Abstract 4142: Differential expression of PDCD4 in response to Resveratrol in breast cancer cells

Abstract

Abstract Background: Programmed cell death 4 (PDCD4) is a key protein involved in protein synthesis, and thus, it controls cell growth and proliferation. Evidence indicates that PDCD4 is often downregulated in breast cancer and is associated with disease progression and metastasis. Resveratrol (RSV), a natural polyphenolic compound present in grapes and red wine, is a well known anti-oxidant capable of modulating various signaling pathways, leading to suppression of cell proliferation and increased apoptosis. However, it remains unclear regarding the effect of RSV on PDCD4. Therefore, in the present study, we investigated the effect of RSV on PDCD4 in human breast cancer MCF-7 and MDA-MB-231 cells. Methods: Cell growth was measured by MTT assays, and cell invasion was determined by matrigel chamber assays. Soft agar assays were used to determine anchorage independent growth. Protein levels from treated cells were analyzed by western blot. Real time RT-PCR was used to determine relative expression of genes. Phosphorylated Akt (pAkt) was also determined by immunohistochemistry in RSV-treated MDA-MB-231 cells. To determine whether microRNAs are involved in the RSV-mediated induction of PDCD4, we cloned PDCD4 3′-UTR into the downstream of the luciferase gene as a reporter. The effect of RSV on luciferase activity was tested in MCF-7 cells. PDCD4 was stably knocked down by RNAi in MCF-7 and MDA-MB-231 cells. Results: We showed that ectopic expression of PDCD4 suppressed anchorage independent tumor cell growth as well as invasion of MDA-MB-231 cells. By contrast, downregulation of PDCD4 by RNAi significantly increased cell invasion. Of interest, cell invasion was suppressed by RSV; at the same time, PDCD4 was induced significantly by RSV in MDA-MB-231 cells, which was associated with suppression of pAkt. Furthermore, we showed that both phosphorylated mTOR and S6K were suppressed by RSV in a dose dependent manner. Since PDCD4 is a downstream effector of Akt and mTOR, this may suggest that up-regulation by RSV is through the Akt-mTOR pathway in MDA-MB-231. On the other hand, PDCD4 was reduced by RSV in estrogen receptor-positive (ERα+) MCF-7 cells. To determine the mechanism of RSV-mediated PDCD4 expression in these two cell lines, we measured the levels of miR-21 which has been previously shown to directly target PDCD4. Strikingly, expression of miR-21 was also regulated differentially. For example, miR-21 was up-regulated in MCF-7 cells while it was slightly suppressed by RSV in MDA-MB-231 cells. In particular, we found that RSV suppressed PDCD4 by transcriptional regulation of miR-21 possibly through interacting with ERα in MCF-7 cells. Conclusion: Together, these results suggest that, as a tumor suppressor gene, PDCD4 expression is dependent on cellular contents in response to RSV, and thus, a better understanding of this RSV-mediated PDCD4 expression will provide new insight into the clinical implication of RSV for breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4142. doi:1538-7445.AM2012-4142