Alterations in Progesterone Receptor Isoform Balance in Normal and Neoplastic Breast Cells Modulates the Stem Cell Population

Abstract

To investigate the role of PR isoforms on the homeostasis of stem cells in the normal and neoplastic mammary gland, we used PRA and PRB transgenic mice and the T47D human breast cancer cell line and its derivatives, T47D YA and YB (manipulated to express only PRA or PRB, respectively). Flow cytometry and mammosphere assays revealed that in murine breast, overexpression of PRB leads to an increase in luminal and basal progenitor/stem cells. Ovariectomy had a negative impact on the luminal compartment and induced an increase in mammosphere-forming capacity in cells derived from WT and PRA mice only. Treatment with ICI 182,780 augmented the mammosphere-forming capacity of cells isolated from WT and PRA mice, whilst those from PRB remained unaltered. T47D YB cells showed an increase in the CD44+/CD24Low/− subpopulation; however, the number of tumorspheres did not vary relative to T47D and YA, even though they were larger, more irregular, and had increased clonogenic capacity. T47D and YA tumorspheres were modulated by estrogen/antiestrogens, whereas YB spheres remained unchanged in size and number. Our results show that alterations in PR isoform balance have an impact on normal and tumorigenic breast progenitor/stem cells and suggest a key role for the B isoform, with implications in response to antiestrogens.

Progesterone receptors in normal breast development and breast cancer

“…Interestingly, ovariectomy or antiestrogen treatment did not diminish the luminal compartment. Moreover, antiestrogen treatment increased the sphere forming capacity of cells [84]. These studies are aligned with previous reports which demonstrate that (a) Pg increases the number of progenitor cells [85], (b) ovariectomy does not affect the basal compartment [68] and (c) when Pg levels are high, such as in pregnancy [68] or in diestrous [69], there is an increase in cells with a stem cell phenotype.…”

“…MG from transgenic mice overexpressing PRA showed an increase in branching, ductal hyperplasia, and a disorganized basal cell membrane with loss of cell-cell adhesion [81,82]. Contrarily, PRB-overexpressing mice have reduced branching [83] and an increase in basal stem and luminal progenitor cells [84]. Interestingly, ovariectomy or antiestrogen treatment did not diminish the luminal compartment.…”

“…T47D-YB xenografts express CK5+ clusters, whereas T47D-YA tumors were CK5-(Figure 3). In vitro, both PR isoforms have been implicated in stemness and, depending on the experimental conditions, it was PRB or PRA the prevailing isoform involved [84,153,154]. The data shown in Figure 3 and the fact that CK6, another cytokeratin related to stemness, are differentially expressed in PRB-H as compared with PRA-H breast carcinomas [155], are in line with the hypothesis that PRB-expressing cells in the absence of exogenous PR ligands may have more stem-like characteristics in vivo.…”

The Role of Progesterone Receptors in Breast Cancer

“…28 PR isoform predominance, generally PRA over its counterpart in a high proportion of ductal carcinomas in situ and invasive breast lesions. 20,[28][29][30][31] Meanwhile, the ratio of PR-A/PR-B can affect the ability of progesterone to impact gene expression in reproductive tissue and the outcome of breast cancer treatment. 30,[32][33][34] A serious difference on the viewpoint of PR-A/PR-B in breast cancer prognosis.…”

Hormone Metabolites and Herbal Bioactive Agents: Potential Drug Candidates for the Luminal A Breast Cancer subtype

“…In cellular models for the Luminal A breast cancer subtypes positive growth regulation by E2 and negative growth regulation by PRG is documented 16 . In tissue explants from estrogen receptor (ER) positive tumors treatment with E2 increases, while that with PRG decreases cell proliferation [17][18][19] . Since E2 and PRG metabolites exhibit divergent growth modulatory effects, molecular/metabolic pathways responsible for E2 and PRG signaling may provide potential mechanistic leads.…”