title: Evidence for functional redundancy of class IA PI3K isoforms in insulin signalling.
abstract: Recent genetic knock-in and pharmacological approaches have suggested that, of class IA PI3Ks (phosphatidylinositol 3-kinases), it is the p110alpha isoform (PIK3CA) that plays the predominant role in insulin signalling. We have used isoform-selective inhibitors of class IA PI3K to dissect further the roles of individual p110 isoforms in insulin signalling. These include a p110alpha-specific inhibitor (PIK-75), a p110alpha-selective inhibitor (PI-103), a p110beta-specific inhibitor (TGX-221) and a p110delta-specific inhibitor (IC87114). Although we find that p110alpha is necessary for insulin-stimulated phosphorylation of PKB (protein kinase B) in several cell lines, we find that this is not the case in HepG2 hepatoma cells. Inhibition of p110beta or p110delta alone was also not sufficient to block insulin signalling to PKB in these cells, but, when added in combination with p110alpha inhibitors, they are able to significantly attenuate insulin signalling. Surprisingly, in J774.2 macrophage cells, insulin signalling to PKB was inhibited to a similar extent by inhibitors of p110alpha, p110beta or p110delta. These results provide evidence that p110beta and p110delta can play a role in insulin signalling and also provide the first evidence that there can be functional redundancy between p110 isoforms. Further, our results indicate that the degree of functional redundancy is linked to the relative levels of expression of each isoform in the target cells.
authors.affiliation: Maurice Wilkins Centre for Molecular Biodiscovery, Department of Molecular Medicine and Pathology, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: Claire
authors.initials: C
authors.lastname: Chaussade
authors.forename: Gordon W
authors.initials: GW
authors.lastname: Rewcastle
authors.forename: Jackie D
authors.initials: JD
authors.lastname: Kendall
authors.forename: William A
authors.initials: WA
authors.lastname: Denny
authors.forename: Kitty
authors.initials: K
authors.lastname: Cho
authors.forename: Line M
authors.initials: LM
authors.lastname: Grønning
authors.forename: Mei Ling
authors.initials: ML
authors.lastname: Chong
authors.forename: Sasha H
authors.initials: SH
authors.lastname: Anagnostou
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Jackson
authors.forename: Nathalie
authors.initials: N
authors.lastname: Daniele
authors.forename: Peter R
authors.initials: PR
authors.lastname: Shepherd
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D015394:Molecular Structure; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D007328:Insulin; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins