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Boric acid induces cytoplasmic stress granule formation, eIF2α phosphorylation, and ATF4 in prostate DU-145 cells.

Henderson KA, Kobylewski SE, Yamada KE, Eckhert CD - Biometals (2014)

Bottom Line: Low ER [Ca(2+)] has been reported to induce ER stress and activate the eIF2α/ATF4 pathway.Mild activation of eIF2α and its downstream transcription factor, ATF4, enables cells to reconfigure gene expression to manage stress conditions and mild activation of ATF4 is also required for the differentiation of osteoblast cells.Our results using physiological levels of boric acid identify the eIF2α/ATF pathway as a plausible mode of action that underpins the reported health effects of dietary boron.

View Article: PubMed Central - PubMed

Affiliation: Interdepartmental Program in Molecular Toxicology, University of California, Los Angeles, CA, USA.

ABSTRACT
Dietary boron intake is associated with reduced prostate and lung cancer risk and increased bone mass. Boron is absorbed and circulated as boric acid (BA) and at physiological concentrations is a reversible competitive inhibitor of cyclic ADP ribose, the endogenous agonist of the ryanodine receptor calcium (Ca(+2)) channel, and lowers endoplasmic reticulum (ER) [Ca(2+)]. Low ER [Ca(2+)] has been reported to induce ER stress and activate the eIF2α/ATF4 pathway. Here we report that treatment of DU-145 prostate cells with physiological levels of BA induces ER stress with the formation of stress granules and mild activation of eIF2α, GRP78/BiP, and ATF4. Mild activation of eIF2α and its downstream transcription factor, ATF4, enables cells to reconfigure gene expression to manage stress conditions and mild activation of ATF4 is also required for the differentiation of osteoblast cells. Our results using physiological levels of boric acid identify the eIF2α/ATF pathway as a plausible mode of action that underpins the reported health effects of dietary boron.

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BA induces formation of TIA-1 positive stress granules. 10 µM BA induced formation of TIA-1 positive stress granules in DU-145 cells at 0.25, 0.5, and 1 h, indicated by TIA-1 protein (green) moving out of the nucleus (blue) with BA treatment. 1 µM thapsigargin (Tg) was used as a positive control, (n = 6–24 cells). All time points showed a significant increase. Pictures are representative of results. Significance differences were represented as *p < 0.05, **p < 0.01, and ***p < 0.001 and error bars represent standard deviations. (Color figure online)
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Fig3: BA induces formation of TIA-1 positive stress granules. 10 µM BA induced formation of TIA-1 positive stress granules in DU-145 cells at 0.25, 0.5, and 1 h, indicated by TIA-1 protein (green) moving out of the nucleus (blue) with BA treatment. 1 µM thapsigargin (Tg) was used as a positive control, (n = 6–24 cells). All time points showed a significant increase. Pictures are representative of results. Significance differences were represented as *p < 0.05, **p < 0.01, and ***p < 0.001 and error bars represent standard deviations. (Color figure online)

Mentions: The absence of eIF2–GTP–tRNAi Met results in eIF2/eIF5-deficient, ‘stalled’ 48S pre-initiation complex (Kedersha et al. 2002). The eIF2/eIF5-deficient pre-initiation complexes and their associated mRNA transcripts are routed to cytoplasmic stress granules (SG) in a process that requires the RNA-binding proteins T-cell intracellular antigen-1 (TIA-1) and TIAR (Anderson and Kedersha 2002). TIA-1 normally resides in the nucleus of unstressed cells but under stress conditions is recruited into SGs. Nearly 90 % of TIA-1 and about 50 % of cytoplasmic poly(A) RNA and poly(A)-binding protein-1 is recruited into SGs (Anderson and Kedersha 2002; Kedersha et al. 2002). We treated cells with 10 µM BA or thapsigargin as a positive control and used a polyclonal antibody to TIA-1 to positively identify cytoplasmic granules as SG. TIA-1 translocation from the nucleus began to occur 15 min after treatment and reached a maximum by 1 h (Fig. 3). This correlated with the timing of 1 h maximum for eIF2α phosphorylation (Fig. 2a).Fig. 3


Boric acid induces cytoplasmic stress granule formation, eIF2α phosphorylation, and ATF4 in prostate DU-145 cells.

Henderson KA, Kobylewski SE, Yamada KE, Eckhert CD - Biometals (2014)

BA induces formation of TIA-1 positive stress granules. 10 µM BA induced formation of TIA-1 positive stress granules in DU-145 cells at 0.25, 0.5, and 1 h, indicated by TIA-1 protein (green) moving out of the nucleus (blue) with BA treatment. 1 µM thapsigargin (Tg) was used as a positive control, (n = 6–24 cells). All time points showed a significant increase. Pictures are representative of results. Significance differences were represented as *p < 0.05, **p < 0.01, and ***p < 0.001 and error bars represent standard deviations. (Color figure online)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig3: BA induces formation of TIA-1 positive stress granules. 10 µM BA induced formation of TIA-1 positive stress granules in DU-145 cells at 0.25, 0.5, and 1 h, indicated by TIA-1 protein (green) moving out of the nucleus (blue) with BA treatment. 1 µM thapsigargin (Tg) was used as a positive control, (n = 6–24 cells). All time points showed a significant increase. Pictures are representative of results. Significance differences were represented as *p < 0.05, **p < 0.01, and ***p < 0.001 and error bars represent standard deviations. (Color figure online)
Mentions: The absence of eIF2–GTP–tRNAi Met results in eIF2/eIF5-deficient, ‘stalled’ 48S pre-initiation complex (Kedersha et al. 2002). The eIF2/eIF5-deficient pre-initiation complexes and their associated mRNA transcripts are routed to cytoplasmic stress granules (SG) in a process that requires the RNA-binding proteins T-cell intracellular antigen-1 (TIA-1) and TIAR (Anderson and Kedersha 2002). TIA-1 normally resides in the nucleus of unstressed cells but under stress conditions is recruited into SGs. Nearly 90 % of TIA-1 and about 50 % of cytoplasmic poly(A) RNA and poly(A)-binding protein-1 is recruited into SGs (Anderson and Kedersha 2002; Kedersha et al. 2002). We treated cells with 10 µM BA or thapsigargin as a positive control and used a polyclonal antibody to TIA-1 to positively identify cytoplasmic granules as SG. TIA-1 translocation from the nucleus began to occur 15 min after treatment and reached a maximum by 1 h (Fig. 3). This correlated with the timing of 1 h maximum for eIF2α phosphorylation (Fig. 2a).Fig. 3

Bottom Line: Low ER [Ca(2+)] has been reported to induce ER stress and activate the eIF2α/ATF4 pathway.Mild activation of eIF2α and its downstream transcription factor, ATF4, enables cells to reconfigure gene expression to manage stress conditions and mild activation of ATF4 is also required for the differentiation of osteoblast cells.Our results using physiological levels of boric acid identify the eIF2α/ATF pathway as a plausible mode of action that underpins the reported health effects of dietary boron.

View Article: PubMed Central - PubMed

Affiliation: Interdepartmental Program in Molecular Toxicology, University of California, Los Angeles, CA, USA.

ABSTRACT
Dietary boron intake is associated with reduced prostate and lung cancer risk and increased bone mass. Boron is absorbed and circulated as boric acid (BA) and at physiological concentrations is a reversible competitive inhibitor of cyclic ADP ribose, the endogenous agonist of the ryanodine receptor calcium (Ca(+2)) channel, and lowers endoplasmic reticulum (ER) [Ca(2+)]. Low ER [Ca(2+)] has been reported to induce ER stress and activate the eIF2α/ATF4 pathway. Here we report that treatment of DU-145 prostate cells with physiological levels of BA induces ER stress with the formation of stress granules and mild activation of eIF2α, GRP78/BiP, and ATF4. Mild activation of eIF2α and its downstream transcription factor, ATF4, enables cells to reconfigure gene expression to manage stress conditions and mild activation of ATF4 is also required for the differentiation of osteoblast cells. Our results using physiological levels of boric acid identify the eIF2α/ATF pathway as a plausible mode of action that underpins the reported health effects of dietary boron.

Show MeSH
Related in: MedlinePlus