title: Septin 9 isoform expression, localization and epigenetic changes during human and mouse breast cancer progression.
abstract: BACKGROUND
  Altered expression of Septin 9 (SEPT9), a septin coding for multiple isoform variants, has been observed in several carcinomas, including colorectal, head and neck, ovarian and breast, compared to normal tissues. The mechanisms regulating its expression during tumor initiation and progression in vivo and the oncogenic function of its different isoforms remain elusive.
  
  
  METHODS
  Using an integrative approach, we investigated SEPT9 at the genetic, epigenetic, mRNA and protein levels in breast cancer. We analyzed a panel of breast cancer cell lines, human primary tumors and corresponding tumor-free areas, normal breast tissues from reduction mammoplasty patients, as well as primary mammary gland adenocarcinomas derived from the polyoma virus middle T antigen, or PyMT, mouse model. MCF7 clones expressing individual GFP-tagged SEPT9 isoforms were used to determine their respective intracellular distributions and effects on cell migration.
  
  
  RESULTS
  An overall increase in gene amplification and altered expression of SEPT9 were observed during breast tumorigenesis. We identified an intragenic alternative promoter at which methylation regulates SEPT9_v3 expression. Transfection of specific GFP-SEPT9 isoforms in MCF7 cells indicates that these isoforms exhibit differential localization and affect migration rates. Additionally, the loss of an uncharacterized SEPT9 nucleolar localization is observed during tumorigenesis.
  
  
  CONCLUSIONS
  In this study, we found conserved in vivo changes of SEPT9 gene amplification and overexpression during human and mouse breast tumorigenesis. We show that DNA methylation is a prominent mechanism responsible for regulating differential SEPT9 isoform expression and that breast tumor samples exhibit distinctive SEPT9 intracellular localization. Together, these findings support the significance of SEPT9 as a promising tool in breast cancer detection and further emphasize the importance of analyzing and targeting SEPT9 isoform-specific expression and function.
authors.affiliation: Department of Genetics, Albert Einstein College of Medicine, Yeshiva University, 1301 Morris Park Avenue, Bronx, NY 10461, USA.
authors.forename: Diana
authors.initials: D
authors.lastname: Connolly
authors.forename: Zhixia
authors.initials: Z
authors.lastname: Yang
authors.forename: Maria
authors.initials: M
authors.lastname: Castaldi
authors.forename: Nichelle
authors.initials: N
authors.lastname: Simmons
authors.forename: Maja H
authors.initials: MH
authors.lastname: Oktay
authors.forename: Salvatore
authors.initials: S
authors.lastname: Coniglio
authors.forename: Melissa J
authors.initials: MJ
authors.lastname: Fazzari
authors.forename: Pascal
authors.initials: P
authors.lastname: Verdier-Pinard
authors.forename: Cristina
authors.initials: C
authors.lastname: Montagna
mesh_terms: D000230:Adenocarcinoma / Q000235:genetics* / Q000473:pathology; D017398:Alternative Splicing; D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000235:genetics; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D005784:Gene Amplification; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics; D012016:Reference Values; D058112:Septins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; C474315:SEPTIN9 protein, human; D058112:Septins; C574402:septin 9, mouse