Involvement of both phosphatidylinositol 3-kinase and p44/p42 mitogen-activated protein kinase pathways in the short-term regulation of pyruvate kinase L by insulin

Pyruvate kinase L (PK-L) is a key regulatory enzyme of the hepatic glycolytic/gluconeogenic pathway that can be dephosphorylated and activated in response to insulin. However, the signaling cascades involved in this insulin effect have not been established. In this work we have investigated the pote...

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Published in:	Endocrinology (Philadelphia) Vol. 142; no. 3; pp. 1057 - 1064
Main Authors:	Carrillo, J J, Ibares, B, Esteban-Gamboa, A, Felíu, J E
Format:	Journal Article
Language:	English
Published:	United States 01-03-2001
Subjects:	Androstadienes - pharmacology Animals Cells, Cultured Chromones - pharmacology Enzyme Activation - drug effects Enzyme Inhibitors - pharmacology Flavonoids - pharmacology Hepatocytes - enzymology Hepatocytes - physiology Insulin - pharmacology Insulin - physiology Male Mitogen-Activated Protein Kinase 1 - antagonists & inhibitors Mitogen-Activated Protein Kinase 1 - physiology Mitogen-Activated Protein Kinase 3 Mitogen-Activated Protein Kinases - antagonists & inhibitors Mitogen-Activated Protein Kinases - physiology Morpholines - pharmacology Phosphatidylinositol 3-Kinases - antagonists & inhibitors Phosphatidylinositol 3-Kinases - physiology Phosphorylation - drug effects Pyruvate Kinase - antagonists & inhibitors Pyruvate Kinase - metabolism Rats Rats, Wistar Ribosomal Protein S6 Kinases - antagonists & inhibitors Ribosomal Protein S6 Kinases - metabolism Sirolimus - pharmacology
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Summary:	Pyruvate kinase L (PK-L) is a key regulatory enzyme of the hepatic glycolytic/gluconeogenic pathway that can be dephosphorylated and activated in response to insulin. However, the signaling cascades involved in this insulin effect have not been established. In this work we have investigated the potential involvement of phosphatidylinositol 3-kinase (PI 3-K) and p44/p42 mitogen-activated protein kinase (MAPK) pathways in the short-term modulation of PK-L by insulin in primary cultures of rat hepatocytes. Wortmannin, at a concentration of 100 nM, caused a marked inhibition of the PI 3-K/protein kinase B pathway, which became complete at 500 nM wortmannin. Likewise, wortmannin at 100 and 500 nM, elicited partial and total inhibitions of insulin-mediated activation of PK-L, respectively. However, this PI 3-K inhibitor also reduced insulin-mediated phosphorylation of p44/p42 MAPK in cultured rat hepatocytes, indicating that both the PI 3-K and MAPK pathways could be involved in PK-L activation by insulin. Three facts appear to reinforce this hypothesis: 1) the selective and complete inhibition of the PI 3-K/protein kinase B pathway by LY294002 (50 microM) was accompanied by a partial blockade of insulin-induced PK-L activation; 2) when signaling through the MAPK cascade was selectively suppressed by the presence of PD98059 (50 microM), a 50% reduction of insulin-induced activation of PK-L was observed; and 3) the effect of PD98059 (50 microM) on PK-L activation was reinforced by the additional presence of 100 nM wortmannin. We also observed that the blockade of p70 S6-kinase by rapamycin did not affect the activation of PK-L by insulin. From these findings it can be concluded that both PI 3-K and MAPK pathways, but not p70 S6-kinase, are involved in the short-term activation of PK-L by insulin in rat hepatocytes.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0013-7227
DOI:	10.1210/en.142.3.1057