G protein βγ subunits interact with αβ- and γ-tubulin and play a role in microtubule assembly in PC12 cells

Abstract

The βγ subunit of G proteins (Gβγ) is known to transfer signals from cell surface receptors to intracellular effector molecules. Recent results suggest that Gβγ also interacts with microtubules and is involved in the regulation of the mitotic spindle. In the current study, the anti-microtubular drug nocodazole was employed to investigate the mechanism by which Gβγ interacts with tubulin and its possible implications in microtubule assembly in cultured PC12 cells. Nocodazole-induced depolymerization of microtubules drastically inhibited the interaction between Gβγ and tubulin. Gβγ was preferentially bound to microtubules and treatment with nocodazole suggested that the dissociation of Gβγ from microtubules is an early step in the depolymerization process. When microtubules were allowed to recover after removal of nocodazole, the tubulin-Gβγ interaction was restored. Unlike Gβγ, however, the interaction between tubulin and the α subunit of the Gs protein (Gsα) was not inhibited by nocodazole, indicating that the inhibition of tubulin-Gβγ interactions during microtubule depolymerization is selective. We found that Gβγ also interacts with γ-tubulin, colocalizes with γ-tubulin in centrosomes, and co-sediments in centrosomal fractions. The interaction between Gβγ and γ-tubulin was unaffected by nocodazole, suggesting that the Gβγ-γ-tubulin interaction is not dependent on assembled microtubules. Taken together, our results suggest that Gβγ may play an important and definitive role in microtubule assembly and/or stability. We propose that βγ-microtubule interaction is an important step for G protein-mediated cell activation. These results may also provide new insights into the mechanism of action of anti-microtubule drugs. © 2007 Wiley-Liss, Inc.