Previous studies have demonstrated that receptor tyrosine kinases (RTKs) use common intracellular signal transduction pathways. This is remarkable due to the divergent cellular responses elicited from different RTKs. The insulin receptor (IR) is involved in blood glucose homeostasis whereas the epidermal growth factor receptor (EGFR) has been linked to liver regeneration. We therefore used rat liver, an organ enriched in both EGF and insulin receptors, to study the specificity of signal transduction in vivo. / Upon EGF administration, the EGFR at the plasma membrane (PM) was tyrosine phosphorylated on the major in vivo activation site, Y 1173, and recruited the adaptor proteins SHC and GRB2. Following ligand-mediated endocytosis, the activated EGFR was associated on endosomal membranes with the signaling complex SHC/GRB2 and the guanine nucleotide exchange factor, SOS. EGF administration also led to tyrosine phosphorylation of the cytosolic proteins focal adhesion kinase (FAK) and SHC. These observations were associated with increased MAP kinase activity and the transcription of c-myc, c-fos and c-jun. / In response to insulin, IR kinase activity and autophosphorylation was observed at the PM but not after IR internalization into endosomes. This is postulated to be due to rapid degradation of insulin in the endosomal lumen allowing for the dephosphorylation of the IR by protein tyrosine phosphatase(s). To evaluate the role of endosomal degradation in IR signaling, an insulin analog, termed H2, was characterized for its clearance and processing in liver. Although liver uptake of H2 was similar to that of insulin, its clearance was slower. This correlated with reduced ligand dissociation from internalized IR as well as slower degradation kinetics. / In response to H2, IR traffic was delayed in the endosomal apparatus. This occurred with increased IR autophosphorylation and tyrosine kinase activity in this compartment. H2 but not insulin induced JNK activity and c-jun transcription. Insulin stimulated MAP kinase and glycogen synthase (GS) activities in rat liver. H2, however, was less efficient in inducing MAP kinase activity than insulin and GS activity was not observed. Impaired GS activity in response to H2 correlated with increased PKC activity. The above observations of insulin and H2 were not due to changes in SHC nor IRS-1 signaling. / These studies indicate that the modification of RTKs at the level of the endosome alters receptor traffic and specificity of signal transduction pathways and support the hypothesis that RTK endocytosis plays a role in the regulation of RTK signaling.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.35690 |
| Date | January 1998 |
| Creators | Di Guglielmo, Gianni M. |
| Contributors | Bergeron, John J. M. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Biochemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001651516, proquestno: NQ50146, Theses scanned by UMI/ProQuest. |
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