RESUMO
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
There is growing evidence that accelerated telomeric attrition and/or aberrant telomerase activity contributes to pathogenesis in a number of diseases. Likewise, there is increasing interest to develop new therapies to restore or replace dysfunctional cells characterized by short telomeric length using telomerase-positive counterparts or stem cells. While telomerase adds telomeric repeats de novo contributing to enhanced proliferative capacity and lifespan, it may also increase cellular survival by conferring resistance to apoptosis. Consequently, we sought to determine the involvement of telomerase for reduced apoptosis using ovarian surface epithelial cells. We found that expression of hTERT, the catalytic component of telomerase, was sufficient and specific to reduce caspase-mediated cellular apoptosis. Further, hTERT expression reduced activation of caspases 3, 8, and 9, reduced expression of pro-apoptotic mitochondrial proteins t-BID, BAD, and BAX and increased expression of the anti-apoptotic mitochondrial protein, Bcl-2. The ability of telomerase to suppress caspase-mediated apoptosis was p-jnk dependent since abrogation of jnk expression with jip abolished resistance to apoptosis. Consequently, these findings indicate that telomerase may promote cellular survival in epithelial cells by suppressing jnk-dependent caspase-mediated apoptosis.
