Low-protein diet regulates a proximal nephron insulin-like growth factor binding protein.
Previous studies have demonstrated that the glomerulus and proximal tubule basolateral membrane possess both insulin-like growth factor (IGF) receptors and IGF-binding proteins (IGFBPs). The purpose of this study is to examine the control of these proteins in defined nephron segments during dietary protein restriction. Animals were fed isocaloric 6% (low-protein [LP]) or 40% (high-protein) protein diets for 7 to 10 days. 125I[IGF] affinity labeling of membranes prepared from isolated glomeruli or proximal tubule basolateral membranes demonstrated two proteins on autoradiograms of 6% polyacrylamide gels with molecular weights of 140,000 d and more than 200,000 d that were blocked by 300 nmol/L unlabeled IGF-I. The lower molecular weight species has been identified previously as the alpha subunit of the IGF-I receptor and was upregulated by a 6% LP diet. The upregulation of the IGF-I receptor was evident on 12% polyacrylamide gels of both glomeruli and basolateral membranes. Another protein with a molecular weight of approximately 38,000 d also was upregulated by LP diet. The protein was evident on 125I-IGF-I ligand blots and was immunostained with IGFBP-5 antibodies. Cytosol prepared from cortical tissue also demonstrated a 31,000-d protein that was immunostained with IGFBP-5 antibodies in animals fed a LP diet, but not in animals fed a high-protein or normal diet. RNA prepared from cortical tissue and hybridized with a IGFBP-5 cDNA probe revealed a 6.0-Kb transcript that was increase by LP diet.(ABSTRACT TRUNCATED AT 250 WORDS)
Hise
M K
MK
Department of Internal Medicine, University of Maryland Medical School, Baltimore.
Mantzouris
N M
NM
Lahn
J S
JS
Sheikh
M S
MS
Shao
Z M
ZM
Fontana
J A
JA
D000345:Affinity Labels; D000818:Animals; D001345:Autoradiography; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage*; D004591:Electrophoresis, Polyacrylamide Gel; D006131:Growth Inhibitors / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins; D007678:Kidney Glomerulus / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008297:Male; D009399:Nephrons / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017526:Receptor, IGF Type 1 / Q000378:metabolism
D000345:Affinity Labels; D002352:Carrier Proteins; D004044:Dietary Proteins; D006131:Growth Inhibitors; D018969:Insulin-Like Growth Factor Binding Proteins; D017526:Receptor, IGF Type 1