BMP-6 promotes E-cadherin expression through repressing δEFI in breast cancer cells

Background: Bone morphogenetic protein-6 (BMP-6) is critically involved in many developmental processes. Recent studies indicate that BMP-6 is closely related to tumor differentiation and metastasis. Methods: Quantitative RT-PCR was used to determine the expression of BMP-6, E-cadherin, and delta EFI at the mRNA level in MCF-7 and MDA-MB-231 breast cancer cells, as well as in 16 breast cancer specimens. Immunoblot analysis was used to measure the expression of delta EFI at the protein level in delta EF-overexpressing and delta EFI-interfered MDA-MB-231 cells. Luciferase assay was used to determine the rhBMP-6 or delta EFI driven transcriptional activity of the E-cadherin promoter in MDA-MB-231 cells. Quantitative CHIP assay was used to detect the direct association of delta EFI with the Ecadherin proximal promoter in MDA-MB-231 cells. Results: MCF-7 breast cancer cells, an ER+ cell line that expressed high levels of BMP-6 and E-cadherin exhibited very low levels of delta EFI transcript. In contrast, MDA-MB-231 cells, an ER-cell line had significantly reduced BMP-6 and Ecadherin mRNA levels, suggesting an inverse correlation between BMP-6/E-cadherin and delta EFI. To determine if the same relationship exists in human tumors, we examined tissue samples of breast cancer from human subjects. In 16 breast cancer specimens, the inverse correlation between BMP-6/E-cadherin and delta EFI was observed in both ER+ cases (4 of 8 cases) and ER-cases (7 of 8 cases). Further, we found that BMP-6 inhibited delta EFI transcription, resulting in an upregulation of E-cadherin mRNA expression. This is consistent with our analysis of the E-cadherin promoter demonstrating that BMP-6 was a potent transcriptional activator. Interestingly, ectopic expression of delta EFI was able to block BMP-6-induced transactivation of E-cadherin, whereas RNA interference-mediated down-regulation of endogenous delta EFI in breast cancer cells abolished E-cadherin transactivation by BMP-6. In addition to down-regulating the expression of delta EFI, BMP-6 also physically dislodged delta EFI from E-cadherin promoter to allow the activation of Ecadherin transcription. Conclusion: We conclude that repression of delta EFI plays a key role in mediating BMP-6-induced transcriptional activation of E-cadherin in breast cancer cells. Consistent with the fact that higher level of delta EFI expression is associated with more invasive phenotype of breast cancer cells, our collective data suggests that delta EFI is likely the switch through which BMP-6 restores E-cadherin-mediated cell-to-cell adhesion and prevents breast cancer metastasis.