RESUMO
Platinating agents constitute the first line treatment for ovarian cancer but treatment failure is common because of intrinsic and acquired resistance. Cancer cells develop the RASP-phenotype (cross resistance against arsenite, antimonite and platinum) associated with decreased accumulation of cisplatin and arsenite. ASNA1 is a possible subunit of a transport system for cisplatin and arsenite due to homology to arsA, an ATPase in the E. coli ars-complex responsible for efflux of arsenite and antimonite. Eukaryotic ASNA1 is a targeting factor for membrane insertion of tail-anchored proteins involved in the secretory pathway and cellular stress responses. The purpose with this study was to evaluate if ASNA1 expression influenced cisplatin, carboplatin, oxaliplatin or arsenite sensitivity in ovarian cancer. Human ovarian cancer cell line 2008 was transfected with a sense or an antisense ASNA1 construct. ASNA1 downregulated and overexpressing clones were identified by Western blots. Cell growth and chemosensitivity was determined by the MTT assay. Down-regulated ASNA1 expression was associated with retarded growth and increased sensitivity to cisplatin, carboplatin, oxaliplatin and arsenite whereas the cisplatin resistant 2008/A overexpresses ASNA1. These observations support the hypothesis that ASNA1 is a target to overcome platinum resistance in ovarian cancer.
Assuntos
Antineoplásicos/farmacologia , ATPases Transportadoras de Arsenito/efeitos dos fármacos , Arsenitos/farmacologia , Resistencia a Medicamentos Antineoplásicos/genética , Neoplasias Ovarianas/genética , Compostos de Platina/farmacologia , ATPases Transportadoras de Arsenito/biossíntese , ATPases Transportadoras de Arsenito/genética , Western Blotting , Linhagem Celular Tumoral , Proliferação de Células/efeitos dos fármacos , Regulação para Baixo , Feminino , Humanos , TransfecçãoRESUMO
Because arsenic is the most prevalent environmental toxin, it is imperative that we understand the mechanisms of metalloid detoxification. In prokaryotes, arsenic detoxification is accomplished by chromosomal and plasmid-borne operon-encoded efflux systems. Bacterial ArsA ATPase is the catalytic component of an oxyanion pump that is responsible for resistance to arsenite (As(III)) and antimonite (Sb(III)). Here, we describe the identification of a Caenorhabditis elegans homolog (asna-1) that encodes the ATPase component of the Escherichia coli As(III) and Sb(III) transporter. We evaluated the responses of wild-type and asna-1-mutant nematodes to various metal ions and found that asna-1-mutant nematodes are more sensitive to As(III) and Sb(III) toxicity than are wild-type animals. These results provide evidence that ASNA-1 is required for C. elegans' defense against As(III) and Sb(III) toxicity. A purified maltose-binding protein (MBP)-ASNA-1 fusion protein was biochemically characterized, and its properties compared with those of ArsAs. The ATPase activity of the ASNA-1 protein was dependent on the presence of As(III) or Sb(III). As(III) stimulated ATPase activity by 2 +/- 0.2-fold, whereas Sb(III) stimulated it by 4.6 +/- 0.15-fold. The results indicate that As(III)- and Sb(III)-stimulated ArsA ATPase activities are not restricted to bacteria, but extend to animals, by demonstrating that the asna-1 gene from the nematode, C. elegans, encodes a functional ArsA ATPase whose activity is stimulated by As(III) and Sb(III) and which is critical for As(III) and Sb(III) tolerance in the intact organism.
