The molecular response to reductive stress in LLC-PK1 renal epithelial cells: coordinate transcriptional regulation of gadd153 and grp78 genes by thiols

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Cell Stress Society International

RESUMO

Organic thiols are toxic to eukaryotic cells. Treatment of cells with thiols activates exporession of grp78, but it is not known if, like other forms of strees, there is a battery of stress response genes that are induced by thiols, In LLC-PK1 renal epithelial cells, mRNAs for both grp78 and gadd153 were induced by thiols with similar time, concentration and structure-activity dependence. Dithiothreitol (DTT) was the most potent reductant and inducer of gene expression among the thiols tested. Nuclear run-on assays demonstrated that DTT activated both grp78 and gadd153 genes transcriptionally. A hamster gadd153 promoter construct which contains enhancer elements necessary for gadd153 activation was stably integrated into the LLC-PK1 cell genome and was activated by DTT. Although auto-oxidation of thiols can generate active oxygen species, trtanscriptional activation of the gadd153 promoter was not due to formation of hydrogen peroxide or superoxide since neither catalase nor superoxide dismutase prevented activation of the inhibition of dome formation and protein synthesis, two toxic effects of DTT in LLC-PK1 cells. Thus, both grp78 and gadd153 are members of a gene battery which is responsive to reductive stress. There appears to be considerable, but not complete, overlap between the upstream signaling pathways for activation of both genes.

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