title: Gene expression of the tumour suppressor LKB1 is mediated by Sp1, NF-Y and FOXO transcription factors.
abstract: The serine/threonine kinase LKB1 is a tumour suppressor that regulates multiple biological pathways, including cell cycle control, cell polarity and energy metabolism by direct phosphorylation of 14 different AMP-activated protein kinase (AMPK) family members. Although many downstream targets have been described, the regulation of LKB1 gene expression is still poorly understood. In this study, we performed a functional analysis of the human LKB1 upstream regulatory region. We used 200 base pair deletion constructs of the 5'-flanking region fused to a luciferase reporter to identify the core promoter. It encompasses nucleotides -345 to +52 relative to the transcription start site and coincides with a DNase I hypersensitive site. Based on extensive deletion and substitution mutant analysis of the LKB1 promoter, we identified four cis-acting elements which are critical for transcriptional activation. Using electrophoretic mobility shift assays as well as chromatin immunoprecipitations, we demonstrate that the transcription factors Sp1, NF-Y and two forkhead box O (FOXO) family members FOXO3 and FOXO4 bind to these elements. Overexpression of these factors significantly increased the LKB1 promoter activity. Conversely, small interfering RNAs directed against NF-Y alpha and the two FOXO proteins greatly reduced endogenous LKB1 expression and phosphorylation of LKB1's main substrate AMPK in three different cell lines. Taken together, these results demonstrate that Sp1, NF-Y and FOXO transcription factors are involved in the regulation of LKB1 transcription.
authors.affiliation: Research Program Infections and Cancer, German Cancer Research Center (DKFZ), Heidelberg, Germany. n.luetzner@dkfz.de
authors.forename: Nicolas
authors.initials: N
authors.lastname: Lützner
authors.forename: Johanna
authors.initials: J
authors.lastname: De-Castro Arce
authors.forename: Frank
authors.initials: F
authors.lastname: Rösl
mesh_terms: D000091162:AMP-Activated Protein Kinase Kinases; D001483:Base Sequence; D001665:Binding Sites; D023081:CCAAT-Binding Factor / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D051858:Forkhead Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D020868:Gene Silencing; D006801:Humans; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D050436:Regulatory Elements, Transcriptional; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D024363:Transcription Initiation Site; D015533:Transcriptional Activation; D025521:Tumor Suppressor Proteins / Q000235:genetics*
chemical_list: D023081:CCAAT-Binding Factor; D051858:Forkhead Transcription Factors; D016329:Sp1 Transcription Factor; D025521:Tumor Suppressor Proteins; D017346:Protein Serine-Threonine Kinases; C109790:STK11 protein, human; D000091162:AMP-Activated Protein Kinase Kinases