Previous Article | Next Article 
Molecular and Cellular Biology, July 2009, p. 3582-3596, Vol. 29, No. 13
0270-7306/09/$08.00+0 doi:10.1128/MCB.01417-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Identification of the Serine 307 of LKB1 as a Novel Phosphorylation Site Essential for Its Nucleocytoplasmic Transport and Endothelial Cell Angiogenesis 
,
Zhonglin Xie,1,
Yunzhou Dong,1,
Junhua Zhang,1
Roland Scholz,2
Dietbert Neumann,2 and
Ming-Hui Zou1*
Division of Endocrinology and Diabetes, Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104,1 Institute of Cell Biology, ETH Zurich, 8093 Zurich, Switzerland2
Received 9 September 2008/ Returned for modification 17 October 2008/ Accepted 26 April 2009
LKB1, a master kinase that controls at least 13 downstream protein kinases including the AMP-activated protein kinase (AMPK), resides mainly in the nucleus. A key step in LKB1 activation is its export from the nucleus to the cytoplasm. Here, we identified S307 of LKB1 as a putative novel phosphorylation site which is essential for its nucleocytoplasmic transport. In a cell-free system, recombinant PKC-
phosphorylates LKB1 at S307. AMPK-activating agents stimulate PKC- activity and LKB1 phosphorylation at S307 in endothelial cells, hepatocytes, skeletal muscle cells, and vascular smooth muscle cells. Like the kinase-dead LKB1 D194A mutant (mutation of Asp194 to Ala), the constitutively nucleus-localized LKB1 SL26 mutant and the LKB1 S307A mutant (Ser307 to Ala) exhibit a decreased association with STRAD
. Interestingly, the PKC- consensus sequence surrounding LKB1 S307 is disrupted in the LKB1 SL26 mutant, thus providing a likely molecular explanation for this mutation causing LKB1 dysfunction. In addition, LKB1 nucleocytoplasmic transport and AMPK activation in response to peroxynitrite are markedly reduced by pharmacological inhibition of CRM1, which normally facilitates nuclear export of LKB1-STRAD complexes. In comparison to the LKB1 wild type, the S307A mutant complexes show reduced association with CRM1. Finally, adenoviral overexpression of wild-type LKB1 suppresses, while the LKB1 S307A mutant increases, tube formation and hydrogen peroxide-enhanced apoptosis in cultured endothelial cells. Taken together, our results suggest that, in multiple cell types the signaling pathways engaged by several physiological stimuli converge upon PKC--dependent LKB1 phosphorylation at S307, which directs the nucleocytoplasmic transport of LKB1 and consequent AMPK activation.
* Corresponding author. Mailing address: Department of Medicine, University of Oklahoma Health Sciences Center, 941 Stanton L. Young Blvd., Oklahoma City, OK 73104. Phone: (405) 271-3974. Fax: (405) 271-3973. E-mail: ming-hui-zou{at}ouhsc.edu
Published ahead of print on 4 May 2009.
Supplemental material for this article may be found at http://mcb.asm.org/.
Z.X. and Y.D. contributed equally to this work.
Molecular and Cellular Biology, July 2009, p. 3582-3596, Vol. 29, No. 13
0270-7306/09/$08.00+0 doi:10.1128/MCB.01417-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»