G Protein β1γ2 Subunits Promote Microtubule Assembly

Sukla Roychowdhury,Mark M Rasenick

doi:10.1074/jbc.272.50.31576

Sukla Roychowdhury, Mark M Rasenick

Open Access

https://doi.org/10.1074/jbc.272.50.31576

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Abstract

alpha and betagamma subunits of G proteins are thought to transduce signals from cell surface receptors to intracellular effector molecules. Galpha and Gbetagamma have also been implicated in cell growth and differentiation, perhaps due to their association with cytoskeletal components. In this report Gbetagamma is shown to modulate the cytoskeleton by regulation of microtubule assembly. Specificity among betagamma species exists, as beta1gamma2 stimulates microtubule assembly, and beta1gamma1 is without any effect. Furthermore, a mutant beta1gamma2, beta1gamma2(C68S), which does not undergo prenylation and subsequent carboxyl-terminal processing on the gamma subunit, does not stimulate the formation of microtubules. beta immunoreactivity was detected exclusively in the microtubule fraction after assembly in the presence of beta1gamma2, suggesting a preferential association with microtubules rather than soluble tubulin. Crude microtubule fractions from ovine brain contain Gbetagamma, and electron microscopy reveals a specific association with microtubules. The decoration of microtubules by Gbetagamma appears to be strikingly similar to the periodic pattern observed for microtubule-associated proteins, suggesting a similar site of activation of microtubule assembly by both agents. It is suggested that reformation of the cytoskeleton represents an additional cellular process mediated by Gbetagamma.

Highlights

G proteins play important roles in signal transduction by transferring signals from cell surface receptors to intracellular effector molecules
Transducin ␤␥ primarily consists of ␤1 and ␥1 isotypes, ␤␥ subunits purified from bovine brain are heterogenous in composition
Tubulin purified free of microtubule-associated proteins was incubated at 37 °C in the presence of ␤1␥2 or ␤1␥1

Summary

Introduction

G proteins play important roles in signal transduction by transferring signals from cell surface receptors to intracellular effector molecules. Tubulin purified free of microtubule-associated proteins was incubated at 37 °C in the presence of ␤1␥2 or ␤1␥1 (transducin ␤␥). Prenylation of ␤1␥2 Is Required for Promotion of Microtubule Assembly—The finding that ␤1␥2 stimulated microtubule assembly, while ␤1␥1 was ineffective, suggests that the ␥ subunit is the determining factor for the observed difference.

Results

Conclusion