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Insulin activates nuclear phospholipase C independently of phosphatidylinositol 3-kinase/Akt in HL-60 cells

Dora Višnjić ; School of Medicine, University of Zagreb, Zagreb, Croatia
Katarina Matković ; School of Medicine, University of Zagreb, Zagreb, Croatia
Vesna Lukinović-Škudar ; School of Medicine, University of Zagreb, Zagreb, Croatia
Hrvoje Banfić ; School of Medicine, University of Zagreb, Zagreb, Croatia

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Background and Purpose: Insulin stimulates proliferation of HL-60 cells in the absence of serum. In various cells, proliferative, antiapoptotic and metabolic effects of insulin are mediated by phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Previous studies had demonstrated the activation of nuclear phosphoinositide-specific phospholipase C (PI-PLC) in insulin-like growth factor (IGF) and serum-stimulated HL-60 cells. The aim of this study was to investigate the signaling mechanisms responsible for the proliferative effects of insulin in HL-60 cells.

Materials and Methods: Serum-starved HL-60 cells were stimulated with insulin. Insulin-mediated proliferation was measured by incorporation of bromodeoxyuridine and flow cytometry. Akt activity was determined by Western blot analysis for the expression of phosphorylated and total Akt protein. PLC activity in lysates and nuclear extracts was determined by an assay using tritium-labeled phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2]. The effects of PI3K inhibitor LY 294002 were investigated.

Results: Insulin-stimulated proliferation of HL-60 cells was inhibited by PI3K inhibitor LY 294002. Insulin increased the amount of phosphorylated Akt in total cell lysates, and time-dependently increased PLC-activity in the nuclei of HL-60 cells. The addition of PI3K inhibitor LY 294002 inhibited insulin-mediated Akt-activation, but had no effects on insulin- mediated PLC activation.

Conclusion: Insulin stimulates Akt activity in lysates, and PLC activity in nuclei ofHL-60 cells. Although Akt activation precedes the activation of the nuclear PLC, insulin-mediated activation of the nuclear PLC occurs independently of PI3K/Akt signaling pathway.

Ključne riječi
insulin, nuclei; phospholipase C; protein kinase B/Akt; phosphatidylinositol 3-kinase; HL-60

Hrčak ID: 29075


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