Abstract
Iron is critical for cellular proliferation and its depletion leads to a suppression of both DNA synthesis and global translation. These observations suggest that iron depletion may trigger a cellular "stress response". A canonical response of cells to stress is the formation of stress granules, which are dynamic cytoplasmic aggregates containing stalled pre-initiation complexes that function as mRNA triage centers. By differentially prioritizing mRNA translation, stress granules allow for the continued and selective translation of stress response proteins. Although the multi-subunit eukaryotic initiation factor 3 (eIF3) is required for translation initiation, its largest subunit, eIF3a, may not be essential for this activity. Instead, eIF3a is a vital constituent of stress granules and appears to act, in part, by differentially regulating specific mRNAs during iron depletion. Considering this, we investigated eIF3a's role in modulating iron-regulated genes/proteins that are critically involved in proliferation and metastasis. In this study, eIF3a was down-regulated and recruited into stress granules by iron depletion as well as by the classical stress-inducers, hypoxia and tunicamycin. Iron depletion also increased expression of the metastasis suppressor, N-myc downstream regulated gene-1 (NDRG1), and a known downstream repressed target of eIF3a, namely the cyclin-dependent kinase inhibitor, p27(kip1). To determine if eIF3a regulates NDRG1 expression, eIF3a was inducibly over-expressed or ablated. Importantly, eIF3a positively regulated NDRG1 expression and negatively regulated p27(kip1) expression during iron depletion. This activity of eIF3a could be due to its recruitment to stress granules and/or its ability to differentially regulate mRNA translation during cellular stress. Additionally, eIF3a positively regulated proliferation, but negatively regulated cell motility and invasion, which may be due to the eIF3a-dependent changes in expression of NDRG1 and p27(kip1) observed under these conditions.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cell Cycle Proteins / antagonists & inhibitors
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Cell Cycle Proteins / genetics*
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Cell Cycle Proteins / metabolism
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Cell Hypoxia / genetics
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Cell Line, Tumor
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Cell Proliferation / drug effects
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Cyclin-Dependent Kinase Inhibitor p27 / antagonists & inhibitors
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Cyclin-Dependent Kinase Inhibitor p27 / genetics*
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Cyclin-Dependent Kinase Inhibitor p27 / metabolism
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Cytoplasmic Granules / drug effects
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Cytoplasmic Granules / genetics
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Cytoplasmic Granules / metabolism
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Eukaryotic Initiation Factor-3 / antagonists & inhibitors
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Eukaryotic Initiation Factor-3 / genetics*
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Eukaryotic Initiation Factor-3 / metabolism
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Fibroblasts / cytology
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Fibroblasts / drug effects*
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Fibroblasts / metabolism
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Gene Expression Regulation / drug effects
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Humans
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Intracellular Signaling Peptides and Proteins / antagonists & inhibitors
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Intracellular Signaling Peptides and Proteins / genetics*
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Intracellular Signaling Peptides and Proteins / metabolism
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Iron / pharmacology
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Iron Deficiencies*
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Mice
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Protein Biosynthesis / drug effects
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RNA, Messenger / biosynthesis
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RNA, Messenger / genetics
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Signal Transduction / drug effects
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Stress, Physiological / drug effects
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Stress, Physiological / genetics
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Tunicamycin / pharmacology
Substances
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CDKN1B protein, human
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Cell Cycle Proteins
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EIF3A protein, human
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Eukaryotic Initiation Factor-3
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Intracellular Signaling Peptides and Proteins
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N-myc downstream-regulated gene 1 protein
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RNA, Messenger
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Tunicamycin
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Cyclin-Dependent Kinase Inhibitor p27
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Iron
Grants and funding
DJRL kindly thanks the Cancer Institute NSW (CINSW) for an Early Career Fellowship [10/ECF/2-18] and the NHMRC for an Early Career Postdoctoral Fellowship. FS thanks the CINSW for a Research Scholar Award [07/RSA/1-22] and the University of Sydney for a PhD Scholarship and University Postgraduate Award. YSR appreciates the support of a CINSW Early Career Fellowship [08/ECF/1-36]. ZK kindly thanks the National Health and Medical Research Council (NHMRC) or Australia for an Early Career Postdoctoral Fellowship. DRR thanks the NHMRC for a Senior Principal Research Fellowship and Project Grants. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.