The phosphatidylinositol 3-kinase inhibitor LY 294002 inhibits GlyT1-mediated glycine uptake

Extreme Depletion of PIP3 Accompanies the Increased Life Span and Stress Tolerance of PI3K-null C. elegans Mutants

The regulation of animal longevity shows remarkable plasticity, in that a variety of genetic lesions are able to extend lifespan by as much as 10-fold. Such studies have implicated several key signaling pathways that must normally limit longevity, since their disruption prolongs life. Little is known, however, about the proximal effectors of aging on which these pathways are presumed to converge, and to date, no pharmacologic agents even approach the life-extending effects of genetic mutation. In the present study, we have sought to define the downstream consequences of age-1 nonsense mutations, which confer 10-fold life extension to the nematode Caenorhabditis elegans – the largest effect documented for any single mutation. Such mutations insert a premature stop codon upstream of the catalytic domain of the AGE-1/p110α subunit of class-I PI3K. As expected, we do not detect class-I PI3K (and based on our sensitivity, it constitutes <14% of wild-type levels), nor do we find any PI3K activity as judged by immunodetection of phosphorylated AKT, which strongly requires PIP₃ for activation by upstream kinases, or immunodetection of its product, PIP₃. In the latter case, the upper 95%-confidence limit for PIP₃ is 1.4% of the wild-type level. We tested a variety of commercially available PI3K inhibitors, as well as three phosphatidylinositol analogs (PIAs) that are most active in inhibiting AKT activation, for effects on longevity and survival of oxidative stress. Of these, GDC-0941, PIA6, and PIA24 (each at 1 or 10 μM) extended lifespan by 7–14%, while PIAs 6, 12, and 24 (at 1 or 10 μM) increased survival time in 5 mM peroxide by 12–52%. These effects may have been conferred by insulinlike signaling, since a reporter regulated by the DAF-16/FOXO transcription factor, SOD-3::GFP, was stimulated by these PIAs in the same rank order (PIA24 > PIA6 > PIA12) as lifespan. A second reporter, PEPCK::GFP, was equally activated (∼40%) by all three.

A new approach to the molecular analysis of docking, priming, and regulated membrane fusion

Studies using isolated sea urchin cortical vesicles have proven invaluable in dissecting mechanisms of Ca(2+)-triggered membrane fusion. However, only acute molecular manipulations are possible in vitro. Here, using selective pharmacological manipulations of sea urchin eggs ex vivo, we test the hypothesis that specific lipidic components of the membrane matrix selectively affect defined late stages of exocytosis, particularly the Ca(2+)-triggered steps of fast membrane fusion. Egg treatments with cholesterol-lowering drugs resulted in the inhibition of vesicle fusion. Exogenous cholesterol recovered fusion extent and efficiency in cholesterol-depleted membranes; α-tocopherol, a structurally dissimilar curvature analogue, selectively restored fusion extent. Inhibition of phospholipase C reduced vesicle phosphatidylethanolamine and suppressed both the extent and kinetics of fusion. Although phosphatidylinositol-3-kinase inhibition altered levels of polyphosphoinositide species and reduced all fusion parameters, sequestering polyphosphoinositides selectively inhibited fusion kinetics. Thus, cholesterol and phosphatidylethanolamine play direct roles in the fusion pathway, contributing negative curvature. Cholesterol also organizes the physiological fusion site, defining fusion efficiency. A selective influence of phosphatidylethanolamine on fusion kinetics sheds light on the local microdomain structure at the site of docking/fusion. Polyphosphoinositides have modulatory upstream roles in priming: alterations in specific polyphosphoinositides likely represent the terminal priming steps defining fully docked, release-ready vesicles. Thus, this pharmacological approach has the potential to be a robust high-throughput platform to identify molecular components of the physiological fusion machine critical to docking, priming, and triggered fusion.