Expression of a cDNA encoding the human insulin receptor-related receptor

The insulin receptor-related receptor (IRR) gene encodes a protein that is homologous to the receptors for insulin and insulin-like growth factor-I (IGF-I). We have cloned a full-length cDNA encoding the human IRR by screening a human kidney cDNA library. The nucleotide sequence of our cDNA is identical to the sequence predicted from the human IRR gene except for the presence of an insertion of 24 base pairs between exons 13 and 14. This insertion was caused by use of an alternative splice acceptor site in the 3' portion of intron 13. Interestingly, this alternative splicing occurs at a position at which alternative splicing of the homologous IGF-I receptor mRNA also occurs. We amplified human kidney IRR by the polymerase chain reaction to quantitate the proportion of transcripts which included the 24-nucleotide sequence between exons 13 and 14. Fewer than 10% of the transcripts contained this additional sequence. We expressed the IRR cDNA lacking the 24-base pair insert in NIH-3T3 cells to study the biosynthesis, tyrosine phosphorylation, and ligand binding properties of the IRR. Like receptors for insulin and IGF-I, the IRR was synthesized as a single polypeptide precursor that underwent proteolytic cleavage and glycosylation to yield an alpha subunit and a beta subunit. However, both subunits of the IRR had smaller apparent molecular mass than the homologous subunits of the insulin receptor (108,000 versus 135,000 for the alpha subunits and 66,000 versus 95,000 for the beta subunits). IRR tyrosine phosphorylation could be stimulated by vanadate plus H2O2, which have been demonstrated previously to increase the phosphotyrosine content of the insulin receptor tyrosine kinase. However, proinsulin, insulin, IGF-I, and IGF-II did not stimulate tyrosine phosphorylation of the IRR. We conclude that these peptides are not the ligands for the IRR.