Role of the ABCE1 gene in human lung adenocarcinoma

The association of ABC proteins with multidrug resistance in cancer

Multidrug resistance (MDR) poses one of the primary challenges for cancer treatment, especially in cases of metastatic disease. Various mechanisms contribute to MDR, including the overexpression of ATP-binding cassette (ABC) proteins. In this context, we reviewed the literature to establish a correlation between the overexpression of ABC proteins and MDR in cancer, considering both in vitro and clinical studies. Initially, we presented an overview of the seven subfamilies of ABC proteins, along with the subcellular localization of each protein. Subsequently, we identified a panel of 20 ABC proteins (ABCA1-3, ABCA7, ABCB1-2, ABCB4-6, ABCC1-5, ABCC10-11, ABCE1, ABCF2, ABCG1, and ABCG2) associated with MDR. We also emphasize the significance of drug sequestration by certain ABC proteins into intracellular compartments. Among the anticancer drugs linked to MDR, 29 were definitively identified as substrates for at least one of the three most crucial ABC transporters: ABCB1, ABCC1, and ABCG2. We further discussed that the most commonly used drugs in standard regimens for mainly breast cancer, lung cancer, and acute lymphoblastic leukemia could be subject to MDR mediated by ABC transporters. Collectively, these insights will aid in conducting new studies aimed at a deeper understanding of the clinical MDR mediated by ABC proteins and in designing more effective pharmacological treatments to enhance the objective response rate in cancer patients.

A pan-cancer analysis of the oncogenic role of ATP binding cassette subfamily E member 1 (ABCE1) in human tumors: An observational study

ATP-binding-cassette subfamily E member 1 (ABCE1) has been identified as an essential component of RNA translation and cell proliferation. However, studies on its role in pan-cancer are limited. Here, we aimed to characterize ABCE1 expression and its potential biological functions in cancer. ABCE1 expression was analyzed using RNA-seq data from The Cancer Genome Atlas (TCGA), the Genotype-Tissue Expression (GTEx) database, and the Clinical Proteomic Tumor Analysis Consortium database. The prognostic value of ABCE1 was analyzed using clinical survival data from TCGA. We downloaded the immune cell infiltration score of TCGA samples from published articles and online databases and performed a correlation analysis between immune cell infiltration levels, chemokines/chemokine receptors, and ABCE1 expression. We further assessed the association between ABCE1-correlated genes and their functions in pancreatic adenocarcinoma (PAAD). In general, ABCE1 gene expression was upregulated in most tumors. There were significant strong correlations between ABCE1 expression and tumor-infiltrating cells in cancers. Furthermore, RNA transport and ribosome biogenesis were significantly related to ABCE1 expression in PAAD. Our study revealed that ABCE1 may serve as a potential prognostic and immunological pan-cancer biomarker. Moreover, ABCE1 may be used in the development of a novel target for PAAD.

ATP-binding cassette (ABC) transporters in cancer: A review of recent updates

The ATP-binding cassette (ABC) transporter superfamily is one of the largest membrane protein families existing in wide spectrum of organisms from prokaryotes to human. ABC transporters are also known as efflux pumps because they mediate the cross-membrane transportation of various endo- and xenobiotic molecules energized by ATP hydrolysis. Therefore, ABC transporters have been considered closely to multidrug resistance (MDR) in cancer, where the efflux of structurally distinct chemotherapeutic drugs causes reduced itherapeutic efficacy. Besides, ABC transporters also play other critical biological roles in cancer such as signal transduction. During the past decades, extensive efforts have been made in understanding the structure-function relationship, transportation profile of ABC transporters, as well as the possibility to overcome MDR via targeting these transporters. In this review, we discuss the most recent knowledge regarding ABC transporters and cancer drug resistance in order to provide insights for the development of more effective therapies.

Translation of ABCE1 Is Tightly Regulated by Upstream Open Reading Frames in Human Colorectal Cells

ATP-binding cassette subfamily E member 1 (ABCE1) belongs to the ABC protein family of transporters; however, it does not behave as a drug transporter. Instead, ABCE1 actively participates in different stages of translation and is also associated with oncogenic functions. Ribosome profiling analysis in colorectal cancer cells has revealed a high ribosome occupancy in the human ABCE1 mRNA 5′-leader sequence, indicating the presence of translatable upstream open reading frames (uORFs). These cis-acting translational regulatory elements usually act as repressors of translation of the main coding sequence. In the present study, we dissect the regulatory function of the five AUG and five non-AUG uORFs identified in the human ABCE1 mRNA 5′-leader sequence. We show that the expression of the main coding sequence is tightly regulated by the ABCE1 AUG uORFs in colorectal cells. Our results are consistent with a model wherein uORF1 is efficiently translated, behaving as a barrier to downstream uORF translation. The few ribosomes that can bypass uORF1 (and/or uORF2) must probably initiate at the inhibitory uORF3 or uORF5 that efficiently repress translation of the main ORF. This inhibitory property is slightly overcome in conditions of endoplasmic reticulum stress. In addition, we observed that these potent translation-inhibitory AUG uORFs function equally in cancer and in non-tumorigenic colorectal cells, which is consistent with a lack of oncogenic function. In conclusion, we establish human ABCE1 as an additional example of uORF-mediated translational regulation and that this tight regulation contributes to control ABCE1 protein levels in different cell environments.

Proteomic Evaluation of Plasma Membrane Fraction Prepared from a Mouse Liver and Kidney Using a Bead Homogenizer: Enrichment of Drug-Related Transporter Proteins

Quantifying the protein levels of drug transporters in plasma membrane fraction helps elucidate the function of these transporters. In this study, we conducted a proteomic evaluation of enriched drug-related transporter proteins in plasma membrane fraction prepared from mouse liver and kidney tissues using the membrane protein extraction kit and a bead homogenizer. Crude and plasma membrane fractions were prepared using either the Dounce or bead homogenizer, and protein levels were determined using quantitative proteomics. In liver tissues, the plasma membrane fractions were more enriched in transporter proteins than the crude membrane fractions; the average enrichment ratios of plasma-to-crude membrane fractions were 3.31 and 6.93 using the Dounce and bead homogenizers, respectively. The concentrations of transporter proteins in plasma membrane fractions determined using the bead homogenizer were higher than those determined using the Dounce homogenizer. Meanwhile, in kidney tissues, the plasma membrane fractions were enriched in transporters localized in the brush-border membrane to the same degree for both the homogenizers; however, the membrane fractions obtained using either homogenizer were not enriched in Na^+/K⁺-ATPase and transporters localized in the basolateral membrane. These results indicate that fractionation, using the bead homogenizer, yielded transporter-enriched plasma membrane fractions from mouse liver and kidney tissues; however, no enrichment of basolateral transporters was observed in plasma membrane fractions prepared from kidney tissues.

Tip60-siRNA regulates ABCE1 acetylation to suppress lung cancer growth via activation of the apoptotic signaling pathway

Lung cancer is a leading cause of cancer-associated mortality and morbidity worldwide. Previous studies have suggested that ATP-binding cassette transporter E1 (ABCE1) acetylation is upregulated in the tissues and cells of lung cancer and is associated with the prognosis of patients with lung cancer. The aim of the present study was to investigate the association between Tat interactive protein 60 kDa (Tip60) expression and ABCE1 acetylation, and the effect of Tip60 on the biological functions of A549 lung carcinoma cells. The expression levels of Tip60 and ABCE1 acetylation were examined using western blot and co-immunoprecipitation (Co-IP) assays in normal bronchial epithelial (HBE) and human lung cancer (A549) cells. The expression of Tip60 then was downregulated in A549 cells using small interfering RNA. Wound healing and Transwell assays were used to assess cell invasion and migration. The biological effects of Tip60 in lung cancer cells were investigated using MTT and flow cytometric assays. Subsequently, tumor xenografts were established to observe the effect of Tip60 on lung cancer in vivo. Western blot and Co-IP assays were performed to investigate the mechanism of Tip60 in A549 cells. Tip60 expression and ABCE1 acetylation were upregulated in the lung cancer cells compared with the normal bronchial epithelial cells. Downregulation of Tip60 decreased the acetylation of ABCE1 and inhibited cell proliferation, invasion and migration. Furthermore, the downregulation of Tip60 activated the apoptotic pathway in order to achieve its suppressive function. In the xenografts, the tumor weight and volume were notably reduced due to the downregulation of Tip60 expression. The results of the present study strongly suggest that Tip60 is a novel target in the prevention and treatment of lung cancer.

Control of mRNA Translation by Versatile ATP-Driven Machines

Translation is organized in a cycle that requires ribosomal subunits, mRNA, aminoacylated transfer RNAs, and myriad regulatory factors. As soon as translation reaches a stop codon or stall, a termination or surveillance process is launched via the release factors eRF1 or Pelota, respectively. The ATP-binding cassette (ABC) protein ABCE1 interacts with release factors and coordinates the recycling process in Eukarya and Archaea. After splitting, ABCE1 stays with the small ribosomal subunit and emerges as an integral part of translation initiation complexes. In addition, eEF3 and ABCF proteins control translation by binding at the E-site. In this review, we highlight advances in the fundamental role of ABC systems in mRNA translation in view of their collective inner mechanics.

Promyelocytic leukemia zinc finger triggers ATP-binding cassette subfamily E member 1-mediated growth inhibition in breast cancer cells

The promyelocytic leukemia zinc finger (PLZF) protein is a transcription factor that is involved in a number of biological processes, including those regulating cellular growth; however, little is known regarding how it achieves its inhibitory effect in different cell and tissue types. It has previously been demonstrated that PLZF expression levels become diminished during the oncogenic transformation of certain tissue types and thus, may serve as a hallmark for tumor aggressiveness. To examine this in breast cancer, survival curves from available oncology databases were analyzed and demonstrated that PLZF expression was positively associated with increased survival in patients with breast cancer. The mRNA and protein levels of PLZF were also revealed to be associated with the tumorigenicity of four breast cancer cell lines. Since ATP-binding cassette subfamily E member 1 (ABCE1), also known as RNase L inhibitor, has been determined to be a target gene of PLZF, the present study also investigated whether the tumor suppressive effect of PLZF was associated with ABCE1 expression. PLZF was revealed to downregulate the expression of ABCE1 in vitro, which relieved the inhibitory effect of ABCE1 on the ribonuclease L enzyme. Finally, it was concluded that PLZF expression caused an ABCE1-mediated increase in cellular cytotoxicity, as demonstrated by a reduction in the proliferation rate of breast cancer cell lines. The results of the present study are important for understanding how PLZF exerts its final inhibitory actions in breast cancer cells, and potentially in other solid tumors, through the modulation of immunological pathways.

The expression and correlation between chemokine CCL7 and ABCE1 in non-small cell lung cancer

Lung cancer is a malignant disease, and has the highest incidence and mortality worldwide. Lung cancer is also a popular subject in the field of cancer research. The molecular mechanisms of lung cancer development, invasion and metastasis need to be determined to prolong survival times and improve the quality of life. Recent studies have demonstrated that ATP-binding cassette sub-family E member 1 (ABCE1) is one of the factors that contributes to the development and metastasis of lung cancer, but the specific mechanism of this phenomenon remains unclear. A polymerase chain reaction microarray was used in the present study to screen for chemokine (C-C motif) ligand 7 (CCL7) expression in cell lines that highly expressed ABCE1, and the results showed that CCL7 was highly expressed in H1299 cells (P<0.01). The expression of CCL7 and ABCE1 in lung cancer tissues obtained from 30 patients with non-small cell lung cancer (NSCLC) was higher than that in adjacent normal lung tissues (P<0.01), and a positive correlation between the expression levels of the two genes in NSCLC was observed. These findings indicate that ABCE1 is involved in the development and progression of lung cancer through the CCL7 signaling pathway.

Diagnosis of thymic epithelial tumor subtypes by a quantitative proteomic approach

This study shows the first depth proteomic profiling of all TET subtypes and six candidate biomarkers were identified and validated.

Tumor metastatic promoter ABCE1 interacts with the cytoskeleton protein actin and increases cell motility

ABCE1, a member of the ATP-binding cassette (ABC) family, is a candidate tumor metastatic promoter in lung cancer. Overexpression of ABCE1 is correlated with aggressive growth and metastasis in lung cancer cells. However, the exact mechanism remains unclear. In the present study, GST pull-down assay provided evidence of the possible interaction between ABCE1 and β-actin using GST-ABCE1 as a bait protein. Co-immunoprecipitation manifested ABCE1 formed complexes with β-actin in vivo. ABCE1 overexpression significantly increased the migration of lung cancer cells which may be attributed to the promotion of F-actin rearrangements. Taken together, these data suggest that overexpression of ABCE1 produces an obvious effect on the motility of lung cancer cells through cytoskeleton rearrangement.

ABCE1 is essential for S phase progression in human cells

ABCE1 is a highly conserved protein universally present in eukaryotes and archaea, which is crucial for the viability of different organisms. First identified as RNase L inhibitor, ABCE1 is currently recognized as an essential translation factor involved in several stages of eukaryotic translation and ribosome biogenesis. The nature of vital functions of ABCE1, however, remains unexplained. Here, we study the role of ABCE1 in human cell proliferation and its possible connection to translation. We show that ABCE1 depletion by siRNA results in a decreased rate of cell growth due to accumulation of cells in S phase, which is accompanied by inefficient DNA synthesis and reduced histone mRNA and protein levels. We infer that in addition to the role in general translation, ABCE1 is involved in histone biosynthesis and DNA replication and therefore is essential for normal S phase progression. In addition, we analyze whether ABCE1 is implicated in transcript-specific translation via its association with the eIF3 complex subunits known to control the synthesis of cell proliferation-related proteins. The expression levels of a few such targets regulated by eIF3A, however, were not consistently affected by ABCE1 depletion.

Low-Dose Cadmium Upregulates VEGF Expression in Lung Adenocarcinoma Cells

Cadmium (Cd) is a heavy metal and environmental toxin. Exposure to Cd has been associated with a variety of human cancers. In this study, we performed in vitro assays to examine the effects of cadmium chloride (CdCl₂) on A549 cells, a human lung adenocarcinoma cell line. Cd does not affect proliferation, migration, or apoptosis of A549 cells at concentrations of 0.1-10 μM. At 0.5 and 1 μM, Cd increases the expression of vascular endothelial growth factor (VEGF) (p < 0.05, p < 0.01, respectively), but not basic fibroblast growth factor (b-FGF) in A549 cells. The conditioned media were collected from the A549 cells treated with 1 μM Cd and were co-cultured with human umbilical vein endothelial cells (HUVECs). Upon treatment with the conditioned media, the proliferation and migration of HUVECs significantly increased (p < 0.01, p < 0.05, respectively), while apoptosis remained unchanged. In addition, 1 μM Cd increases the level of hypoxia inducible factor 1-α (HIF1-α), which is a positive regulator of VEGF expression. Although low-dose Cd does not directly affect the growth of lung adenocarcinoma cells, it might facilitate the development of tumors through its pro-angiogenic effects.

The role of ABC transporters in ovarian cancer progression and chemoresistance

Over 80% of ovarian cancer patients develop chemoresistance which results in a lethal course of the disease. A well-established cause of chemoresistance involves the family of ATP-binding cassette transporters, or ABC transporters that transport a wide range of substrates including metabolic products, nutrients, lipids, and drugs across extra- and intra-cellular membranes. Expressions of various ABC transporters, shown to reduce the intracellular accumulation of chemotherapy drugs, are increased following chemotherapy and impact on ovarian cancer survival. Although clinical trials to date using ABC transporter inhibitors have been disappointing, ABC transporter inhibition remains an attractive potential adjuvant to chemotherapy. A greater understanding of their physiological functions and role in ovarian cancer chemoresistance will be important for the development of more effective targeted therapies. This article will review the role of the ABC transporter family in ovarian cancer progression and chemoresistance as well as the clinical attempts used to date to reverse chemoresistance.

Downregulation of ABCE1 via siRNA affects the sensitivity of A549 cells against chemotherapeutic agents

ATP-binding cassette E1 (ABCE1) is involved in several biological functions in cancer cells such as tumor proliferation, antiapoptotic pathway and chemoresistance mechanism. This work aimed to investigate the alterations in chemosensitivity of A549 lung cancer cells for 5-Fluorouracil (5-FU) and irinotecan by silencing ABCE1 using specific small interfering RNAs (siRNA). The cells were treated with low doses of drugs, alone and also their combinations with ABCE1 siRNA. Cytotoxicity, cell proliferation and apoptosis/necrosis evaluations were performed in order to examine the effects of the combined treatment. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to confirm the downregulation of ABCE1. We also investigated the levels of B cell lymphoma 2 (Bcl-2) and mammalian target of rapamycin (mTOR) after the treatments by RT-PCR. Downregulation of ABCE1 improved the anticancer effects of 5-FU in inducing cell viability/proliferation inhibition and apoptosis/necrosis, whereas interestingly, almost did not change or slightly reduced the anticancer effects of irinotecan. ABCE1 expression significantly decreased by transfecting the cells with ABCE1 siRNA. Moreover, Bcl-2 and mTOR levels changed after the single or combined therapy in parallel with the apoptotic and antiproliferation effect. In conclusion, the simultaneous treatment of lung cancer cells with ABCE1 siRNA and 5-FU exhibited synergistic or additive effects; however, ABCE1 siRNA and irinotecan had unexpected antagonistic effects. Our findings demonstrate that the strategy of downregulation of ABCE1 may be included in conventional 5-FU chemotherapy for lung cancer, minimizing the usage of 5-FU at high dosages.

ABC transporters and neuroblastoma

Neuroblastoma is the most common cancer of infancy and accounts for 15% of all pediatric oncology deaths. Survival rates of high-risk neuroblastoma remain less than 50%, with amplification of the MYCN oncogene the most important aberration associated with poor outcome. Direct transcriptional targets of MYCN include a number of ATP-binding cassette (ABC) transporters, of which ABCC1 (MRP1), ABCC3 (MRP3), and ABCC4 (MRP4) are the best characterized. These three transporter genes have been shown to be strongly prognostic of neuroblastoma outcome in primary untreated neuroblastoma. In addition to their ability to efflux a number of chemotherapeutic drugs, evidence suggests that these transporters also contribute to neuroblastoma outcome independent of any role in cytotoxic drug efflux. Endogenous substrates of ABCC1 and ABCC4 that may be potential candidates affecting neuroblastoma biology include molecules such as prostaglandins and leukotrienes. These bioactive lipid mediators have the ability to influence biological processes contributing to cancer initiation and progression, such as angiogenesis, cell signaling, inflammation, proliferation, and migration and invasion. ABCC1 and ABCC4 are thus potential targets for therapeutic suppression in high-risk neuroblastoma, and recently developed small-molecule inhibitors may be an effective strategy in treating aggressive forms of this cancer, as well as other cancers that express high levels of these transporters.

Knock-down of ABCE1 gene induces G1/S arrest in human oral cancer cells

PURPOSE

This study aims to explore the clinical characteristics of ATP binding cassette E1 (ABCE1) in oral squamous cell carcinomas (OSCC) and its roles in the proliferation, invasiveness, migration and apoptosis of the human oral squamous cell carcinoma cells CAL-27.

METHODS

The expression of ABCE1 and its target protein-RNase L, were first studied in tumor tissues of OSCC and adjacent non-tumor tissues. Moreover, CAL-27cells were transfected by ABCE1-specific shRNA, then MTT assay, the transwell and scratch assay were used to study cell proliferation and migration activity; the apoptosis rate and cell cycle distribution were tested by flow cytometry. Western blot and RT-PCR assay were adopted to measure their silencing efficacy.

RESULTS

ABCE1 expression is low in the adjacent non-tumor tissues while the expression is high in the oral cancer; the expression is reversely proportional to the differentiation degrees. The expression of RNaseL was in contrary to ABCE1. After transfected with ABCE1-siRNA, the proliferation, invasiveness and migration capabilities of cells decreased significantly whilst the apoptosis rate enhanced greatly (P < 0.01). Meanwhile, the expression of ABCE1 in CAL-27 cells was blocked (P < 0.01) while the expression of RNase L increased significantly (P < 0.01).

CONCLUSION

ABCE1 is closely connected with the pathogenesis and development of oral cancer, which acts through the cellular pathways of 2-5A/RNase L.

siRNA‑induced ABCE1 silencing inhibits proliferation and invasion of breast cancer cells

Breast cancer is the most common type of cancer among females and the adenosine triphosphate (ATP) binding cassette E1 (ABCE1) gene is a member of the ATP‑binding cassette (ABC) family. Studies in lung cancer have shown that overexpression of ABCE1 in tumor cells promotes growth and inhibits apoptosis. However, little is known about whether the ABCE1 gene is associated with breast cancer. In the present study, ABCE1 expression was assessed in breast cancer tissue and adjacent normal breast tissue using immunohistochemistry. Furthermore, small interfering (si)RNA targeting ABCE1 was constructed and transfected into MCF‑7 human breast cancer cells to downregulate ABCE1 expression. The effect of ABCE1 knockdown on cell proliferation, invasion, apoptosis and gene expression was then assessed using MTT assay, Transwell migration assay, flow cytometry and western blot analysis, respectively. ABCE1 was observed to be overexpressed in breast cancer tissue compared with adjacent normal breast tissue. Furthermore, ABCE1‑siRNA was found to inhibit proliferation and invasion in breast cancer cells, significantly induce breast cancer cell apoptosis (P<0.05) in vitro and increase the protein expression of RNase L. These findings showed that ABCE1 had an important role in proliferation, invasion and apoptosis in MCF‑7 human breast cancer cells and that ABCE1 may inhibit intracellular RNase L activity, which inhibits the 2‑5A/RNase L pathway, interfering with the biological characteristics of breast cancer cells.

Depleting ABCE1 expression induces apoptosis and inhibits the ability of proliferation and migration of human esophageal carcinoma cells

OBJECTIVE

This study aims to explore the clinical characteristics of ABCE1 in esophageal cancers and its roles in the proliferation, invasiveness, migration and apoptosis of the esophageal carcinoma Eca109 cell line.

METHODS

The expression of ABCE1 and its target protein-RNase L, were first studied in tumor tissues of esophageal carcinoma and adjacent non-tumor tissues. The siRNA green fluorescent protein (GFP) expression vector of ABCE1 was prepared and transfected into the esophageal carcinoma Eca109 cells, then the fluorescence microscope was used to study the transfection efficiency. The MTT assay, cell invasion, the transwell and scratch assay were used to study cell proliferation and migration activity; the apoptosis rate was tested by flow cytometry. Western blot and RT-PCR assay were adopted to measure their silencing efficacy.

RESULTS

ABCE1 expression is low in the adjacent non-tumor tissues while the expression is high in the esophageal carcinoma; the expression is reversely proportional to the differentiation degrees. The expression of RNase L was in contrary to ABCE1. After transfected with ABCE1-siRNA, the proliferation, invasiveness and migration capabilities of cells decreased significantly whilst the apoptosis rate enhanced greatly (P<0.01). Meanwhile, the expression of ABCE1 in Eca109 cells was blocked (P<0.01) while the expression of RNase L increased significantly (P<0.01).

CONCLUSION

ABCE1 is closely connected with the pathogenesis and development of esophageal carcinoma, which act through the cellular pathways of 2-5A/RNase L.

The association of elevated 2',5'-oligoadenylate-dependent RNase L with lung cancer correlated with deficient enzymatic activity and decreased capacity of RNase L dimerization

RNase L mediates critical cellular functions including antiviral, proapoptotic, antiproliferative and tumor suppressive activities. In this study, the expression and function of RNase L in lung cancer cells were examined. Interestingly we have found that the expression of RNase L in lung cancer cells was 3- and 9-fold higher in its mRNA and protein levels, but a significant decrease of its enzymatic activity when compared to that in corresponding normal lung cells. Further investigation revealed that 2-5A-induced dimerization of the RNase L protein, a necessary prerequisite for activation of RNase L, was inhibited, as a result of that RLI, a specific inhibitor of RNase L, was remarkably up-regulated in the cancer cells. Our findings provide new insight into how cancer cells escape normal growth-regulating mechanisms to form a tumor and the information may be useful for the design of novel strategies for treating lung cancer through regulating RNase L activity.

The essential iron-sulfur protein Rli1 is an important target accounting for inhibition of cell growth by reactive oxygen species

Reactive oxygen species (ROS) are linked to various degenerative conditions, but it is unclear which molecular target(s) may be the cell's primary “Achilles’ heel,” accounting for inhibition by ROS. Our results indicate that the FeS protein Rli1p, with essential and conserved functions in protein synthesis, is an important target of ROS toxicity.

Oxidative stress mediated by reactive oxygen species (ROS) is linked to degenerative conditions in humans and damage to an array of cellular components. However, it is unclear which molecular target(s) may be the primary “Achilles’ heel” of organisms, accounting for the inhibitory action of ROS. Rli1p (ABCE1) is an essential and highly conserved protein of eukaryotes and archaea that requires notoriously ROS-labile cofactors (Fe-S clusters) for its functions in protein synthesis. In this study, we tested the hypothesis that ROS toxicity is caused by Rli1p dysfunction. In addition to being essential, Rli1p activity (in nuclear ribosomal-subunit export) was shown to be impaired by mild oxidative stress in yeast. Furthermore, prooxidant resistance was decreased by RLI1 repression and increased by RLI1 overexpression. This Rlip1 dependency was abolished during anaerobicity and accentuated in cells expressing a FeS cluster–defective Rli1p construct. The protein's FeS clusters appeared ROS labile during in vitro incubations, but less so in vivo. Instead, it was primarily ⁵⁵FeS-cluster supply to Rli1p that was defective in prooxidant-exposed cells. The data indicate that, owing to its essential nature but dependency on ROS-labile FeS clusters, Rli1p function is a primary target of ROS action. Such insight could help inform new approaches for combating oxidative stress–related disease.