Functional effects of APS and SH2-B on insulin receptor signalling.
APS [for 'adapter protein with a pleckstrin homology (PH) and Src homology 2 (SH2) domain'] belongs to a family of adapter proteins involved in signalling by the receptors for insulin, insulin-like growth factor 1, platelet-derived growth factor and nerve growth factor. Other members include alternatively spliced SH2-B isoforms (SH2Balpha, SH2-Bbeta and SH2-Bgamma) and Lnk. These have a C-terminal SH2 domain, a central PH domain and an N-terminal proline-rich region. SH2Balpha, APS and Lnk have a conserved C-terminal tyrosine phosphorylation site, whereas the alternatively spliced SH2-Bbeta and SH2-Bgamma have distinct C-termini. There is considerable sequence similarity between APS, SH2-B and Lnk, particularly in the SH2 domain. Both APS and SH2-Balpha interact with the insulin-receptor activation loop phosphorylation sites and undergo insulin-stimulated tyrosine phosphorylation, although the phosphorylation of SH2-B is considerably weaker. APS couples c-Cbl to the insulin receptor, resulting in ubiquitination of the insulin receptor. We established cell lines [Chinese hamster ovary (CHO). T-APS and CHO. T-SH2-B cells] overexpressing APS and SH2-Balpha to study their roles in insulin receptor signalling. Either adapter protein enhances insulin receptor and ERK (extracellular-signal-regulated kinase) phosphorylation. In CHO. T-APS cells, Akt phosphorylation is observed earlier than in CHO.T-SH2-B cells. Both enhance insulin-stimulated Akt activation but APS seems to cause greater activation. Thus APS and SH2-B have similar effects on insulin receptor signalling, although the effects of SH2-B are independent of its phosphorylation.
Ahmed
Z
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Molecular Endocrinology Group, Institute of Cell Signalling and School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK.
Pillay
T S
TS
D000818:Animals; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D053614:Janus Kinase 2; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000502:physiology*; D011518:Proto-Oncogene Proteins; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D011972:Receptor, Insulin / Q000502:physiology*; D011961:Receptors, Fc / Q000502:physiology; D017479:Receptors, Platelet-Derived Growth Factor / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D018909:src Homology Domains
D011506:Proteins; D011518:Proto-Oncogene Proteins; D011961:Receptors, Fc; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D017479:Receptors, Platelet-Derived Growth Factor; D053614:Janus Kinase 2