Immediate Early Gene X1 (IEX-1) Is Organized in Subnuclear Structures and Partially Co-localizes with Promyelocytic Leukemia Protein in HeLa Cells

Kruse, Marie‐Luise; Arlt, Alexander; Sieke, Alexander; Grohmann, Frauke; Grossmann, M; Minkenberg, Jörg; Fölsch, Ulrich R.; Schäfer, Heiner

doi:10.1074/jbc.m501571200

Cited by 16 publications

(25 citation statements)

References 51 publications

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“…Conversely, a K60A/R63A mutant with an altered nuclear localization sequence showed no apoptosis-enhancing effects over background (Fig. 4A), in contrast to its insignificance in cell survival, confirming early investigation (26). Thus, our results delineate distinct regions of IEX-1 for its anti-and pro-apoptotic activities and as a corollary, discrete nonoverlapping mechanisms are likely to mediate these two opposing activities conferred by IEX-1.…”

Section: Resultssupporting

confidence: 64%

“…Additionally, N-linked glycosylation and phosphorylation as well as the C-terminal sequence of IEX-1, are all crucial for anti-apoptosis activity of IEX-1, but these structures appear to exert no discernible role in pro-apoptosis. On the contrary, mutation of nuclear localization sequence, despite its importance in apoptosis, did not impede IEX-1-mediated cell survival (26). IEX-1-mediated cell survival is found to correlate well with its ability of reducing intracellular ROS formation either at basal levels or immediately after apoptotic stimulation.…”

mentioning

confidence: 68%

“…IEX-1 contains a polybasic sequence HRKRSRR, spanning amino residues from 58 to 64, respectively. The sequence matches a canonical nuclear localization sequence motif, K(K/R)X(K/R) (13,26,31). Targeting Lys and Arg at positions 60 and 63 for Ala replacement generated a K60A/R63A mutant.…”

Section: Resultsmentioning

confidence: 99%

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Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

Shen

Guo

Santos‐Berríos

et al. 2006

Journal of Biological Chemistry

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IEX-1 (immediate early response gene X-1) is a stress-inducible gene. Its overexpression can suppress or enhance apoptosis dependent on the nature of stress, yet the polypeptide does not possess any of the functional domains that are homologous to those present in well characterized effectors or inhibitors of apoptosis. This study using sequence-targeting mutagenesis reveals a transmembranelike integrated region of the protein to be critical for both pro-apoptotic and anti-apoptotic functions. Substitution of the key hydrophobic residues with hydrophilic ones within this region impairs the capacity IEX-1 to positively and negatively regulate apoptosis. Mutations at N-linked glycosylation and phosphorylation sites or truncation of the C terminus of IEX-1 also abrogated its potential to promote cell survival. However, distinguished from the transmembrane-like domain, these mutants preserved pro-apoptotic activity of IEX-1 fully. On the contrary, mutation of nuclear localization sequence, despite its importance in apoptosis, did not impede IEX-1-mediated cell survival. Strikingly, all the mutants that lose their anti-apoptotic ability are unable to prevent acute increases in production of intracellular reactive oxygen species (ROS) at the initial onset of apoptosis, whereas those mutants that can sustain antideath function also control acute ROS production as sufficiently as wild-type IEX-1. These findings suggest a critical role of IEX-1 in regulation of intracellular ROS homeostasis, providing new insight into the mechanism underlying IEX-1-mediated cell survival.A coordinated balance between cell survival and apoptosis is essential for embryonic development, tissue homeostasis, and cellular responses to various types of stress (1). Defects in this balance may contribute to a variety of diseases, including cancers, autoimmune disorders, and aberrant embryonic development (2). Programmed cell death occurs in mitochondrion-dependent and independent pathways, and the former accounts for most forms of apoptosis in response to cellular stress, loss of survival factors, and developmental cues (3, 4). The mitochondrial pathway triggers cell death as a consequence of alteration in mitochondrial membrane permeability induced by apoptotic effectors like oxidative stress and signaling-mediated translocation of Bax, Bad, Bid, or Bim, leading to the release of cytochrome c and other proteins contained in the mitochondrial intermembrane space (5, 6). Substantial evidence indicates that prior to an irreparable loss of mitochondrial structural integrity, apoptotic effectors often stimulate an acute increase in the mitochondrial membrane potential ⌬ m that facilitates the formation of reactive oxygen species (ROS), 2 the amplitude of which determines a cell to die by apoptosis or to adapt (4, 7-11). Conceivably, prevention of ROS production in the initial phase of apoptosis is essential to guard the integrity of mitochondrial membrane, protecting cells from undergoing apoptosis.IEX-1 (immediate early response gene X-1), also know...

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Section: Resultssupporting

confidence: 64%

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confidence: 68%

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Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

Shen

Guo

Santos‐Berríos

et al. 2006

Journal of Biological Chemistry

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“…In the present study, the expression of at least two proteins, S-100 and GFAP were stimulated by overexpression of IEX-1. A recent detailed subcellular localization analysis [Kruse et al, 2005] has revealed that IEX-1 is recruited to and exported from the nucleus. This typical movement to and from nucleus is common for the molecules involved in the regulation of gene transcription or reorganization of nuclear proteins.…”

Section: Discussionmentioning

confidence: 99%

Immediate early gene IEX‐1 induces astrocytic differentiation of U87‐MG human glioma cells

You

Osawa

Hayashi

2006

J of Cellular Biochemistry

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The immediate early response gene IEX-1 is involved in the regulation of apoptosis and cell growth. In order to increase the apoptotic sensitivity to chemotherapeutic drugs and g-ray, we attempted to establish U87-MG human glioma cell line expressing IEX-1. Unexpectedly, however, transfection of IEX-1 into U87-MG glioma cells resulted in morphological changes to astrocytic phenotype and increase in glial differentiation marker proteins, S-100 and glial fibrillary acidic protein (GFAP). Glial cell differentiation was used to examine in rat C6 glioma cell line, since this cell line express astrocytic phenotypes by increase in intracellular cAMP concentration. Stimulation of human U87-MG glioma cells by membrane-permeable dibutyryl cAMP (dbcAMP) not only elicited their morphological changes but also induced expression of IEX-1 as well as S-100 and GFAP. H89, an inhibitor of protein kinase A (PKA), blocked dbcAMP-induced morphological changes of U87-MG cells and expression of IEX-1. In contrast, morphological changes and expression of S-100 and GFAP induced by IEX-1 were not affected by H89. Morphological changes induced by dbcAMP were totally abolished by functional disruption of IEX-1 expression by anti-sense RNA. These results indicate that IEX-1 plays an important role in astrocytic differentiation of human glioma cells and that IEX-1 functions at downstream of PKA.

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“…In some cell types, expression of IEX-1 promotes apoptosis (1), while in others, it is protective (92). The protein is found to be associated with ND10 domains (40) and shuttles between the nucleus and the cytoplasm in response to certain stimuli (38). Even though IEX-1 mRNA is up-regulated and stabilized in HSV-infected cells, Taddeo and colleagues report that the protein is not detectable later than 1 h after infection (85), implying that the protein is degraded and/or its mRNA is not translated.…”

Section: Icp27mentioning

confidence: 99%

Herpes Simplex Virus ICP27 Is Required for Virus-Induced Stabilization of the ARE-Containing IEX-1 mRNA Encoded by the Human IER3 Gene

Corcoran

Hsu

Smiley

2006

J Virol

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Herpes simplex virus (HSV) stifles cellular gene expression during productive infection of permissive cells, thereby diminishing host responses to infection. Host shutoff is achieved largely through the complementary actions of two viral proteins, ICP27 and virion host shutoff (vhs), that inhibit cellular mRNA biogenesis and trigger global mRNA decay, respectively. Although most cellular mRNAs are thus depleted, some instead increase in abundance after infection; perhaps surprisingly, some of these contain AU-rich instability elements (AREs) in their 3-untranslated regions. ARE-containing mRNAs normally undergo rapid decay; however, their stability can increase in response to signals such as cytokines and virus infection that activate the p38/MK2 mitogen-activated protein kinase (MAPK) pathway. We and others have shown that HSV infection stabilizes the ARE mRNA encoding the stress-inducible IEX-1 mRNA, and a previous report from another laboratory has suggested vhs is responsible for this effect. However, we now report that ICP27 is essential for IEX-1 mRNA stabilization whereas vhs plays little if any role. A recent report has documented that ICP27 activates the p38 MAPK pathway, and we detected a strong correlation between this activity and stabilization of IEX-1 mRNA by using a panel of HSV type 1 (HSV-1) isolates bearing an array of previously characterized ICP27 mutations. Furthermore, IEX-1 mRNA stabilization was abrogated by the p38 inhibitor SB203580. Taken together, these data indicate that the HSV-1 immediate-early protein ICP27 alters turnover of the ARE-containing message IEX-1 by activating p38. As many ARE mRNAs encode proinflammatory cytokines or other immediate-early response proteins, some of which may limit viral replication, it will be of great interest to determine if ICP27 mediates stabilization of many or all ARE-containing mRNAs.Host protein synthesis is rapidly shut off during productive infection with herpes simplex virus type 1 (HSV-1), thereby tempering host responses to infection and allowing viral mRNAs to dominate the host translational apparatus (69). Host shutoff is achieved largely through the complementary actions of ICP27 and the virion host shutoff (vhs) protein, which inhibit host mRNA biogenesis and trigger accelerated mRNA decay, respectively (26,27,41,64,75).The immediate-early ICP27 protein is an essential multifunctional regulator of viral and cellular gene expression, possessing both activating and repressive functions (47, 76). It binds RNA (50) and shuttles between the nucleus and the cytoplasm (46,49,59,70,77), properties that likely contribute to its ability to activate expression of certain viral genes. In this context, it has been proposed to aid in the transport of intronless viral messages to the cytoplasm via interactions with the cellular mRNA transport factors Aly/Ref (7, 39) and/or TAP1 (8); however, the functional significance of the interaction with Aly/Ref remains uncertain, as a mutation that eliminates the interaction interface has a relatively minor ef...

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Immediate Early Gene X1 (IEX-1) Is Organized in Subnuclear Structures and Partially Co-localizes with Promyelocytic Leukemia Protein in HeLa Cells

Cited by 16 publications

References 51 publications

Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

Immediate early gene IEX‐1 induces astrocytic differentiation of U87‐MG human glioma cells

Herpes Simplex Virus ICP27 Is Required for Virus-Induced Stabilization of the ARE-Containing IEX-1 mRNA Encoded by the Human IER3 Gene

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