title: Aldehyde dehydrogenase and estrogen receptor define a hierarchy of cellular differentiation in the normal human mammary epithelium.
abstract: BACKGROUND
  Although estrogen and progesterone play a key role in normal mammary development and in breast cancer, the potential for proliferation and lineage differentiation as well as origin of cells that express the estrogen receptor (ER) in normal breast epithelium are not known. Some evidence suggests that normal human mammary stem/progenitor cells are ER-, but the identity of these cells and the cellular hierarchy of breast epithelium are still subjects of controversy. It is likely that elucidation of these aspects will bring insight into the cellular origin of breast cancer subtypes.
  
  
  METHODS
  We used fluorescence-activated cell sorting of primary human mammary epithelial cells along with in vitro and in vivo functional assays to examine the hierarchic relation between cells with aldehyde dehydrogenase enzymatic activity (ALDH+ cells) and ER+ cells in the normal human breast epithelium. We assessed the proliferation and lineage differentiation potential of these cells in vitro and in vivo. A gene reporter assay was used to separate live ER+ and ER- mammary epithelial cells. With shRNA-mediated knockdown, we investigated the role of ALDH isoforms in the functionality of mammary epithelial progenitor cells.
  
  
  RESULTS
  We describe a cellular hierarchy in the normal human mammary gland in which ER-/ALDH+ cells with functional properties of stem/progenitor cells generate ER+ progenitor cells, which in turn give rise to cells of luminal lineage. We show that the ALDH1A1 isoform, through its function in the retinoic acid metabolism, affects the proliferation and/or early differentiation of stem/progenitor cells and is important for branching morphogenesis.
  
  
  CONCLUSIONS
  This study presents direct evidence that ER+ cells are generated by ER-/ALDH+ stem/progenitor cells. We also show that ER+ cells are able to generate cell progeny of luminal lineage in vitro and in vivo. Loss of ALDH1A1 function impairs this process, as well as branching morphogenesis and clonogenicity in suspension culture. This latter effect is reversed by treatment with retinoic acid.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Honeth
authors.forename: Sara
authors.initials: S
authors.lastname: Lombardi
authors.forename: Christophe
authors.initials: C
authors.lastname: Ginestier
authors.forename: Minhee
authors.initials: M
authors.lastname: Hur
authors.forename: Rebecca
authors.initials: R
authors.lastname: Marlow
authors.forename: Bharath
authors.initials: B
authors.lastname: Buchupalli
authors.forename: Ireneusz
authors.initials: I
authors.lastname: Shinomiya
authors.forename: Patrycja
authors.initials: P
authors.lastname: Gazinska
authors.forename: Silvia
authors.initials: S
authors.lastname: Bombelli
authors.forename: Vernie
authors.initials: V
authors.lastname: Ramalingam
authors.forename: Anand D
authors.initials: AD
authors.lastname: Purushotham
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Pinder
authors.forename: Gabriela
authors.initials: G
authors.lastname: Dontu
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D000080924:Aldehyde Dehydrogenase 1 Family; D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D002454:Cell Differentiation; D019070:Cell Lineage; D049109:Cell Proliferation; D002478:Cells, Cultured; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D042361:Mammary Glands, Human / Q000166:cytology / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics; D034622:RNA Interference; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen / Q000096:biosynthesis / Q000378:metabolism*; D050697:Retinal Dehydrogenase; D013234:Stem Cells / Q000166:cytology / Q000201:enzymology; D014212:Tretinoin / Q000378:metabolism / Q000494:pharmacology*
chemical_list: D020033:Protein Isoforms; D034741:RNA, Small Interfering; D011960:Receptors, Estrogen; D014212:Tretinoin; D000445:Aldehyde Oxidoreductases; D000080924:Aldehyde Dehydrogenase 1 Family; D000444:Aldehyde Dehydrogenase; C510223:ALDH1A1 protein, human; D050697:Retinal Dehydrogenase; C018699:aldehyde dehydrogenase (NAD(P)+)