TRIB3 increases cell resistance to arsenite toxicity by limiting the expression of the glutathione-degrading enzyme CHAC1

Arsenic, a metalloid with cytotoxic and carcinogenic effects related to the disruption of glutathione homeostasis, induces the expression of ATF4, a central transcription factor in the cellular stress response. However, the interplay between factors downstream of ATF4 is incompletely understood. In this article, we investigate the role of Tribbles homolog 3 (TRIB3), a regulatory member of the ATF4 pathway, in determining cell sensitivity to arsenite. Our results show that arsenite potently upregulates Trib3 mRNA and protein in an ATF4-dependent manner in mouse embryonic fibroblasts. Trib3-deficient cells display increased susceptibility to arsenite-induced cell death, which is rescued by re-expressing TRIB3. In cells lacking TRIB3, arsenite stress leads to markedly elevated mRNA and protein levels of Chac1, a gene that encodes a glutathione-degrading enzyme and is not previously known to be repressed by TRIB3. Analysis of the Chac1 promoter identified two regulatory elements that additively mediate the induction of Chac1 by arsenite and ATF4, as well as the robust suppression of Chac1 by TRIB3. Crucially, Chac1 silencing enhances glutathione levels and eliminates the increased susceptibility of Trib3-deficient cells to arsenite stress. Moreover, Trib3-deficient cells demonstrate an increased rate of glutathione consumption, which is abolished by Chac1 knockdown. Taken together, these data indicate that excessive Chac1 expression is detrimental to arsenite-treated cell survival and that TRIB3 is critical for restraining the pro-death potential of Chac1 during arsenite stress, representing a novel mechanism of cell viability regulation that occurs within the ATF4 pathway.