Mutations in Cu/Zn superoxide dismutase (encoded by SOD1), one of the causes of familial amyotrophic lateral sclerosis (ALS), lead to progressive death of motoneurons through a gain-of-function mechanism. RNA interference (RNAi) mediated by viral vectors allows for long-term reduction in gene expression and represents an attractive therapeutic approach for genetic diseases characterized by acquired toxic properties. We report that in SOD1(G93A) transgenic mice, a model for familial ALS, intraspinal injection of a lentiviral vector that produces RNAi-mediated silencing of SOD1 substantially retards both the onset and the progression rate of the disease.

Phosphorylation is involved in numerous neurodegenerative diseases. In particular, alpha-synuclein is extensively phosphorylated in aggregates in patients suffering from synucleinopathies. However, the share of this modification in the events that lead to the conversion of alpha-synuclein to aggregated toxic species needed to be clarified. The rat model that we developed through rAAV2/6-mediated expression of alpha-synuclein demonstrates a correlation between neurodegeneration and formation of small filamentous alpha-synuclein aggregates. A mutation preventing phosphorylation (S129A) significantly increases alpha-synuclein toxicity and leads to enhanced formation of beta-sheet-rich, proteinase K-resistant aggregates, increased affinity for intracellular membranes, a disarrayed network of neurofilaments and enhanced alpha-synuclein nuclear localization. The expression of a mutation mimicking phosphorylation (S129D) does not lead to dopaminergic cell loss. Nevertheless, fewer but larger aggregates are formed, and signals of apoptosis are also activated in rats expressing the phosphorylation-mimicking form of alpha-synuclein. These observations strongly suggest that phosphorylation does not play an active role in the accumulation of cytotoxic pre-inclusion aggregates. Unexpectedly, the study also demonstrates that constitutive expression of phosphorylation-mimicking forms of alpha-synuclein does not protect from neurodegeneration. The role of phosphorylation at Serine 129 in the early phase of Parkinson's disease is examined, which brings new perspective to therapeutic approaches focusing on the modulation of kinases/phosphatases activity to control alpha-synuclein toxicity.

RNA interference (RNAi) is a form of posttranscriptional gene silencing mediated by short double-stranded RNA, known as small interfering RNA (siRNA). These siRNAs are capable of binding to a specific mRNA sequence and causing its degradation. The recent demonstration of a plasmid vector that directs siRNA synthesis in mammalian cells prompted us to examine the ability of lentiviral vectors to encode siRNA as a means of providing long-term gene silencing in mammalian cells. The RNA-polymerase III dependent promoter (H1-RNA promoter) was inserted in the lentiviral genome to drive the expression of a small hairpin RNA (shRNA) against enhanced green fluorescent protein (EGFP). This construct successfully silenced EGFP expression in two stable cell lines expressing this protein, as analyzed by fluorescence microscopy, flow cytometry, and Western blotting. The silencing, which is dose dependent, occurs as early as 72 hr postinfection and persists for at least 25 days postinfection. The ability of lentiviruses encoding siRNA to silence genes specifically makes it possible to take full advantage of the possibilities offered by the lentiviral vector and provides a powerful tool for gene therapy and gene function studies.

The heat-shock protein 90 (Hsp90) is a cytosolic molecular chaperone that is highly abundant even at normal temperature. Specific functions for Hsp90 have been proposed based on the characterization of its interactions with certain transcription factors and kinases including Raf in vertebrates and flies. We therefore decided to address the role of Hsp90 for MAP kinase pathways in the budding yeast, an organism amenable to both genetic and biochemical analyses. We found that both basal and induced activities of the pheromone-signaling pathway depend on Hsp90. Signaling is defective in strains expressing low levels or point mutants of yeast Hsp90 (Hsp82), or human Hsp90␤ instead of the wild-type protein. Ste11, a yeast equivalent of Raf, forms complexes with wild-type Hsp90 and depends on Hsp90 function for accumulation. For budding yeast, Ste11 represents the first identified endogenous "substrate" of Hsp90. Moreover, Hsp90 functions in steroid receptor and pheromone signaling can be genetically separated as the Hsp82 point mutant T525I and the human Hsp90␤ are specifically defective for the former and the latter, respectively. These findings further corroborate the view that molecular chaperones must also be considered as transient or stable components of signal transduction pathways. INTRODUCTIONThe 90-kDa heat-shock protein (Hsp90) 1 (for reviews, see Jakob and Buchner, 1994;Csermely et al., 1998) is an ubiquitous and abundantly expressed cytosolic protein even at normal temperature. It is highly conserved from bacteria to mammals. Two genes encode closely related isoforms in mammals as well as in the budding yeast Saccharomyces cerevisiae. Deletion experiments in yeast have shown that the expression of at least one of the two Hsp90 isoforms, either Hsp82 or Hsc82, is essential for viability (Borkovich et al., 1989). Similarly, many mutant alleles of the Drosophila HSP90 homolog, HSP83, are embryonic lethals over a deficiency of the locus (van der Straten et al., 1997), whereas the Escherichia coli homolog of Hsp90, HtpG, appears to be dispensable (Bardwell and Craig, 1988). Hsp90 can act as a molecular chaperone in vitro to promote refolding of denatured proteins (Wiech et al., 1992;Yonehara et al., 1996; see also Shaknovich et al., 1992;Shue and Kohtz, 1994), to hold denatured proteins in a folding-competent state for other chaperones (Freeman and Morimoto, 1996;Yonehara et al., 1996) and to prevent protein unfolding and aggregation (Miyata and Yahara, 1992;Jakob et al., 1995aJakob et al., , 1995bYonehara et al., 1996).The interaction of Hsp90 with steroid receptors, which can be thought of as a signal transduction complex, has been the most extensively investigated. A variety of in vitro and in vivo studies have revealed that steroid receptors are complexed with Hsp90 and several other proteins in the absence of hormone (for review, see Pratt and Toft, 1997). Upon ligand binding, the hormone binding domain (HBD) undergoes a conformational change that results in the release of Hsp90 and the concomitant acti...

Huntington's disease (HD) is an inherited neurodegenerative disorder caused by an expansion of glutamine repeats in the huntingtin (htt) protein. Abnormal protein folding and the accumulation of mutated htt are hallmarks of HD neuropathology. Heat-shock proteins (hsps), which refold denatured proteins, might therefore mitigate HD. We show here that hsp104 and hsp27 rescue striatal dysfunction in primary neuronal cultures and HD rat models based on lentiviral-mediated overexpression of a mutated htt fragment. In primary rat striatal cultures, production of hsp104 or hsp27 with htt171-82Q restored neuronal nuclei (NeuN)-positive cell density to that measured after infection with vector expressing the wild-type htt fragment (htt171-19Q). In vivo, both chaperones significantly reduced mutated-htt-related loss of DARPP-32 expression. Furthermore, hsps affected the distribution and size of htt inclusions, with the density of neuritic aggregates being remarkably increased in striatal neurons overexpressing hsps. We also found that htt171-82Q induced the up-regulation of endogenous hsp70 that was co-localized with htt inclusions, and that the overexpression of hsp104 and hsp27 modified the subcellular localization of hsp70 that became cytoplasmic. Finally, hsp104 induced the production of endogenous hsp27. These data demonstrate the protective effects of chaperones in mammalian models of HD.

The highly abundant molecular chaperone Hsp90 functions with assistance from auxiliary factors, collectively referred to as Hsp90 cochaperones, and the Hsp70 system. Hsp104, a molecular chaperone required for stress tolerance and for maintenance of [psi ؉ ] prions in the budding yeast Saccharomyces cerevisiae, appears to collaborate only with the Hsp70 system. We now report that several cochaperones previously thought to be dedicated to Hsp90 are shared with Hsp104. We show that the Hsp90 cochaperones Sti1, Cpr7, and Cns1, which utilize tetratricopeptide repeat (TPR) domains to interact with a common surface on Hsp90, form complexes with Hsp104 in vivo and that Sti1 and Cpr7 interact with Hsp104 directly in vitro. The interaction is Hsp90 independent, as further emphasized by the fact that two distinct TPR domains of Sti1 are required for binding Hsp90 and Hsp104. In a striking parallel to the sequence requirements of Hsp90 for binding TPR proteins, binding of Sti1 to Hsp104 requires a related acidic sequence at the C-terminal tail of Hsp104. While Hsp90 efficiently sequesters the cochaperones during fermentative growth, respiratory conditions induce the interaction of a fraction of Hsp90 cochaperones with Hsp104. This suggests that cochaperone sharing may favor adaptation to altered metabolic conditions.

The molecular chaperone Cdc37 is thought to act in part as a targeting subunit of the heat-shock protein 90 (Hsp90) chaperone complex. We demonstrate here that Cdc37 is required for activity of the kinase Ste11 in budding yeast. A cdc37 mutant strain is defective in Ste11-mediated pheromone signaling and in accumulation and functional maturation of the constitutively active Ste11 version Ste11v vN. Moreover, Cdc37, Ste11v vN and Hsp90 coprecipitate pairwise. Thus, Hsp90 and Cdc37 may transiently associate with Ste11 to promote proper folding and/or association with additional regulatory factors. Our results establish Ste11 as the first endogenous Cdc37 client protein in yeast.z 2000 Federation of European Biochemical Societies.

Cdc37 associates with the heat-shock protein 90 (Hsp90) molecular chaperone as one of several auxiliary proteins that are collectively referred to as Hsp90 co-chaperones. Cdc37 has been proposed to be a specificity factor for Hsp90, directing it notably towards kinases. It is not known whether Cdc37 is essential for viability in the budding yeast Saccharomyces cerevisiae because of Hsp90-dependent or -independent functions or both. Sti1 and Cpr7 are non-essential Hsp90 co-chaperones that bind to a common surface on Hsp90 through tetratricopeptide repeats (TPR). We have found that Sti1 is specifically retained from yeast extracts by immobilized Cdc37. Similarly, the endogenous proteins are also found in a complex. Moreover, purified recombinant Sti1 and Cdc37 interact in the complete absence of Hsp90. Complexes between Cdc37 and Sti1 are not unique to this TPR protein since endogenous Cdc37 can be co-purified with exogenously expressed Cpr7 fused to glutathione-S-transferase. The heterogeneity of Cdc37 complexes, both with and without Hsp90, may expand the functional diversity of Cdc37. Here we show that the combination of cdc37 and sti1 mutations is synthetically lethal, suggesting that direct contacts between Cdc37 and Sti1 may at least contribute to vital functions in yeast.