title: CD44 isoforms are heterogeneously expressed in breast cancer and correlate with tumor subtypes and cancer stem cell markers.
abstract: BACKGROUND
  The CD44 cell adhesion molecule is aberrantly expressed in many breast tumors and has been implicated in the metastatic process as well as in the putative cancer stem cell (CSC) compartment. We aimed to investigate potential associations between alternatively spliced isoforms of CD44 and CSCs as well as to various breast cancer biomarkers and molecular subtypes.
  
  
  METHODS
  We used q-RT-PCR and exon-exon spanning assays to analyze the expression of four alternatively spliced CD44 isoforms as well as the total expression of CD44 in 187 breast tumors and 13 cell lines. ALDH1 protein expression was determined by IHC on TMA.
  
  
  RESULTS
  Breast cancer cell lines showed a heterogeneous expression pattern of the CD44 isoforms, which shifted considerably when cells were grown as mammospheres. Tumors characterized as positive for the CD44+/CD24- phenotype by immunohistochemistry were associated to all isoforms except the CD44 standard (CD44S) isoform, which lacks all variant exons. Conversely, tumors with strong expression of the CSC marker ALDH1 had elevated expression of CD44S. A high expression of the CD44v2-v10 isoform, which retain all variant exons, was correlated to positive steroid receptor status, low proliferation and luminal A subtype. The CD44v3-v10 isoform showed similar correlations, while high expression of CD44v8-v10 was correlated to positive EGFR, negative/low HER2 status and basal-like subtype. High expression of CD44S was associated with strong HER2 staining and also a subgroup of basal-like tumors. Unsupervised hierarchical cluster analysis of CD44 isoform expression data divided tumors into four main clusters, which showed significant correlations to molecular subtypes and differences in 10-year overall survival.
  
  
  CONCLUSIONS
  We demonstrate that individual CD44 isoforms can be associated to different breast cancer subtypes and clinical markers such as HER2, ER and PgR, which suggests involvement of CD44 splice variants in specific oncogenic signaling pathways. Efforts to link CD44 to CSCs and tumor progression should consider the expression of various CD44 isoforms.
authors.affiliation: Department of Oncology, Clinical Sciences, Lund University, Lund, Sweden. Eleonor.Olsson@med.lu.se
authors.forename: Eleonor
authors.initials: E
authors.lastname: Olsson
authors.forename: Gabriella
authors.initials: G
authors.lastname: Honeth
authors.forename: Pär-Ola
authors.initials: PO
authors.lastname: Bendahl
authors.forename: Lao H
authors.initials: LH
authors.lastname: Saal
authors.forename: Sofia
authors.initials: S
authors.lastname: Gruvberger-Saal
authors.forename: Markus
authors.initials: M
authors.lastname: Ringnér
authors.forename: Johan
authors.initials: J
authors.lastname: Vallon-Christersson
authors.forename: Göran
authors.initials: G
authors.lastname: Jönsson
authors.forename: Karolina
authors.initials: K
authors.lastname: Holm
authors.forename: Kristina
authors.initials: K
authors.lastname: Lövgren
authors.forename: Mårten
authors.initials: M
authors.lastname: Fernö
authors.forename: Dorthe
authors.initials: D
authors.lastname: Grabau
authors.forename: Ake
authors.initials: A
authors.lastname: Borg
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hegardt
mesh_terms: D017398:Alternative Splicing; D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000145:classification* / Q000235:genetics* / Q000401:mortality; D045744:Cell Line, Tumor; D016000:Cluster Analysis; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics* / Q000378:metabolism; D053208:Kaplan-Meier Estimate; D014411:Neoplastic Stem Cells / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D018960:Hyaluronan Receptors; D020033:Protein Isoforms; D012333:RNA, Messenger