K. Takahashi et al., INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR-ACTIVATED BY A TRANSMEMBRANE MUTATION, The Journal of biological chemistry, 270(32), 1995, pp. 19041-19045
We constructed mutant receptors by mutating transmembrane Val(922) of
the human insulin-like growth factor I receptor (IGF-IR). Assays of re
ceptor kinase and autophosphorylation revealed constitutively augmente
d tyrosine kinase activity of V922E IGF-IR in both transient and stabl
e expression. The constitutively active tyrosine kinase of this mutant
was verified by promoted tyrosine phosphorylation of insulin receptor
substrate-1 (IRS-1) in the absence of IGF-I. In CHO cells stably expr
essing V922E IGF-IR, both IRS-1 phosphorylation and the IRS-1-associat
ed phosphoinositide 3-kinase activity were stimulated in the absence o
f IGF-I to the level attained by 1 nM IGF-I stimulation of wild type I
GF-IR, whereas the Ras-mitogen-activated protein kinase pathway was no
t activated under the same condition. In these CHO cells, V922E IGF-IR
significantly stimulated glucose uptake but did not promote mitogenes
is in the absence of IGF-I. We thus conclude that the V922E mutation o
f IGF-IR switches on the intrinsic tyrosine kinase and differentially
activates the downstream pathways. This mutant is extremely useful in
clarifying the turning on mechanism of IGF-IR as well as the different
ial roles of individual downstream pathways of receptor tyrosine kinas
es.