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Mechanism of gene regulation employed by the bHLH transcription factor TWIST2: Repression of the CHRDL1 gene
Author(s) -
Casasnovas Jose,
Franco Hector,
Cadilla Carmen
Publication year - 2013
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.27.1_supplement.lb90
Subject(s) - psychological repression , transcription factor , gene silencing , microbiology and biotechnology , binding site , repressor , transcription (linguistics) , hek 293 cells , luciferase , gene , reporter gene , biology , mutant , dna binding site , gene expression , chemistry , promoter , genetics , transfection , linguistics , philosophy
Puerto Rican Setleis Syndrome (SS) patients harbor a nonsense mutation in TWIST2 (Q119X) which truncates the C‐terminus. We found that chordin‐like 1 (CHRDL1) is up‐regulated in SS patients skin fibroblasts and silencing of TWIST2 caused an increase in CHRDL1 expression. CHRDL1 codes for a BMP antagonist expressed in mesenchymal tissues. Putative TWIST binding sites were found upstream from the transcription start site of CHRDL1. EMSA analysis showed specific binding of Twist1 and TWIST2 homodimers, as well as E12/Twist heterodimers, to the −2421 site. Q1191X was only able to bind to the −2421 site as a heterodimer with E12. An adjoining E‐box was bound by SREBP1c/ADD1, a bHLH protein known to be repressed by TWIST2. EMSA analysis suggest that TWIST2 and ADD1 could compete for binding. Luciferase reporter assay revealed that the CHRDL1 upstream region drives its expression and ADD1 increased it 2.6X over basal levels. TWIST2, but not Q119X, blocked activation by ADD1. Overexpression of Q119X increased the expression of the reporter gene. The dysregulation of CHRDL1 in SS patients could be due to the lack of binding of Q119X as a homodimer and thus not competing with ADD1. The binding of Q119X‐E12 heterodimer could increase the expression of CHRDL1. In addition, Q119X could be sequestering other transcription factors important for CHRDL1 repression. Supported by NIH Grants G12RR03051, G12MD007600 and R25GM061838.