title: Mapping of ESE-1 subdomains required to initiate mammary epithelial cell transformation via a cytoplasmic mechanism.
abstract: BACKGROUND
  The ETS family transcription factor ESE-1 is often overexpressed in human breast cancer. ESE-1 initiates transformation of MCF-12A cells via a non-transcriptional, cytoplasmic process that is mediated by a unique 40-amino acid serine and aspartic acid rich (SAR) subdomain, whereas, ESE-1's nuclear transcriptional property is required to maintain the transformed phenotype of MCF7, ZR-75-1 and T47D breast cancer cells.
  
  
  RESULTS
  To map the minimal functional nuclear localization (NLS) and nuclear export (NES) signals, we fused in-frame putative NLS and NES motifs between GFP and the SAR domain. Using these GFP constructs as reporters of subcellular localization, we mapped a single NLS to six basic amino acids (242 HGKRRR 247) in the AT-hook and two CRM1-dependent NES motifs, one to the pointed domain (NES1: 102 LCNCALEELRL 112) and another to the DNA binding domain (DBD), (NES2: 275 LWEFIRDILI 284). Moreover, analysis of a putative NLS located in the DBD (316 GQKKKNSN 323) by a similar GFP-SAR reporter or by internal deletion of the DBD, revealed this sequence to lack NLS activity. To assess the role of NES2 in regulating ESE-1 subcellular localization and subsequent transformation potency, we site-specifically mutagenized NES2, within full-length GFP-ESE-1 and GFP-NES2-SAR reporter constructs. These studies show that site-specific mutation of NES2 completely abrogates ESE-1 transforming activity. Furthermore, we show that exclusive cytoplasmic targeting of the SAR domain is sufficient to initiate transformation, and we report that an intact SAR domain is required, since block mutagenesis reveals that an intact SAR domain is necessary to maintain its full transforming potency. Finally, using a monoclonal antibody targeting the SAR domain, we demonstrate that the SAR domain contains a region accessible for protein - protein interactions.
  
  
  CONCLUSIONS
  These data highlight that ESE-1 contains NLS and NES signals that play a critical role in regulating its subcellular localization and function, and that an intact SAR domain mediates MEC transformation exclusively in the cytoplasm, via a novel nontranscriptional mechanism, whereby the SAR motif is accessible for ligand and/or protein interactions. These findings are significant, since they provide novel molecular insights into the functions of ETS transcription factors in mammary cell transformation.
authors.affiliation: Medical Scientist Training Program, University of Colorado Denver, Aurora, CO 80045, USA.
authors.forename: Jason D
authors.initials: JD
authors.lastname: Prescott
authors.forename: Joanna M
authors.initials: JM
authors.lastname: Poczobutt
authors.forename: John J
authors.initials: JJ
authors.lastname: Tentler
authors.forename: Darius M
authors.initials: DM
authors.lastname: Walker
authors.forename: Arthur
authors.initials: A
authors.lastname: Gutierrez-Hartmann
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D042361:Mammary Glands, Human / Q000378:metabolism / Q000473:pathology*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D010449:Peptide Mapping; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D050783:Proto-Oncogene Proteins c-ets; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C105529:ELF3 protein, human; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors