Abstract 2887: Regulation of PAR-4 and PHLDA1 expression by estrogen and epidermal growth factor in MCF-7 breast cancer cells
Authors: de Bessa-Garcia Simone A. , Pereira Michelly C. , Nagai Maria A. 
Published: June 2012

Abstract
Crosstalk between the estrogens and growth factor signaling pathways has been associated with proliferation and survival of breast cancer cells and resistance to endocrine therapies. Although the role of estrogen and growth factors signaling for breast cancer proliferation has been extensively studied the identification of genes that are modulated by these factors to promote cell survival would likely provide us new targets for breast cancer treatment. The present study, aimed to determine the possible crosstalk between estrogen and epidermal growth factor (EGF) signaling pathways on the expression regulation of two proapototic genes, PAR-4 and PHLDA1. To accomplish that, MCF-7 cells growing in stripped serum for 48 hours were treated with E2 (10nM) and EGF (50 nM) alone or in the presence of ICI 182,780 (ICI, 1μM) for 2, 6 and 24 h. mRNA and protein expression were evaluated by Real Time PCR and Western blot, respectively. E2 (10nM) or EGF (30 nM) down-regulated PAR-4 expression after 24 hours of treatment. The expression of PHLDA1 increased 2,25-fold after E2 treatment for 6h and 2,8-fold after EGF treatment for 2h. MCF-7 cells exposed to E2 after the pre-treatment with ICI showed PAR-4 and PHLDA1 expression similar to that observed after the ICI treatments alone, indicating that the effect of E2 was via estrogen receptor activation. Pretreatment with ICI do not modified the effect of EGF on PHLDA1 expression. In constrast, in MCF-7 cells pre-treated with ICI the inhibitory effect of EGF on PAR-4 expression was reduced and did not reach the levels displayed by the cells treated with EGF alone. The effects of EGF on PAR-4 and PHLDA1 expression was inhibited by pretreatment of the cells with LY294002 (5μM) for 1 hour before treatment, suggesting that the activation of PI-3K/AKT is involved in PAR-4 and PHLDA1 regulation by EGF. Treatment of the MCF-7 cells with 5μM of the p38MAPK inhibitor (SB202190) or pERK1/2 inhibitor (PD98059) affects PHLDA1 transcriptional regulation by EGF. Both E2 and EGF increased ER phosphorylation on the critical residue serine 118. EGF promoted PAR-4 and PHLDA1 transcriptional modulation through the activation of different cell signaling pathways. In addition, there is a crosstalk between E2 and EGF signaling pathways on the PAR-4 transcriptional regulation while the effects of EGF on PHLDA1 expression is ER-independent and mediated by ERK1/2 and p38 MAPK pathways. Our results show for the first time that estrogens and growth factors inhibit PAR-4 and increase PHLDA1 expression in MCF-7 breast cancer cells. Expression modulation of these genes might provide a selective advantage for breast cencer cell survival.
Supprted by: FAPESP and CNPq.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2887. doi:10.1158/1538-7445.AM2011-2887