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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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Related in: MedlinePlus

BA induces the eIF2α/ATF4 pathway. a 50 µM BA treated for 24 h induced phosphorylation of eIF2α in DU-145 cells at 1, and 3 h of treatment (n = 3–5). DU-145 cells treated with 1 µM thapsigargin (Tg) or DMSO (DM) for 1 h, n = 3. b DU-145 cells treated with 50 µM BA for 0, 0.5, 3, 6, 12 and 24 h. GAPDH was used as an internal loading control. Translation of GRP78/BiP increased in cells treated at 6–24 h, (n = 3–4). c Treatment of DU-145 cells with 10 µM BA for 24 h caused a significant increase in ATF4. d DU-145 cells were treated with different doses of BA for 24 h and ATF4 mRNA levels measured using real-time PCR (n = 3–6). Significant increases in mRNA were observed at 10, 50 and 100 μM BA. e A time course study following treatment of DU-145 cells with 10 μM BA showed significantly higher ATF4 mRNA levels at 0.5, 1, 2, and 24 h (n = 3–6). Significance differences from 0 concentration or time are shown and represented using *p < 0.05, **p < 0.01 and ***p < 0.001. Error bars represent standard deviations
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Fig2: BA induces the eIF2α/ATF4 pathway. a 50 µM BA treated for 24 h induced phosphorylation of eIF2α in DU-145 cells at 1, and 3 h of treatment (n = 3–5). DU-145 cells treated with 1 µM thapsigargin (Tg) or DMSO (DM) for 1 h, n = 3. b DU-145 cells treated with 50 µM BA for 0, 0.5, 3, 6, 12 and 24 h. GAPDH was used as an internal loading control. Translation of GRP78/BiP increased in cells treated at 6–24 h, (n = 3–4). c Treatment of DU-145 cells with 10 µM BA for 24 h caused a significant increase in ATF4. d DU-145 cells were treated with different doses of BA for 24 h and ATF4 mRNA levels measured using real-time PCR (n = 3–6). Significant increases in mRNA were observed at 10, 50 and 100 μM BA. e A time course study following treatment of DU-145 cells with 10 μM BA showed significantly higher ATF4 mRNA levels at 0.5, 1, 2, and 24 h (n = 3–6). Significance differences from 0 concentration or time are shown and represented using *p < 0.05, **p < 0.01 and ***p < 0.001. Error bars represent standard deviations

Mentions: Cells respond to changes in their environment by reprogramming translation to adapt to the new conditions (Kawai et al. 2004). eIF2α is the regulatory subunit of the large ternary complex, eIF2–GTP–tRNAi Met, which positions the initiator methionine at the first codon of mRNA to commence translation and protein synthesis. Phosphorylation of eIF2α on serine 51 inhibits the formation of the complex, thus inhibiting global translation allowing cells to recover from ER stress (Zoll et al. 2002). We observed an increase in phosphorylation of eIF2α from 1 to 3 h following treatment of DU-145 cells with 50 µM BA (Fig. 2a). We used thapsigargin as positive control since it induces ER stress by decreasing ER luminal Ca2+. Thapsigargin also significantly activated phosphorylation of eIF2α in DU-145 cells at 24 h (Fig. 2a).Fig. 2


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 the eIF2α/ATF4 pathway. a 50 µM BA treated for 24 h induced phosphorylation of eIF2α in DU-145 cells at 1, and 3 h of treatment (n = 3–5). DU-145 cells treated with 1 µM thapsigargin (Tg) or DMSO (DM) for 1 h, n = 3. b DU-145 cells treated with 50 µM BA for 0, 0.5, 3, 6, 12 and 24 h. GAPDH was used as an internal loading control. Translation of GRP78/BiP increased in cells treated at 6–24 h, (n = 3–4). c Treatment of DU-145 cells with 10 µM BA for 24 h caused a significant increase in ATF4. d DU-145 cells were treated with different doses of BA for 24 h and ATF4 mRNA levels measured using real-time PCR (n = 3–6). Significant increases in mRNA were observed at 10, 50 and 100 μM BA. e A time course study following treatment of DU-145 cells with 10 μM BA showed significantly higher ATF4 mRNA levels at 0.5, 1, 2, and 24 h (n = 3–6). Significance differences from 0 concentration or time are shown and represented using *p < 0.05, **p < 0.01 and ***p < 0.001. Error bars represent standard deviations
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Related In: Results  -  Collection

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Fig2: BA induces the eIF2α/ATF4 pathway. a 50 µM BA treated for 24 h induced phosphorylation of eIF2α in DU-145 cells at 1, and 3 h of treatment (n = 3–5). DU-145 cells treated with 1 µM thapsigargin (Tg) or DMSO (DM) for 1 h, n = 3. b DU-145 cells treated with 50 µM BA for 0, 0.5, 3, 6, 12 and 24 h. GAPDH was used as an internal loading control. Translation of GRP78/BiP increased in cells treated at 6–24 h, (n = 3–4). c Treatment of DU-145 cells with 10 µM BA for 24 h caused a significant increase in ATF4. d DU-145 cells were treated with different doses of BA for 24 h and ATF4 mRNA levels measured using real-time PCR (n = 3–6). Significant increases in mRNA were observed at 10, 50 and 100 μM BA. e A time course study following treatment of DU-145 cells with 10 μM BA showed significantly higher ATF4 mRNA levels at 0.5, 1, 2, and 24 h (n = 3–6). Significance differences from 0 concentration or time are shown and represented using *p < 0.05, **p < 0.01 and ***p < 0.001. Error bars represent standard deviations
Mentions: Cells respond to changes in their environment by reprogramming translation to adapt to the new conditions (Kawai et al. 2004). eIF2α is the regulatory subunit of the large ternary complex, eIF2–GTP–tRNAi Met, which positions the initiator methionine at the first codon of mRNA to commence translation and protein synthesis. Phosphorylation of eIF2α on serine 51 inhibits the formation of the complex, thus inhibiting global translation allowing cells to recover from ER stress (Zoll et al. 2002). We observed an increase in phosphorylation of eIF2α from 1 to 3 h following treatment of DU-145 cells with 50 µM BA (Fig. 2a). We used thapsigargin as positive control since it induces ER stress by decreasing ER luminal Ca2+. Thapsigargin also significantly activated phosphorylation of eIF2α in DU-145 cells at 24 h (Fig. 2a).Fig. 2

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