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Cadmium induces transcription independently of intracellular calcium mobilization.

Tvermoes BE, Bird GS, Freedman JH - PLoS ONE (2011)

Bottom Line: It has been proposed that cadmium activates transcription by altering intracellular calcium concentration ([Ca(2+)](i)) and disrupting calcium-mediated intracellular signaling processes.In HEK293 constitutively expressing YC3.60, this calcium sensor was found to be insensitive to cadmium.Exposing HEK293::YC3.60 cells to non-cytotoxic cadmium concentrations was sufficient to induce transcription of cadmium-responsive genes but did not affect [Ca(2+)](i) mobilization or increase steady-state mRNA levels of calcium-responsive genes.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, United States of America.

ABSTRACT

Background: Exposure to cadmium is associated with human pathologies and altered gene expression. The molecular mechanisms by which cadmium affects transcription remain unclear. It has been proposed that cadmium activates transcription by altering intracellular calcium concentration ([Ca(2+)](i)) and disrupting calcium-mediated intracellular signaling processes. This hypothesis is based on several studies that may be technically problematic; including the use of BAPTA chelators, BAPTA-based fluorescent sensors, and cytotoxic concentrations of metal.

Methodology/principal finding: In the present report, the effects of cadmium on [Ca(2+)](i) under non-cytotoxic and cytotoxic conditions was monitored using the protein-based calcium sensor yellow cameleon (YC3.60), which was stably expressed in HEK293 cells. In HEK293 constitutively expressing YC3.60, this calcium sensor was found to be insensitive to cadmium. Exposing HEK293::YC3.60 cells to non-cytotoxic cadmium concentrations was sufficient to induce transcription of cadmium-responsive genes but did not affect [Ca(2+)](i) mobilization or increase steady-state mRNA levels of calcium-responsive genes. In contrast, exposure to cytotoxic concentrations of cadmium significantly reduced intracellular calcium stores and altered calcium-responsive gene expression.

Conclusions/significance: These data indicate that at low levels, cadmium induces transcription independently of intracellular calcium mobilization. The results also support a model whereby cytotoxic levels of cadmium activate calcium-responsive transcription as a general response to metal-induced intracellular damage and not via a specific mechanism. Thus, the modulation of intracellular calcium may not be a primary mechanism by which cadmium regulates transcription.

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Related in: MedlinePlus

Venn diagram illustrating genes whose steady-state levels of expression change in HEK293::YC3.60 cells following exposure to 1 or 30 µM cadmium for 4 or 24 h, or 2 µM thapsigargin for 4 h.The identity and description of the eleven common genes are presented in Table 4.
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pone-0020542-g005: Venn diagram illustrating genes whose steady-state levels of expression change in HEK293::YC3.60 cells following exposure to 1 or 30 µM cadmium for 4 or 24 h, or 2 µM thapsigargin for 4 h.The identity and description of the eleven common genes are presented in Table 4.

Mentions: PCR arrays were used to assess the ability of cadmium to affect the steady-state levels of mRNAs encoded by 84 cAMP/calcium -responsive target genes. Consistent with the [Ca2+]i measurements (Fig. 4), 1 µM cadmium did not significantly affect the transcription of the majority of the cAMP/calcium-responsive genes (Tables 1 and 2). Exposure to 30 µM cadmium for 4 or 24 h, however, significantly affected the mRNA levels of many of the cAMP/calcium -responsive target genes. This response may be the result of 30 µM cadmium depleting ER calcium stores thus increasing [Ca2+]i (Fig. 4D), or a consequence of cadmium-mediated cell death (Fig. 2C), which also alters [Ca2+]i. To determine whether the ability of cadmium to induce transcription was due to changes in [Ca2+]i, the patterns of cadmium-responsive gene expression were compared to those produced following thapsigargin exposure (Table 3). Exposure to 1 µM cadmium resulted in the differential expression of four genes that were also affected by thapsigargin exposure (Fig. 5). For these genes (TNF, FOS, PTGS2, and ERG1) however, cadmium exposure caused a significant decrease in the steady-state level of mRNA, whereas thapsigargin exposure produced a significant increase in mRNA levels.


Cadmium induces transcription independently of intracellular calcium mobilization.

Tvermoes BE, Bird GS, Freedman JH - PLoS ONE (2011)

Venn diagram illustrating genes whose steady-state levels of expression change in HEK293::YC3.60 cells following exposure to 1 or 30 µM cadmium for 4 or 24 h, or 2 µM thapsigargin for 4 h.The identity and description of the eleven common genes are presented in Table 4.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3111418&req=5

pone-0020542-g005: Venn diagram illustrating genes whose steady-state levels of expression change in HEK293::YC3.60 cells following exposure to 1 or 30 µM cadmium for 4 or 24 h, or 2 µM thapsigargin for 4 h.The identity and description of the eleven common genes are presented in Table 4.
Mentions: PCR arrays were used to assess the ability of cadmium to affect the steady-state levels of mRNAs encoded by 84 cAMP/calcium -responsive target genes. Consistent with the [Ca2+]i measurements (Fig. 4), 1 µM cadmium did not significantly affect the transcription of the majority of the cAMP/calcium-responsive genes (Tables 1 and 2). Exposure to 30 µM cadmium for 4 or 24 h, however, significantly affected the mRNA levels of many of the cAMP/calcium -responsive target genes. This response may be the result of 30 µM cadmium depleting ER calcium stores thus increasing [Ca2+]i (Fig. 4D), or a consequence of cadmium-mediated cell death (Fig. 2C), which also alters [Ca2+]i. To determine whether the ability of cadmium to induce transcription was due to changes in [Ca2+]i, the patterns of cadmium-responsive gene expression were compared to those produced following thapsigargin exposure (Table 3). Exposure to 1 µM cadmium resulted in the differential expression of four genes that were also affected by thapsigargin exposure (Fig. 5). For these genes (TNF, FOS, PTGS2, and ERG1) however, cadmium exposure caused a significant decrease in the steady-state level of mRNA, whereas thapsigargin exposure produced a significant increase in mRNA levels.

Bottom Line: It has been proposed that cadmium activates transcription by altering intracellular calcium concentration ([Ca(2+)](i)) and disrupting calcium-mediated intracellular signaling processes.In HEK293 constitutively expressing YC3.60, this calcium sensor was found to be insensitive to cadmium.Exposing HEK293::YC3.60 cells to non-cytotoxic cadmium concentrations was sufficient to induce transcription of cadmium-responsive genes but did not affect [Ca(2+)](i) mobilization or increase steady-state mRNA levels of calcium-responsive genes.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina, United States of America.

ABSTRACT

Background: Exposure to cadmium is associated with human pathologies and altered gene expression. The molecular mechanisms by which cadmium affects transcription remain unclear. It has been proposed that cadmium activates transcription by altering intracellular calcium concentration ([Ca(2+)](i)) and disrupting calcium-mediated intracellular signaling processes. This hypothesis is based on several studies that may be technically problematic; including the use of BAPTA chelators, BAPTA-based fluorescent sensors, and cytotoxic concentrations of metal.

Methodology/principal finding: In the present report, the effects of cadmium on [Ca(2+)](i) under non-cytotoxic and cytotoxic conditions was monitored using the protein-based calcium sensor yellow cameleon (YC3.60), which was stably expressed in HEK293 cells. In HEK293 constitutively expressing YC3.60, this calcium sensor was found to be insensitive to cadmium. Exposing HEK293::YC3.60 cells to non-cytotoxic cadmium concentrations was sufficient to induce transcription of cadmium-responsive genes but did not affect [Ca(2+)](i) mobilization or increase steady-state mRNA levels of calcium-responsive genes. In contrast, exposure to cytotoxic concentrations of cadmium significantly reduced intracellular calcium stores and altered calcium-responsive gene expression.

Conclusions/significance: These data indicate that at low levels, cadmium induces transcription independently of intracellular calcium mobilization. The results also support a model whereby cytotoxic levels of cadmium activate calcium-responsive transcription as a general response to metal-induced intracellular damage and not via a specific mechanism. Thus, the modulation of intracellular calcium may not be a primary mechanism by which cadmium regulates transcription.

Show MeSH
Related in: MedlinePlus