Culture and serologic survey for Mycobacterium avium subsp. paratuberculosis infection among southeastern white-tailed deer (Odocoileus virginianus)

From July 1998 through October 2002, radiometric culture (ileocecal lymph node, mesenteric lymph node, and feces) and serologic testing by enzyme-linked immunosorbent assay (ELISA) were used to survey white-tailed deer (Odocoilens virgianus) from the soutlheastern United States for infection by Mycobacterium avium subsp. paratuberculosis (Mptb), the causative agent of paratuberculosis (Johne's disease). Mycobacterium avium subsp. paratuberculosis was isolated from the ileocecal lymph node of one of 313 deer (0.3%) originating from 63 populations in Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, South Carolina, Tennessee, and West Virginia (USA). Six deer (2%), all from different populations, had ELISA results above a 0.25 sample-to-positive cutoff value, but none of the ELISA reactors originated from the population from which the single Mptb isolation was made. These six deer were seronegative when tested by agar gel immunodiffusion (AGID). Collectively, these data indicate that white-tailed deer currently do not constitute a broad regional reservoir for Mptb; however, further study is warranted to clarify the significance, if any, of infected deer to the epizootiology of paratuberculosis on a local scale. Adaptation and validation of an ELISA or another serologic assay for use with deer and other wildlife would markedly enhance Mptb surveillanece among wild populations and would be a powerful tool for gaining information on the role of wild species in epidemiology of paratuberculosis.     

Negative regulation of yeast WASp by two SH3 domain-containing proteins

BACKGROUND: WASp family proteins promote actin filament assembly by activating Arp2/3 complex and are regulated spatially and temporally to assemble specialized actin structures used in diverse cellular processes. Some WASp family members are autoinhibited until bound by activating ligands; however, regulation of the budding yeast WASp homolog (Las17/Bee1) has not yet been explored. RESULTS: We isolated full-length Las17 and characterized its biochemical activities on yeast Arp2/3 complex. Purified Las17 was not autoinhibited; in this respect, it is more similar to SCAR/WAVE than to WASp proteins. Las17 was a much stronger activator of Arp2/3 complex than its carboxyl-terminal (WA) fragment. In addition, actin polymerization stimulated by Las17-Arp2/3 was much less sensitive to the inhibitory effects of profilin compared to polymerization stimulated by WA-Arp2/3. Two SH3 domain-containing binding partners of Las17, Sla1 and Bbc1, were purified and were shown to cooperate in inhibiting Las17 activity. The two SLA1 SH3 domains required for this inhibitory activity in vitro were also required in vivo, in combination with BBC1, for cell viability and normal actin organization. CONCLUSIONS: Full-length Las17 is not autoinhibited and activates Arp2/3 complex more strongly than its WA domain alone, revealing an important role for the Las17 amino terminus in Arp2/3 complex activation. Two of the SH3 domain-containing ligands of Las17, Sla1 and Bbc1, cooperate to inhibit Las17 activity in vitro and are required for a shared function in actin organization in vivo. Our results show that, like SCAR/WAVE, WASp proteins can be controlled by negative regulation through the combined actions of multiple ligands.     

Tuberous sclerosis complex gene products,Tuberin and Hamartin,control mTOR signaling by acting as a GTPase-activating protein complex toward Rheb

BACKGROUND: Tuberous Sclerosis Complex (TSC) is a genetic disorder that occurs through the loss of heterozygosity of either TSC1 or TSC2, which encode Hamartin or Tuberin, respectively. Tuberin and Hamartin form a tumor suppressor heterodimer that inhibits the mammalian target of rapamycin (mTOR) nutrient signaling input, but how this occurs is unclear. RESULTS: We show that the small G protein Rheb (Ras homolog enriched in brain) is a molecular target of TSC1/TSC2 that regulates mTOR signaling. Overexpression of Rheb activates 40S ribosomal protein S6 kinase 1 (S6K1) but not p90 ribosomal S6 kinase 1 (RSK1) or Akt. Furthermore, Rheb induces phosphorylation of eukaryotic initiation factor 4E binding protein 1 (4E-BP1) and causes 4E-BP1 to dissociate from eIF4E. This dissociation is completely sensitive to rapamycin (an mTOR inhibitor) but not wortmannin (a phosphoinositide 3-kinase [PI3K] inhibitor). Rheb also activates S6K1 during amino acid insufficiency via a rapamycin-sensitive mechanism, suggesting that Rheb participates in nutrient signaling through mTOR. Moreover, Rheb does not activate a S6K1 mutant that is unresponsive to mTOR-mediated signals, confirming that Rheb functions upstream of mTOR. Overexpression of the Tuberin-Hamartin heterodimer inhibits Rheb-mediated S6K1 activation, suggesting that Tuberin functions as a Rheb GTPase activating protein (GAP). Supporting this notion, TSC patient-derived Tuberin GAP domain mutants were unable to inactivate Rheb in vivo. Moreover, in vitro studies reveal that Tuberin, when associated with Hamartin, acts as a Rheb GTPase-activating protein. Finally, we show that membrane localization of Rheb is important for its biological activity because a farnesylation-defective mutant of Rheb stimulated S6K1 activation less efficiently. CONCLUSIONS: We show that Rheb acts as a novel mediator of the nutrient signaling input to mTOR and is the molecular target of TSC1 and TSC2 within mammalian cells.     

Endotoxin/lipopolysaccharide activates NF-kappa B and enhances tumor cell adhesion and invasion through a beta 1 integrin-dependent mechanism

Beta(1) integrins play a crucial role in supporting tumor cell attachment to and invasion into the extracellular matrix. Endotoxin/LPS introduced by surgery has been shown to enhance tumor metastasis in a murine model. Here we show the direct effect of LPS on tumor cell adhesion and invasion in extracellular matrix proteins through a beta(1) integrin-dependent pathway. The human colorectal tumor cell lines SW480 and SW620 constitutively expressed high levels of the beta(1) subunit, whereas various low levels of alpha(1), alpha(2), alpha(4), and alpha(6) expression were detected. SW480 and SW620 did not express membrane-bound CD14; however, LPS in the presence of soluble CD14 (sCD14) significantly up-regulated beta(1) integrin expression; enhanced tumor cell attachment to fibronectin, collagen I, and laminin; and strongly promoted tumor cell invasion through the Matrigel. Anti-beta(1) blocking mAbs (4B4 and 6S6) abrogated LPS- plus sCD14-induced tumor cell adhesion and invasion. Furthermore, LPS, when combined with sCD14, resulted in NF-kappaB activation in both SW480 and SW620 cells. Inhibition of the NF-kappaB pathway significantly attenuated LPS-induced up-regulation of beta(1) integrin expression and prevented tumor cell adhesion and invasion. These results provide direct evidence that although SW480 and SW620 cells do not express membrane-bound CD14, LPS in the presence of sCD14 can activate NF-kappaB, up-regulate beta(1) integrin expression, and subsequently promote tumor cell adhesion and invasion. Moreover, LPS-induced tumor cell attachment to and invasion through extracellular matrix proteins is beta(1) subunit-dependent.     

Cutting edge: bacterial lipoprotein induces endotoxin-independent tolerance to septic shock

Tolerance to bacterial cell wall components is an adaptive host response. Endotoxin/LPS tolerance is characterized by a survival advantage against subsequent lethal LPS challenge. However, it is uncertain whether LPS tolerance can afford protection against other septic challenges. In this study, we show that tolerance induced by bacterial lipoprotein (BLP) protects mice against not only BLP-induced lethality, but also LPS-, live bacteria-, and polymicrobial sepsis-induced lethality. In contrast, LPS tolerance offers no survival benefit against the latter two challenges. Furthermore, induction of BLP tolerance results in overexpression of complement receptor type 3 and FcgammaIII/IIR on neutrophils (polymorphonuclear neutrophils) and peritoneal macrophages, with increased bacterial recognition and bactericidal activity, whereas LPS-tolerized mice exhibit an impaired ability to ingest and to kill bacteria. These results indicate that BLP tolerance is a novel adaptive host response associated with a unique protective effect during septic shock.     

Mechanism of nicotinamide inhibition and transglycosidation by Sir2 histone/protein deacetylases

Silent information regulator 2 (Sir2) enzymes catalyze NAD+-dependent protein/histone deacetylation, where the acetyl group from the lysine epsilon-amino group is transferred to the ADP-ribose moiety of NAD+, producing nicotinamide and the novel metabolite O-acetyl-ADP-ribose. Sir2 proteins have been shown to regulate gene silencing, metabolic enzymes, and life span. Recently, nicotinamide has been implicated as a direct negative regulator of cellular Sir2 function; however, the mechanism of nicotinamide inhibition was not established. Sir2 enzymes are multifunctional in that the deacetylase reaction involves the cleavage of the nicotinamide-ribosyl, cleavage of an amide bond, and transfer of the acetyl group ultimately to the 2'-ribose hydroxyl of ADP-ribose. Here we demonstrate that nicotinamide inhibition is the result of nicotinamide intercepting an ADP-ribosyl-enzyme-acetyl peptide intermediate with regeneration of NAD+ (transglycosidation). The cellular implications are discussed. A variety of 3-substituted pyridines was found to be substrates for enzyme-catalyzed transglycosidation. A Br?nsted plot of the data yielded a slope of +0.98, consistent with the development of a nearly full positive charge in the transition state, and with basicity of the attacking nucleophile as a strong predictor of reactivity. NAD+ analogues including beta-2'-deoxy-2'-fluororibo-NAD+ and a His-to-Ala mutant were used to probe the mechanism of nicotinamide-ribosyl cleavage and acetyl group transfer. We demonstrate that nicotinamide-ribosyl cleavage is distinct from acetyl group transfer to the 2'-OH ribose. The observed enzyme-catalyzed formation of a labile 1'-acetylated-ADP-fluororibose intermediate using beta-2'-deoxy-2'-fluororibo-NAD+ supports a mechanism where, after nicotinamide-ribosyl cleavage, the carbonyl oxygen of acetylated substrate attacks the C-1' ribose to form an initial iminium adduct.     

Phospholipase C-gamma contains introns shared by src homology 2 domains in many unrelated proteins

Many proteins with novel functions were created by exon shuffling around the time of the metazoan radiation. Phospholipase C-gamma (PLC-gamma) is typical of proteins that appeared at this time, containing several different modules that probably originated elsewhere. To gain insight into both PLC-gamma evolution and structure-function relationships within the Drosophila PLC-gamma encoded by small wing (sl), we cloned and sequenced the PLC-gamma homologs from Drosophila pseudoobscura and D. virilis and compared their gene structure and predicted amino acid sequences with PLC-gamma homologs in other animals. PLC-gamma has been well conserved throughout, although structural differences suggest that the role of tyrosine phosphorylation in enzyme activation differs between vertebrates and invertebrates. Comparison of intron positions demonstrates that extensive intron loss has occurred during invertebrate evolution and also reveals the presence of conserved introns in both the N- and C-terminal PLC-gamma SH2 domains that are present in SH2 domains in many other genes. These and other conserved SH2 introns suggest that the SH2 domains in PLC-gamma are derived from an ancestral domain that was shuffled not only into PLC-gamma, but also into many other unrelated genes during animal evolution.     

Fanconi anemia protein complex is a novel target of the IKK signalsome

Fanconi anemia (FA), a genetic disorder predisposing to aplastic anemia and cancer, is characterized by hypersensitivity to DNA-damaging agents and oxidative stress. Five of the cloned FA proteins (FANCA, FANCC, FANCE, FANCF, FANCG) appear to be involved in a common functional pathway that is required for the monoubiquitination of a sixth gene product, FANCD2. Here, we report that FANCA associates with the IkappaB kinase (IKK) signalsome via interaction with IKK2. Components of the FANCA complex undergo rapid, stimulus-dependent changes in phosphorylation, which are blocked by kinase-inactive IKK2 (IKK2 K > M). When exposed to mitomycin C, cells expressing IKK2 K > M develop a cell cycle abnormality characteristic of FA. Thus, FANCA may function to recruit IKK2, thus providing the cell a means of rapidly responding to stress.