SummaryThe biguanide drug metformin is widely prescribed to treat type 2 diabetes and metabolic syndrome, but its mode of action remains uncertain. Metformin also increases lifespan in Caenorhabditis elegans cocultured with Escherichia coli. This bacterium exerts complex nutritional and pathogenic effects on its nematode predator/host that impact health and aging. We report that metformin increases lifespan by altering microbial folate and methionine metabolism. Alterations in metformin-induced longevity by mutation of worm methionine synthase (metr-1) and S-adenosylmethionine synthase (sams-1) imply metformin-induced methionine restriction in the host, consistent with action of this drug as a dietary restriction mimetic. Metformin increases or decreases worm lifespan, depending on E. coli strain metformin sensitivity and glucose concentration. In mammals, the intestinal microbiome influences host metabolism, including development of metabolic disease. Thus, metformin-induced alteration of microbial metabolism could contribute to therapeutic efficacy—and also to its side effects, which include folate deficiency and gastrointestinal upset.PaperClip

Tau in Alzheimer disease brain is highly phosphorylated and aggregated into paired helical filaments comprising characteristic neurofibrillary tangles. Here we have analyzed insoluble Tau (PHF-tau) extracted from Alzheimer brain by mass spectrometry and identified 11 novel phosphorylation sites, 10 of which were assigned unambiguously to specific amino acid residues. This brings the number of directly identified sites in PHFtau to 39, with an additional six sites indicated by reactivity with phosphospecific antibodies to Tau. We also identified five new phosphorylation sites in soluble Tau from control adult human brain, bringing the total number of reported sites to nine. To assess which kinases might be responsible for Tau phosphorylation, we used mass spectrometry to determine which sites were phosphorylated in vitro by several kinases. Casein kinase 1␦ and glycogen synthase kinase-3␤ were each found to phosphorylate numerous sites, and each kinase phosphorylated at least 15 sites that are also phosphorylated in PHF-tau from Alzheimer brain. A combination of casein kinase 1␦ and glycogen synthase kinase-3␤ activities could account for over three-quarters of the serine/threonine phosphorylation sites identified in PHF-tau, indicating that casein kinase 1␦ may have a role, together with glycogen synthase kinase-

Polymorphonuclear leukocyte (PMN)–derived microparticles display inhibitory properties on target cells as assessed in vitro; since PMNs contain abundant amounts of the endogenous anti-inflammatory protein annexin 1 (AnxA1), we tested here whether biologically active AnxA1 could be present in PMN-derived microparticles. PMN adhesion to human umbilical vein endothelial cell (HUVEC) monolayers led to the generation of microparticles that contained AnxA1, as detected by Western blotting, flow cytometry, and mass spectrometry analyses. Addition of these microparticles to recipient PMNs prior to flow over HUVEC monolayers significantly inhibited cell adhesion, an effect abrogated by a neutralizing anti-AnxA1 antibody, or an antibody raised against the AnxA1 receptor, that is termed lipoxin A4 receptor or ALX. Intravenous delivery of human PMN–derived microparticles markedly inhibited PMN recruitment to an air pouch inflamed with IL-1β. This anti-inflammatory effect was also dependent on endogenous AnxA1, since injection of microparticles produced from wild-type PMNs (bone marrow derived), but not from AnxA1-null PMNs, inhibited IL-1β–induced leukocyte trafficking. In conclusion, PMN-derived microparticles contain functionally active AnxA1 that confers them anti-inflammatory properties; generation of these microparticles in the microcirculation could promote inflammatory resolution by time-dependent dampening of cell recruitment.

SummaryFluoropyrimidines are the first-line treatment for colorectal cancer, but their efficacy is highly variable between patients. We queried whether gut microbes, a known source of inter-individual variability, impacted drug efficacy. Combining two tractable genetic models, the bacterium E. coli and the nematode C. elegans, we performed three-way high-throughput screens that unraveled the complexity underlying host-microbe-drug interactions. We report that microbes can bolster or suppress the effects of fluoropyrimidines through metabolic drug interconversion involving bacterial vitamin B6, B9, and ribonucleotide metabolism. Also, disturbances in bacterial deoxynucleotide pools amplify 5-FU-induced autophagy and cell death in host cells, an effect regulated by the nucleoside diphosphate kinase ndk-1. Our data suggest a two-way bacterial mediation of fluoropyrimidine effects on host metabolism, which contributes to drug efficacy. These findings highlight the potential therapeutic power of manipulating intestinal microbiota to ensure host metabolic health and treat disease.

Glycine decarboxylase (GLDC) acts in the glycine cleavage system to decarboxylate glycine and transfer a one-carbon unit into folate one-carbon metabolism. GLDC mutations cause a rare recessive disease non-ketotic hyperglycinemia (NKH). Mutations have also been identified in patients with neural tube defects (NTDs); however, the relationship between NKH and NTDs is unclear. We show that reduced expression of Gldc in mice suppresses glycine cleavage system activity and causes two distinct disease phenotypes. Mutant embryos develop partially penetrant NTDs while surviving mice exhibit post-natal features of NKH including glycine accumulation, early lethality and hydrocephalus. In addition to elevated glycine, Gldc disruption also results in abnormal tissue folate profiles, with depletion of one-carbon-carrying folates, as well as growth retardation and reduced cellular proliferation. Formate treatment normalizes the folate profile, restores embryonic growth and prevents NTDs, suggesting that Gldc deficiency causes NTDs through limiting supply of one-carbon units from mitochondrial folate metabolism.

Tau is a major microtubule-associated protein of axons and is also the principal component of the paired helical filaments (PHFs) that comprise the neurofibrillary tangles found in Alzheimer's disease and other tauopathies. Besides phosphorylation of tau on serine and threonine residues in both normal tau and tau from neurofibrillary tangles, Tyr-18 was reported to be a site of phosphorylation by the Src-family kinase Fyn. We examined whether tyrosine residues other than Tyr-18 are phosphorylated in tau and whether other tyrosine kinases might phosphorylate tau. Using mass spectrometry, we positively identified phosphorylated Tyr-394 in PHF-tau from an Alzheimer brain and in human fetal brain tau. When wild-type human tau was transfected into fibroblasts or neuroblastoma cells, treatment with pervanadate caused tau to become phosphorylated on tyrosine by endogenous kinases. By replacing each of the five tyrosines in tau with phenylalanine, we identified Tyr-394 as the major site of tyrosine phosphorylation in tau. Tyrosine phosphorylation of tau was inhibited by PP2 (4-amino-5-(4-chlorophenyl-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), which is known to inhibit Src-family kinases and c-Abl. Cotransfection of tau and kinases showed that Tyr-18 was the major site for Fyn phosphorylation, but Tyr-394 was the main residue for Abl. In vitro, Abl phosphorylated tau directly. Abl could be coprecipitated with tau and was present in pretangle neurons in brain sections from Alzheimer cases. These results show that phosphorylation of tau on Tyr-394 is a physiological event that is potentially part of a signal relay and suggest that Abl could have a pathogenic role in Alzheimer's disease.

The in vivo and in vitro cross-binding of the colicin endonuclease-specific immunity proteins toward the DNase domain of colicin E9 is described. In vivo cross-protection was tested by toxin plate assays in which bacterial cells overexpressing each immunity (Im2, Im7, Im8, and Im9) were challenged with the ColE9 toxin. Im9, the cognate immunity protein, renders cells completely resistant toward very high concentrations of the toxin (> 1 mg/mL), whereas the noncognate immunities display a spectrum of weaker cross-reactivities (< 0.01 mg/mL). The order of biological protection in this assay was Im9 >> Im2 > Im8, with Im7 providing no colicin E9 resistance. In vitro binding between the immunity proteins and the E9 DNase was analyzed by determining the dissociation constants for E9 DNase-Im protein complexes at pH 7.0 in the presence of 200 mM salt and at 25 degrees C. Stopped-flow fluorescence experiments suggest that both Im2 and Im8 associate with the E9 DNase by a two-step mechanism, in which the rate constants for both the bimolecular association (k1 = approximately 6 x 10(7) M-1 s-1) and the subsequent conformational change (k2 + k-2 = 4-5 s-1) are very similar to Im9 binding under the same conditions. Fluorescence chase experiments defined the dissociation rate constants for Im2 and Im8. The estimated values are 10(6)- and 10(8)-fold, respectively, faster than the off-rate for the Im9 protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The endonuclease group of E colicins are a family of bacterial toxins whose cytotoxic activity in a producing host is inactivated by a specific immunity protein. The DNase of colicin E9 can be bound and inhibited by both cognate and noncognate immunity proteins, the dissociation constants for which span a range of 12-orders of magnitude. DNase binding specificity of the immunity proteins is governed primarily by helix II, the sequence of which is variable in this family of proteins. Heteronuclear NMR experiments have identified helix III along with helix II as the likely DNase binding site, although other regions of Im9 also showed perturbations on binding the E9 DNase. In the present work, we have used the NMR experiments as a guide for alanine scanning mutagenesis of Im9. Our data show that helices II and III of Im9 are indeed the DNase binding site and in addition quantitate the relative binding energy associated with each helix. We find that the conserved residues of helix III make the largest relative contribution toward E9 DNase binding. In conjunction with previous studies, the data suggest that specificity in the colicin-immunity system is governed by a dual recognition mechanism in which highly stabilizing interactions emanating from the conserved regions of an immunity protein act as the binding site anchor and these are modulated by interactions from neighboring, nonconserved amino acid residues. This modulation is likely to take the form of both favorable and unfavorable interactions, the balance of which define the specificity of the protein-protein interaction. The generality of such a dual recognition mechanism in other systems is also discussed.