A set of synthetic phosphoinositolglycan (PIG) compounds has been demonstrated to exert insulin-mimetic activity on glucose and lipid metabolism in rat adipocytes differing considerably in potency [compound 41 > 37 > 45 ≫ 7 > 1; W. Frick, A. Bauer, J. Bauer, S. Wied and G. Müller, G. (1998) Biochemistry 37, 13421–13436]. In the present study we examine whether these differences are based on the capability of the PIG compounds to stimulate signalling components which are thought to mediate metabolic insulin action. Studies using a tyrosine kinase inhibitor and introduction into adipocytes of anti-phosphotyrosine or inhibitory anti-insulin receptor β-subunit antibodies demonstrated dependence on tyrosine phosphorylation but independence of insulin receptor kinase activation of the insulin-mimetic signalling and metabolic activity of the PIG compounds. The five compounds elicited in rat adipocytes a significant increase in tyrosine phosphorylation of both insulin receptor substrate 1 (IRS-1) and IRS-3 and, to a minor degree, IRS-2, in IRS-1/3-associated phosphatidylinositol 3-kinase (PI 3-K) protein as well as activity, and in protein kinase B (PKB) activity as well as phosphorylation. This was most pronounced for compound 41, approaching 65–95% of the maximal insulin response (MIR) at 20 µM, and declined in the order of compounds 37, 45, 7 and 1. The same ranking was true for the maximal inhibition of glycogen synthase kinase 3 activity (GSK-3) (41, 75% of MIR; compound 37, 65%; compound 7, 25%; compound 1, 10%) and GSK-3 autophosphorylation. The half-maximal concentrations effective for signalling (compound 41, 2–5 µM; compound 37, 10–20 µM) corresponded well to those stimulating glucose and lipid metabolism. Interestingly, compounds 37 and 41 stimulated mitogen-activated protein kinase (MAPK) and protein synthesis in rat adipocytes to only about 20–30% (at 50 µM) of MIR. We conclude that in rat adipocytes: (i) the potency of PIG compounds to regulate glucose/lipid metabolism depends on the activation of PI 3-K and PKB and inhibition of GSK-3; (ii) initiation of tyrosine phosphorylation of IRS-1/3 is sufficient and activation of the PI 3-K cascade is required for insulin-mimetic metabolic signalling; and (iii) PIG compounds are quite selective for the PI 3-K compared to the MAPK cascade, (iv) PIG compounds seem to use the same signalling components downstream of PI 3-K (including Rab4) for stimulation of glucose transport as does insulin. Thus the early signalling step(s) used by PIG, but not by insulin, may represent a target for the treatment of insulin-resistant states.
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November 1998
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Research Article|
November 15 1998
Insulin-mimetic signalling of synthetic phosphoinositolglycans in isolated rat adipocytes
Wendelin FRICK;
Wendelin FRICK
1Hoechst Marion Roussel Deutschland GmbH, Chemical and Metabolic Diseases Research Frankfurt, D-65926 Frankfurt am Main, Germany
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Andrea BAUER;
Andrea BAUER
1Hoechst Marion Roussel Deutschland GmbH, Chemical and Metabolic Diseases Research Frankfurt, D-65926 Frankfurt am Main, Germany
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Jochen BAUER;
Jochen BAUER
1Hoechst Marion Roussel Deutschland GmbH, Chemical and Metabolic Diseases Research Frankfurt, D-65926 Frankfurt am Main, Germany
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Susanne WIED;
Susanne WIED
1Hoechst Marion Roussel Deutschland GmbH, Chemical and Metabolic Diseases Research Frankfurt, D-65926 Frankfurt am Main, Germany
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Günter MÜLLER
Günter MÜLLER
1
1Hoechst Marion Roussel Deutschland GmbH, Chemical and Metabolic Diseases Research Frankfurt, D-65926 Frankfurt am Main, Germany
1To whom correspondence should be addressed (e-mail [email protected]).
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Publisher: Portland Press Ltd
Received:
June 18 1998
Revision Received:
August 10 1998
Accepted:
August 28 1998
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1998
1998
Biochem J (1998) 336 (1): 163–181.
Article history
Received:
June 18 1998
Revision Received:
August 10 1998
Accepted:
August 28 1998
Citation
Wendelin FRICK, Andrea BAUER, Jochen BAUER, Susanne WIED, Günter MÜLLER; Insulin-mimetic signalling of synthetic phosphoinositolglycans in isolated rat adipocytes. Biochem J 15 November 1998; 336 (1): 163–181. doi: https://doi.org/10.1042/bj3360163
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