Placental supernatants' enhancement of the metastatic potential of breast cancer cells: is estrogen receptor (ERα) essential for this phenomenon?

PURPOSE: Pregnancy-associated breast cancer (PABC) is usually diagnosed at an advanced stage in comparison to non-pregnant women. The placenta secretes hormones and cytokines, which affect breast cancer progression. Previously, we demonstrated that human placental secretome facilitates the survival and migration of ERα+ breast cancer cells (BCCL), but pregnant women have a relatively high frequency of ERα-negative tumors. In the current study, we analyzed the effect of placental secretome on ERα-negative BCCL. METHODS: BCCL [MCF-7(estrogen/progesterone receptor positive (ERα+/PR+), ERα reduced MCF-7 (siRNA, MCF-7 ERα-), HS-578 and BT-549 cells (both ER-/PR-)] were exposed to supernatants (collected from first trimester human placental explants and from control BCCL) or to E2 + P4 (estrogen + progesterone) in placental supernatant concentrations and then tested for cell proliferation (number, cell cycle, PCNA), cell-death, cell migration, STAT3 pathway activation and functionality. RESULTS: Silencing ERα in the MCF-7 cells negated the placental supernatant and E2 + P4 enhancement of cell migration (> 130%, p < 0.05), number (> 120%) and survival (~ 130%). However, it had no such effect on MCF-7-ER- migration, which was still elevated in the presence of placental secretome. ER-/PR- BCCL were unaffected by the hormones, but placental secretome significantly elevated their migration (115%), number (140-170%), STAT3 phosphorylation (~ 180%) and BT-549 STAT3 level. These effects were negated by the STAT3 inhibitor. CONCLUSIONS: Placental supernatant facilitates BCCL malignant characteristics by activating ERα in estrogen responsive cells and STAT3 in ERα- BCCL. This indicates a possible mechanism that may underlie PABC's advanced state and suggests STAT3 pathway as a therapeutic target for PABC.

Placenta-conditioned extracellular matrix (ECM) activates breast cancer cell survival mechanisms: A key for future distant metastases.

The extracellular matrix (ECM) affects cancer cell characteristics. Inability of normal epithelial cells to attach to the ECM induces apoptosis (anoikis). Cancer cells are often anoikis resistant, a prerequisite for their metastatic spread. Previously we demonstrated that the placenta manipulates its surrounding ECM in a way that prevents breast cancer cells (BCCL) attachment and induces their motility and aggregation. This fits with the fact that although breast cancer during pregnancy is often advanced, metastasis to the placenta is rarely observed. Placental intervillous space provides suitable conditions for cancer cell arrival. Yet, the outcome of the short communication between the placental ECM to the BCCL and its effect on BCCL malignant potential are unknown, and are the focus of our study. In the current study we analyzed the effect of placental ECM on BCCL survival pathways and drug resistance. Microarray analysis suggested activation of the NF-κB and stress response pathways. Indeed, the placenta-conditioned ECM induced autophagy in ERα + BCCL, inactivated the NF-κB inhibitor (IκB) and increased integrin α5 in the BCCL. The autophagy mediated MCF-7 and T47D migration and the placental ECM-BCCL interactions reduced the BCCL sensitivity to Taxol. We also demonstrated by using siRNA that integrin α5 was responsible for the MCF-7 autophagy and suggest this molecule as a suitable target for therapy.

Heat shock protein-27 (HSP27) regulates STAT3 and eIF4G levels in first trimester human placenta.

During placental implantation, cytotrophoblast cells differentiate to extravillous trophoblast (EVT) cells that invade from the placenta into the maternal uterine blood vessels. The heat shock protein-27 (HSP27), the signal transducer and activator of transcription-3 (STAT3) and the eukaryotic translation initiation factor 4E (EIF4E) are involved in regulating EVT cell differentiation/migration. EIF4E and EIF4G compose the translation initiation complex, which is a major control point in protein translation. The molecular chaperone distinctiveness of HSP27 implies that it directly interferes with many target proteins. STAT3, EIF4E, and EIF4G were found to be HSP27 client proteins in tumor cells. We aimed to analyze if HSP27 regulate STAT3 and EIF4G levels in first trimester human placenta. We found that like STAT3, EIF4G is highly expressed in the EVT cells (immunohistochemistry). Silencing HSP27 in HTR-8/SVneo cells (siRNA, EVT cell line) and in placental explants reduced STAT3 level (47 and 33 %, respectively, p < 0.05). HSP27 silencing reduced the levels of STAT3 phosphorylation (33 % reduction, p < 0.05) and targets (IRF1, MUC1, MMP2/9 and EIF4E, 30-49 % reduction, p < 0.05) in the HTR-8/SVneo cells. Moreover, HSP27 silencing significantly reduced EIF4G level and elevated the level of its fragments in HTR-8/SVneo cells and in the placental explants (p < 0.05). In conclusion, Placental implantation and development are accompanied by trophoblast cell proliferation and differentiation, which necessitates intense protein translation and STAT3 activation. HSP27 was found to be regulator of translation initiation and STAT3 level. Therefore, it suggests that HSP27 is a key protein during placental development and trophoblast cell differentiation.