Abstract 4276: PGE2 induces LEF-1 expression in breast cancer cells, but is not required for the nuclear localization of beta-catenin

We have previously demonstrated that poorly differentiated MDA-MB-231 cells displayed delayed tumor onset, reduced frequency of occurrence and loss of their capacity for extrapulmonary colonization when transfected stably with a potent and specific cyclooxygenase (COX) −2 shRNA sequence. We attributed the reduction in tumor growth and extrapulmonary colonization to reduced invasive capabilities, reduced angiogenesis, altered metabolism and differences in the stabilization of hypoxia-inducible factor-1α. We also observed loss of expression of oncogenes, receptors and degradative enzymes associated with tumor growth and metastasis including matrix metalloproteinase-1, CXC Receptor-4, roundabout-1, hyaluronan synthase-2, and monocarboxylate transporter 2. In addition to these previously reported transcriptome changes, we observed that the most highly downregulated transcription factor was Lymphoid-Enhancer Factor-1 (LEF-1) a result validated by qPCR showing an 8-fold loss of LEF-1 in COX-2-silenced cells. Here, we present evidence demonstrating that LEF-1 accumulation in the nucleus of COX-2-silenced cells is reduced compared to COX-2 containing parental cells. Induction of COX-2 by phorbol esters resulted in nuclear accumulation of LEF-1 in COX-2 containing, but not in COX-2-silenced, cells. Addition of physiological concentrations of PGE2 to COX-2-silenced cells partially restored LEF-1 expression in the nucleus of these cells. LEF-1 is a member of the T-cell specific factor (TCF) family of transcription factors that direct transcription of downstream target genes upon nuclear translocation of β-catenin from the cytoplasm. β-catenin translocation to the nucleus occurs in response to canonical signaling of the ligand Wnt to its receptor Frizzled. An earlier study showed that the COX-2 product prostaglandin E2 promoted the translocation of β-catenin to the nucleus of colon cancer cells via G-protein coupled receptor signaling. As expected, immunofluorescence of COX-2 containing MDA-MB-231 breast cancer cells showed nuclear expression of β-catenin. However, the nuclear localization of β-catenin persisted even in the absence of PGE2, as observed in COX-2-silenced cells, suggesting that PGE2 expression is not necessary for the nuclear localization of β-catenin in MDA-MB-231 cells. Taken together, our results demonstrate that while PGE2 is not necessary for the nuclear localization of β-catenin in MDA-MB-231 cells, it can promote the nuclear accumulation of the TCF family member LEF-1, thereby further promoting the non-canonical activation of the Wnt pathway in 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 4276. doi:1538-7445.AM2012-4276