Parity induces differentiation and reduces Wnt/Notch signaling ratio and proliferation potential of basal stem/progenitor cells isolated from mouse mammary epithelium

Abstract

IntroductionEarly pregnancy has a strong protective effect against breast cancer in humans and rodents, but the underlying mechanism is unknown. Because breast cancers are thought to arise from specific cell subpopulations of mammary epithelia, we studied the effect of parity on the transcriptome and the differentiation/proliferation potential of specific luminal and basal mammary cells in mice.MethodsMammary epithelial cell subpopulations (luminal Sca1-, luminal Sca1+, basal stem/progenitor, and basal myoepithelial cells) were isolated by flow cytometry from parous and age-matched virgin mice and examined by using a combination of unbiased genomics, bioinformatics, in vitro colony formation, and in vivo limiting dilution transplantation assays. Specific findings were further investigated with immunohistochemistry in entire glands of parous and age-matched virgin mice.ResultsTranscriptome analysis revealed an upregulation of differentiation genes and a marked decrease in the Wnt/Notch signaling ratio in basal stem/progenitor cells of parous mice. Separate bioinformatics analyses showed reduced activity for the canonical Wnt transcription factor LEF1/TCF7 and increased activity for the Wnt repressor TCF3. This finding was specific for basal stem/progenitor cells and was associated with downregulation of potentially carcinogenic pathways and a reduction in the proliferation potential of this cell subpopulation in vitro and in vivo. As a possible mechanism for decreased Wnt signaling in basal stem/progenitor cells, we found a more than threefold reduction in the expression of the secreted Wnt ligand Wnt4 in total mammary cells from parous mice, which corresponded to a similar decrease in the proportion of Wnt4-secreting and estrogen/progesterone receptor-positive cells. Because recombinant Wnt4 rescued the proliferation defect of basal stem/progenitor cells in vitro, reduced Wnt4 secretion appears to be causally related to parity-induced alterations of basal stem/progenitor cell properties in mice.ConclusionsBy revealing that parity induces differentiation and downregulates the Wnt/Notch signaling ratio and the in vitro and in vivo proliferation potential of basal stem/progenitor cells in mice, our study sheds light on the long-term consequences of an early pregnancy. Furthermore, it opens the door to future studies assessing whether inhibitors of the Wnt pathway may be used to mimic the parity-induced protective effect against breast cancer.

ISMARA: automated modeling of genomic signals as a democracy of regulatory motifs

“…Thus, whereas many laboratories are now routinely producing high-throughput data sets, and methodologies for analyzing such data have been described in the literature, the vast majority of groups that produce data have to develop collaborations with expert computational groups to apply these methods. Indeed, in recent years MARA has been applied to a large range of mammalian systems studied by various experimental collaborators and experimentally validated predicted regulatory circuitry in these systems (Summers et al 2010;Aceto et al 2012;Arner et al 2012;Hasegawa et al 2012;Pérez-Schindler et al 2012;Suzuki et al 2012;Eisele et al 2013;Meier-Abt et al 2013;Tiwari et al 2013a,b;Vervoort et al 2013). Although these studies further validated the power of the method, they required a considerable investment of time and effort for the analysis of each new data set.…”

Bringing androgens up a NOTCH in breast cancer

“…Altogether, these studies point to HS-MECs exerting a powerful developmental influence on the normal MEC population. Accumulating evidence indicates that HS-MECs also influence breast cancer susceptibility (Choudhury et al 2013, Hodgson et al 2013, Meier-Abt et al 2013, Tarulli et al 2013, an effect that may extend to both ERa-positive and ERa-negative breast cancers, and supports the use of androgen modulation as a form of breast cancer therapy as it principally targets the HS-MEC population.…”

Targeting of miR34a–NOTCH1 Axis Reduced Breast Cancer Stemness and Chemoresistance

“…In recent studies, it was reported that Notch and Wnt signaling is the main cell fate regulator in breast cancer (3,4), making them potential therapeutic targets in BCSCs. miRNAs are a conserved class of noncoding small RNAs that regulate the expression of certain key genes involved in selfrenewal, survival, and tumor progression (5).…”

“…Primary cells from nude mice were infected with control or miR34a lentivirus (GenTarget Inc.; multiplicity of infection, [3][4][5] in the presence of 5 mg/mL polybrene. Mice were anesthetized with 150 mL of saline/Zoletil/Rompun (7:1:1) and inoculated subcutaneously with 1 Â 10 6 stable MCF7/ADR primary cells into each flank.…”