title: Hypoxic repression of STAT1 and its downstream genes by a pVHL/HIF-1 target DEC1/STRA13.
abstract: DEC1/STRA13 is a bHLH type transcriptional regulator involved with immune regulation, hypoxia response and carcinogenesis. We recently demonstrated that STRA13 interacts with STAT3 in the transcriptional activation of STAT-dependent promoters. Here, we pursue STRA13 involvement in the JAK/STAT pathway by studying its role in STAT1 expression. First, we showed that VHL deficiency or HIF-1 activation resulted in the repression of endogenous STAT1 mediated by STRA13. We then characterized the STAT1 proximal promoter to assess its response to STRA13 by transient coexpression in a luciferase reporter assay. Using sequential truncation and site-directed mutagenesis of the STAT1 promoter with STRA13 deletion constructs, we showed that the STRA13 C-terminal trans-activation domain, which is known to bind HDAC1, mostly determines the repressive activity. Involvement of HDAC activity in STAT1 regulation was validated by TSA inhibition and chromatin immunoprecipitation (ChIP) assay. Thus, we demonstrate that STRA13-mediated repression of STAT1 transcription utilizes an HDAC1-dependent mechanism. Furthermore, we show that targets of unphosphorylated STAT1, such as antigen presenting genes and CASP1, are also repressed by hypoxia possibly through the same STRA13-mediated mechanism. Thus, the newly discovered link between HIF-1 and STAT1 reveals a previously unknown role of STRA13 in hypoxia and carcinogenesis.
authors.affiliation: Basic Research Program, SAIC-Frederick, Inc., Frederick, MD 21702, USA. Sergey.Ivanov@med.nyu.edu
authors.forename: S V
authors.initials: SV
authors.lastname: Ivanov
authors.forename: K
authors.initials: K
authors.lastname: Salnikow
authors.forename: A V
authors.initials: AV
authors.lastname: Ivanova
authors.forename: L
authors.initials: L
authors.lastname: Bai
authors.forename: M I
authors.initials: MI
authors.lastname: Lerman
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D015687:Cell Hypoxia / Q000235:genetics; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D018398:Homeodomain Proteins / Q000378:metabolism*; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D020598:Proto-Oncogene Proteins c-myb / Q000235:genetics / Q000378:metabolism; D050794:STAT1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics; D015533:Transcriptional Activation
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D003546:Cysteine Endopeptidases; D006655:Histone Deacetylases; D018398:Homeodomain Proteins; D051793:Hypoxia-Inducible Factor 1; D020598:Proto-Oncogene Proteins c-myb; D050794:STAT1 Transcription Factor; C107989:BHLHE40 protein, human; C491539:Bhlhe40 protein, mouse; C494079:STAT1 protein, human; C071313:LMP-2 protein