Notch3-Frizzled7 signaling regulates luminal cell fate in human breast tissue
| dc.contributor.author | Bhat, Vasudeva | |
| dc.contributor.examiningcommittee | Uzonna, Jude (Immunology) Ogilvie, Tamra (Biochemistry and Medical Genetics) Davie, James (Biochemistry and Medical Genetics) Egan, Sean (University of Toronto) | en_US |
| dc.contributor.supervisor | Raouf, Afshin (Immunology) | en_US |
| dc.date.accessioned | 2019-03-25T14:55:06Z | |
| dc.date.available | 2019-03-25T14:55:06Z | |
| dc.date.issued | 2019 | en_US |
| dc.date.submitted | 2019-03-22T21:03:17Z | en |
| dc.degree.discipline | Immunology | en_US |
| dc.degree.level | Doctor of Philosophy (Ph.D.) | en_US |
| dc.description.abstract | Human breast tissue is composed of a network of ducts and alveolar structures that are formed during puberty. During pregnancy, breast tissue expands and subsequently regresses back to its non-pregnant state during involution. This dynamic process of tissue expansion and regression indicates that the mammary gland has a unique regenerative capability that allows it to support multiple pregnancy cycles. This regenerative capacity is due to a small population of self-renewing breast epithelial stem cells (BESCs). BESCs differentiate into bipotential progenitors that give rise to lineage-restricted luminal and myoepithelial progenitors which in turn produce the mature and functionally distinct luminal and myoepithelial cells. Luminal and myoepithelial cells make up the functional cells of the mammary gland. Evolutionarily conserved signaling pathways have been shown to regulate the special functions of these breast stem and progenitor cells. Previous, research from our laboratory demonstrated that signaling through the NOTCH3 receptor (NR3) specifically commits bipotent progenitors to the luminal cell fate. The work presented in this thesis explores the underpinning mechanism by which NR3 regulates luminal cell fate. Through gain and loss of function studies, I found that Frizzled7 (FZD7), a Wnt receptor, is uniquely regulated by NR3 in non-malignant human breast epithelial cells, 184-hTerts. Also, we found that luminal progenitors showed higher expression of FZD7 as compared to bipotent progenitors. This suggests that FZD7 can play an important role in regulating luminal cell differentiation. I, therefore, hypothesized that the commitment of bipotent progenitors to the luminal cell fate is regulated by NR3-specific target genes. Using transcriptome profiling, I found that activation of NR3 signaling in breast epithelial cells is enriched for a Wnt signaling pathway gene signature compared to other Notch receptors. Interestingly, I found that the NR3-FZD7 signaling axis is important for bipotent progenitor commitment to luminal cell fate in ex vivo cultures. Next, I observed that a Wnt ligand, Wnt7A, enhances commitment of the bipotent progenitors to the luminal cell fate in a FZD7-dependent manner. Further characterization of breast epithelial cells revealed for the first time, the presence of a Notch and Wnt signaling-responsive (NR3+FZD7+CD90+) basal-like luminal progenitors (BLPs). This is in sharp contrast to the previously identified luminal-restricted progenitors that are non-responsive to Notch and Wnt. My data then suggest that two highly conserved cellular signaling networks, the Notch and Wnt signaling pathways, play essential roles in committing bipotent progenitors to luminal cell lineage. It is inviting to hypothesize that alterations to this signaling axis could lead to an uncontrolled expansion of the luminal progenitor pool, a possible antecedent event to the generation of luminal type tumors. These findings are likely to be important in understanding how alterations in NOTCH3-FZD7 signaling may lead to the development and/or progression of luminal type breast cancers. | en_US |
| dc.description.note | May 2019 | en_US |
| dc.identifier.citation | Stem Cells Dev. 2016 Apr 1;25(7):522-9. doi: 10.1089/scd.2015.0315 | en_US |
| dc.identifier.uri | http://hdl.handle.net/1993/33792 | |
| dc.language.iso | eng | en_US |
| dc.rights | open access | en_US |
| dc.subject | Breast development | en_US |
| dc.subject | BLPs | en_US |
| dc.subject | Luminal cell fate | en_US |
| dc.subject | Luminal cell differentiation | en_US |
| dc.title | Notch3-Frizzled7 signaling regulates luminal cell fate in human breast tissue | en_US |
| dc.type | doctoral thesis | en_US |