Cadmium favors F-actin depolymerization in rat renal mesangial cells by site-specific, disulfide-based dimerization...

Cadmium is a toxic metal that produces oxidative stress and has been shown to disrupt the actin cytoskeleton in rat renal mesangial cells (RMC). In a survey of proteins that might undergo Cd²⁺-dependent disulfide crosslinking, we identified the adenylyl cyclase-associated protein, CAP1, as undergoing a dimerization in response to Cd²⁺ (5-40 µM) that was sensitive to disulfide reducing agents, was reproduced by the disulfide crosslinking agent diamide, and was shown by site-directed mutagenesis to involve the Cys²⁹ residue of the protein. Reactive oxygen species are not involved in the thiol oxidation, and glutathione modulates background levels of dimer. CAP1 is known to enhance cofilin's F-actin severing activity through binding to F-actin and cofilin. F-actin sedimentation and GST-cofilin pulldown studies of CAP1 demonstrated enrichment of the CAP1 dimer's association with cofilin, and in the cofilin-F-actin pellet, suggesting that Cd²⁺-induced dimer increases the formation of a CAP1-cofilin-F-actin complex. Both siRNA-based silencing of CAP1 and overexpression of a CAP1 mutant lacking Cys²⁹ (and therefore, incapable of dimerization in response to Cd²⁺) increased RMC viability and provided some protection of F-actin structures against Cd²⁺. It is concluded that Cd²⁺ brings about disruption of the RMC cytoskeleton in part through formation of a CAP1 dimer that increases recruitment of cofilin to F-actin filaments.