RESUMO
Sex Hormone-Binding Globulin, the specific carrier for sex steroids, regulates hormone bioavailable fraction and estrogen signaling system in breast cancer cells. A common single nucleotide polymorphism in the human SHBG gene results in an amino acid substitution (Asp327Asn), which introduces an additional N-glycosylation site, and is associated with reduced breast cancer risk in postmenopausal women. The frequency of this polymorphism was evaluated in a group of patients that developed breast cancer while taking hormonal replacement therapy (HRT) for menopause, an interesting model of estrogen exposure. The polymorphism frequency was significantly higher in women taking HRT that didn't develop any breast cancer than in breast cancer patients (P<0.05). To get insight into the underlying mechanisms, we compared the ability of recombinant wild type and variant (D327N) SHBG to influence estradiol effects in MCF-7 breast cancer cells. D327N SHBG was more effective than wild type protein in inhibiting estradiol-induced cell proliferation and anti-apoptosis. This depended on the fact that D327N SHBG binding to MCF-7 cells was significantly higher than that of wild type protein. As a consequence, D327N caused a larger induction of the second messenger cAMP and a deeper inhibition of the estradiol-induced Erk (1/2) phosphorylation. Our observations, demonstrating the increased efficiency of D327N SHBG in counteracting estradiol action and a significantly higher frequency of Asp327Asn polymorphism in women not developing breast cancer after estrogen exposure, first provide evidence for the mechanism of D327N SHBG protective action.
Assuntos
Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Estrogênios/metabolismo , Polimorfismo de Nucleotídeo Único , Globulina de Ligação a Hormônio Sexual/genética , Globulina de Ligação a Hormônio Sexual/fisiologia , Animais , Apoptose , Neoplasias da Mama/etiologia , Células CHO , Linhagem Celular Tumoral , Cricetinae , Cricetulus , AMP Cíclico/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Feminino , Terapia de Reposição Hormonal , Humanos , Globulina de Ligação a Hormônio Sexual/biossíntese , Transdução de SinaisRESUMO
Treatment efficacy of breast cancer can be impaired by cell resistance. The aim of the study was to investigate the anti-tumour effects of valproic acid (VPA), the only clinically available histone deacetylase inhibitor, on both estrogen-sensitive and -insensitive breast cancer cells. VPA, at a concentration lacking severe adverse effects in human, reduces cell viability in estrogen-sensitive cell lines, inducing p21 expression and impairing cell cycle. In ZR-75-1, cell cycle is selectively arrested in G1, whereas MCF-7 cells massively accumulated in sub-G1. Actually, in MCF-7 cells, VPA induces apoptosis, down-regulates Bcl-2 and up-regulates Bak expression. In conclusion, VPA is a powerful antiproliferative agent in estrogen-sensitive breast cancer cells, making this drug of clinical interest as a new approach to treat breast cancer.
Assuntos
Antineoplásicos/farmacologia , Neoplasias da Mama/tratamento farmacológico , Proliferação de Células/efeitos dos fármacos , Inibidores Enzimáticos/farmacologia , Estrogênios/metabolismo , Inibidores de Histona Desacetilases , Neoplasias Hormônio-Dependentes/tratamento farmacológico , Ácido Valproico/farmacologia , Antineoplásicos/uso terapêutico , Apoptose/efeitos dos fármacos , Neoplasias da Mama/enzimologia , Neoplasias da Mama/patologia , Caspase 8/metabolismo , Caspase 9/metabolismo , Ciclo Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Sobrevivência Celular/efeitos dos fármacos , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Relação Dose-Resposta a Droga , Inibidores Enzimáticos/uso terapêutico , Feminino , Histona Desacetilases/metabolismo , Humanos , Neoplasias Hormônio-Dependentes/enzimologia , Neoplasias Hormônio-Dependentes/patologia , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , RNA Mensageiro/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Ácido Valproico/uso terapêutico , Proteína Killer-Antagonista Homóloga a bcl-2/genética , Proteína Killer-Antagonista Homóloga a bcl-2/metabolismoRESUMO
Poorly differentiated thyroid carcinoma is an aggressive human cancer that is resistant to conventional therapy. Histone deacetylase inhibitors are a promising class of drugs, acting as antiproliferative agents by promoting differentiation, as well as inducing apoptosis and cell cycle arrest. Valproic acid (VPA), a class I selective histone deacetylase inhibitor widely used as an anticonvulsant, promotes differentiation in poorly differentiated thyroid cancer cells by inducing Na(+)/I(-) symporter and increasing iodine uptake. Here, we show that it is also highly effective at suppressing growth in poorly differentiated thyroid cancer cell lines (N-PA and BHT-101). Apoptosis induction and cell cycle arrest are the underlying mechanisms of VPA's effect on cell growth. It induces apoptosis by activating the intrinsic pathway; caspases 3 and 9 are activated but not caspase 8. Cell cycle is selectively arrested in G(1) and is associated with the increased expression of p21 and the reduced expression of cyclin A. Both apoptosis and cell cycle arrest are induced by treatment with 1 mm VPA, a dose that promotes cell redifferentiation and that is slightly above the serum concentration reached in patients treated for epilepsy. These multifaceted properties make VPA of clinical interest as a new approach to treating poorly differentiated thyroid cancer.