Pertussis toxin-sensitive and insensitive intracellular signalling pathways in undifferentiated 3T3-L1 cells stimulated by insulin converge with phosphatidylinositol 3-kinase upstream of the Ras mitogen-activated protein kinase cascade

Takashi Uehara, Yukiko Tokumitsu, Yasuyuki Nomura

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

We have previously reported that pertussis toxin (PTX)-sensitive GTP binding protein (G-protein) and phosphatidylinositol 3-kinase (PI 3-K) are involved in adipocyte differentiation of 3T3-L1 cells induced by insulin/dexamethasone/methylisobutyl xanthine. The aim of this study was to examine the effect of PTX on the tyrosine kinase cascade stimulated by insulin acting through insulin-like growth factor-I (IGF-I) receptors in undifferentiated 3T3-L1 cells. A high level of mitogen-activated protein kinase (MAPK) activation was sustained for up to 4 h after insulin treatment, and mobility shifted and tyrosine phosphorylated MAPK was also detected. MAPK kinase activity measured by the incorporation of 32P into kinase-negative recombinant MAPK was enhanced by insulin treatment. We previously discovered that insulin activates Ras and that this is mediated by wortmannin-sensitive PI 3-K. Tyrosine-phosphorylation of IRS-1 and Shc also occurred in response to insulin. Subsequently, we investigated the effects of PTX on the activation of these proteins by insulin. Interestingly, treating 3T3-L1 cells with PTX attenuates the activation by insulin of both the Ras-MAPK cascade and PI 3-K. In contrast, neither tyrosine-phosphorylation of IRS-1 and Shc nor the interaction between IRS-1 and PI 3-K is sensitive to PTX. However, activation of the Ras-MAPK cascade and tyrosine-phosphorylation of Shc by epidermal growth factor are insensitive to PTX. These results indicate that there is another pathway which regulates PI 3-K and Ras-MAPK, independent of the pathway mediated by IGF-I receptor kinase. These findings suggest that in 3T3-L1 fibroblasts, PTX-sensitive G-proteins cross-talk with the Ras-MAPK pathway via PI 3-K by insulin acting via IGF-I receptors.

Original languageEnglish
Pages (from-to)801-808
Number of pages8
JournalEuropean Journal of Biochemistry
Volume259
Issue number3
DOIs
Publication statusPublished - Feb 1 1999
Externally publishedYes

Keywords

  • Adipocyte differentiation
  • G-protein
  • Insulin
  • MAP kinase
  • Phosphatidylinositol 3-kinase

ASJC Scopus subject areas

  • Biochemistry

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