title: Human breast progenitor cell numbers are regulated by WNT and TBX3.
abstract: BACKGROUND
  Although human breast development is mediated by hormonal and non-hormonal means, the mechanisms that regulate breast progenitor cell activity remain to be clarified. This limited understanding of breast progenitor cells has been due in part to the lack of appropriate model systems to detect and characterize their properties.
  
  
  METHODS
  To examine the effects of WNT signaling and TBX3 expression on progenitor activity in the breast, primary human mammary epithelial cells (MEC) were isolated from reduction mammoplasty tissues and transduced with lentivirus to overexpress WNT1 or TBX3 or reduce expression of their cognate receptors using shRNA. Changes in progenitor activity were quantified using characterized assays. We identified WNT family members expressed by cell populations within the epithelium and assessed alterations in expression of WNT family ligands by MECs in response to TBX3 overexpression and treatment with estrogen and progesterone.
  
  
  RESULTS
  Growth of MECs on collagen gels resulted in the formation of distinct luminal acinar and basal ductal colonies. Overexpression of TBX3 in MECs resulted in increased ductal colonies, while shTBX3 expression diminished both colony types. Increased WNT1 expression led to enhanced acinar colony formation, shLRP6 decreased both types of colonies. Estrogen stimulated the formation of acinar colonies in control MEC, but not shLRP6 MEC. Formation of ductal colonies was enhanced in response to progesterone. However, while shLRP6 decreased MEC responsiveness to progesterone, shTBX3 expression did not alter this response.
  
  
  CONCLUSIONS
  We identified two phenotypically distinguishable lineage-committed progenitor cells that contribute to different structural elements and are regulated via hormonal and non-hormonal mechanisms. WNT signaling regulates both types of progenitor activity. Progesterone favors the expansion of ductal progenitor cells, while estrogen stimulates the expansion of acinar progenitor cells. Paracrine WNT signaling is stimulated by estrogen and progesterone, while autocrine WNT signaling is induced by the embryonic T-box transcription factor TBX3.
authors.affiliation: Developmental, Molecular, and Chemical Biology Department, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America; Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Arendt
authors.affiliation: Developmental, Molecular, and Chemical Biology Department, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America; Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Jessica
authors.initials: J
authors.lastname: St Laurent
authors.affiliation: Developmental, Molecular, and Chemical Biology Department, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America; Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Ania
authors.initials: A
authors.lastname: Wronski
authors.affiliation: Developmental, Molecular, and Chemical Biology Department, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America; Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Silvia
authors.initials: S
authors.lastname: Caballero
authors.affiliation: Department of Cancer Biology, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America.
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Lyle
authors.affiliation: Department of Pathology, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Naber
authors.affiliation: Developmental, Molecular, and Chemical Biology Department, Sackler School of Graduate Biomedical Sciences, Tufts University School of Medicine, Boston, Massachusetts, United States of America; Molecular Oncology Research Institute, Tufts Medical Center, Boston, Massachusetts, United States of America.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Kuperwasser
mesh_terms: D000818:Animals; D001940:Breast / Q000166:cytology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003094:Collagen / Q000737:chemistry; D004847:Epithelial Cells / Q000166:cytology*; D004967:Estrogens / Q000737:chemistry; D005260:Female; D006801:Humans; D016086:Lentivirus / Q000235:genetics; D008024:Ligands; D060488:Low Density Lipoprotein Receptor-Related Protein-6 / Q000378:metabolism; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D010641:Phenotype; D061251:Primary Cell Culture; D011374:Progesterone / Q000737:chemistry; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013234:Stem Cells / Q000166:cytology*; D020825:T-Box Domain Proteins / Q000378:metabolism*; D051153:Wnt Proteins / Q000378:metabolism*
chemical_list: D004967:Estrogens; D008024:Ligands; D060488:Low Density Lipoprotein Receptor-Related Protein-6; C555476:Lrp6 protein, mouse; D034741:RNA, Small Interfering; D020825:T-Box Domain Proteins; C106884:TBX3 protein, human; C491460:Tbx3 protein, mouse; D051153:Wnt Proteins; D011374:Progesterone; D003094:Collagen