Effect of Arkadia knockdown on Nrf2 ubiquitylation. A, HepG2 cells were transfected with 200 nM of control siRNA or 50 nM, 100 nM or 200 nM ofsiArkadiato detect the effeciency of Arkadia knockdown. B, C, HepG2 cells were transfected with 50 nM of control siRNA or siArkadia along with plasmid encoding wild-type HA-Ub, HA-Ub-K48R or HA-Ub-K48 only. After 48 h, cells were treated with As203 (5 μM) for 4h and harvested. Whole cell lysates were generated and immunoprecipitated with anti-Nrf2 antibody and blotted with anti-HA antibody (B) or anti-K48-specific ubiquitin antibody (C). The same whole cell lysates were immunoblotted with anti-Nrf2 antibody and anti-β-actin as a loading control.