Calmodulin modulation of adverse effects of Cd(2+) on microtubules and tubulin polymerization in vitro

The contribution of calmodulin to the effects of Cd(2+) on microtubules has been investigated in the detergent-extracted cytoskeletons of cultured cells and on tubulin polymerization in vitro. When incubated with micromolar concentrations of Cd(2+) or Ca(2+) alone, or a mixture of both ions, microtubules in the extracted cytoskeletons disassembled. This disassembly was prevented by compound 48/80, a potent calmodulin inhibitor. In bovine brain microtubule protein containing microtubule-associated proteins, calmodulin also enhanced the Cd(2+)-mediated inhibition of tubulin polymerization; further, this enhancing effect of calmodulin was reversed by compound 48/80. These results demonstrate that Cd(2+) can affect microtubules by binding to and activating calmodulin.