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

Area of Science:

• Endocrinology
• Stem Cell Biology
• Oncology

Background:

• Progesterone receptors (PR) exist as isoforms, PRA and PRB, with distinct functions.
• PR isoforms play critical roles in mammary gland development and homeostasis.
• Dysregulation of PR isoforms is implicated in breast cancer development and progression.

Purpose of the Study:

• To investigate the differential roles of PR isoforms (PRA and PRB) in maintaining normal and neoplastic mammary stem cell populations.
• To understand the impact of PR isoform balance on breast progenitor/stem cell behavior and response to hormonal therapies.

Main Methods:

• Utilized PRA and PRB transgenic mice and T47D human breast cancer cell lines engineered to express specific PR isoforms (T47D YA for PRA, T47D YB for PRB).
• Employed flow cytometry and mammosphere assays to quantify progenitor/stem cell populations and their sphere-forming capacity.
• Administered ovariectomy and ICI 182,780 (an antiestrogen) treatments to assess the influence of hormonal manipulation on stem cell properties.

Main Results:

• PRB overexpression in murine breast tissue led to an expansion of both luminal and basal progenitor/stem cell compartments.
• Ovariectomy negatively affected the luminal compartment and increased mammosphere formation in WT and PRA mice, but not PRB mice.
• ICI 182,780 treatment enhanced mammosphere formation in WT and PRA cells, while PRB cells showed no change.
• T47D YB (PRB-expressing) cells exhibited increased CD44+/CD24Low/- subpopulations and enhanced clonogenic capacity, but tumor sphere number remained unchanged.
• T47D and T47D YA tumor spheres were responsive to estrogen/antiestrogens, whereas T47D YB spheres were not.

Conclusions:

• Altered PR isoform balance significantly impacts both normal and tumorigenic breast progenitor/stem cells.
• The PRB isoform plays a crucial role in mammary stem cell regulation and influences the response to antiestrogen therapies.
• Targeting PR isoform balance may offer novel therapeutic strategies for breast cancer treatment, particularly in overcoming resistance to antiestrogens.