Regulation of estrogenic and nuclear factor κB functions by polyamines and their role in polyamine analog-induced apoptosis of breast cancer cells

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Abstract
The natural polyamines -putrescine, spermidine, and spermine- are essential for cell growth and differentiation. Polyamines are involved in several gene regulatory functions, although their mechanism(s) of action has not been elucidated. We investigated the role of polyamines in the function of NF-κB and estrogen receptor-α (ERα), two transcription factors implicated in breast cancer cell proliferation and cell survival, using MCF-7 breast cancer cells. We found that spermine facilitated the binding of ERα and NF-κB to estrogen response element (ERE)- and NF-κB response element (NRE), respectively, and enhanced ERα-mediated transcriptional activation in transient transfection experiments. We also found that the association of the co-regulatory protein CBP/p300 with ERα and NF-κB was increased by spermine treatment of MCF-7 cells. Spermine also increased the nuclear translocation of NF-κB compared to the control. In contrast, treatment of MCF-7 cells with polyamine analogs, BE-3-4-3 and BE-3-3-3, resulted in transcriptional inhibition of both ERE- and NRE-driven reporter plasmids. In addition, polyamine analogs inhibited the association of ERα and NF-κB with CBP/p300 and were unable to facilitate nuclear translocation of NF-κB. APO-BRDU assay demonstrated that polyamine analogs induced apoptosis, with a loss of the anti-apoptotic protein Bcl-2. These data show a gene regulatory function of polyamines involving transcriptional activation of ERα and NF-κB, potentially leading to the up-regulation of genes involved in breast cancer cell proliferation. Our results with BE-3-4-3 and BE-3-3-3 suggest that down-regulation of ERα- and NF-κB-regulated genes is a possible mechanism for the action of polyamine analogs in inducing apoptosis of breast cancer cells.