Clinical association of progesterone receptor isoform A with breast cancer metastasis consistent with its unique mechanistic role in preclinical models.

BACKGROUND: Luminal breast cancer (L-BCa) comprises the majority of incurable, distally metastatic breast cancer cases. Estrogen supports growth of L-BCa cells but suppresses invasiveness. Estrogen also induces the progesterone receptor (PR). Invasiveness and metastasis of L-BCa cells is supported by the short PR isoform (PR-A), in response to the range of pre- and post-menopausal plasma hormone levels, by counteracting the effects of estrogen via micro RNA-mediated cross-talk with the estrogen receptor (ER). PR-B directly supports L-BCa invasion and metastasis and also inhibits tumor growth, both only at high progesterone levels. As public datasets on L-BCa tumors cannot distinguish PR-A, this study was designed to seek clinical evidence for the role of PR-A in metastasis in comparison with PR-B and ER. METHODS: Measurement of tumor PR-A, PR-B and ER mRNA expression in 125 treatment-naive primary L-BCa patients with differential node involvement and analysis using linear mixed effects models. Transcriptional activity assays of PR-A and PR-B. RESULTS: Lymph node involvement was strongly associated with PR-A expression (median, 3-fold higher vs. node-negative), independent of age, pathologic type, tumor grade, HER2 and PR-B. PR-B and ER correlated weakly with PR-A, but whereas PR-B and the PR-A/PR-B ratio were not significantly associated with node involvement, ER weakly negatively correlated with node positivity. PR-A was hypersensitive to mifepristone compared with PR-B. CONCLUSIONS: Taken together with previous mechanistic studies, the findings provide clinical evidence in support of the role of PR-A in L-BCa metastasis. They also suggest the possibility of developing selective PR-A modulators for future interventions in appropriate clinical situations.

Inhibition of CDK-mediated Smad3 phosphorylation reduces the Pin1-Smad3 interaction and aggressiveness of triple negative breast cancer cells.

Triple negative breast cancer (TNBC) is a highly aggressive breast cancer subtype that lacks effective targeted therapies. Although TNBC is not defined by specific therapeutic targets, a subset of patients have tumors that overexpress cyclins. High cyclin D/E expression catalyzes CDK4/2 activity. In turn, CDK4/2 can non-canonically phosphorylate Smad3, a key TGFß signaling intermediate, and this phosphorylation has been associated with the shift from tumor-suppressive to oncogenic TGFß pathway action in breast oncogenesis. Additionally, CDK-mediated Smad3 phosphorylation facilitates an interaction between Smad3 and Pin1, a cis-trans isomerase that is also overexpressed in aggressive breast cancers. Treatment with CYC065, a CDK2/9 inhibitor, decreased non-canonical Smad3 phosphorylation and inhibited the Pin1-Smad3 interaction. We hypothesized that the interaction of Pin1 and Smad3, facilitated by CDK-mediated Smad3 phosphorylation, promotes TNBC cell aggressiveness. Inhibition of the Pin1-Smad3 interaction in TNBC cell lines, through depletion of Pin1 or CYC065 treatment, resulted in decreased cell migration/invasion and impeded the EMT program. Inhibition of CDK-mediated phosphorylation of Smad3 by mutagenesis also decreased cell migration, underscoring the importance of non-canonical CDK2 phosphorylation of Smad3 to enable cell motility. Pin1 depletion restored Smad3 protein levels and tumor-suppressive activity, suggesting that the Pin1-Smad3 interaction has a negative impact on canonical Smad3 action. Collectively, the data show that the Pin1-Smad3 interaction, facilitated by CDK-mediated Smad3 phosphorylation, is associated with oncogenic TGFß signaling and breast cancer progression. Inhibition of this interaction with CYC065 treatment may provide an important therapeutic option for TNBC patients.