Characterization of insulin-like growth factor binding proteins and regulation of IGFBP3 in human mesangial cells.
IGF-I regulates renal growth and development. Insulin-like growth factor binding proteins (IGFBPs) are synthesized by the kidney and may modulate the local autocrine and/or paracrine actions of IGF-I. We have previously demonstrated that mesangial cells (MC) release IGF-I and IGF-binding activity; however, the specific IGFBPs produced by these cells and the factors involved in their regulation are unknown. We examined MC for expression of IGFBP-1 to -6 mRNAs and proteins. RNase protection assays using total RNA demonstrated that MC express all of the IGFBPs. [125I]IGF-I Western ligand blot of conditioned medium demonstrated that MC release IGFBPs of 24, 29, 32 kDa, and a doublet at 46 kDa, consistent with IGFBP-4, -5, -2 and -3, respectively. IGFBP species of 28 and 34 kDa were also detected. Since IGF-I and TGF-beta are implicated in glomerular hypertrophy and matrix expansion, we tested their effect on IGFBPs released by MC. IGF-I (100 ng/ml), TGF-beta (2 ng/ml) and forskolin (10(-5) M) differentially regulated the abundance of IGFBPs released in the conditioned medium in a time-dependent manner. IGF-I and TGF-beta were potent inducers of the release of IGFBP3 protein; however, TGF-beta, but not IGF-I, increased IGFBP3 mRNA levels. Recombinant IGFBP3 was tested for its effect on IGF-I-induced mitogenesis. IGFBP3 inhibited IGF-I-stimulated DNA synthesis in a dose-dependent manner with a peak effect observed at 50 nM IGFBP3. Although TGF-beta is a potent inhibitor of IGF-I-stimulated DNA synthesis, this effect is not mediated via IGFBPs. Expression of IGFBP-1 to -6 by MC suggests that these proteins may modulate IGF-I bioavailability in the glomerulus. IGF-I itself, TGF-beta and cAMP agonists may indirectly modulate the effects of IGF-I via the release of IGFBPs by MC.
Grellier
P
P
Department of Medicine, University of Texas Health Science Center, USA.
Sabbah
M
M
Fouqueray
B
B
Woodruff
K
K
Yee
D
D
Abboud
H E
HE
Abboud
S L
SL
D005576:Colforsin / Q000494:pharmacology; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D015870:Gene Expression / Q000187:drug effects; D005920:Glomerular Mesangium / Q000737:chemistry / Q000166:cytology*; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D011485:Protein Binding / Q000502:physiology; D011994:Recombinant Proteins / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D017077:Culture Media, Conditioned; D018972:Insulin-Like Growth Factor Binding Protein 3; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D005576:Colforsin; D007334:Insulin-Like Growth Factor I; D004247:DNA