title: Protein kinase D1 maintains the epithelial phenotype by inducing a DNA-bound, inactive SNAI1 transcriptional repressor complex.
abstract: BACKGROUND
  Protein kinase D1 is downregulated in its expression in invasive ductal carcinoma of the breast and in invasive breast cancer cells, but its functions in normal breast epithelial cells is largely unknown. The epithelial phenotype is maintained by cell-cell junctions formed by E-cadherin. In cancer cells loss of E-cadherin expression contributes to an invasive phenotype. This can be mediated by SNAI1, a transcriptional repressor for E-cadherin that contributes to epithelial-to-mesenchymal transition (EMT).
  
  
  RESULTS
  Here we show that PKD1 in normal murine mammary gland (NMuMG) epithelial cells is constitutively-active in its basal state and prevents a transition to a mesenchymal phenotype. Investigation of the involved mechanism suggested that PKD1 regulates the expression of E-cadherin at the promoter level through direct phosphorylation of the transcriptional repressor SNAI1. PKD1-mediated phosphorylation of SNAI1 occurs in the nucleus and generates a nuclear, inactive DNA/SNAI1 complex that shows decreased interaction with its co-repressor Ajuba. Analysis of human tissue samples with a newly-generated phosphospecific antibody for PKD1-phosphorylated SNAI1 showed that regulation of SNAI1 through PKD1 occurs in vivo in normal breast ductal tissue and is decreased or lost in invasive ductal carcinoma.
  
  
  CONCLUSIONS
  Our data describe a mechanism of how PKD1 maintains the breast epithelial phenotype. Moreover, they suggest, that the analysis of breast tissue for PKD-mediated phosphorylation of SNAI1 using our novel phosphoS11-SNAI1-specific antibody may allow predicting the invasive potential of breast cancer cells.
authors.affiliation: Department of Cancer Biology, Mayo Clinic, Jacksonville, Florida, United States of America.
authors.forename: Ligia I
authors.initials: LI
authors.lastname: Bastea
authors.forename: Heike
authors.initials: H
authors.lastname: Döppler
authors.forename: Bolanle
authors.initials: B
authors.lastname: Balogun
authors.forename: Peter
authors.initials: P
authors.lastname: Storz
mesh_terms: D000818:Animals; D015820:Cadherins / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D004247:DNA / Q000378:metabolism*; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005260:Female; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D066298:In Vitro Techniques; D060588:LIM Domain Proteins / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000166:cytology; D051379:Mice; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D000071250:Snail Family Transcription Factors; D046888:Tissue Array Analysis; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D015820:Cadherins; D060588:LIM Domain Proteins; C000604407:SNAI1 protein, human; C000604429:Snai1 protein, mouse; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors; C485607:ajuba protein, mouse; D004247:DNA; C089212:protein kinase D; D011493:Protein Kinase C