Progesterone receptor isoforms, agonists and antagonists differentially reprogram estrogen signaling.

Area of Science:

• Endocrinology
• Genomics
• Breast Cancer Research

Background:

• Effective progesterone receptor (PR)-targeted therapies for breast cancer are hindered by a lack of specific modulators and understanding of PR isoform and ligand networks.
• Cross-talk between PR and estrogen receptor (ER) signaling pathways remains incompletely understood, complicating treatment strategies.

Purpose of the Study:

• To investigate how PR activation or inhibition reprograms ER signaling and to clarify the distinct roles of PR isoforms (PRA and PRB) in breast cancer.
• To address the controversy surrounding the clinical utility of PR agonists and antagonists, alone or with tamoxifen.

Main Methods:

• Genomic analyses of xenografts treated with clinically relevant ER and PR-targeting drugs.
• Differential gene expression analysis in patient tumors based on PRA and PRB richness.
• Correlation of gene signatures with survival outcomes and therapeutic responses.

Main Results:

• PR activation/inhibition differentially reprograms ER signaling, segregating transcriptomes into PR agonist and antagonist groups.
• PR isoform PRA significantly inhibited gene expression and ER chromatin binding more than PRB.
• PRA-rich tumors showed poorer survival, but gene signatures associated with PR antagonists predicted better outcomes, supporting antiprogestin responsiveness.

Conclusions:

• Distinguishing isoform- and ligand-specific effects from general receptor-ligand interactions is crucial for developing PR-targeted therapies.
• PR antagonists, particularly in combination with tamoxifen, show promise for improving patient survival in breast cancer.
• Findings will inform the development of biomarkers for patient selection and the clinical translation of PR-targeted breast cancer therapies.