Autoinhibition of the insulin-like growth factor I receptor by the juxtamembrane region.
The juxtamembrane (JM) regions of several receptor tyrosine kinases are involved in autoinhibitory interactions that maintain the low basal activity of the receptors; mutations can give rise to constitutive kinase activity and signaling. In this report, we show that the JM region of the human insulin-like growth factor I receptor (IGF1R) plays a role in kinase regulation. We mutated JM residues that were conserved in this subfamily of receptor tyrosine kinases, and expressed and purified the cytoplasmic domains using the Sf9/baculovirus system. We show that a kinase-proximal mutation (Y957F) and (to a lesser extent) a mutation in the central part of the JM region (N947A) increase the autophosphorylation activity of the kinase. Steady-state kinetic measurements show the mutations cause an increase in V(max) for phosphorylation of peptide substrates. When the holoreceptors were expressed in fibroblasts derived from IGF1R-deficient mice, the Y957F mutation led to a large increase in basal and in IGF1-stimulated receptor autophosphorylation. Together, these data demonstrate that the JM region of IGF1R plays an important role in limiting the basal activity of the receptor.
Craddock
Barbara P
BP
Department of Physiology and Biophysics, School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
Cotter
Christopher
C
Miller
W Todd
WT
D000595:Amino Acid Sequence; D000818:Animals; D020134:Catalytic Domain / Q000502:physiology; D002478:Cells, Cultured; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017434:Protein Structure, Tertiary / Q000187:drug effects; D017526:Receptor, IGF Type 1 / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D018411:Spodoptera; D014162:Transfection
D050505:Mutant Proteins; D017526:Receptor, IGF Type 1