RESUMO
OBJECTIVE: Aggressive clinical course and difficult detection of ovarian cancer are major challenges to improving patient survival and necessitate avid investigation into more effective therapeutic approaches. Understanding early molecular and pathological changes in high risk patients, such as BRCA1 mutation carriers, can provide candidates for molecular profiling and novel targets for effective therapies. METHODS: Using a culture model system for normal human ovarian surface epithelial cells with and without the BRCA1 185delAG frameshift mutation for the truncated protein product, BRAt, we investigated the role of BRAt in enhanced chemosensitivity. We used MTS, Western immunoblot, semi-quantitative RT-PCR, luciferase reporter and siRNA assays, to identify novel downstream targets of BRAt that promote apoptosis following chemotherapeutic treatment. RESULTS: We identified maspin as a novel downstream target of BRAt. BRAt increases maspin expression with preferential nuclear localization of maspin. Further, Brat-mediated maspin expression is transcriptionally regulated through an AP1 site within the (-520) to (-297) region of the promoter. Lastly, BRAt, enhances chemosensitivity in normal ovarian surface epithelial cells through c-Jun by a mechanism that may involve maspin. CONCLUSIONS: BRAt-mediated enhanced chemosensitivity correlates clinically with enhanced chemotherapeutic response in BRCA1 mutation carriers. BRAt-mediated maspin expression also correlates with improved prognostic outlook for ovarian tumors with high levels of nuclear maspin. Consequently, understanding early genotypic and phenotypic changes in the context of high risk disease may provide a better understanding of the mechanism of mutation-associated ovarian cancer and provide new targets for therapeutic intervention.
Assuntos
Proteína BRCA1/genética , Mutação da Fase de Leitura , Neoplasias Ovarianas/genética , Serpinas/genética , Proteína BRCA1/metabolismo , Sítios de Ligação , Células Epiteliais/metabolismo , Células Epiteliais/patologia , Feminino , Genes BRCA1 , Humanos , Neoplasias Ovarianas/tratamento farmacológico , Neoplasias Ovarianas/metabolismo , Neoplasias Ovarianas/patologia , Regiões Promotoras Genéticas , Serpinas/biossíntese , Fator de Transcrição AP-1/metabolismo , Transfecção , Células Tumorais Cultivadas , Regulação para CimaRESUMO
Breast and ovarian cancer patients with germline mutations in BRCA1 respond more favorably to initial chemotherapy. We previously reported that cells from women carrying the BRCA1 185delAG founder mutation undergo an enhanced caspase-3-mediated apoptotic response. Here, we report on the transient and stable transfection of cDNA coding for the putative truncated protein product of the BRCA1 185delAG mutant gene into BRCA1 wild-type human ovarian surface epithelial cells and ovarian cancer cells, resulting in cells with a heterozygous background containing two BRCA1 wild-type alleles and the BRCA1 185delAG transcript. The BRCA1 185delAG truncation (BRAt) protein did not alter epithelial cell morphology or induce tumorigenesis. However, upon treatment with staurosporine, BRAt cells showed increased levels of active caspase-3 and increased cleavage of caspase-3 substrates, PARP and DFF45. Additionally, XIAP and cIAP-1 protein are at reduced levels in untreated BRAt cells as compared to control cells. BRAt also reduced levels of phosphorylated Akt and overexpression of activated Akt in BRAt cells restored caspase-3 activity to that seen in wild-type cells. Further, BRAt expression increased chemosensitivity in platinum-resistant ovarian cancer cells. Taken together, our data demonstrate that truncated proteins arising from BRCA1 185delAG mutation increase Akt-mediated apoptosis, suggesting a possible mechanism by which ovarian cancer patients with this germline BRCA1 mutation may respond better to initial chemotherapy.
Assuntos
Apoptose/genética , Proteína BRCA1/genética , Caspases/metabolismo , Neoplasias Ovarianas/genética , Deleção de Sequência/genética , Sequência de Aminoácidos , Proteína BRCA1/metabolismo , Sequência de Bases , Células Epiteliais/citologia , Células Epiteliais/metabolismo , Feminino , Humanos , Proteínas Inibidoras de Apoptose/metabolismo , Dados de Sequência Molecular , Mutação , Neoplasias Ovarianas/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , RNA Mensageiro/metabolismo , Transfecção , Células Tumorais Cultivadas , Ubiquitina-Proteína Ligases , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismoRESUMO
MicroRNAs (miRNA) represent a novel class of genes that function as negative regulators of gene expression. Recently, miRNAs have been implicated in several cancers. However, aberrant miRNA expression and its clinicopathologic significance in human ovarian cancer have not been well documented. Here, we show that several miRNAs are altered in human ovarian cancer, with the most significantly deregulated miRNAs being miR-214, miR-199a*, miR-200a, miR-100, miR-125b, and let-7 cluster. Further, we show the frequent deregulation of miR-214, miR-199a*, miR-200a, and miR-100 in ovarian cancers. Significantly, miR-214 induces cell survival and cisplatin resistance through targeting the 3'-untranslated region (UTR) of the PTEN, which leads to down-regulation of PTEN protein and activation of Akt pathway. Inhibition of Akt using Akt inhibitor, API-2/triciribine, or introduction of PTEN cDNA lacking 3'-UTR largely abrogates miR-214-induced cell survival. These findings indicate that deregulation of miRNAs is a recurrent event in human ovarian cancer and that miR-214 induces cell survival and cisplatin resistance primarily through targeting the PTEN/Akt pathway.
