Two alternatively spliced forms of the human insulin-like growth factor I receptor have distinct biological activities and internalization kinetics.
Two alternatively spliced human insulin-like growth factor I (IGF I) receptor mRNA transcripts have been described that differ by three nucleotides (CAG) starting at position 2829. This results in an amino acid coding sequence change from Thr-Gly to Arg in the extracellular portion of the receptor beta subunit. To investigate the functional significance of this sequence difference, we obtained full-length cDNAs for the CAG+ and CAG- receptor forms, transfected CHO cells, and isolated multiple clones expressing approximately equal numbers of receptors (0.57-0.73 x 10(6) receptors/cell). The two receptors bound IGF I with similar affinity (Kd approximately 1.7 nM), but the CAG- form exhibited an approximately 2-fold increase in IGF I stimulation of receptor autophosphorylation, insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, thymidine incorporation, and IRS-1-associated phosphatidylinositol 3-kinase activity. In contrast to its higher signaling activity, the rate of receptor-mediated internalization of IGF I by the CAG-receptor was decreased by 50% in comparison with the CAG+ receptor. We conclude that proteins corresponding to the two alternatively spliced human IGF I receptor transcripts are biologically active, but have distinct signaling properties. These experiments further indicate a previously unrecognized role for the extramembranous portion of the beta subunit in receptor signaling and internalization.
Condorelli
G
G
Joslin Diabetes Center, Boston, Massachusetts 02215.
Bueno
R
R
Smith
R J
RJ
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D016466:CHO Cells; D002455:Cell Division / Q000187:drug effects; D003001:Cloning, Molecular; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D015870:Gene Expression; D006801:Humans; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis* / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D018076:DNA, Complementary; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D046911:Macromolecular Substances; D009838:Oligodeoxyribonucleotides; D010750:Phosphoproteins; D012333:RNA, Messenger; D019000:Phosphotyrosine; D014443:Tyrosine; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1