Progesterone/RANKL Is a Major Regulatory Axis in the Human Breast

Abstract

Estrogens and progesterones are major drivers of breast development but also promote carcinogenesis in this organ. Yet, their respective roles and the mechanisms underlying their action in the human breast are unclear. Receptor activator of nuclear factor kB ligand (RANKL) has been identified as a pivotal paracrine mediator of progesterone function in mouse mammary gland development and mammary carcinogenesis. Whether the factor has the same role in humans is of clinical interest because an inhibitor for RANKL, denosumab, is already used for the treatment of bone disease and might benefit breast cancer patients. We show that progesterone receptor (PR) signaling failed to induce RANKL in PR + breast cancer cell lines and in dissociated, cultured breast epithelial cells. In clinical specimens from healthy donors and intact breast tissue microstructures, hormone response was maintained and RANKL expression was under progesterone control, which increased RNA stability. RANKL was sufficient to trigger cell proliferation and was required for progesterone-induced proliferation. The findings were validated in vivo where RANKL protein expression in the breast epithelium correlated with serum progesterone levels and the protein was expressed in a subset of luminal cells that express PR. Thus, important hormonal control mechanisms are conserved across species, making RANKL a potential target in breast cancer treatment and prevention.

Progesterone signalling in breast cancer: a neglected hormone coming into the limelight

“…Moreover, RANKL is sufficient to elicit cell proliferation and is required for progesterone-induced proliferation. The findings in the ex vivo system were validated by the in vivo observation that RANKL protein expression correlated with serum progesterone levels in women 47 .…”

“…Using freshly isolated human breast tissue microstructures we have found that expression of both RANKL and WNT4 mRNA is induced by PR signalling 47 . Moreover, RANKL is sufficient to elicit cell proliferation and is required for progesterone-induced proliferation.…”

“…However, the experimental approaches also differed substantially in that most human work was carried out using cultured cells, whereas the work in mice was generally carried out in the whole organism. We have recently developed an ex vivo approach using reduction mammoplasty specimens and shown that in fresh breast tissue microstructures progesterone elicits cell proliferation whereas 17β-oestradiol does so only in a subset of the breast tissue samples 47 . Moreover, important downstream mediators of PR signalling that were identified in the mouse mammary gland but that were not induced in human three-dimensional cultures were also induced in the tissue microstructures that maintain cellular interactions.…”

Progesterone Stimulates Proliferation and Promotes Cytoplasmic Localization of the Cell Cycle Inhibitor p27 in Steroid Receptor Positive Breast Cancers

“…For example, the P-dependent paracrine factor Wnt-4 has been reported to be important for proliferation in the normal mouse mammary gland [34]. Another P-regulated paracrine factor, receptor activator of nuclear factor kappa B ligand (RANKL), has been demonstrated to increase proliferation and mammary cancer development in the mouse and mediates P-induced proliferation in the normal human breast tissue [35][36][37]. However, whether or not Wnt-4 and RANKL contribute to breast cancer development or proliferation of breast cancer cells in vivo remains unclear.…”

Prevention of breast cancer by RANKL/RANK blockade

“…Of note, the ability of BRCA1 mutations to drive mammary transformation has previously been shown to rely on proficient progesterone signaling [8], which is known to drive RANKL expression in the mammary epithelium [7,9]. It will therefore be interesting to fully characterize the molecular mechanisms through which the progesterone system and RANKL/RANK cooperate to support carcinogenesis driven by BRCA1 or BRCA2 mutations.…”