Insulinlike growth factor-II/mannose 6-phosphate receptor is expressed on CCl4-exposed rat fat-storing cells and facilitates activation of latent transforming growth factor-beta in cocultures with sinusoidal endothelial cells.
Transforming growth factor beta (TGF-beta), a potent fibrogenic cytokine, is secreted in latent form. We examined which cell type in both normal and carbon tetrachloride (CCl4)-induced fibrotic rat liver bears surface type II IGF/mannose 6-phosphate (IGF-II/M6P) receptor, known to facilitate activation of TGF-beta. In addition, the role of the IGF-II/M6P receptor in activation of latent TGF-beta was investigated in a coculture system with sinusoidal endothelial cells. Northern hybridization analysis for IGF-II/M6P receptor messenger RNA (mRNA) was performed on total RNA of different isolated and purified liver cell types. In normal liver, cells expressed little IGF-II/M6P receptor mRNA. In fibrotic liver, we found significant expression only in fat-storing cells. The presence of IGF-II/M6P receptors was established by [125I]IGF-II binding assays on freshly isolated fat-storing cells from normal and CCl4-exposed rat livers. We found specific binding of [125I]IGF-II only on CCl4 exposed fat-storing cells. As determined by polyacrylamide gel electrophoresis after affinity labeling, the specific binding involved 220 kD type II IGF receptors. Scatchard analysis revealed the presence of 3,043 +/- 1,378 IGF-II/M6P high-affinity receptors/fat-storing cell, with a Kd of 387 = 165 pmol/L. With a mink lung epithelial cell (Mv1Lu) proliferation inhibition assay, inhibition of proliferation (a measure of active TGF-beta function) was determined using conditioned media of activated fat-storing cells, cocultures of fat-storing cells, and endothelial cells and pure endothelial cell cultures.(ABSTRACT TRUNCATED AT 250 WORDS)
de Bleser
P J
PJ
Laboratory for Cell Biology and Histology, Free University Brussels V.U.B., Belgium.
Jannes
P
P
van Buul-Offers
S C
SC
Hoogerbrugge
C M
CM
van Schravendijk
C F
CF
Niki
T
T
Rogiers
V
V
van den Brande
J L
JL
Wisse
E
E
Geerts
A
A
D000818:Animals; D015152:Blotting, Northern; D002251:Carbon Tetrachloride / Q000494:pharmacology*; D002478:Cells, Cultured; D003432:Cross-Linking Reagents; D003584:Cytological Techniques; D004727:Endothelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D050356:Lipid Metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017527:Receptor, IGF Type 2 / Q000378:metabolism* / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000502:physiology*
D003432:Cross-Linking Reagents; D017527:Receptor, IGF Type 2; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D002251:Carbon Tetrachloride