New insights into insulin signalling : the roles of 80K-H, PKC[zeta] and munc18c in GLUT4 vesicle trafficking

Abstract

Insulin is the principal anabolic hormone and is responsible for a vast array of cellular and physiological processes. One of the most fundamental of insulin's actions is the maintenance of glucose homeostasis, primarily ahieved by the selective targeting of the GLUT4 (glucose tansporter 4) vesicle from intracellular stores to the plasma membrane. Insulin triggered signalling cascades activate kinases, notably PKC£, which influence proteins required for GLUT4 vesicle targeting to the plasma membrane. These vesicle targeting proteins include syntaxin4, VAMP2 and muncl8c. Muncl8c is thought to preclude interaction between VAMP2, present in the GLUT4 vesicle, and syntaxin4 which is found in the plasma membrane, thus preventing GLUT4 vesicle exocytosis in the basal state. Previously, insulin action was thought to release muncl8c from syntaxin4, thus enabling GLUT4 vesicle docking at the plasma membrane. 80K-H forms a complex with PKC^ and muncl8c in response to insulin, thus acting as a bridge to enable the cell signalling to affect the GLUT4 vesicle trafficking machinery. In this thesis, a number of in vitro and in vivo techniques, including fluorescence correlation spectroscopy (FCS), were used to determine the nature and role of the protein:protein interactions in GLUT4 vesicle trafficking. The results show that insulin activated PKC£ acts on 80K-H to release it from a membrane tether. This un-tethering of 80K-H causes a repositioning of muncl8c on syntaxin4. It is this repositioning of muncl8c, rather than the release of this protein from syntaxin4, that enables VAMP2 to bind syntaxin4 thus facilitating the docking of the GLUT4 vesicle at the plasma membrane. This is the first time that it has been shown that muncl8c isn't merely released from syntaxin4 in response to insulin. These results further elucidate the molecular mechanisms of insulin action, which will hopefully lead to treatments for diseases such as Type II diabetes in the future.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata