Enhancement of kinesin-driven microtubule gliding by bile acids

Abstract

We tested the effects of four bile acids, taurochenodeoxycholate, taurocholate, tauroursodeoxycholate and taurodeoxycholate, on kinesin-driven microtubule motility, which may have a major influence on membrane organelle transport in cholestasis. Reconstituted microtubules were incubated with kinesin purified from rabbit liver and brain. Binding and gliding of microtubules were visualized by video-enhanced differential interference contrast microscopy. Liver and brain kinesin produced similar microtubule gliding velocities. The effect of bile acids on liver and brain kinesin was also similar. Low concentrations of the four bile acids (0.25–0.5 mM) enhanced the speed of microtubule gliding by up to 152%. Higher concentrations of taurochenodeoxycholate and taurodeoxycholate inhibited attachment, but did not slow the speed of gliding. Detachment was inhibited by the addition of tauroursodeoxycholate. ATPase activity showed no changes in the presence of low concentrations of tauroursodeoxycholate and taurochenodeoxycholate. Triton X-100, a nonionic detergent, increased microtubule gliding by up to 147% at lower concentrations, while higher concentrations (up to 5%) caused a return to normal speed without detachment. Low concentrations of bile acids in hepatocytes may enhance kinesin-driven microtubule dependent organelle transport. In contrast, higher concentrations of toxic bile acids, chenodeoxycholate and deoxycholate, associated with cholestasis may inhibit kinesin-driven motility by detaching microtubules from kinesin.