Protein kinase Czeta-dependent LKB1 serine 428 phosphorylation increases LKB1 nucleus export and apoptosis in endothelial cells.
LKB1 is a serine-threonine protein kinase that, when inhibited, may result in unregulated cell growth and tumor formation. However, how LKB1 is regulated remains poorly understood. The aim of the present study was to define the upstream signaling events responsible for peroxynitrite (ONOO(-))-induced LKB1 activation. Exposure of cultured human umbilical vein endothelial cells to a low concentration of ONOO(-) (5 microM) significantly increased the phosphorylation of LKB1 at Ser(428) and protein kinase Czeta (PKCzeta) at Thr(410). These effects were accompanied by increased activity of the lipid phosphatase PTEN, decreased activity and phosphorylation (Ser(473)) of Akt, and induction of apoptosis. ONOO(-) enhanced Akt-Ser(473) phosphorylation in LKB1-deficient HeLa S3 cells or in HeLa S3 cells transfected with kinase-dead LKB1. Conversely, ONOO(-) inhibited Akt Ser(473) phosphorylation when wild type LKB1 were reintroduced in HeLa S3 cells. Further analysis revealed that PKCzeta directly phosphorylated LKB1 at Ser(428) in vitro and in intact cells, resulting in increased PTEN phosphorylation at Ser(380)/Thr(382/383). Finally, ONOO(-) enhanced PKCzeta nuclear import and LKB1 nuclear export. We conclude that PKCzeta mediates LKB1-dependent Akt inhibition in response to ONOO(-), resulting in endothelial apoptosis.
Song
Ping
P
Section of Endocrinology and Diabetes, Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, 73104, USA.
Xie
Zhonglin
Z
Wu
Yong
Y
Xu
Jian
J
Dong
Yunzhou
Y
Zou
Ming-Hui
MH
D000091162:AMP-Activated Protein Kinase Kinases; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology*; D042783:Endothelial Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D006367:HeLa Cells; D006801:Humans; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D030421:Peroxynitrous Acid / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013816:Thermodynamics; D000099221:Protein Kinase C zeta
D000091162:AMP-Activated Protein Kinase Kinases; D051059:PTEN Phosphohydrolase; D030421:Peroxynitrous Acid; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D012694:Serine; D000099221:Protein Kinase C zeta; C109790:STK11 protein, human; C494929:PTEN protein, human