Evidence that two naturally occurring human insulin receptor alpha-subunit variants are immunologically distinct.
The IgG from a patient (Italy 2 [I2]) with hypoglycemia, due to autoantibodies to the insulin receptor, was purified on protein A Sepharose into two fractions that were tested in various human tissues and cells. The IgG fraction that bound protein A (absorbed IgG [IgGa]) nearly completely inhibited the binding of 125I-labeled insulin to various cells or tissues (placenta, IM-9, adipocytes, HEp-2-larynx cells, Epstein-Barr virus lymphocytes) but not greater than 50% of 125I-labeled insulin binding to human liver membranes. Conversely, both the IgG fraction from this patient, which did not bind protein A (flow-through IgG [IgGb]), and the IgGa fraction from a second similar patient (Italy 1 [I-1]) almost completely inhibited the binding of 125I-labeled insulin to liver membranes. The IgGa fraction from patient I-2 did not change receptor affinity because 50% inhibition of 125I-labeled insulin binding was not affected by either the presence or absence of these IgG fractions. Furthermore, liver binding data were not due to cross-reaction of 125I-labeled insulin to the insulinlike growth factor I receptor, and treatment of liver membranes with neuraminidase did not alter the inhibitory effect of the IgGa fraction from patient I-2 on 125I-labeled insulin binding to liver. Binding inhibition experiments performed with cells transfected with and overexpressing the -12 (human insulin receptor [HIR]-A) or the +12 (HIR-B) variant of HIR revealed that the IgGa fraction from patient I-2 inhibited 125I-labeled insulin binding to the HIR-A receptor but not to the HIR-B receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Sesti
G
G
Department of Internal Medicine, II University of Rome, Italy.
Marini
M A
MA
Montemurro
A
A
Condorelli
L
L
Borboni
P
P
Haring
H U
HU
Ullrich
A
A
Goldfine
I D
ID
De Pirro
R
R
Lauro
R
R
D000273:Adipose Tissue / Q000378:metabolism; D000911:Antibodies, Monoclonal; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D014644:Genetic Variation; D006801:Humans; D007003:Hypoglycemia / Q000276:immunology; D007074:Immunoglobulin G / Q000145:classification; D007328:Insulin / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D046911:Macromolecular Substances; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D011972:Receptor, Insulin / Q000235:genetics* / Q000276:immunology / Q000378:metabolism
D000911:Antibodies, Monoclonal; D007074:Immunoglobulin G; D007328:Insulin; D046911:Macromolecular Substances; D007334:Insulin-Like Growth Factor I; D011972:Receptor, Insulin