Eukaryotic Initiation Factor 2α-independent Pathway of Stress Granule Induction by the Natural Product Pateamine A

Abstract

Stress granules are aggregates of small ribosomal subunits, mRNA, and numerous associated RNA-binding proteins that include several translation initiation factors. Stress granule assembly occurs in the cytoplasm of higher eukaryotic cells under a wide variety of stress conditions, including heat shock, UV irradiation, hypoxia, and exposure to arsenite. Thus far, a unifying principle of eukaryotic initiation factor 2␣ phosphorylation prior to stress granule formation has been observed from the majority of experimental evidence. Pateamine A, a natural product isolated from marine sponge, was recently reported to inhibit eukaryotic translation initiation and induce the formation of stress granules. In this report, the protein composition and fundamental progression of stress granule formation and disassembly induced by pateamine A was found to be similar to that for arsenite. However, pateamine A-induced stress granules were more stable and less prone to disassembly than those formed in the presence of arsenite. Most significantly, pateamine A induced stress granules independent of eukaryotic initiation factor 2␣ phosphorylation, suggesting an alternative mechanism of formation from that previously described for other cellular stresses. Taking into account the known inhibitory effect of pateamine A on eukaryotic translation initiation, a model is proposed to account for the induction of stress granules by pateamine A as well as other stress conditions through perturbation of any steps prior to the rejoining of the 60S ribosomal subunit during the entire translation initiation process. Stress granules (SGs)2 were first observed as cellular bodies visible by microscopy in tomato cells subjected to heat shock (1-3). Subsequently, SGs were identified in mammalian cells exposed to a variety of stress conditions, including oxidative stress, energy depletion, UV irradiation, and hypoxia (4). SG assembly is part of an adaptive response that recruits selected mRNAs and associated proteins for storage or triage to processing bodies (PBs) (5) that are sites of mRNA decay, allowing survival under adverse conditions. Sequestration of these components may help cells to recover post-stress by replenishing the cellular pool of mRNA without the need for new transcription. The physiological relevance of SGs is underscored by the presence of SGs in tissues of animals under stress (4), and SGs have been implicated in radioresistance of tumor cells (6) and tumor necrosis factor ␣ signaling (7). The study of SGs, their mechanism of formation, and biological role is a relatively new field in cell biology. Thus, a deeper understanding of the mechanism of SG formation and cellular functions may be clinically relevant.A critical step in SG formation shared by most stress conditions is phosphorylation of the ␣ subunit of eukaryotic initiation factor 2 (eIF2) (8), which is a component of the eIF2-GTPtRNAi Met ternary complex. The ternary complex is part of the 43S complex (40S particle, eIF3, and ternary complex) that is recruited to mRNA by ...

Stable Formation of Compositionally Unique Stress Granules in Virus-Infected Cells

“…More recently hippuristanol and pateamine A, two compounds that inhibit translation initiation via interaction with eIF4A, another eIF4F component, were found to promote the formation of SGs (5,6,27,29). Notably, SG formation by pateamine A does not require phosphorylation of eIF2␣ (10,29). Similarly, poliovirus, which inhibits host protein synthesis via cleavage of eIF4G and PABP, also induces SG formation without significant eIF2␣ phosphorylation (29).…”

Metazoan stress granule assembly is mediated by P-eIF2α-dependent and -independent mechanisms

“…However, SG formation can occur by P-eIF2a-independent mechanisms, when steps downstream from eIF2a are inhibited. For instance, the drugs pateamine A and hippuristanol initiate SG formation by inhibiting RNA helicase eIF4A activity, thereby halting ribosome scanning and preventing further initiation events (Dang et al 2006;Mazroui et al 2006). By either mechanism, once new initiation events are inhibited, polysomes are disassembled and SGs can form.…”

Ataxin-2 Interacts with the DEAD/H-Box RNA Helicase DDX6 and Interferes with P-Bodies and Stress Granules

“…This causes a decline of the ternary complex eIF2-GTP-tRNA Met and an accumulation of the 48S* preinitiation complex resulting in the disassembly of polysomes and the assembly of SGs (Anderson and Kedersha, 2002a,b;Kedersha and Anderson, 2002). However, recently eIF2␣ phosphorylation-independent pathways, which target translation initiation, have been reported (Dang et al, 2006;Mazroui et al, 2006). Interference with the activity of another initiation factor, eIF4A, induces assembly of SGs.…”