Dual cytoplasmic and nuclear distribution of the novel arsenite‐stimulated human ATPase (hASNA‐I)

Molecular characterization and analysis of the ATPase ASNA1 homolog gene of Eimeria tenella in a drug sensitive strain and drug resistant strains

The widespread use of drugs has exacerbated the resistance of Eimeria tenalla to anti-coccidial drugs. Using RNA-seq, we previously found the ATPase ASNA1 homolog of E. tenella (EtASNA1) was differentially expressed in resistant strains and drug sensitive (DS) strain. In our study, we used western blotting and quantitative real-time PCR (qRT-PCR) to analyze the translational and transcriptional levels of EtASNA1 in a diclazuril-resistant (DZR) strain, maduramicin-resistant (MRR) strain, salinomycin-resistant (SMR) strain, and DS strain and found EtASNA1 was highly expressed in three drug-resistant strains. The qRT-PCR and western blotting results also showed that the expression levels of EtASNA1 increased with increasing drug concentration, and the transcription levels of the DZR strains isolated from the field were higher than those of the DS strain. In addition, we used in vivo and in vitro tests to analyze the changes of EtASNA1 expression after DZR, MRR, and DS strain infections in chickens, and in vitro inoculation of DF-1 cells in the presence of drugs. The addition of drugs caused expression to be upregulated. The results of qRT-PCR and western blotting also showed that the expression levels of EtASNA1 in second-generation merozoites (SM) and unsporulated oocysts (UO) were significantly higher than those in the other two developmental stages. The immunofluorescence localization of EtASNA1 indicated that the protein was distributed throughout the sporozoites (SZ) and SM, except for the refractile bodies of SZ. In vitro inhibition experiments showed that anti-EtASNA1 antibody incubation significantly inhibited SZ invasion of DF-1 cells. The above results showed that EtASNA1 may be related to host cell invasion of E. tenella and may be involved in the development of E. tenella resistance to some drugs.

ASNA-1 activity modulates sensitivity to cisplatin

Cancer can be cured by platinum-based chemotherapy, but resistance is a major cause of treatment failure. Here we present the nematode Caenorhabditis elegans as a model to study interactions between the platinum drug cisplatin and signaling pathways in vivo. Null mutation in a single gene, asna-1, makes worms hypersensitive to cisplatin. The metalloregulated ATPase ASNA-1 promotes insulin secretion and membrane insertion of tail-anchored proteins. Using structural data from ASNA-1 homologues, we identify specific ASNA-1 mutants that are sensitive to cisplatin while still able to promote insulin signaling. Mutational analysis reveals that hypersensitivity of ASNA-1 mutants to cisplatin remains in absence of CEP-1/p53 or apoptosis. Human ASNA1 can substitute for the worm gene, indicating a conserved function. Cisplatin sensitivity is not affected by decreased insulin signaling in wild-type nematodes or restored insulin signaling in asna-1 mutants. These findings provide a functional insight into ASNA-1, demonstrate that C. elegans can be used to characterize cisplatin resistance mechanisms, and suggest that rationally designed drugs against ASNA-1 can sensitize cancer cells to cisplatin.

ASNA1, an ATPase targeting tail-anchored proteins, regulates melanoma cell growth and sensitivity to cisplatin and arsenite

PURPOSE

ASNA1 is homologous to E. coli ArsA, a well characterized ATPase involved in efflux of arsenite and antimonite. Cells resistant to arsenite and antimonite are cross-resistant to the chemotherapeutic drug cisplatin. ASNA1 is also an essential ATPase for the insertion of tail-anchored proteins into ER membranes and a novel regulator of insulin secretion. The aim of this study was to determine if altered ASNA1 levels influenced growth and sensitivity to arsenite and cisplatin in human melanoma cells.

METHODS

Cultured melanoma T289 cells were transfected with plasmids containing sense or antisense ASNA1. Cells were exposed to cisplatin, arsenite and zinc. Cell growth and chemosensitivity were evaluated by the MTT assay and apoptosis by a TUNEL assay.

RESULTS

ASNA1 expression was necessary for growth. T289 clones with decreased ASNA1 expression exhibited 51 +/- 5% longer doubling times than wildtype T289 (P = 0.0091). After exposure to cisplatin, ASNA1 downregulated cells displayed a significant increase in apoptosis. The cisplatin IC(50) in ASNA1 underexpressing cells was 41.7 +/- 1.8% compared to wildtype (P = 0.00097) and the arsenite IC(50) was 59.9 +/- 3.2% of wildtype IC(50) (P = 0.0067).

CONCLUSIONS

Reduced ASNA1 expression is associated with significant inhibition of cell growth, increased apoptosis and increased sensitivity to cisplatin and arsenite.

Low-level self-tolerance to arsenite in human HepG2 cells is associated with a depressed induction of micronuclei

Arsenic (As) is one of the most important global environmental toxicants. There is evidence that humans may develop tolerance to As's toxicity. For instance, it is known that uptake of small amounts of As leads to an acquisition of elevated resistance to the element's acute toxicity. Moreover, it was suggested that As-exposed native Andean females of Atacameño ethnicity may have acquired resistance to skin cancer. It is not known how such adaptation could be mechanistically conferred. In this context, the biological selection and cloning of human cells tolerant to As provides a valuable approach to investigate this question. By the means of a 12 weeks culture with increasing doses of As, three different As-resistant clones of the human hepatoma cell line HepG2 were selected. These three clones were similarly and roughly two-fold resistant to the acute toxicity of arsenite (50% reduction of neutral red (NR) uptake at 65 microM versus 115 microM; HepG2 control versus clones HepG2 K1, HepG2 K11 and HepG2 K14, respectively). Moreover, in the cytokinesis-block micronucleus test, these clones showed a significantly reduced induction of micronuclei (MNi) indicating elevated resistance to As genotoxicity as well (e.g. mean MNi rates at a concentration of 25 microM arsenite: 28.5 (control) versus 21.6 (HepG2 K1), 18 (HepG2 K11), and 16 (HepG2 K14), respectively, each P<0.05). The tolerance was neither associated with mRNA induction of putatively As-extruding membrane transporters multidrug resistance-associated protein 1 (MRP1), 2, or 3 nor to mRNA induction of the ubiquitously expressed mammalian ABC half-transporter UMAT (ABCB6). Changes in the metabolic methylation of As could not be detected. There were no differences in the cellular levels of GSH when comparing the clones and the parental line. Taken together the data showed that low-level tolerance to As-mediated cytotoxicity in human HepG2 cells was associated with enhanced resistance to As-induced DNA damage as well.