Involvement of calcium ion in elevation of mRNA for gamma-glutamylcysteine synthetase (gamma-GCS) induced by low-dose gamma-rays.
OBJECTIVE
To investigate the mechanism of the intracellular glutathione elevation induced by low-dose gamma-radiation.


METHODS
RAW 264.7 cells were irradiated with 1-400cGy gamma-rays. Intracellular total glutathione content was determined by DTNB-recycling assay. Expression of mRNA for intracellular glutathione synthesis-related enzymes with or without treatment with various inhibitors of second messengers of gene expression were examined by Northern blot analysis.


RESULTS
Expression of mRNA for gamma-glutamylcysteine synthetase (gamma-GCS), a rate-limiting enzyme of the de novo glutathione synthesis pathway, was elevated much more than that of glutathione reductase (GR) mRNA after exposure to 50cGy gamma-rays. The low-dose gamma-ray-induced gamma-GCS mRNA elevation was abolished by inhibitors of protein kinase C and protein tyrosine kinase, as well as by the calcium ion channel blocker, nifedipine. Calcium-related reagents, such BAPTA/AM and EGTA, chelators of intra- and extracellular Ca2+ respectively, and a Ca2+ ionophore (A23187), also strongly blocked the elevation of gamma-GCS mRNA expression induced by gamma-rays.


CONCLUSIONS
The increase of intracellular glutathione in RAW 264.7 soon after low-dose gamma-ray exposure mainly occurs through the operation of the de novo pathway, following by the induction of gamma-GCS mRNA, for which elevation of intracellular calcium is required.
Teshima
K
K
Department of Pharmaceutical Sciences, Science University of Tokyo, Noda-shi, Chiba, Japan.
Yamamoto
A
A
Yamaoka
K
K
Honda
Y
Y
Honda
S
S
Sasaki
T
T
Kojima
S
S
D000818:Animals; D015152:Blotting, Northern; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D002614:Chelating Agents / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005720:Gamma Rays; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D007477:Ions; D008264:Macrophages / Q000528:radiation effects; D051379:Mice; D008954:Models, Biological; D009543:Nifedipine / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000528:radiation effects*; D015398:Signal Transduction / Q000528:radiation effects; D013997:Time Factors
D002121:Calcium Channel Blockers; D002614:Chelating Agents; D007476:Ionophores; D007477:Ions; D012333:RNA, Messenger; D000001:Calcimycin; D004533:Egtazic Acid; D005980:Glutathione Reductase; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione; D009543:Nifedipine; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium