title: DNAJB6 governs a novel regulatory loop determining Wnt/β-catenin signalling activity.
abstract: DKK1 (dickkopf 1 homologue) is a secreted inhibitor of the Wnt signalling pathway and a critical modulator of tumour promotion and the tumour microenvironment. However, mechanisms regulating DKK1 expression are understudied. DNAJB6 {DnaJ [HSP40 (heat-shock protein 40 kDa)] homologue, subfamily B, member 6} is an HSP40 family member whose expression is compromised during progression of breast cancer and melanoma. Inhibition of the Wnt/β-catenin signalling pathway by up-regulation of DKK1 is one of the key mechanisms by which DNAJB6 suppresses tumour metastasis and EMT (epithelial-mesenchymal transition). Analysis of the DKK1 promoter to define the cis-site responsible for its up-regulation by DNAJB6 revealed the presence of two binding sites for a transcriptional repressor, MSX1 (muscle segment homeobox 1). Our investigations showed that MSX1 binds the DKK1 promoter and inhibits DKK1 transcription. Interestingly, silencing DNAJB6 resulted in up-regulation of MSX1 concomitant with increased stabilization of β-catenin. ChIP (chromatin immunoprecipitation) studies revealed that β-catenin binds the MSX1 promoter and stabilization of β-catenin elevates MSX1 transcription, indicating that β-catenin works as a transcription co-activator for MSX1. Functionally, exogenous expression of MSX1 in DNAJB6-expressing cells promotes the mesenchymal phenotype by suppression of DKK1. Thus we have identified a novel regulatory mechanism of DNAJB6-mediated DKK1 transcriptional up-regulation that can influence EMT. DKK1 is a feedback regulator of β-catenin levels and thus our studies also define an additional negative control of this β-catenin/DKK1 feedback loop by MSX1, which may potentially contribute to excessive stabilization of β-catenin.
authors.affiliation: Department of Oncologic Sciences, Mitchell Cancer Institute, University of South Alabama, 1660 Spring Hill Avenue, Mobile, AL 36604, USA.
authors.forename: Mitchell E
authors.initials: ME
authors.lastname: Menezes
authors.forename: Aparna
authors.initials: A
authors.lastname: Mitra
authors.forename: Lalita A
authors.initials: LA
authors.lastname: Shevde
authors.forename: Rajeev S
authors.initials: RS
authors.lastname: Samant
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D045744:Cell Line, Tumor; D005260:Female; D050956:HSP40 Heat-Shock Proteins / Q000502:physiology*; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000502:physiology*; D051957:MSX1 Transcription Factor / Q000502:physiology*; D051379:Mice; D008819:Mice, Nude; D018832:Molecular Chaperones / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000502:physiology*; D055550:Protein Stability; D051153:Wnt Proteins / Q000502:physiology; D060449:Wnt Signaling Pathway / Q000502:physiology*; D051176:beta Catenin / Q000502:physiology*
chemical_list: C495270:CTNNB1 protein, human; C501126:DKK1 protein, human; C485565:DNAJB6 protein, human; D050956:HSP40 Heat-Shock Proteins; D036341:Intercellular Signaling Peptides and Proteins; D051957:MSX1 Transcription Factor; C484083:MSX1 protein, human; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D051153:Wnt Proteins; D051176:beta Catenin