Shear stress-induced activation of the AMP-activated protein kinase regulates FoxO1a and angiopoietin-2 in endothelial cells.
OBJECTIVE
Phosphorylation of forkhead box O (FoxO) transcription factors induces their nuclear exclusion and proteosomal degradation. Here, we investigated the effect of fluid shear stress on FoxO1a in primary cultures of human endothelial cells and the kinases that regulate its phosphorylation.


RESULTS
Shear stress (12 dynes/cm2) elicited the phosphorylation, nuclear exclusion, and degradation of FoxO1a. Inhibition of Akt signalling using either a dominant negative (DN) mutant of Akt or downregulation of Gab1 largely failed to affect the shear stress-induced changes in FoxO1a, while a DN-AMP-activated protein kinase (AMPK) abrogated its shear stress-induced phosphorylation and degradation. Similar effects were observed using the AMPK inhibitor compound C. Moreover, in an in vitro assay, the AMPK directly phosphorylated FoxO1a. As FoxO1a regulates the expression of angiopoietin-2 (Ang-2), we determined the role of shear stress and the AMPK in this phenomenon. Not only did the DN-AMPK increase the expression of Ang-2 in cells maintained under static conditions, it also abrogated the shear stress-induced decrease in FoxO1a and Ang-2 protein levels. Functionally, Ang-2 sensitizes endothelial cells to the effects of tumour necrosis factor (TNF)-alpha, and DN-AMPK increased basal endothelial cell E-selectin expression and permeability as well as the increase induced by TNF-alpha.


CONCLUSIONS
These data indicate that the AMPK activated by fluid shear stress is a novel regulator of FoxO1a phosphorylation and protein levels. Moreover, as the AMPK-dependent phosphorylation and degradation of FoxO1a attenuates Ang-2 expression and protects against the pro-inflammatory actions of TNF-alpha, this kinase may be a useful target to prevent the progression of vascular diseases.
Dixit
Madhulika
M
Vascular Signalling Group, Institut für Kardiovaskuläre Physiologie, Johann Wolfgang Goethe Universität, Theodor-Stern-Kai 7, D-60590 Frankfurt am Main, Germany.
Bess
Elke
E
Fisslthaler
Beate
B
Härtel
Frauke V
FV
Noll
Thomas
T
Busse
Rudi
R
Fleming
Ingrid
I
D055372:AMP-Activated Protein Kinases; D042702:Angiopoietin-2 / Q000032:analysis* / Q000502:physiology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000737:chemistry / Q000378:metabolism*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism*; D006801:Humans; D009097:Multienzyme Complexes / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D013314:Stress, Mechanical; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D042702:Angiopoietin-2; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D009097:Multienzyme Complexes; D014409:Tumor Necrosis Factor-alpha; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D055372:AMP-Activated Protein Kinases