Rat fibroblast cells overexpressing kinase-inactive human insulin receptors are insulin responsive: influence of growth conditions.
The effects of insulin to stimulate metabolic and mitogenic responses were examined in Rat 1 fibroblast cells that overexpressed either normal (HIRc) or kinase-deficient human insulin receptors. When studied at the optimal growth stage for each cell line, insulin-stimulated responses measured in cells containing kinase-defective receptors with a Lys1018-Ala1018 substitution in the ATP-binding site of the kinase domain (A/K1018). Maximal insulin responsiveness for all these effects, measured as fold-increase over basal, was comparable in parental and HIRc cells (1.8- to 2.4-fold increases). Relative insulin responsiveness for all effects was greatest in A/K 1018 cells. One clone (AK-I) expressing a similar number of kinase-inactive receptors as in the HIRc cells displayed maximal responsiveness of 3.6- to 5.5-fold increases. A second A/K cell line containing 1/10 the number of kinase-inactive receptors displayed responsiveness intermediate between AK-I and parental or HIRc cells (1.5- to 4.8-fold increases). Both clones of kinase-deficient A/K1018 cells displayed impaired insulin sensitivity compared with HIRc cells. These findings suggest that expression of insulin receptor kinase activity is a determinant of insulin sensitivity but not necessarily of the final biological responsiveness of cells to insulin.
Wong
E H
EH
Department of Biochemistry, National University of Singapore, Kent Ridge.
Tan
C H
CH
Khoo
H E
HE
Ng
F H
FH
Lim
K L
KL
Ciaraldi
T P
TP
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis; D003847:Deoxyglucose / Q000378:metabolism; D004622:Embryo, Mammalian; D004789:Enzyme Activation; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D019000:Phosphotyrosine; D051381:Rats; D011972:Receptor, Insulin / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D007328:Insulin; D019000:Phosphotyrosine; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D004247:DNA; D003847:Deoxyglucose; D006006:Glycogen Synthase; D011972:Receptor, Insulin; D005947:Glucose