A chemical genetics approach identified a cellular target of several proapoptotic farnesyl transferase inhibitors (FTIs). Treatment with these FTIs caused p53-independent apoptosis in Caenorhabditis elegans, which was mimicked by knockdown of endosomal trafficking proteins, including Rab5, Rab7, the HOPS complex, and notably the enzyme Rab geranylgeranyl transferase (RabGGT). These FTIs were found to inhibit mammalian RabGGT with potencies that correlated with their proapoptotic activity. Knockdown of RabGGT induced apoptosis in mammalian cancer cell lines, and both RabGGT subunits were overexpressed in several tumor tissues. These findings validate RabGGT, and by extension endosomal function, as a therapeutically relevant target for modulation of apoptosis, and enhance our understanding of the mechanism of action of FTIs.

Mutations in the human presenilin genes PS1 and PS2 cause early-onset Alzheimer's disease. Studies in Caenorhabditis elegans and in mice indicate that one function of presenilin genes is to facilitate Notch-pathway signaling. Notably, mutations in the C. elegans presenilin gene sel-12 reduce signaling through an activated version of the Notch receptor LIN-12. To investigate the function of a second C. elegans presenilin gene hop-1 and to examine possible genetic interactions between hop-1 and sel-12, we used a reverse genetic strategy to isolate deletion alleles of both loci. Animals bearing both hop-1 and sel-12 deletions displayed new phenotypes not observed in animals bearing either single deletion. These new phenotypes-germ-line proliferation defects, maternal-effect embryonic lethality, and somatic gonad defectsresemble those resulting from a reduction in signaling through the C. elegans Notch receptors GLP-1 and LIN-12. Thus SEL-12 and HOP-1 appear to function redundantly in promoting Notch-pathway signaling. Phenotypic analyses of hop-1 and sel-12 single and double mutant animals suggest that sel-12 provides more presenilin function than does hop-1.Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the central nervous system involving loss of memory and cognitive function. Amyloid plaques, whose major component is the ␤-amyloid, or A␤, peptide, are a neuropathological hallmark of AD. Dominant mutations in any of three genes, PS1, PS2, or APP, cause early-onset familial AD. PS1 and PS2 encode related proteins termed presenilins 1 and 2 (PS1 and PS2) (1-3), and APP encodes the amyloid precursor protein (APP), from which the A␤ peptide is generated by proteolytic processing (for review, see ref. 4).Three presenilin genes, spe-4 (5), sel-12 (6), and hop-1 (7), have been identified in the nematode Caenorhabditis elegans. Rescue experiments using transgenes have shown that human PS1 and PS2 can substitute for SEL-12, demonstrating that at least some aspects of presenilin function have been conserved from nematodes to mammals (8, 9). Experiments by Levitan and Greenwald (6) indicate that sel-12 acts as a positive regulator of Notch-pathway signaling mediated by the C. elegans Notch receptor homologs GLP-1 and LIN-12: loss-offunction mutations in sel-12 suppress lin-12 gain-of-function phenotypes and enhance lin-12 and glp-1 partial loss-offunction phenotypes. A similar interaction has been proposed to occur in mice: the lethal phenotype of PS1 knockout mice resembles that seen in Notch ligand and receptor knockouts (10, 11).sel-12 mutations do not cause strong Glp-1 or Lin-12 lossof-function phenotypes, suggesting that sel-12 might act redundantly with other presenilin genes (6). To examine the function of hop-1 and to test this hypothesis, we used a reverse genetic strategy to generate hop-1 and sel-12 deletion mutations. Our analysis of hop-1; sel-12 double mutant phenotypes indicates that hop-1 functions redundantly with sel-12 to promote Notch-pathway signaling in C. elegans. Thi...

The CRF (corticotropin releasing factor) system is a key mediator of the stress response. Alterations in CRF signaling have been implicated in drug craving and ethanol consumption. The development of negative reinforcement via activation of brain stress systems has been proposed as a mechanism that contributes to alcohol dependence. Here we isolated a gain-of-function allele of seb-3, a CRF receptor-like GPCR in C. elegans, providing an in vivo model of a constitutively activated stress system. We also characterized a loss-of-function allele of seb-3 and showed that SEB-3 positively regulates a stress response that leads to an enhanced active state of locomotion, behavioral arousal, and tremor. SEB-3 also contributed to acute tolerance to ethanol and to the development of tremor during ethanol withdrawal. Furthermore, we found that a specific CRF1 receptor antagonist reduced acute functional tolerance to ethanol in mice. These findings demonstrate functional conservation of the CRF system in responses to stress and to ethanol in vertebrates and invertebrates.

Normal aging leads to an inexorable decline in motor performance, contributing to medical morbidity and decreased quality of life. While much has been discovered about genetic determinants of lifespan, less is known about modifiers of age-related behavioral decline and whether new gene targets may be found which extend vigorous activity, with or without extending lifespan. Using Caenorhabditis elegans, we have developed a model of declining neuromuscular function and conducted a screen for increased behavioral activity in aged animals. In this model, behavioral function suffers from profound reductions in locomotory frequency, but coordination is strikingly preserved until very old age. By screening for enhancers of locomotion at advanced ages we identified the ras-related Rag GTPase raga-1 as a novel modifier of behavioral aging. raga-1 loss of function mutants showed vigorous swimming late in life. Genetic manipulations revealed that a gain of function raga-1 curtailed behavioral vitality and shortened lifespan, while a dominant negative raga-1 lengthened lifespan. Dietary restriction results indicated that a raga-1 mutant is relatively protected from the life-shortening effects of highly concentrated food, while RNAi experiments suggested that raga-1 acts in the highly conserved target of rapamycin (TOR) pathway in C. elegans. Rag GTPases were recently shown to mediate nutrient-dependent activation of TOR. This is the first demonstration of their dramatic effects on behavior and aging. This work indicates that novel modulators of behavioral function can be identified in screens, with implications for future study of the clinical amelioration of age-related decline.