TY - JOUR
T1 - Cap-independent Nrf2 translation is part of a lipoic acid-stimulated detoxification stress response
AU - Shay, Kate Petersen
AU - Michels, Alexander J.
AU - Li, Wenge
AU - Kong, Ah Ng Tony
AU - Hagen, Tory M.
N1 - Funding Information:
This work was supported by grants from the National Institutes of Health R01 2AG17141 and P01 AT002034-01 . KPS was supported by T32 AT002688-01 .
PY - 2012/6
Y1 - 2012/6
N2 - Little is known about either the basal or stimulated homeostatic mechanisms regulating nuclear tenure of Nf-e2-related factor 2 (Nrf2), a transcription factor that mediates expression of over 200 detoxification genes. Our data show that stress-induced nuclear Nrf2 accumulation is largely from de novo protein synthesis, rather than translocation from a pre-existing cytoplasmic pool. HepG2 cells were used to monitor nuclear Nrf2 24. h following treatment with the dithiol micronutrient (R)-α-lipoic acid (LA; 50 μM), or vehicle. LA caused a ≥ 2.5-fold increase in nuclear Nrf2 within 1 h. However, pretreating cells with cycloheximide (50 μg/ml) inhibited LA-induced Nrf2 nuclear accumulation by 94%. Providing cells with the mTOR inhibitor, rapamycin, decreased basal Nrf2 levels by 84% after 4. h, but LA overcame this inhibition. LA-mediated de novo protein translation was confirmed using HepG2 cells transfected with a bicistronic construct containing an internal ribosome entry sequence (IRES) for Nrf2, with significant (P < 0.05) increase in IRES use under LA treatment. These results suggest that a dithiol stimulus mediates Nrf2 nuclear tenure via cap-independent protein translation. Thus, translational control of Nrf2 synthesis, rather than reliance solely on pre-existing protein, may mediate the rapid burst of Nrf2 nuclear accumulation following stress stimuli.
AB - Little is known about either the basal or stimulated homeostatic mechanisms regulating nuclear tenure of Nf-e2-related factor 2 (Nrf2), a transcription factor that mediates expression of over 200 detoxification genes. Our data show that stress-induced nuclear Nrf2 accumulation is largely from de novo protein synthesis, rather than translocation from a pre-existing cytoplasmic pool. HepG2 cells were used to monitor nuclear Nrf2 24. h following treatment with the dithiol micronutrient (R)-α-lipoic acid (LA; 50 μM), or vehicle. LA caused a ≥ 2.5-fold increase in nuclear Nrf2 within 1 h. However, pretreating cells with cycloheximide (50 μg/ml) inhibited LA-induced Nrf2 nuclear accumulation by 94%. Providing cells with the mTOR inhibitor, rapamycin, decreased basal Nrf2 levels by 84% after 4. h, but LA overcame this inhibition. LA-mediated de novo protein translation was confirmed using HepG2 cells transfected with a bicistronic construct containing an internal ribosome entry sequence (IRES) for Nrf2, with significant (P < 0.05) increase in IRES use under LA treatment. These results suggest that a dithiol stimulus mediates Nrf2 nuclear tenure via cap-independent protein translation. Thus, translational control of Nrf2 synthesis, rather than reliance solely on pre-existing protein, may mediate the rapid burst of Nrf2 nuclear accumulation following stress stimuli.
KW - Cap-independent translation
KW - Cellular stress
KW - Lipoic acid
KW - Mammalian target of rapamycin (mTOR)
KW - Nrf2
KW - Protein homeostasis
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U2 - 10.1016/j.bbamcr.2012.04.002
DO - 10.1016/j.bbamcr.2012.04.002
M3 - Article
C2 - 22521877
AN - SCOPUS:84860598278
SN - 0167-4889
VL - 1823
SP - 1102
EP - 1109
JO - Biochimica et Biophysica Acta - Molecular Cell Research
JF - Biochimica et Biophysica Acta - Molecular Cell Research
IS - 6
ER -