Protein kinase C-zeta phosphorylates insulin receptor substrate-1, -3, and -4 but not -2: isoform specific determinants of specificity in insulin signaling.
Endocrinology
; 149(5): 2451-8, 2008 May.
Article
en En
| MEDLINE
| ID: mdl-18202124
Protein kinase C-zeta, a downstream effector of phosphatidylinositol 3-kinase (PI3K), phosphorylates insulin receptor substrate (IRS)-1 on serine residues impairing activation of PI3K in response to insulin. Because IRS-1 is upstream from PI3K, this represents a negative feedback mechanism that may contribute to signal specificity in insulin action. To determine whether similar feedback pathways exist for other IRS isoforms, we evaluated IRS-2, -3, and -4 as substrates for PKC-zeta. In an in vitro kinase assay, purified recombinant PKC-zeta phosphorylated IRS-1, -3 and -4 but not IRS-2. Similar results were obtained with an immune-complex kinase assay demonstrating that wild-type, but not kinase-deficient mutant PKC-zeta, phosphorylated IRS-1, -3, and -4 but not IRS-2. We evaluated functional consequences of serine phosphorylation of IRS isoforms by PKC-zeta in NIH-3T3(IR) cells cotransfected with epitope-tagged IRS proteins and either PKC-zeta or empty vector control. Insulin-stimulated IRS tyrosine phosphorylation was impaired by overepxression of PKC-zeta for IRS-1, -3, and -4 but not IRS-2. Significant insulin-stimulated increases in PI3K activity was coimmunoprecipitated with all IRS isoforms. In cells overexpressing PKC-zeta there was marked inhibition of insulin-stimulated PI3K activity associated with IRS-1, -3 and -4 but not IRS-2. That is, PI3K activity associated with IRS-2 in response to insulin was similar in control cells and cells overexpressing PKC-zeta. We conclude that IRS-3 and -4 are novel substrates for PKC-zeta that may participate in a negative feedback pathway for insulin signaling similar to IRS-1. The inability of PKC-zeta to phosphorylate IRS-2 may help determine specific functional roles for IRS-2.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Fosfoproteínas
/
Proteína Quinasa C
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Péptidos y Proteínas de Señalización Intracelular
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Proteínas Adaptadoras Transductoras de Señales
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Insulina
Límite:
Animals
Idioma:
En
Revista:
Endocrinology
Año:
2008
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Estados Unidos