title: Progesterone induces adult mammary stem cell expansion.
abstract: Reproductive history is the strongest risk factor for breast cancer after age, genetics and breast density. Increased breast cancer risk is entwined with a greater number of ovarian hormone-dependent reproductive cycles, yet the basis for this predisposition is unknown. Mammary stem cells (MaSCs) are located within a specialized niche in the basal epithelial compartment that is under local and systemic regulation. The emerging role of MaSCs in cancer initiation warrants the study of ovarian hormones in MaSC homeostasis. Here we show that the MaSC pool increases 14-fold during maximal progesterone levels at the luteal dioestrus phase of the mouse. Stem-cell-enriched CD49fhi cells amplify at dioestrus, or with exogenous progesterone, demonstrating a key role for progesterone in propelling this expansion. In aged mice, CD49fhi cells display stasis upon cessation of the reproductive cycle. Progesterone drives a series of events where luminal cells probably provide Wnt4 and RANKL signals to basal cells which in turn respond by upregulating their cognate receptors, transcriptional targets and cell cycle markers. Our findings uncover a dynamic role for progesterone in activating adult MaSCs within the mammary stem cell niche during the reproductive cycle, where MaSCs are putative targets for cell transformation events leading to breast cancer.
authors.affiliation: Ontario Cancer Institute, Department of Medical Biophysics and Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto M5G 2M9, Ontario, Canada.
authors.forename: Purna A
authors.initials: PA
authors.lastname: Joshi
authors.forename: Hartland W
authors.initials: HW
authors.lastname: Jackson
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Beristain
authors.forename: Marco A
authors.initials: MA
authors.lastname: Di Grappa
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Mote
authors.forename: Christine L
authors.initials: CL
authors.lastname: Clarke
authors.forename: John
authors.initials: J
authors.lastname: Stingl
authors.forename: Paul D
authors.initials: PD
authors.lastname: Waterhouse
authors.forename: Rama
authors.initials: R
authors.lastname: Khokha
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D004967:Estrogens / Q000494:pharmacology; D030762:Estrous Cycle / Q000097:blood / Q000502:physiology; D005260:Female; D006706:Homeostasis / Q000187:drug effects; D039503:Integrin alpha6 / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000166:cytology*; D051379:Mice; D010052:Ovariectomy; D019899:Paracrine Communication / Q000187:drug effects; D011374:Progesterone / Q000097:blood / Q000378:metabolism / Q000494:pharmacology*; D053245:RANK Ligand / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism; D011980:Receptors, Progesterone / Q000378:metabolism; D055153:Stem Cell Niche / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D051153:Wnt Proteins / Q000378:metabolism; D060528:Wnt4 Protein
chemical_list: D004967:Estrogens; D039503:Integrin alpha6; D053245:RANK Ligand; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C505689:Tnfsf11 protein, mouse; D051153:Wnt Proteins; D060528:Wnt4 Protein; C555582:Wnt4 protein, mouse; D011374:Progesterone
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