Arsenite enhances ERO1α expression via ryanodine receptor dependent and independent mechanisms.

Arsenite is a potent carcinogen and toxic compound inducing an array of deleterious effects via different mechanisms, which include the Ca2+-dependent formation of reactive oxygen species. The mechanism whereby the metalloid affects Ca2+ homeostasis involves an initial stimulation of the inositol 1, 4, 5-triphosphate receptor, an event associated with an endoplasmic reticulum (ER) stress leading to increased ERO1α expression, and ERO1α dependent activation of the ryanodine receptor (RyR). Ca2+ release from the RyR is then critically connected with the mitochondrial accumulation of Ca2+. We now report that the resulting formation of mitochondrial superoxide triggers a second mechanism of ER stress dependent ERO1α expression, which however fails to impact on Ca2+ release from the RyR or, more generally, on Ca2+ homeostasis. Our results therefore demonstrate that arsenite stimulates two different and sequential mechanisms leading to increased ERO1α expression with different functions, possibly due to their different subcellular compartmentalization.