Myosin Va Is Required for P Body but Not Stress Granule Formation

Mary W. McCaffrey,Andrew J. Lindsay

doi:10.1074/jbc.m110.182808

Abstract

In the present study we demonstrate an association between mammalian myosin Va and cytoplasmic P bodies, microscopic ribonucleoprotein granules that contain components of the 5'-3' mRNA degradation machinery. Myosin Va colocalizes with several P body markers and its RNAi-mediated knockdown results in the disassembly of P bodies. Overexpression of a dominant-negative mutant of myosin Va reduced the motility of P bodies in living cells. Co-immunoprecipitation experiments demonstrate that myosin Va physically associates with eIF4E, an mRNA binding protein that localizes to P bodies. In contrast, we find that myosin Va does not play a role in stress granule formation. Stress granules are ribonucleoprotein structures that are involved in translational silencing and are spatially, functionally, and compositionally linked to P bodies. Myosin Va is found adjacent to stress granules in stressed cells but displays minimal localization within stress granules, and myosin Va knockdown has no effect on stress granule assembly or disassembly. Combined with recently published reports demonstrating a role for Drosophila and mammalian class V myosins in mRNA transport and the involvement of the yeast myosin V orthologue Myo2p in P body assembly, our results provide further evidence that the class V myosins serve an important role in the transport and turnover of mRNA.

Highlights

It is well established that the yeast class V myosin Myo4p actively transports Ash1 mRNA to the bud tip of dividing cells [7], but it is emerging that class V myosins from higher eukaryotes play roles in RNA transport
Myosin Va has been found associated with several RNA binding proteins in a messenger ribonucleoprotein complex precipitated from a mouse brain extract [8]
We found that it physically associates with the mRNA cap binding protein eIF4E and showed that the siRNA-mediated depletion of myosin Va affects the assembly of P bodies but has no effect on the formation of the closely related stress granules

Summary

Introduction

It is well established that the yeast class V myosin Myo4p actively transports Ash1 mRNA to the bud tip of dividing cells [7], but it is emerging that class V myosins from higher eukaryotes play roles in RNA transport. We found that it physically associates with the mRNA cap binding protein eIF4E and showed that the siRNA-mediated depletion of myosin Va affects the assembly of P bodies but has no effect on the formation of the closely related stress granules. Knockdown of myosin Va resulted in an almost 2-fold reduction in the number of cells displaying P bodies, when compared with the targeting control siRNA, siLamA/C (Fig. 2, B and C).

Results

Conclusion