2021-11-092021-11-092012-03-30Alaide Morcavallo, Marco Genua, Angela Palummo, Emilia Kletvikova, Jiri Jiracek, Andrzej M. Brzozowski, Renato V. Iozzo, Antonino Belfiore, Andrea Morrione. Insulin and Insulin-like Growth Factor II Differentially Regulate Endocytic Sorting and Stability of Insulin Receptor Isoform A*, Journal of Biological Chemistry, 287,(14), 2012, 11422-11436, ISSN 0021-9258, https://doi.org/10.1074/jbc.M111.252478.1083-351Xhttp://dx.doi.org/10.34944/dspace/7076http://hdl.handle.net/20.500.12613/7096The insulin receptor isoform A (IR-A) binds both insulin and insulin-like growth factor (IGF)-II, although the affinity for IGF-II is 3–10-fold lower than insulin depending on a cell and tissue context. Notably, in mouse embryonic fibroblasts lacking the IGF-IR and expressing solely the IR-A (R−/IR-A), IGF-II is a more potent mitogen than insulin. As receptor endocytosis and degradation provide spatial and temporal regulation of signaling events, we hypothesized that insulin and IGF-II could affect IR-A biological responses by differentially regulating IR-A trafficking. Using R−/IR-A cells, we discovered that insulin evoked significant IR-A internalization, a process modestly affected by IGF-II. However, the differential internalization was not due to IR-A ubiquitination. Notably, prolonged stimulation of R−/IR-A cells with insulin, but not with IGF-II, targeted the receptor to a degradative pathway. Similarly, the docking protein insulin receptor substrate 1 (IRS-1) was down-regulated after prolonged insulin but not IGF-II exposure. Similar results were also obtained in experiments using [NMeTyrB26]-insulin, an insulin analog with IR-A binding affinity similar to IGF-II. Finally, we discovered that IR-A was internalized through clathrin-dependent and -independent pathways, which differentially regulated the activation of downstream effectors. Collectively, our results suggest that a lower affinity of IGF-II for the IR-A promotes lower IR-A phosphorylation and activation of early downstream effectors vis à vis insulin but may protect IR-A and IRS-1 from down-regulation thereby evoking sustained and robust mitogenic stimuli.15 pagesengAttribution CC BYhttps://creativecommons.org/licenses/by/4.0/EndocytosisGrowth factorsInsulinInsulin-like growth factor (IGF)Signal transductionIGF-IIInsulin receptor isoform ASignalingText