title: LKB1 is recruited to the p21/WAF1 promoter by p53 to mediate transcriptional activation.
abstract: The tumor suppressor LKB1 is an evolutionarily conserved serine/threonine kinase. In humans, LKB1 can be inactivated either by germ-line mutations resulting in Peutz-Jeghers syndrome or by somatic mutations causing predisposition to multiple sporadic cancers. LKB1 has wide-ranging functions involved in tumor suppression and cell homeostasis, including establishing cell polarity, setting energy metabolic balance (via phosphorylation of AMP-dependent kinase), regulating the cell cycle, and promoting apoptosis. LKB1 function was previously linked to the tumor suppressor p53 and shown to activate the p53 target gene p21/WAF1. In this study, we further investigated LKB1 activation of the p21/WAF1 gene and addressed whether LKB1 is directly involved at the gene promoter. We find that, consistent with previous studies, LKB1 stabilizes p53 in vivo, correlating with activation of p21/WAF1. We show that LKB1 physically associates with p53 in the nucleus and directly or indirectly phosphorylates p53 Ser15 (previously shown to be phosphorylated by AMP-dependent kinase) and p53 Ser392. Further, these two p53 residues are required for LKB1-dependent cell cycle G(1) arrest. Chromatin immunoprecipitation analyses show that LKB1 is recruited directly to the p21/WAF1 promoter, as well as to other p53 activated promoters, in a p53-dependent fashion. Finally, a genetic fusion of LKB1 to defective p53, deleted for its activation domains, promotes activation of p21/WAF1. These results indicate that LKB1 has a direct role in activation of p21/WAF1 gene.
authors.affiliation: Gene Expression and Regulation Program, The Wistar Institute, Philadelphia, Pennsylvania and Cancer Research Institute, Xiangya School of Medicine, Central South University, Changsha, Hunan Province, P.R. China.
authors.forename: Ping-Yao
authors.initials: PY
authors.lastname: Zeng
authors.forename: Shelley L
authors.initials: SL
authors.lastname: Berger
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics*; D016193:G1 Phase / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic; D045325:HCT116 Cells; D006801:Humans; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics* / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases