Introduction: The importance of epigenetic in the onset and progression of breast cancer has led many researchers to incorporate this new and exciting theme in the development of anti-cancer drugs. Breast cancer is the most common cancer among women. Human chorionic gonadotropin (hCG) has been correlated to antitumoral actions in the breast epithelium. It has anti-proliferative, pro-apoptotic and differentiative effects on this tissue. In contrast, estradiol (E2) is correlated to tumor development and progression. This steroid hormone increases cell proliferation, invasion and metastasis, as well as it inhibits anti-apoptotic and dedifferentiation processes.
Objective: To obtain an expression profile of chromatin remodeling-related genes, such as histone deacetylase, histone acetylases and nuclear receptors in the breast tumor cell line (SK-BR3) after treatment with the glycoprotein hormone, hCG, and the steroid hormone, E2.
Experimental Procedures: Her-2 overexpressing breast tumor cells SK-BR3 were divided into three groups: control (no treatment), hCG and E2. Cells were treated for 11 days. After each treatment, these cells had their mRNA extracted, purified, analyzed and then used to quantify the expression of chromatin remodeling-related genes — histone acetylases (KAT5, NCOA1, NCOA3 and KAT2B), histone deacetylases (HDACs 1 to 7) and other chromatin modifiers (ESR1, HMGA1, NCOA6 and PPARGC1B) by quantitative PCR (qPCR).
Results: hCG and E2 treatments downregulated histone deacetylases 5 and 6 (HDAC5, and HDAC6) and nuclear receptor coactivator 3 (NCOA3) when compared to control. However hCG caused a more potent inhibitory effect than E2 on HDCA5, HDAC6 and NCOA3 expressions, hCG (-5.3, -3.3 and -3.3 fold respectively, p <0.0001) and E2 (-1.9 - 1.2, and -2.4 fold respectively, p <0.001). Furthermore, both treatments slightly upregulated KAT2B expression, hCG by 2.0 fold (p <0.01) and E2 by 1.3 fold (p <0.001).
Conclusions: Our results show that hCG has a more potent effect on the expression control of chromatin remodeling-related-genes of the highly undifferentiated and estrogen receptor-negative cell line, SK-BR3 than E2 has. Both hormones hCG and E2, inhibited NCOA3 (AIB1) expression, suggesting that this nuclear factor, overexpressed in breast tumors, interacts with steroid and nonsteroid intracellular activated pathways. Treatments also downregulated two out of seven deacetylase-related genes (HDACs 5 and 6). None was upregulated. and hCG upregulated one out of three assessed acetylase-related genes (KAT2A). hCG inhibits deacetylation and stimulates acetylation of histone tails in SK-BR3, therefore positively regulating gene transcription. It is known that HDACs have an important role in mammary tumor cell growth control. Its differential expression, mainly induced by hCG, might contribute to breast cancer malignancy attenuation induced by the hormone. (De) Acetylation mechanisms of specific histone tail-amino acid residues, as well as cytoskeletal microtubule assembling control exerted by HDAC6 that alters cell motility might also contribute.
Financial support: FAPESP
Citation Format: Isidoro Binda-Neto, Silvana Aparecida Alves Correa-Noronha, Jorge Kede, Maria del Carmen GM Wolgien, Ismael DCG Silva, Samuel Marcos Ribeiro de Noronha. Epigenetic mechanisms of human chorionic gonadotropin (hCG) intracellular pathways activation in mammary tumor cells SKBR3. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr A53.