Progestin Effects on Breast Cancer Cell Proliferation, Proteases Activation, andin VivoDevelopment of Metastatic Phenotype All Depend on Progesterone Receptor Capacity to Activate Cytoplasmic Signaling Pathways

Abstract

Accumulating evidence indicates that progestins are involved in controlling mammary gland tumorigenesis. Here, we assessed the molecular mechanisms of progestin action in breast cancer models with different phenotypes. We examined C4HD cells, an estrogen (ER) and progesterone (PR) receptor-positive murine breast cancer model in which progestins exert sustained proliferative response, the LM3 murine metastatic mammary tumor cell line, which lacks PR and ER expression, and human PR null T47D-Y breast cancer cells. In addition to acting as a transcription factor, PR can also function as an activator of signaling pathways. To explore which of these two functions were involved in progestin responses, reconstitution experiments in the PR-negative models were performed with wild-type PR-B, with a DNA binding mutant C587A-PR, and with mutant PR-BmPro, which lacks the ability to activate cytoplasm signaling pathways. We found that in a cell context either ER-positive or -negative, progestins induced cell growth and modulation of matrix metalloproteinases-9 (MMP-9) and -2 (MMP-2), and urokinase-type plasminogen activator (uPA) activities, via MAPK and phosphatidylinositol 3-kinase/Akt pathways, in cells expressing wild-type PR-B or DNA binding mutant C587A-PR. In contrast, in cells expressing mutant PR-BmPro, progestins did not induce growth. We also found that unliganded PR expression conferred breast cancer cells an in vitro less proliferative phenotype, as compared with cells lacking PR expression. Modulation of this behavior occurred when PR was functioning either as transcription factor or as signaling activator. Finally, we for the first time demonstrated that progestins favor development of breast tumor metastasis via PR function as activator of signaling pathways. Our present findings provide mechanistic support to the design of a novel therapeutic intervention in PR-positive breast tumors involving blockage of PR capacity to activate cytoplasmic signaling.

Emerging functional roles of nuclear receptors in breast cancer

“…However, these effects are ligand, PGR isoform and context dependent. In general, progestins acting through nuclear PGR inhibit cell migration and invasiveness (Lin et al 2000, 2001, McGowan et al 2004, Carnevale et al 2007. In cells transfected with PGR, progestin treatment increases actin stress fibers and focal contacts, consistent with increased adhesion and decreased migration (Lin et al 2000(Lin et al , 2001.…”

“…Using a DNA-binding mutant PGR, Carnevale and coworkers (Carnevale et al 2007) reported that PGR activated cytoplasmic signaling cascades that contributed to breast cancer metastasis. Progestin activation of MAPK, PI3K/Akt and GTPase/RhoA modulated the expression of genes such as urokinase plasminogen activator (uPA), uPA receptor (uPAR), matrix metalloproteases (MMPs), β1-integrin and PAI-1 (Carnevale et al 2007, Bellance et al 2013 suggesting a mechanism through which migration is increased by progestins.…”

“…Using a DNA-binding mutant PGR, Carnevale and coworkers (Carnevale et al 2007) reported that PGR activated cytoplasmic signaling cascades that contributed to breast cancer metastasis. Progestin activation of MAPK, PI3K/Akt and GTPase/RhoA modulated the expression of genes such as urokinase plasminogen activator (uPA), uPA receptor (uPAR), matrix metalloproteases (MMPs), β1-integrin and PAI-1 (Carnevale et al 2007, Bellance et al 2013 suggesting a mechanism through which migration is increased by progestins. In addition, progesterone/ progestins also enhance the phosphorylation of focal adhesion kinase (FAK) (Graham et al 2005, Bellance et al 2013, and this is enhanced with PGRA predominance (Graham et al 2005), promoting the formation and turnover of focal adhesion points and cytoskeletal reorganization involved in cellular motility and influencing breast cancer progression and metastasis (Luo & Guan 2010).…”

“…In addition, progesterone/ progestins also enhance the phosphorylation of focal adhesion kinase (FAK) (Graham et al 2005, Bellance et al 2013, and this is enhanced with PGRA predominance (Graham et al 2005), promoting the formation and turnover of focal adhesion points and cytoskeletal reorganization involved in cellular motility and influencing breast cancer progression and metastasis (Luo & Guan 2010). PGR has also been reported to exert ligandindependent effects on breast cancer cell morphology and migration (Jacobsen et al 2005, Carnevale et al 2007, Bellance et al 2013. Un-liganded PGRA was shown to differentially regulate genes involved in cell adhesion and increase adhesiveness and migration in inducible cells expressing just one isoform (Jacobsen et al 2005).…”

Comparative Effect of Maitake Pro4x with Chemotherapy Breast Cancer Treatment

“…These murine cells lacked progesterone receptor (PR) and estrogen receptor (ER) expression [29]. The LM3 cells were kindly provided by Dr. Elisa Bal from Roffo Hospital, Buenos AiresArgentina.…”