Transient formation of Stress Granules requires the sequential action of retrograde and anterograde molecular motors

LOSCHI, MARIELA; BOCCACCIO, GRACIELA L.

Bariloche, Río Negro, Argentina

Simposio; Gene Expression and RNA processing; 2007

International Centre for Genetics Engineering and Biotechnology (ICGEB), FCEyN, UBA, IFIMYME-CONICET

Transient formation of Stress Granules requires the sequential action of retrograde and anterograde molecular motors Loschi, M and Boccaccio, GL.Fundación Instituto Leloir. IIB-FCEyN-UBA IIBBA-CONICET; Argentina mloschi@leloir.org.ar Cellular stress provokes the phosphorylation of the eukaryotic initiation factor 2a thus inhibiting protein translation. Concomitantly with translation blockage, the stalled translational preinitiation complexes aggregate in the cytoplasm along with a number of RNA-binding proteins forming novel structures named Stress Granules (SG). SG are proposed to serve as a triage site that controls the fate of transiently silenced mRNAs. The accumulation of the translational machinery and ribonucleoparticles in SG implies an active transport that we are aimed to investigate. To study the participation of molecular motors in SG formation, the effect of drugs that disrupt specific cytoskeletal structures was assessed. We found that the absence of microfilaments or microtubules differentially affects SG size and distribution. These results suggest that microtubule and microfilament-dependent molecular motors are involved in SG assembly. We found that impairment of dynein function by overexpression of dominant negative constructs or deletion by specific siRNA prevents the formation of SG upon oxidative or endoplasmic reticulum-stress induction, without affecting eIF2a phosphorylation. The effect was specific for SG, as PB, another type of silencing foci were not disrupted. Conversely, impairment of kinesin1 function by molecular strategies delays SG dispersion. The action of molecular motors in aggregation and dispersion of SG is likely to be direct, as we found a strong immunofluorescence signal for dynein and kinesin present in SG. Thus, our results indicate that transport of RNPs by the minus-end directed motor dynein, followed by their anterograde transport driven by kinesin is mediating the transient formation of SG. How anterograde and retrograde transport of RNPs is regulated upon stress remains to be investigated.