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| Author(s): |
Juliana Xavier de Miranda
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2012-11-05 |
| Examining board members: |
Thomas Prates Ong;
Sérgio Verjovski de Almeida;
Silvia Maria Franciscato Cozzolino
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| Advisor: | Thomas Prates Ong |
| Abstract | |
Breast cancer is a global public health problem and the most frequent cause of cancer death among women. The identification of agents able to modulate epigenetic marks, such as global DNA methylation and histone post-translational modifications, comprises promising alternative for establishing control strategies on mammary carcinogenesis. Among the nutrients, the essential trace element selenium (Se) can be highlighted as a dietary agent with potential anti-breast cancer and could act by modulating epigenetic processes. However its mechanisms of action are poorly understood. This study aimed, therefore, to identify the effects of selenium treatment on growth and epigenetic marks of MCF-7 human breast adenocarcinoma cells. MCF-7 cells, positive for estrogen receptor, were treated with methylseleninic acid (MSA) or sodium selenite (ST) for different times and in different concentrations. Evaluated parameters included: cell proliferation (crystal violet assay) and cell viability (trypan blue exclusion assay); plasma membrane integrity (flow cytometry); levels of DNA fragmentation (flow cytometry), apoptosis (flow cytometry - double labeling with Annexin V - propidium iodide); distribution of cell cycle phases (flow cytometry); acetylated (H3K9ac) and trimethylated (H3K9me3) lysine 9 levels on histone H3; acetylated (H4K16ac) lysine 16 level on histone H4 (Western blot); global DNA methylation (HPLC-DAD); tumor suppressor gene expression (RASSF1a; qPCR) and promoter methylation (RASSF1a, RARβ; MS-PCR); DNA methyltransferase 1 (DNMT1) expression (Western blot). Compared to untreated cells (controls), both MSA and ST inhibited (p< 0.05) MCF-7 cell proliferation and viability in a dose- and time-dependent manner. Treatments with MSA favored cell death by apoptosis, that was associated with increased (p< 0.05) DNA fragmentation level, reduced plasma membrane rupture associated with high (p< 0.05) phosphatidylserine exposure. On the other hand, ST increased (p< 0.05) DNA fragmentation, enhanced (p< 0.05) propidium iodide positivity associated to necrosis induction (p< 0,05). Both chemical forms of Se induced nduced cell cycle arrest, increasing (p< 0.05) the proportion of cells in G2/M phase and reducing (p< 0.05) the proportion of those in G0/G1 and S phases. Among the epigenetic mechanisms investigated, 1.6µM and 2µM of MSA reduced acetylation of H3K9ac (72h, p< 0.05) and increased the H4K16ac (96h, p< 0.05). The treatment for 96h with 2µM of MSA reduced (p< 0.05) the H3K9me3 methylation. Neither MSA nor ST altered (p> 0.05) global DNA methylation, while both compounds reduced (p< 0.05) DNMT1 protein expression, after 96h with 2µM of MSA (p< 0.001; 88%) and after 120h with 10µm of ST (p< 0.001; 94%). ST, but not MSA, increased (p< 0.05; 45%) RASSF1a gene expression. In control and Se-treated cells promoter regions of RASSF1a and RARβ were predominantly methylated. These results provide evidence that the anti-breast cancer actions of selenium compounds depend on its chemical form. Additionally, modulation of epigenetic processes seems to represent a relevant feature of MSA inhibitory effects in breast cancer cells. (AU) | |
| FAPESP's process: | 10/03994-9 - Selenium epigenetic targets in breast cancer. |
| Grantee: | Juliana Xavier de Miranda |
| Support Opportunities: | Scholarships in Brazil - Master |