A nonsense mutation of the bHLH transcription factor TWIST2 found in Setleis Syndrome patients causes dysregulation of the human periostin gene

Abstract

Setleis Syndrome (SS, MIM #227260) is a rare autosomal recessive disorder characterized by abnormal facial and skin development. Recently, we have shown that nonsense mutations in the basic helix‐loop‐helix (bHLH) transcription factor TWIST2 cause Setleis Syndrome. Microarray analysis suggests that periostin (POSTN), a cell adhesion protein involved in connective tissue development and maintenance, is down regulated in Setleis Syndrome patient fibroblasts. Overexpression and knockdown of TWIST2 resulted in increased and decreased expression of POSTN mRNA, respectively. Functional analysis of the Q119X TWIST2 mutant form revealed that it maintains the ability to localize to the nucleus, form homo and heterodimers with the ubiquitous bHLH protein E12 and shows binding to dsDNA. Chromatin immunoprecipitation assays suggest that both wild‐type TWIST2 and its mutant form can bind the POSTN regulatory region, however only wild‐type TWIST2 is associated with higher levels of acetylated histone H3 of the POSTN promoter. Reporter gene assays using deletion constructs of the POSTN regulatory region also reveal that wild‐type TWIST2 can activate this gene, but not the Q119X TWIST2 mutant. This data suggests that the C‐terminal domain of TWIST2, which is missing in Q119X TWIST2, is responsible for proper transactivation of POSTN. This research is supported by MBRS RISE Grant R25GM061838 and RCMI Grant G12RR03051.