Phosphorylation of LKB1 at Serine 428 by Protein Kinase C-ζ Is Required for Metformin-Enhanced Activation of the AMP-Activated Protein Kinase in Endothelial Cells
Open Access
- 19 February 2008
- journal article
- research article
- Published by Ovid Technologies (Wolters Kluwer Health) in Circulation
- Vol. 117 (7), 952-962
- https://doi.org/10.1161/circulationaha.107.744490
Abstract
Background— Metformin, one of most commonly used antidiabetes drugs, is reported to exert its therapeutic effects by activating AMP-activated protein kinase (AMPK); however, the mechanism by which metformin activates AMPK is poorly defined. The objective of the present study was to determine how metformin activates AMPK in endothelial cells. Methods and Results— Exposure of human umbilical vein endothelial cells or bovine aortic endothelial cells to metformin significantly increased AMPK activity and the phosphorylation of both AMPK at Thr172 and LKB1 at Ser428, an AMPK kinase, which was paralleled by increased activation of protein kinase C (PKC)-ζ, as evidenced by increased activity, phosphorylation (Thr410/403), and nuclear translocation of PKC-ζ. Consistently, either pharmacological or genetic inhibition of PKC-ζ ablated metformin-enhanced phosphorylation of both AMPK-Thr172 and LKB1-Ser428, suggesting that PKC-ζ might act as an upstream kinase for LKB1. Furthermore, adenoviral overexpression of LKB1 kinase-dead mutants abolished but LKB1 wild-type overexpression enhanced the effects of metformin on AMPK in bovine aortic endothelial cells. In addition, metformin increased the phosphorylation and nuclear export of LKB1 into the cytosols as well as the association of AMPK with LKB1 in bovine aortic endothelial cells. Similarly, overexpression of LKB1 wild-type but not LKB1 S428A mutants (serine replaced by alanine) restored the effects of metformin on AMPK in LKB1-deficient HeLa-S3 cells, suggesting that Ser428 phosphorylation of LKB1 is required for metformin-enhanced AMPK activation. Moreover, LKB1 S428A, like kinase-dead LKB1 D194A, abolished metformin-enhanced LKB1 translocation as well as the association of LKB1 with AMPK in HeLa-S3 cells. Finally, inhibition of PKC-ζ abolished metformin-enhanced coimmunoprecipitation of LKB1 with both AMPKα1 and AMPKα2. Conclusions— We conclude that PKC-ζ phosphorylates LKB1 at Ser428, resulting in LKB1 nuclear export and hence AMPK activation.This publication has 56 references indexed in Scilit:
- Effect of Acute Exercise on AMPK Signaling in Skeletal Muscle of Subjects With Type 2 DiabetesDiabetes, 2007
- Deficiency of LKB1 in skeletal muscle prevents AMPK activation and glucose uptake during contractionThe EMBO Journal, 2005
- MO25 / interact with STRAD / enhancing their ability to bind, activate and localize LKB1 in the cytoplasmThe EMBO Journal, 2003
- Activation of the tumour suppressor kinase LKB1 by the STE20-like pseudokinase STRADThe EMBO Journal, 2003
- Leptin stimulates fatty-acid oxidation by activating AMP-activated protein kinaseNature, 2002
- Role of AMP-activated protein kinase in mechanism of metformin actionJCI Insight, 2001
- Loss of Cytoplasmic Retention Ability of Mutant LKB1 Found in Peutz-Jeghers Syndrome PatientsBiochemical and Biophysical Research Communications, 1999
- Metformin Improves Hemodynamic and Rheological Responses to L-Arginine in NIDDM PatientsDiabetes Care, 1996
- Acute Sympathoinhibitory Actions of Metformin in Spontaneously Hypertensive RatsHypertension, 1996
- Mammalian AMP-activated Protein Kinase SubfamilyJournal of Biological Chemistry, 1996