STAUFEN MODULATES THE ASSEMBLY OF STRESS GRANULES

MARTINEZ TOSAR,; M. ANDREA DESBATS;; BOCCACCIO, GRACIELA L

Los Cocos, Cordoba, Argentina

Congreso; VIII Taller Argentino de Neurociencias; 2006

STAUFEN MODULATES THE ASSEMBLY OF STRESS GRANULESMartínez Tosar, Leandro J.; Desbats, María Andrea and Boccaccio, Graciela LFundación Instituto Leloir, IIB-BA CONICET - IIB-FCEyN UBA - Buenos Aires, Argentina<lmartinezt@leloir.org.ar>Normal oxidative metabolism in the brain represents a continuous potential source of oxidative stress, a hazardous chemical state to which nerve cells are particularly sensitive. Moreover, oxidative stress is associated to several pathological conditions of the nervous system such us multiple sclerosis, Alzheimer´s and Parkinson´s diseases, as well as events of reperfusion following ischemia. Several stress conditions (including oxidative stress, UV irradiation, heat shock, and aminoacid deprivation, among others) are known to trigger a plethora of cellular adaptations collectively known as stress response, in many cell types. Under stress, translation ceases for most mRNAs, which become incorporated into large cytoplasmic ribonucleoparticles known as stress granules (SG) where they are believed to be selectively targeted for stabilization, decay, or redirected to resume normal translation. Typical components of SG are the 48S pre-initiation complex, PABP, the nucleo-cytoplasmic shuttling proteins TIAR and TIA-1, the mRNA stabilizing protein HuR, and the mRNA destabilizing protein Tristetraprolin, among others. Previous and recent results from our lab show that the double-stranded RNA-binding protein Staufen1, normally associated to polysomes, accumulates in SG induced by different stressors and in several cell types, including primary oligodendrocytes and neurons (Thomas et al. MBC 2005, Baez and Boccaccio, unpublished results). However, the role of Staufen in SG physiology remains unknown. To address this issue, we have conducted transient oxidative or ER stress in cell lines where Staufen levels had been manipulated by RNA interference-mediated knock down or by overexpression. We found that Staufen-depleted cells display facilitated SG assembly under oxidative stress (induced by sodium arsenite) and endoplasmic reticulum stress (induced by thapsigargin). In these same conditions, Staufen1-EGFP overexpression inhibits SG formation in a dose-dependent manner, an effect much weaker in Staufen2 overexpressing cells, and not observed with EGFP alone. Furthermore, Staufen1 overexpression also inhibits formation of cytoplasmic foci specialized in mRNA degradation known as P-bodies. Interestingly, P-bodies are known to recede upon polysome stabilization. High Staufen levels do not interfere with phosphorylation of eukaryotic initiation factor 2α, a well known trigger of SG assembly under different sorts of stress, suggesting that Staufen-mediated SG inhibition takes place at a downstream step in the stress response cascade. Finally, overexpression of Staufen1 deletional constructs allowed us to map the SG inhibitory activity to the N-terminal portion of the protein. These results suggest a potential role for Staufen1 in the regulation of SG assembly under oxidative stress. We hypothesize that Staufen shifts the balance between polysomes and stress granules, stabilizing polysomes and inhibiting SG assembly. Supported by NIH and Wadsworth Foundation (USA), ANPCyT (Argentina), and Fundación Antorchas(Argentina).