Human insulin receptor juxtamembrane domain independent insulin signaling

AbstractThe exon 16‐encoded juxtamembrane (JM) domain of human insulin receptor (hIR) harbors the NPEY motif which couples the insulin‐activated hIR kinase to downstream signal transduction molecules. We sought to determine if signal transduction requires the entire exon 16‐encoded 22‐amino acid JM domain. Transfected CHO cells were generated stably expressing either the wild‐type hIR (hIR‐WT) or two mutant hIRs (hIRΔEx16 in which the JM domain was deleted, and hIRrosJM in which the deleted segment was replaced by the corresponding domain of v‐ros protein). The mutant hIRΔEx16 and hIRrosJM exhibited similar insulin‐binding as the hIRWT. Insulin internalization and insulin dose‐response experiments toward activation of downstream signal transduction molecules demonstrated that: i) the presence of intact hIR‐JM domain which harbors the NPEY motif is essential for Shc phosphorylation but not for IRS‐1 phosphorylation; ii) insulin signal transduction can occur independent of the JM domain of hIR and without participation of the NPEY motif; iii) engagement of this putative alternative downstream signal transduction is Shc independent and is dependent on insulin concentration; and iv) insulin internalization does not necessarily require the hIR specific aa sequence of the JM domain which can be partially substituted by the JM domain of the v‐ros tyrosine kinase.