Arsenite Disrupts Zinc-Dependent TGFb2-SMAD Activity During Murine Cardiac Progenitor Cell Differentiation.

TGFβ (transforming growth factor-β) is a key growth factor regulating epithelial to mesenchymal transition (EMT). TGFβ triggers cardiac progenitor cells to differentiate into mesenchymal cells and give rise to the cellular components of coronary vessels as well as cells of aortic and pulmonary valves. TGFb signaling is dependent on a dynamic on and off switch in Smad activity. Arsenite exposure of 1.34 μM for 24-48h has been reported to disrupt Smad phosphorylation leading to deficits in TGFβ-mediated cardiac precursor differentiation and transformation. In this study, the molecular mechanism of acute arsenite toxicity on TGFβ-induced Smad2/3 nuclear shuttling and TGFβ-mediated cardiac EMT was investigated. A 4-h exposure to 5 μM arsenite blocks nuclear accumulation of Smad2/3 in response to TGFβ without disrupting Smad phosphorylation or nuclear importation. The depletion of nuclear Smad is restored by knocking-down Smad-specific exportins, suggesting that arsenite augments Smad2/3 nuclear exportation. The blockage in TGFβ-Smad signaling is likely due to the loss of Zn2+ cofactor in Smad proteins, as Zn2+ supplementation reverses the disruption in Smad2/3 nuclear translocation and transcriptional activity by arsenite. This coincides with Zn2+ supplementation rescuing arsenitemediated deficits in cardiac EMT. Thus, zinc partially protects cardiac EMT from developmental toxicity by arsenite. [ABSTRACT FROM AUTHOR]