Microtubules govern stress granule mobility and dynamics

Stress granules (SGs) are ribonucleoprotein (RNP)-containing assemblies that are formed in the cytoplasm in response to stress. Previously, we demonstrated that microtubule depolymerization inhibited SG formation. Here, we show that arsenate-induced SGs move throughout the cytoplasm in a microtubule-dependent manner, and microtubules are required for SG disassembly, but not for SG persistence. Analysis of SG movement revealed that SGs exhibited obstructed diffusion on an average, though sometimes SGs demonstrated rapid displacements. Microtubule depolymerization did not influence preformed SG number and size, but significantly reduced the average velocity of SG movement, the frequency of quick movement events, and the apparent diffusion coefficient of SGs. Actin filament disruption had no effect on the SG motility. In cycloheximide-treated cells SGs dissociated into constituent parts that then dissolved within the cytoplasm. Microtubule depolymerization inhibited cycloheximide-induced SG disassembly. However, microtubule depolymerization did not influence the dynamics of poly(A)-binding protein (PABP) in SGs, according to FRAP results. We suggest that the increase of SG size is facilitated by the transport of smaller SGs along microtubules with subsequent fusion of them. At least some protein components of SGs can exchange with the cytoplasmic pool independently of microtubules.