title: Role of Notch signaling in cell-fate determination of human mammary stem/progenitor cells.
abstract: BACKGROUND
  Notch signaling has been implicated in the regulation of cell-fate decisions such as self-renewal of adult stem cells and differentiation of progenitor cells along a particular lineage. Moreover, depending on the cellular and developmental context, the Notch pathway acts as a regulator of cell survival and cell proliferation. Abnormal expression of Notch receptors has been found in different types of epithelial metaplastic lesions and neoplastic lesions, suggesting that Notch may act as a proto-oncogene. The vertebrate Notch1 and Notch4 homologs are involved in normal development of the mammary gland, and mutated forms of these genes are associated with development of mouse mammary tumors.
  
  
  METHODS
  In order to determine the role of Notch signaling in mammary cell-fate determination, we have utilized a newly described in vitro system in which mammary stem/progenitor cells can be cultured in suspension as nonadherent 'mammospheres'. Notch signaling was activated using exogenous ligands, or was inhibited using previously characterized Notch signaling antagonists.
  
  
  RESULTS
  Utilizing this system, we demonstrate that Notch signaling can act on mammary stem cells to promote self-renewal and on early progenitor cells to promote their proliferation, as demonstrated by a 10-fold increase in secondary mammosphere formation upon addition of a Notch-activating DSL peptide. In addition to acting on stem cells, Notch signaling is also able to act on multipotent progenitor cells, facilitating myoepithelial lineage-specific commitment and proliferation. Stimulation of this pathway also promotes branching morphogenesis in three-dimensional Matrigel cultures. These effects are completely inhibited by a Notch4 blocking antibody or a gamma secretase inhibitor that blocks Notch processing. In contrast to the effects of Notch signaling on mammary stem/progenitor cells, modulation of this pathway has no discernable effect on fully committed, differentiated, mammary epithelial cells.
  
  
  CONCLUSIONS
  These studies suggest that Notch signaling plays a critical role in normal human mammary development by acting on both stem cells and progenitor cells, affecting self-renewal and lineage-specific differentiation. Based on these findings we propose that abnormal Notch signaling may contribute to mammary carcinogenesis by deregulating the self-renewal of normal mammary stem cells.
authors.affiliation: Comprehensive Cancer Center, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan, USA. gdontu@umich.edu
authors.forename: Gabriela
authors.initials: G
authors.lastname: Dontu
authors.forename: Kyle W
authors.initials: KW
authors.lastname: Jackson
authors.forename: Erin
authors.initials: E
authors.lastname: McNicholas
authors.forename: Mari J
authors.initials: MJ
authors.lastname: Kawamura
authors.forename: Wissam M
authors.initials: WM
authors.lastname: Abdallah
authors.forename: Max S
authors.initials: MS
authors.lastname: Wicha
mesh_terms: D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005260:Female; D006801:Humans; D042361:Mammary Glands, Human / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology*; D051881:Receptor, Notch1; D000074562:Receptor, Notch4; D011956:Receptors, Cell Surface / Q000819:agonists / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology*; D051880:Receptors, Notch; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects; D014157:Transcription Factors / Q000819:agonists / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology*
chemical_list: C000715470:MAS1 protein, human; C497761:NOTCH1 protein, human; C106075:NOTCH4 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D051881:Receptor, Notch1; D000074562:Receptor, Notch4; D011956:Receptors, Cell Surface; D051880:Receptors, Notch; D014157:Transcription Factors