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PI3K signaling mediates diverse regulation of ATF4 expression for the survival of HK-2 cells exposed to cadmium

  • Molecular Toxicology
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Abstract

Cadmium exposure causes endoplasmic reticulum (ER) stress and accumulation of activating transcription factor 4 (ATF4), an ER stress marker. To elucidate the role of phosphatidylinositol-3-kinase (PI3K) signaling in this process, we examined the effects of PI3K signaling on cadmium chloride (CdCl2) exposure-induced ATF4 expression in HK-2 human renal proximal tubular cells. ATF4 knockdown by siRNA enhanced CdCl2-induced cellular damage, indicating a cytoprotective function of ATF4. Treatment with LY294002, a PI3K inhibitor, suppressed CdCl2-induced ATF4 expression and Akt phosphorylation at Thr308 with little effect on phosphorylation of eukaryotic translation initiation factor 2 subunit α at Ser51. Activation of PI3K signaling with epidermal growth factor treatment enhanced CdCl2-induced Akt phosphorylation and ATF4 expression. Suppression of CdCl2-induced ATF4 expression by LY294002 treatment was markedly blocked by cycloheximide, a translation inhibitor, but not by MG-132, a proteasome inhibitor, or actinomycin D, a transcription inhibitor. CdCl2 exposure also induced phosphorylation of mammalian target of rapamycin (mTOR) at Ser2448, glycogen synthase kinase-3α (GSK-3α) at Ser21, GSK-3β at Ser9, and 90 kDa ribosomal S6 kinase 2 (RSK2) at Ser227 in HK-2 cells. Treatment with rapamycin, an mTOR inhibitor, MK2206, an Akt inhibitor, and BI-D1870, a RSK inhibitor, partially suppressed CdCl2-induced ATF4 expression. Conversely, SB216763, a GSK-3 inhibitor, markedly inhibited the potency of LY294002 to suppress CdCl2-induced ATF4 expression. These results suggest that PI3K signaling diversely regulates the expression of ATF4 in a translation-dependent manner via downstream molecules, including mTOR, GSK-3α/β, and RSK2, and plays a role in protecting HK-2 cells from cadmium-induced damage.

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Acknowledgments

This study was supported by the Department Fund of the Tokyo Women’s Medical University School of Medicine.

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The authors declare that they have no conflict of interest.

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  1. Department of Hygiene and Public Health I, Tokyo Women’s Medical University, Tokyo, 162-8666, Japan

    Kota Fujiki, Hisako Inamura & Masato Matsuoka

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  1. Kota Fujiki
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  2. Hisako Inamura
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  3. Masato Matsuoka
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Correspondence to Masato Matsuoka.

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Fujiki, K., Inamura, H. & Matsuoka, M. PI3K signaling mediates diverse regulation of ATF4 expression for the survival of HK-2 cells exposed to cadmium. Arch Toxicol 88, 403–414 (2014). https://doi.org/10.1007/s00204-013-1129-y

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  • DOI: https://doi.org/10.1007/s00204-013-1129-y

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