for IGF in the C6 glial cell line, since [3H]thymidine incorporation into DNA was stimulated equally well by IGF-I-deficient rat serum and normal serum, and added IGF did not stimulate [3H]thymidine incorporation into DNA when tested alone or when added to IGF-I-deficient serum. We propose that neuroglial cell-derived IGF-I may serve as a paracrine growth stimulus in the central nervous system.
Kiess
W
W
Metabolism Branch, National Cancer Institute, Bethesda, Maryland 20892.
Lee
L
L
Graham
D E
DE
Greenstein
L
L
Tseng
L Y
LY
Rechler
M M
MM
Nissley
S P
SP
D000818:Animals; D015152:Blotting, Northern; D002462:Cell Membrane / Q000032:analysis / Q000648:ultrastructure; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D005786:Gene Expression Regulation; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D009457:Neuroglia / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000096:biosynthesis*
D012333:RNA, Messenger; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D004247:DNA