Comparisons of CapG and gelsolin-null macrophages: demonstration of a unique role for CapG in receptor-mediated ruffling, phagocytosis, and vesicle rocketing

Capping the barbed ends of actin filaments is a critical step for regulating actin-based motility in nonmuscle cells. The in vivo function of CapG, a calcium-sensitive barbed end capping protein and member of the gelsolin/villin family, has been assessed using a null Capg allele engineered into mice. Both CapG-null mice and CapG/gelsolin double-null mice appear normal and have no gross functional abnormalities. However, the loss of CapG in bone marrow macrophages profoundly inhibits macrophage colony stimulating factor-stimulated ruffling; reintroduction of CapG protein by microinjection fully restores this function. CapG-null macrophages also demonstrate approximately 50% impairment of immunoglobulin G, and complement-opsonized phagocytosis and lanthanum-induced vesicle rocketing. These motile functions are not impaired in gelsolin-null macrophages and no additive effects are observed in CapG/gelsolin double-null macrophages, establishing that CapG function is distinct from, and does not overlap with, gelsolin in macrophages. Our observations indicate that CapG is required for receptor-mediated ruffling, and that it is a major functional component of macrophage phagocytosis. These primary effects on macrophage motile function suggest that CapG may be a useful target for the regulation of macrophage-mediated inflammatory responses.

Shigella actin-based motility in the presence of truncated vinculin

Mounting evidence supports the role of truncated vinculin in the intracellular actin-based motility of Shigella flexneri. Vinculin's role was recently questioned by Goldberg [1997: Cell Motil Cytoskeleton 37:44-53] who observed Shigella motility in mouse embryonal carcinoma 5.51 cells, a genetically modified cell line that reputedly lacked vinculin. That challenge implicitly relied on the assumption that 5.51 cells had no detectable vinculin polypeptide and lacked full-length vinculin mRNA. Despite the appearance of being an unambiguous test of vinculin's role in Shigella motility, 5.51 cells were shown to contain adequate amounts of truncated vinculin (as well as the corresponding mRNA transcript) to support bacterial locomotion. We also examined Shigella locomotion in gamma229 cells, a related embryonal carcinoma cell line containing approximately one-half the vinculin content found in 5.51 cells. We observed that there was a commensurate twofold decrease in the Shigella motility rate, as compared to 5.51 cells; this finding raises the possibility that vinculin can become a rate-limiting factor under some circumstances. Immunofluorescence microscopy using vin 11-5 monoclonal antibody directed against the vinculin head domain showed intense staining of Shigella rocket tails in both gamma229 and 5.51 cells. Our findings clearly demonstrate that motility in 5.51 cells cannot be regarded as a valid criterion for evaluating the role of truncated vinculin in Shigella motility.

Profilin promotes barbed-end actin filament assembly without lowering the critical concentration

The mechanism of profilin-promoted actin polymerization has been systematically reinvestigated. Rates of barbed-end elongation onto Spectrin.4.1. Actin seeds were measured by right angle light scattering to avoid confounding effects of pyrenyl-actin, and KINSIM was used to analyze elongation progress curves. Without thymosin-beta4, both actin and Profilin. Actin (P.A) are competent in barbed-end polymerization, and kinetic simulations yielded the same bimolecular rate constant ( approximately 10 x 10(6) M(-1) s(-1)) for actin monomer or Profilin. Actin. When measured in the absence of profilin, actin assembly curves over a 0.7-4 microM thymosin-beta4 concentration range fit a simple monomer sequestering model (1 microM K(D) for Thymosin-beta4. Actin). The corresponding constant for thymosin-beta4.pyrenyl-Actin, however, was significantly higher ( approximately 9-10 microM), suggesting that the fluorophore markedly weakens binding to thymosin-beta4. With solutions of actin (2 microM) and thymosin-beta4 (2 or 4 microM), the barbed-end assembly rate rose with increasing profilin concentration (0.7-2 microM). Actin assembly in presence of thymosin-beta4 and profilin fit a simple thermodynamic energy cycle, thereby disproving an earlier claim (D. Pantaloni and M.-F. Carlier (1993) Cell 75, 1007-1014) that profilin promotes nonequilibrium filament assembly by accelerating hydrolysis of filament-bound ATP. Our findings indicate that profilin serves as a polymerization catalyst that captures actin monomers from Thymosin-beta4. Actin and ushers actin as a Profilin. Actin complex onto growing barbed filament ends.

Actin-based motility of the intracellular pathogen Listeria monocytogenes: assessing the inhibitory specificity of ABM-1 peptide analogues

Actin-Based Motility motifs [ABM-1 sequence = (D/E)FPPPPX(D/E), where X = P or T, and ABM-2 sequence = XPPPPP, where X denotes G, A, L, P, and S] facilitate assembly of an activated motility complex. Potent inhibition of intracellular motility of pathogens by ABM-1 and ABM-2 peptide analogues has served as a criterion for investigating actin-based motility. To assess the specificity of ABM-1 peptide inhibitors, we microinjected proline-rich peptides into Listeria-infected PtK2 host cells. Use of a combinatorial ABM-1 peptide library (empirical formula = D1E2F2P4T1) demonstrated that high-potency inhibition requires a precise sequence, and not merely a particular amino acid composition. Calculated concentrations of specific sequences in this library indicate that the entire (D/E)FPPPPX(D/E) motif is needed to achieve high-affinity inhibition in living cells. The failure of the well known proline-rich SH3 binding antagonists VSL-12 or APP-12 to inhibit Listeria motility also indicates that SH3 interactions are unlikely to control actin-based motility directly.

Vaccinia locomotion in host cells: evidence for the universal involvement of actin-based motility sequences ABM-1 and ABM-2

Vaccinia uses actin-based motility for virion movement in host cells, but the specific protein components have yet to be defined. A cardinal feature of Listeria and Shigella actin-based motility is the involvement of vasodilator-stimulated phosphoprotein (VASP). This essential adapter recognizes and binds to actin-based motility 1 (ABM-1) consensus sequences [(D/E)FPPPPX(D/E), X = P or T] contained in Listeria ActA and in the p90 host-cell vinculin fragment generated by Shigella infection. VASP, in turn, provides the ABM-2 sequences [XPPPPP, X = G, P, L, S, A] for binding profilin, an actin-regulatory protein that stimulates actin filament assembly. Immunolocalization using rabbit anti-VASP antibody revealed that VASP concentrates behind motile virions in HeLa cells. Profilin was also present in these actin-rich rocket tails, and microinjection of 10 microM (intracellular) ABM-2 peptide (GPPPPP)3 blocked vaccinia actin-based motility. Vinculin did not colocalize with VASP on motile virions and remained in focal adhesion contacts; however, another ABM-1-containing host protein, zyxin, was concentrated at the rear of motile virions. We also examined time-dependent changes in the location of these cytoskeletal proteins during vaccinia infection. VASP and zyxin were redistributed dramatically several hours before the formation of actin rocket tails, concentrating in the viral factories of the perinuclear cytoplasm. Our findings underscore the universal involvement of ABM-1 and ABM-2 docking sites in actin-based motility of Listeria, Shigella, and now vaccinia.

Gelsolin, a protein that caps the barbed ends and severs actin filaments, enhances the actin-based motility of Listeria monocytogenes in host cells

The actin-based motility of Listeria monocytogenes requires the addition of actin monomers to the barbed or plus ends of actin filaments. Immunofluorescence micrographs have demonstrated that gelsolin, a protein that both caps barbed ends and severs actin filaments, is concentrated directly behind motile bacteria at the junction between the actin filament rocket tail and the bacterium. In contrast, CapG, a protein that strictly caps actin filaments, fails to localize near intracellular Listeria. To explore the effect of increasing concentrations of gelsolin on bacterial motility, NIH 3T3 fibroblasts stably transfected with gelsolin cDNA were infected with Listeria. The C5 cell line containing 2.25 times control levels of gelsolin supported significantly higher velocities of bacterial movement than did control fibroblasts (mean +/- standard error of the mean, 0.09 +/- 0.003 micro(m)/s [n = 176] versus 0.05 +/- 0.003 micro(m)/s [n = 65]). The rate of disassembly of the Listeria-induced actin filament rocket tail was found to be independent of gelsolin content. Therefore, if increases in gelsolin content result in increases in Listeria-induced rocket tail assembly rates, a positive correlation between gelsolin content and tail length would be expected. BODIPY-phalloidin staining of four different stably transfected NIH 3T3 fibroblast cell lines confirmed this expectation (r = 0.92). Rocket tails were significantly longer in cells with a high gelsolin content. Microinjection of gelsolin 1/2 (consisting of the amino-terminal half of native gelsolin) also increased bacterial velocity by more than 2.2 times. Microinjection of CapG had no effect on bacterial movement. Cultured skin fibroblasts derived from gelsolin-null mice were capable of supporting intracellular Listeria motility at velocities comparable to those supported by wild-type skin fibroblasts. These experiments demonstrated that the surface of Listeria contains a polymerization zone that can block the barbed-end-capping activity of both gelsolin and CapG. The ability of Listeria to uncap actin filaments combined with the severing activity of gelsolin can accelerate actin-based motility. However, gelsolin is not absolutely required for the actin-based intracellular movement of Listeria because its function can be replaced by other actin regulatory proteins in gelsolin-null cells, demonstrating the functional redundancy of the actin system.

Vinculin proteolysis unmasks an ActA homolog for actin-based Shigella motility

To generate the forces needed for motility, the plasma membranes of nonmuscle cells adopt an activated state that dynamically reorganizes the actin cytoskeleton. By usurping components from focal contacts and the actin cytoskeleton, the intracellular pathogens Shigella flexneri and Listeria monocytogenes use molecular mimicry to create their own actin-based motors. We raised an antibody (designated FS-1) against the FEFPPPPTDE sequence of Listeria ActA, and this antibody: (a) localized at the trailing end of motile intracellular Shigella, (b) inhibited intracellular locomotion upon microinjection of Shigella-infected cells, and (c) cross-reacted with the proteolytically derived 90-kD human vinculin head fragment that contains the Vinc-1 oligoproline sequence, PDFPPPPPDL. Antibody FS-1 reacted only weakly with full-length vinculin, suggesting that the Vinc-1 sequence in full-length vinculin may be masked by its tail region and that this sequence is unmasked by proteolysis. Immunofluoresence staining with a monoclonal antibody against the head region of vinculin (Vin 11-5) localized to the back of motile bacteria (an identical staining pattern observed with the anti-ActA FS-1 antibody), indicating that motile bacteria attract a form of vinculin containing an unmasked Vinc-1 oligoproline sequence. Microinjection of submicromolar concentrations of a synthetic Vinc-1 peptide arrested Shigella intracellular motility, underscoring the functional importance of this sequence. Western blots revealed that Shigella infection induces vinculin proteolysis in PtK2 cells and generates p90 head fragment over the same 1-3 h time frame when intracellular bacteria move within the host cell cytoplasm. We also discovered that microinjected p90, but not full-length vinculin, accelerates rates of pathogen motility by a factor of 3 +/- 0.4 in Shigella-infected PtK2 cells. These experiments suggest that vinculin p90 is a rate-limiting component in actin-based Shigella motility, and that supplementing cells with p90 stimulates rocket tail growth. Earlier findings demonstrated that vinculin p90 binds to IcsA (Suzuki, T.A., S. Saga, and C. Sasakawa. 1996. J. Biol. Chem. 271:21878-21885) and to vasodilator-stimulated phosphoprotein (VASP) (Brindle, N.P.J., M. R. Hold, J.E. Davies, C.J. Price, and D.R. Critchley. 1996. Biochem. J. 318:753-757). We now offer a working model in which proteolysis unmasks vinculin's ActA-like oligoproline sequence. Unmasking of this site serves as a molecular switch that initiates assembly of an actin-based motility complex containing VASP and profilin.

Profilin interacts with the Gly-Pro-Pro-Pro-Pro-Pro sequences of vasodilator-stimulated phosphoprotein (VASP): implications for actin-based Listeria motility

Intracellular actin-based motility of Listeria monocytogenes requires protein-protein interactions involving two different proline-rich sequences: first, the tightly bound bacterial surface protein ActA uses its multiple oligoproline registers [consensus sequence = FE(D)FPPPPTD(E)E(D)] to tether vasodilator-stimulated phosphoprotein (VASP) to the bacterial surface; and second, VASP then deploys its own multiple GPPPPP (or GP5) registers to localize the actin-regulatory protein profilin to promote actin polymerization. We now report that fluorescence titration showed that GP5GP5GP5 peptide binds to profilin (KD of 84 microM), and the peptide weakly inhibits exchange of actin-bound nucleotide in the absence or presence of profilin. Microinjection of synthetic GPPPPP triplet into Listeria-infected PtK2 cells promptly arrested motility at an intracellular concentration of 10 microM. This inhibition was completely neutralized when equimolar concentrations of profilin and GP5GP5GP5 were simultaneously microinjected. Fluorescence studies with [His-133-Ser]-profilin, a site-directed mutant previously shown to be defective in binding poly-l-proline [Bjorkegren, C., Rozycki, M., Schutt, C. E., Lindberg, U., & Karlsson, R. (1993) FEBS Lett. 333, 123-126], exhibits little or no evidence of saturable GP5GP5GP5 binding. When an equimolar concentration of this [His-133-Ser]-profilin mutant was co-injected with GP5GP5GP5, the peptide's inhibitory action remained completely unaffected, indicating that GP5GP5GP5 binding to wild-type profilin represents a key step in actin-based pathogen motility. We also present a model that shows how the focal binding of VASP with its GPPPPP registers can greatly increase the local concentration of profilin and/or profilin-actin-ATP complex at the bacteria/rocket-tail interface.

ABM-1 and ABM-2 homology sequences: consensus docking sites for actin-based motility defined by oligoproline regions in Listeria ActA surface protein and human VASP

Actin-based motility involves a cascade of binding interactions designed to assemble actin regulatory proteins into functional locomotory units. Listeria ActA surface protein contains a series of nearly identical EFPPPPTDE-type oligoproline sequences for binding vasodilator-stimulated phosphoprotein (VASP). The latter is a tetrameric protein with numerous GPP-PPP docking sites for profilin, a 15 kDa regulatory protein that promotes actin filament assembly. Analysis of known actin regulatory proteins led to the identification of distinct Actin-Based Motility homology sequences ABM-1; (D/E)FPPPPX(D/E); and ABM-2, XPPPPP (where X denotes G, A, L, and S).

Recognition of two classes of oligoproline sequences in profilin-mediated acceleration of actin-based Shigella motility

The gram negative rod Shigella flexneri uses it surface protein IcsA to induce host cell actin assembly and to achieve intracellular motility. Yet, the IcsA protein lacks the oligoproline sequences found in ActA, the surface protein required for locomotion of the gram positive rod Listeria monocytogenes. Microinjection of a peptide matching the second ActA oligoproline repeat (FEFPPPPTDE) stops Listeria locomotion (Southwick, F.S., and D.L. Purich. 1994a. Proc. Natl. Acad. Sci. USA. 91:5168-5172), and submicromolar concentrations (intracellular concentration 80-800 nM) similarly arrest Shigella rocket-tail assembly and intracellular motility. Coinjection of a binary solution containing profilin and the ActA analogue increased the observed rates of intracellular motility by a factor of three (mean velocity 0.90 +/- 0.07 mu m/s, SD n=16 before injection vs 0.3 +/- 0.1 mu m/s, n=33 postinjection, intracellular concentration = 80 nM profilin plus 80 nM ActA analogue). Recent evidence suggests the ActA analogue may act by displacing the profilin-binding protein VASP (Pistor, S.C., T. Chakaborty, V. Walter, and J. Wehland. 1995. Curr. Biol. 5:517-525). At considerably higher intracellular concentrations (10 muM), the VASP oligoproline sequence (GPPPPP)3 thought to represent the profilin-binding site (Reinhard, M., K. Giehl, K. Abel, C. Haffner, T. Jarchau, V. Hoppe, B.M. Jockusch, and U. Walter. 1995. EMBO (Eur. Mol. Biol. Organ.) J. 14:1583-1589) also inhibited Shigella movement. A binary mixture of the VASP analogue and profilin (each 10 muM intracellular concentration) led to a doubling of Shigella intracellular migration velocity (0.09 +/- 0.06 mu m/s, n = 25 preinjection vs 0.18 +/- 0.10 mu m/s, n = 61 postinjection). Thus, the two structurally divergent bacteria, Listeria and Shigella, have adopted convergent mechanisms involving profilin recognition of VASP oligoproline sequences and VASP recognition of oligoproline sequences in ActA or an ActA-like host protein to induce host cell actin assembly and to provide the force for intracellular locomotion and cell-cell spread.

Purification and properties of a Ca(2+)-independent barbed-end actin filament capping protein, CapZ, from human polymorphonuclear leukocytes

In human polymorphonuclear leukocytes (PMN), changes in the actin architecture are critical for the shape changes required for chemotaxis and phagocytosis. Barbed-end capping proteins are likely to regulate actin assembly in PMN. The previously identified barbed-end blocking proteins in PMN, gelsolin and CapG, require Ca(2+) to initiate capping of actin filaments. Because chemoattractants can stimulate PMN actin assembly by a calcium-independent signal transduction pathway, we sought to purify a calcium-independent barbed-end capping activity from PMN cytoplasmic extracts. A Ca(2+) -insensitive actin polymerization inhibitory activity was partially purified from human PMN [Southwick & Stossel (1981) J. Biol. Chem 256, 3030]. Using five column chromatography steps, we purified the protein to homogeneity as assessed by silver staining. Purification was associated with an increase in specific activity of greater than 40 X. Western blot analysis identified the protein as the nonmuscle isoform of the heterodimeric capping protein capZ. Human PMN capZ has an apparent disassociation constant of 3 nM for capping in the presence or absence of micromolar Ca(2+), as assessed by both pyrenylactin elongation and depolymerization assays. Similar to the activity reported for the actin polymerization inhibitor, activity of PMN capZ was inhibited by increasing the KC1 concentration from 0.1 M to 0.6 M. The capping function was also inhibited by phosphatidylinositol 4,5-bisphosphate (PIP(2)) micelles, with half-maximal inhibition occurring at 5.5 micrograms mL(-1). PMN capZ did not nucleate actin assembly, sequester actin monomers, or sever actin filaments. Quantitative Western blot analysis revealed that capZ levels corresponded to 0.7-1.0% of the total human PMN cytoplasmic protein. Given its abundance and high affinity for barbed filament ends, capZ is likely to play an important role in the calcium-independent regulation of actin filament assembly associated with PMN chemotaxis.

Gain-of-function mutations conferring actin-severing activity to human macrophage cap G

Nonmuscle cell motility requires marked changes in the consistency and shape of the peripheral cytoplasm. These changes are regulated by a gel-sol transformation of the actin filament network, and actin filament-severing proteins are responsible for network solation. Macrophage Cap G, unlike all other proteins in the gelsolin family, caps but does not sever actin filaments. Two amino acid stretches in Cap G diverge markedly from the severing proteins: 84LNTLLGE and 124AFHKTS. Discrete mutations in Cap G have been generated to determine if these amino acid sequences are critical for actin filament severing. Conversion of 84LNTLLGE to the gelsolin actin-binding helix sequence (84LDDYLGG) renders Cap G capable of severing actin filaments (half-maximal severing, 1-2 microM). Adding a second set of mutations, converting 124AFHKTS to 124GFKHV, enhances severing by 10-fold (half-maximal severing, 0.1-0.2 microM). These experiments support a critical role for these two regions in actin filament severing and showcase the power of gain-of-function mutations in clarifying structure-function relationships.

Listeria monocytogenes intracellular migration: inhibition by profilin, vitamin D-binding protein and DNase I

Infection of host cells by Listeria monocytogenes results in the recruitment of cytoplasmic actin into a tail-like appendage that projects from one end of the bacterium. Each filamentous actin tail progressively lengthens, providing the force which drives the bacterium in a forward direction through the cytoplasm and later results in Listeria cell-to-cell spread. Host cell actin monomers are incorporated into the filamentous actin tail at a discrete site, the bacterial-actin tail interface. We have studied the consequences of microinjecting three different actin monomer-binding proteins on the actin tail assembly and Listeria intracellular movement. Introduction of high concentrations of profilin (estimated injected intracellular concentration 11-22 microM) into infected PtK2 cells causes a marked slowing of actin tail elongation and bacterial migration. Lower intracellular concentrations of two other injected higher affinity monomer-sequestering proteins, Vitamin D-binding protein (DBP; 1-2 microM) and DNase I (6-7 microM) completely block bacterial-induced actin assembly and bacterial migration. The onset of inhibition by each protein is gradual (10-20 min) indicating that the mechanisms by which these proteins interfere with Listeria-induced actin assembly are likely to be complex. To exclude the possibility that Listeria recruits preformed actin filaments to generate the tails and that these monomer-binding proteins act by depolymerizing such performed actin filaments, living infected cells have been injected with fluorescently labeled phalloidin (3 microM). Although the stress fibers are labeled, no fluorescent phalloidin is found in the tails of the moving bacteria. These results demonstrate that Listeria-induced actin assembly in PtK2 cells is the result of assembly of actin monomers into new filaments and that Listeria's ability to recruit polymerization competent monomeric actin is very sensitive to the introduction of exogenous actin monomer-binding proteins.

Inhibition of Listeria locomotion by mosquito oostatic factor, a natural oligoproline peptide uncoupler of profilin action

Mosquito oostatic factor, a naturally occurring decapeptide (YDPAPPPPPP), strikingly resembles the primary structure of oligoproline-rich regions within the protein ActA, a bacterial surface protein required for Listeria motility in host cells. When microinjected into Listeria-infected PtK2 cells, the insect oostatic factor rapidly blocks Listeria-induced actin rocket tail assembly as well as intracellular locomotion of this pathogen. At intracellular concentrations of about 90 nM, transient inhibition of rocket tail formation and bacterial locomotion occurs, followed by full recovery of tail length and motility. However, at 0.9 microM oostatic factor, both processes are permanently arrested. Introduction of oostatic factor by microinjection also causes PtK2 peripheral membrane retraction in both Listeria-infected and uninfected cells. Epifluorescence microscopy with bodipy-phallacidin reveals that cells microinjected with the insect factor lose all actin stress fibers and accumulate F-actin in regions of membrane retraction. When the insect peptide is combined with profilin as an equimolar binary solution (1 microM [final concentration] each), intracellular addition fails to inhibit Listeria rocket-tail formation, fails to block intracellular bacterial movement, and no longer causes marked membrane retraction. The ability of profilin to neutralize the inhibitory action of oostatic factor is consistent with complex formation, and this finding suggests that profilin may interact directly with ActA peptide as well as a host cell peripheral membrane component to promote actin filament assembly by locally generating ATP-actin. Dispersal of profilin from such sites by oligoproline-rich peptide inhibitors suggests that profilin is directly involved in intracellular pathogen locomotion and reorganization of actin cytoskeleton of the host cell peripheral membrane.

Dynamic remodeling of the actin cytoskeleton: lessons learned from Listeria locomotion

The bacterial pathogen Listeria monocytogenes displays the remarkable ability to reorganize the actin cytoskeleton within host cells as a means for promoting cell-to-cell transfer of the pathogen, in a manner that evades humoral immunity. In a series of events commencing with the biosynthesis of the bacterial surface protein ActA, host cell actin and many actin-associated proteins self-assemble to form rocket-tail structures that continually grow at sites proximal to the bacterium and depolymerize distally. Widespread interest in the underlying molecular mechanism of Listeria locomotion stems from the likelihood that the dynamic remodeling of the host cell actin cytoskeleton at the cell's leading edge involves mechanistically analogous interactions. Recent advances in our understanding of these fundamental cytoskeletal rearrangements have been achieved through a clearer recognition of the central role of oligo-proline sequence repeats present in ActA, and these findings provide a basis for inferring the role of analogous host cell proteins in the force-producing and position-securing steps in pseudopod and lamellipod formation at the peripheral membrane.

The human actin-regulatory protein cap G: gene structure and chromosome location

Cap G (formerly called macrophage capping protein or gCap39) is a member of the gelsolin/villin family of actin-regulatory proteins. Unlike all other members of this family, Cap G caps the barbed ends of actin filaments, but does not sever them. This protein is half the molecular weight and contains half the number of repeat subunits (3 vs 6) of gelsolin and villin, suggesting that these two proteins may have arisen by gene duplication of the Cap G gene. To investigate this possibility we have cloned and sequenced the human Cap G gene (gene symbol CAPG). The gene is 16.6 kb in size, contains 10 exons and 9 introns, and is located on the proximal short arm of chromosome 2. The open reading frame is 6.9 kb, having 9 exons and 8 introns. This region contains 3 splice sites that are nearly identical to the human gelsolin gene, but shares only one with villin, indicating that CAPG is more closely related to gelsolin. Further comparisons of these three genes, however, indicate that the evolutionary steps resulting in human gelsolin and villin are likely to have been more complex than a simple tandem duplication of the Cap G gene.

Arrest of Listeria movement in host cells by a bacterial ActA analogue: implications for actin-based motility

Upon entering the host cell's cytoplasm, the pathogen Listeria monocytogenes can subvert the normal contractile system of the host cell; subsequent assembly of polar actin-filament structures is likely to provide the force for rapid intracellular bacterial movement and its cell-to-cell spread. We have now investigated the functional consequences of microinjecting Listeria-infected PtK2 cells with a synthetic peptide, CFEFPPPPTDE. This peptide represents one of four related oligoproline stretches in ActA, a bacterial surface protein necessary for Listeria-induced actin assembly. Over an estimated intracellular concentration range of 80 nM to 0.8 microM, this analogue rapidly blocks the formation of the actin-filament tails and arrests intracellular bacterial motility. Over the same time scale and concentration range, introduction of the ActA analogue also causes host cell membrane retraction. Bodipyphallacidin staining reveals that microinjection of the ActA analogue results in massive retraction of the actin cytoskeleton. Microinjection of 1-20 microM poly(L-proline) (intracellular concentration) fails to block Listeria intracellular movement or polar actin-filament assembly. As observed with ActA, however, poly(L-proline) does cause membrane retraction. Our findings demonstrate the efficacy of low molecular weight peptides in efforts to distinguish mechanistic features in Listeria motility and PtK2 host cell membrane reorganization. These observations also suggest that a cytoskeletal component sensitive to specific oligoproline peptides may participate in protein-protein interactions essential for both of these actin-associated processes.

Calcium regulation of actin filament capping and monomer binding by macrophage capping protein

Macrophage capping protein (MCP) is a unique member of the gelsolin-villin family of calcium-activated barbed end capping proteins which in micromolar Ca2+ also binds actin monomers and nucleates actin assembly. Unlike gelsolin, MCP cannot sever actin filaments, and its Ca(2+)-dependent interaction with actin is completely reversible. The Ca2+ binding properties of MCP and its Ca(2+)-dependent functions were studied quantitatively. MCP undergoes a Ca(2+)-induced conformational change as evidenced by different chymotryptic digest patterns in 0.2 mM CaCl2 compared with 2 mM EGTA. MCP has a single low affinity Ca2+ binding site (KD = 37 microM). Binding of MCP to actin monomers requires a similar Ca2+ concentration ([Ca2+]0.5 = 62 microM) suggesting that MCP.Ca2+ complex formation promotes monomer binding. In contrast, filament capping by MCP requires 1/60th of the Ca2+ concentration required for monomer binding, half-maximal capping occurring at 1 microM Ca2+. The marked difference in the Ca2+ sensitivity of these two functions indicate that MCP's primary actin regulatory role in the macrophage is likely to be capping of the barbed ends of actin filaments.

Acute bacterial meningitis in adults. A review of 493 episodes

BACKGROUND AND METHODS

To characterize acute bacterial meningitis in adults, we reviewed the charts of all persons 16 years of age or older in whom acute bacterial meningitis was diagnosed at Massachusetts General Hospital from 1962 through 1988. We included patients who were admitted after initial treatment at other hospitals.

RESULTS

During the 27-year period, 445 adults were treated for 493 episodes of acute bacterial meningitis, of which 197 (40 percent) were nosocomial. Gram-negative bacilli (other than Haemophilus influenzae) caused 33 percent of the nosocomial episodes but only 3 percent of the community-acquired episodes. In the 296 episodes of community-acquired meningitis, the most common pathogens were Streptococcus pneumoniae (37 percent), Neisseria meningitidis (13 percent), and Listeria monocytogenes (10 percent); these organisms accounted for only 8 percent of the nosocomial episodes. Only 19 of the 493 episodes of meningitis (4 percent) were due to H. influenzae. Nine percent of all patients had recurrent meningitis; many had a cerebrospinal fluid leak. Seizures occurred in 23 percent of patients with community-acquired meningitis, and 28 percent had focal central nervous system findings. Risk factors for death among those with single episodes of community-acquired meningitis included older age (> or = 60 years), obtunded mental state on admission, and seizures within the first 24 hours. Among those with single episodes, the in-hospital mortality rate was 25 percent for community-acquired and 35 percent for nosocomial meningitis. The overall case fatality rate was 25 percent and did not vary significantly over the 27 years.

CONCLUSIONS

In our large urban hospital, a major proportion of cases of acute bacterial meningitis in adults were nosocomial. Recurrent episodes of meningitis were frequent. The overall mortality rate remained high.

Diminished actin polymerization by neutrophils from newborn infants

During the newborn period, abnormalities of neutrophil (PMN) function predispose infants to serious bacterial disease. Actin is a major contributor to PMN shape change and motile behavior. To determine the mechanism underlying defects in newborn granulocyte polarity and chemotaxis, we investigated actin polymerization by cord blood PMN from healthy term infants and adult controls. F-actin (filamentous) content was quantified in the resting state and after stimulation by fluorescence-activated cell-sorter analysis of nitrobenzoxadiazole-phallacidin-stained cells. PMN from newborn infants demonstrated similar basal F-actin levels when compared with adults. N-formyl methionyl leucyl phenylalanine induced a marked increase in actin polymerization that was maximal at 30 s in both neonates and adults and that then declined slowly (depolymerization) over the following 10 min. However, the F-actin content of PMN from newborn infants was significantly diminished when compared with adults at 30 and 60 s after N-formyl methionyl leucyl phenylalanine stimulation (p < 0.05). Both the rate and dose response of N-formyl methionyl leucyl phenylalanine-induced actin polymerization were similar for adult and neonatal PMN. PMN from newborn infants also demonstrated significantly diminished actin polymerization when compared with adults 60 s after stimulation with platelet-activating factor (p < 0.05). Decreased concentrations of F-actin may help explain the observed abnormalities of PMN polarity and chemotaxis in healthy newborn infants.

Host cell actin assembly is necessary and likely to provide the propulsive force for intracellular movement of Listeria monocytogenes

Listeria monocytogenes is able to escape from the phagolysosome and grow within the host cell cytoplasm. By 3 h after initiation of infection, actin filaments begin to concentrate at one end of the bacterium. Polarization of F-actin is associated with intracellular bacterial movement, long projections of actin filaments forming directly behind the moving bacteria. New actin monomers are added to the region of the projection in proximity to the bacterium. The rate of new actin filament growth correlates closely with the speed of bacterial migration. This actin structure is anchored within the cytoplasm, serving as a fixed platform for directional expansion of the actin filament network. The actin projection progressively lengthens as the bacterium migrates. Cytochalasin blocks both elongation of the projection and bacterial movement but does not result in complete depolymerization of the bacterially induced actin structure, residual actin and alpha-actinin persisting in proximity to one end of the bacterium. Bacteria initially migrate within the cortical cytoplasm but later move to the peripheral membrane, where they form filopodiumlike structures which pivot and undulate in the extracellular medium. In the filopodia, bacteria are occasionally seen to abruptly change direction, turn 180 degrees, and move back into the medullary region of the host cell. All filopodium movement ceases once the bacterium containing the F-actin projection returns to the cortical cytoplasm. These results indicate that host cell actin polymerization is necessary for intracellular migration of listeriae and suggest that directional actin assembly may in fact generate the propulsive force for bacterial and filopodial movement.

Molecular cloning of human macrophage capping protein cDNA. A unique member of the gelsolin/villin family expressed primarily in macrophages

Macrophage capping protein (MCP) is a Ca(2+)-sensitive protein which reversibly blocks the barbed ends of actin filaments but does not sever preformed actin filaments. The human cDNA for MCP has been cloned and sequenced. The derived amino acid sequence predicts a polypeptide of 38.4 kDa. Human MCP expressed in Escherichia coli using a pET12a vector was functionally identical to the native protein purified from rabbit alveolar macrophages with respect to Ca2+ sensitivity and ability to block monomer exchange at the barbed end of actin filaments. Sequence comparison with other actin-binding protein sequences indicates that MCP is a member of the gelsolin/villin family of barbed end blocking proteins. Unlike gelsolin, this protein has a limited tissue distribution being detected primarily in macrophages where it was abundant, representing 0.9-1% of the total cytoplasmic protein. Northern blot analysis of U937 and HL60 cells differentiated to macrophage-like cells demonstrated that MCP message increases to 2.6 and greater than 7 times initial levels, respectively. Human MCP displays a 93% amino acid sequence identity with two recently described mouse proteins, gCap39 and Mbh1. Its abundance in macrophages and the corresponding increases in mRNA levels upon promyelocyte and monocyte development into macrophages indicate that MCP may play an important role in macrophage function.

Stimulation of human polymorphonuclear leukocyte phosphatidylinositol-4-phosphate kinase by concanavalin A and formyl-methionyl-leucyl-phenylalanine is calcium-independent. Correlation with maintenance of actin assembly

Chemoattractants directly stimulate the enzyme activity that synthesizes phosphatidylinositol-4,5-bisphosphate (PIP2), phosphoinositol-4-monophosphate (PIP) kinase. The present study determined whether stimulation of this enzyme correlates with actin assembly by assessing the calcium dependence of this reaction. Incubation of neutrophils with 5 to 100 micrograms/ml Con A caused a concentration-dependent increase in PIP kinase activity ranging from 1.38- to 3.4-fold. The effective concentration which stimulated PIP kinase by 50% (17 micrograms/ml, EC50) corresponded with the EC50 for Con A-induced superoxide production (32 micrograms/ml). Like chemoattractants, the increase in PIP kinase by Con A was characterized by a 2.6-fold increase in the maximum velocity (Vmax) of the enzyme, and no change in the Km for ATP. The kinetics of FMLP- and Con A-induced filamentous actin formation preceded stimulation of PIP kinase and was sustained over the same time period that this increased enzyme activity was noted. Although transmembrane signaling by FMLP and Con A requires an increase in intracellular calcium for some polymorphonuclear leukocyte (PMN) functional responses, calcium depletion of PMN by incubation with 100 microM Quin 2 A/M and 5 mM EGTA did not prevent the stimulation of PIP kinase by FMLP or Con A. In addition, calcium depletion did not prevent the increase in filamentous actin formation by FMLP and Con A in PMN. These findings demonstrate that Con A increases PIP kinase activity in human PMN and that PIP kinase stimulation and maintenance of actin assembly are independent of calcium fluxes in these cells. Because PIP2 controls the function of the actin-regulatory proteins, profilin and gelsolin, changes in the synthetic rate of PIP2 through regulation of PIP kinase may provide a molecular basis for the prolonged stimulation of actin assembly in human PMN by agonists such as Con A and FMLP.

Stimulation of human polymorphonuclear leukocyte phosphatidylinositol-4-phosphate kinase by concanavalin A and formyl-methionyl-leucyl-phenylalanine is calcium-independent. Correlation with maintenance of actin assembly

Chemoattractants directly stimulate the enzyme activity that synthesizes phosphatidylinositol-4,5-bisphosphate (PIP2), phosphoinositol-4-monophosphate (PIP) kinase. The present study determined whether stimulation of this enzyme correlates with actin assembly by assessing the calcium dependence of this reaction. Incubation of neutrophils with 5 to 100 micrograms/ml Con A caused a concentration-dependent increase in PIP kinase activity ranging from 1.38- to 3.4-fold. The effective concentration which stimulated PIP kinase by 50% (17 micrograms/ml, EC50) corresponded with the EC50 for Con A-induced superoxide production (32 micrograms/ml). Like chemoattractants, the increase in PIP kinase by Con A was characterized by a 2.6-fold increase in the maximum velocity (Vmax) of the enzyme, and no change in the Km for ATP. The kinetics of FMLP- and Con A-induced filamentous actin formation preceded stimulation of PIP kinase and was sustained over the same time period that this increased enzyme activity was noted. Although transmembrane signaling by FMLP and Con A requires an increase in intracellular calcium for some polymorphonuclear leukocyte (PMN) functional responses, calcium depletion of PMN by incubation with 100 microM Quin 2 A/M and 5 mM EGTA did not prevent the stimulation of PIP kinase by FMLP or Con A. In addition, calcium depletion did not prevent the increase in filamentous actin formation by FMLP and Con A in PMN. These findings demonstrate that Con A increases PIP kinase activity in human PMN and that PIP kinase stimulation and maintenance of actin assembly are independent of calcium fluxes in these cells. Because PIP2 controls the function of the actin-regulatory proteins, profilin and gelsolin, changes in the synthetic rate of PIP2 through regulation of PIP kinase may provide a molecular basis for the prolonged stimulation of actin assembly in human PMN by agonists such as Con A and FMLP.

Binding of IgG containing immune complexes to human neutrophil Fc gamma RII and Fc gamma RIII induces actin polymerization by a pertussis toxin-insensitive transduction pathway

The ability of a phagocytic stimulus, rabbit IgG anti-BSA/BSA immune complexes, to increase the F-actin content of human polymorphonuclear leukocytes was quantitated by flow cytometry following staining with nitrobenzoxadiazole-phallacidin. A significant rise in F-actin assembly was induced by addition of 5 micrograms/ml immune complex. Concentrations of immune complex of more than 200 micrograms/ml caused a maximal (approximately twofold) increase in F-actin content. After a delay of 5 s, the F-actin levels rose and reached maximum levels by 60 s after adding immune complexes. The twofold elevation in F-actin persisted for up to 60 min. Both anti-Fc gamma RII and anti-Fc gamma RIII mAb blocked immune complex stimulated actin polymerization. Exposure to pertussis toxin failed to affect the rate or extent of immune complex-induced actin polymerization. Cells incubated with immune complexes and then lysed with Triton had an increased number of sites able to nucleate actin polymerization. These findings suggest that immune complex binding to both polymorphonuclear leukocytes Fc gamma RII and Fc gamma RIII is required for actin filament assembly and that the induction of assembly occurs via transduction pathways that differ from those used by chemoattractants. As with adhesion this phagocytic stimulus induces actin assembly by a pertussis toxin insensitive pathway and produces a rise in actin filament content that persists for prolonged periods of time.

Binding of IgG containing immune complexes to human neutrophil Fc gamma RII and Fc gamma RIII induces actin polymerization by a pertussis toxin-insensitive transduction pathway

The ability of a phagocytic stimulus, rabbit IgG anti-BSA/BSA immune complexes, to increase the F-actin content of human polymorphonuclear leukocytes was quantitated by flow cytometry following staining with nitrobenzoxadiazole-phallacidin. A significant rise in F-actin assembly was induced by addition of 5 micrograms/ml immune complex. Concentrations of immune complex of more than 200 micrograms/ml caused a maximal (approximately twofold) increase in F-actin content. After a delay of 5 s, the F-actin levels rose and reached maximum levels by 60 s after adding immune complexes. The twofold elevation in F-actin persisted for up to 60 min. Both anti-Fc gamma RII and anti-Fc gamma RIII mAb blocked immune complex stimulated actin polymerization. Exposure to pertussis toxin failed to affect the rate or extent of immune complex-induced actin polymerization. Cells incubated with immune complexes and then lysed with Triton had an increased number of sites able to nucleate actin polymerization. These findings suggest that immune complex binding to both polymorphonuclear leukocytes Fc gamma RII and Fc gamma RIII is required for actin filament assembly and that the induction of assembly occurs via transduction pathways that differ from those used by chemoattractants. As with adhesion this phagocytic stimulus induces actin assembly by a pertussis toxin insensitive pathway and produces a rise in actin filament content that persists for prolonged periods of time.

Listeria monocytogenes moves rapidly through the host-cell cytoplasm by inducing directional actin assembly

Listeria monocytogenes is an intracellular parasite that can readily infect the macrophage-like cell line J774 and the kidney epithelial cell PtK2. After being ingested, the organism escapes from the phagolysosome into the host-cell cytoplasm. N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)-phallacidin, a specific stain for actin filaments (F-actin), demonstrates that within 1 hr of initiation of infection, the bacteria become surrounded by host-cell cytoplasmic actin filaments. By 3 hr, long projections of F-actin begin to form at one end of the bacteria. These actin structures colocalize with the actin-bundling protein alpha-actinin as well as with tropomyosin. Microinjection of fluorescently labeled alpha-actinin in living cells demonstrates that the formation of these F-actin projections is associated with bacterial movement, actin filaments rapidly assembling behind the bacteria as they migrate through the cytoplasm. These F-actin tails attain lengths up to 40 microns. The movement of the bacteria through the cytoplasm is rapid, 0.12-1.46 microns/sec. Within 2 min of cytochalasin D (0.5 micrograms/ml) treatment, all bacterial intracellular movement stops, and additional bacteria-associated actin assembly is blocked. A nonmotile Listeria mutant induces comparable actin assembly and moves at speeds similar to the wild type, indicating that the forces required for intracellular bacterial movement are generated by the host cell. L. monocytogenes can dramatically stimulate host-cell actin assembly in a directional manner, which serves to rapidly propel the bacteria through the cytoplasm, allowing the organisms to move to peripheral membranes and spread to uninfected cells.

Septic cortical thrombophlebitis

Thrombosis of cortical veins has been postulated as an important cause of seizures and focal neurologic deficits in patients with bacterial meningitis. Diagnoses from autopsies, angiograms, and medical records at Massachusetts General Hospital, 1960-1984, were reviewed to identify patients with septic cortical thrombophlebitis. Only 10 confirmed cases of septic cortical vein thrombosis without sagittal sinus thrombosis were found. Meningitis was present in nine patients; Streptococcus pneumoniae was isolated from the blood or cerebrospinal fluid of five patients. Common clinical manifestations included fever, seizures, and focal neurologic signs. Half the patients survived, but three had persistent disabilities. Cortical vein thrombosis could be documented in only approximately 1% of 790 cases of bacterial meningitis. In 97 patients with meningitis who died and had autopsies, cortical thrombophlebitis was identified in 5%. In autopsied patients, other pathologic processes including arteritis, ventriculitis, cavernous sinus thrombosis, and cerebral infarctions were usually more prominent than venous thrombosis. Cortical thrombophlebitis does not appear to be the major cause of seizures or focal neurologic signs during bacterial meningitis.

The actin released from profilin--actin complexes is insufficient to account for the increase in F-actin in chemoattractant-stimulated polymorphonuclear leukocytes

Chemoattractant stimulation of polymorphonuclear leukocytes is associated with a nearly two-fold rise in actin filament content. We examined the role of the actin monomer sequestering protein, profilin, in the regulation of PMN actin filament assembly during chemoattractant stimulation using a Triton extraction method. Poly-L-proline-conjugated Sepharose beads were used to assess the relative concentration of actin bound to profilin with high enough affinity to withstand dilution (profilin-actin complex) and DNase I-conjugated beads to measure the relative concentration of actin in the Triton-soluble fraction not bound to profilin. Actin associated with the Triton-insoluble fraction (F-actin) was also measured. In unstimulated PMN, the relative concentration of actin bound to profilin was maximum. After FMLP stimulation, profilin released actin monomers within 10 s, with the profilin-actin complex concentration reaching a nadir by 40 s and remaining low as long as the cells were exposed to chemoattractant (up to 30 min). If FMLP was dissociated from PMN membrane receptors using t-BOC, actin reassociated with profilin within 20 s. Quantitative analysis of these reactions, however, revealed that profilin release of and rebinding to actin could account for only a small percentage of the total change in F-actin content. Determination of the total profilin and actin concentrations in PMN revealed that the molar ratio of profilin to actin was 1 to 5.2. When purified actin was polymerized in PMN Triton extract containing EGTA, removal of profilin from the extract minimally affected (12% reduction) the high apparent critical concentration at which actin began to assemble. Although profilin released actin at the appropriate time to stimulate actin assembly during exposure to chemoattractants, the concentration of profilin in PMN was insufficient to explain the high unpolymerized actin content in unstimulated PMN and the quantity of actin released from profilin too small to account for the large shifts from unpolymerized to polymerized actin associated with maximal chemoattractant stimulation.

Kinetics of the interaction of a 41-kilodalton macrophage capping protein with actin: promotion of nucleation during prolongation of the lag period

A 41-kilodalton macrophage capping protein (MCP) has been isolated which is capable of forming complexes with actin monomers in addition to capping the barbed ends of actin filaments (Southwick & DiNubile, 1986). The protein is calcium activated in a fully reversible manner. Using kinetic assays, we determined a capping constant, defined here as a modified Kd, of 1 nM and a Kd of 3-4 microM for MCP-actin monomer complex formation. MCP weakly nucleates actin polymerization: more than 0.5 microM MCP is necessary to shorten the lag period, and 1 microM MCP at an actin/MCP ratio of 10 reduces the average length of actin filaments to about 200 molecules per filament. We determined that the actin nucleus that survives MCP inactivation contains a minimum number of five actin molecules. These experiments also make a point with respect to the interpretation of the prolongation of the lag period. We directly demonstrate that in the presence of an actin binding protein a prolongation of the lag period can be associated with increased nucleation, contrary to the usual interpretation in the literature that it indicates no or decreased nucleation by the actin binding protein.

Polymorphonuclear leukocyte adherence induces actin polymerization by a transduction pathway which differs from that used by chemoattractants

Nitrobenzoxadiazole-phallacidin in combination with quantitative fluorescent microscopy have been used to measure F-actin concentrations in human polymorphonuclear leukocytes (PMN) as they adhere to a plastic surface. Like stimulation with chemoattractants, adherence is associated with a twofold rise in F-actin content. However unlike the rapid rise in F-actin induced by chemoattractants which peaks within 30 s, actin assembly induced by adherence is slower, maximum F-actin values not being observed until 10 min. Furthermore the rise in F-actin induced by adherence is persistent, remaining constant over 60 min while F-actin returns to near basal levels after 20 min exposure to chemoattractant. The combination of adherence (5 min) followed by chemoattractant (FMLP 5 x 10(-8) M for 40 s) resulted in an additive rise in F-actin content to greater than threefold over unstimulated values. Unlike chemoattractant induced actin assembly, adherence-associated PMN actin polymerization was not inhibited by pertussis toxin, but was markedly reduced by lowering extracellular Ca2+. Fluorescent micrographs of adherent PMN stained with nitrobenzoxadiazole-phallacidin revealed F-actin in the lamellipodia and in small foci on the adherent surface. These findings suggest that the transduction mechanisms by which adherence induces PMN actin polymerization differ from those used by chemoattractant receptors.

The relationship between CR3 deficiency and neutrophil actin assembly

Polymorphonuclear leukocytes (PMN) with a deficiency of the complement receptor type 3 (CR3) membrane glycoprotein family have impairments in the ability to adhere to surfaces as well as chemotactic and phagocytic defects, processes that require a functional contractile apparatus. PMN from the patient with neutrophil actin dysfunction (NAD) displayed similar functional characteristics to those with CR3 deficiency suggesting the two disorders may be the same disease. In order to evaluate the relationship between CR3 deficiency and actin assembly, actin filament assembly was measured in PMN from six previously reported homozygotes (two severe and four moderate CR3-deficient patients) as well as five heterozygotes for CR3 deficiency. PMN from all patients had normal unstimulated concentrations of F-actin and after exposure to the chemotactic peptide FMLP (5 x 10(-7) mol/L for 5 to 40 seconds at 25 degrees C) assembled actin normally. Pretreatment of normal PMN with concentrations of monoclonal anti-alpha CR3 antibody, capable of blocking PMN adherence, also failed to impair FMLP-induced actin filament assembly. CR3 glycoprotein expression was measured in PMNs from the mother, father, and older sister of the NAD patient (N Engl J Med 291:1093, 1974). Actin filament assembly was recently shown to be defective in PMNs from all three family members. The total concentrations of the alpha and beta CR3 subunits were below normal in PMN detergent extracts from the mother (25% of simultaneous controls) and older sister (56% of control). PMN surface expression of these two subunits was also found to be depressed (mother, 50%; older sister, 63% of control). These findings suggest these two NAD family members are heterozygote carriers for CR3 deficiency as well as NAD. Simultaneous studies of the father, however, demonstrated normal total concentrations of both the alpha and beta CR3 subunits (126% of controls) as well as normal surface expression of both subunits after phorbol myristate acetate stimulation and incubation at 37 degrees C (mean, 112% of controls) but slightly lower than normal levels after FMLP stimulation (mean, 83%). These findings indicate that CR3 deficiency generally is not associated with defective actin filament assembly and support the conclusion that NAD represents a unique kindred in which PMN actin function differs from previously reported genotypes of CR3 deficiency.

Neutrophil actin dysfunction is a genetic disorder associated with partial impairment of neutrophil actin assembly in three family members

A male infant with a severe neutrophil motility disorder and poorly polymerizable actin in PMN extracts was reported over a decade ago to have neutrophil actin dysfunction (NAD) (1974. N. Engl. J. Med. 291:1093-1099). Polymerized actin (F-actin) content of fixed and permeabilized intact neutrophils from the father, mother, and sister of the NAD index case have been measured using nitrobenzoxadiazole-phallacidin, a fluorescent compound which binds specifically to actin filaments. F-actin content of unstimulated PMN from all three family members was significantly lower than unstimulated control PMN (mean 23.6 +/- 0.4 SEM fluorescent units vs. 32.6 +/- 0.6 for controls). After stimulation with the chemotactic peptide FMLP, maximal F-actin content of NAD family member PMN was below that of controls (52.7 +/- 1.3 vs. 72.6 +/- 1.8). F-actin content of detergent insoluble cytoskeletons after stimulation with FMLP was also significantly lower in PMN from NAD family members as compared with controls (21 +/- 6% vs. 73 +/- 8%). PMN extracts from the father and mother, when treated with 0.6 M KCl, polymerized half as much actin as controls. Whereas diisopropylfluorophosphate treatment of normal PMN decreased actin polymerizability in cell extracts, this treatment increased the assembly of actin in parental PMN extract. Addition of purified actin to NAD extracts failed to reveal an abnormal actin polymerization inhibitory activity, and no obvious structural defect in actin purified from the father's PMNs was noted by HPLC and two dimensional thin layer chromatography of tryptic digests. The present studies of actin assembly in intact PMNs confirm that NAD is associated with a true defect in PMN actin assembly and is a genetic disorder that is recessively inherited.

Recurrent cystitis and bladder mass in two adults with chronic granulomatous disease

Two men, aged 23 and 20 years, with recurrent episodes of severe cystitis and X-linked chronic granulomatous disease were studied. Ultrasonography showed large discrete bladder masses that mimicked bladder carcinoma in both patients. Urine and bladder biopsy cultures were negative and histopathologic findings were consistent with chronic inflammation. One patient improved with symptomatic therapy on two occasions; the other patient required prolonged intravenous antibiotic therapy before fever and dysuria resolved. The possible mechanisms by which such inflammatory bladder masses might arise are discussed and eight previously reported cases of chronic granulomatous disease with cystitis are reviewed. From this clinical experience, we recommend prolonged antibiotic therapy. In patients who fail to respond to antibiotic therapy, steroids may be cautiously administered.

Platelet-activating factor both stimulates and "primes" human polymorphonuclear leukocyte actin filament assembly

The phospholipid inflammatory mediator, platelet-activating factor (PAF), can stimulate polymorphonuclear leukocyte (PMN) chemotaxis. Conversion of cytoplasmic actin from monomers to filaments is associated with PMN motile functions. Using the fluorescent actin filament stain nitrobenzodiaxole phallicidin, we have investigated PAF's effects on human PMN actin polymerization. Concentrations of PAF between 1 x 10(-11) to 1 x 10(-6) mol/L induced actin filament (F-actin) assembly. An optimal concentration of PAF (1-5 x 10(-8) mol/L) induced a significantly lower rise in relative F-actin content (1.72 +/- 0.07 SEM) than an optimal concentration (5 x 10(-7) mol/L) of the chemotactic peptide FMLP (2.21 +/- 0.06). Unlike FMLP (F-actin content: 1.25 +/- 0.04 at five seconds), PAF stimulation was associated with a delay of more than five seconds (1.04 +/- 0.01 at five seconds) before an increase in F-actin could be detected. F-actin concentration reached maximum levels by 30 to 60 seconds. Prolonged stimulation (20 minutes) with PAF was associated with two phases of polymerization and depolymerization. Like FMLP, the initiation of actin filament assembly by PAF required receptor occupancy, this reaction being totally blocked by the PAF receptor inhibitor, SKI 63-441. As evidenced by the lack of inhibition by nordihydroguaiaretic acid (5 to 20 mumol/L), the production of leukotriene B4 was not required for the PAF-induced changes in F-actin. Like FMLP, PAF's ability to stimulate PMN actin polymerization was inhibited by pertussis toxin (.05 to 2.5 micrograms/mL) but not impaired by the addition of EGTA and/or the calcium ionophore A23187. Preincubation with 1 x 10(-11) to 1 x 10(-8) mol/L PAF for 2 to 60 minutes enhanced the rise in F-actin content induced by low concentrations of FMLP (5 x 10(-12) to 1 x 10(-10) mol/L) indicating that this phospholipid was capable of "priming" the PMN actin polymerization response.

Rabbit alveolar macrophages contain a Ca2+-sensitive, 41,000-dalton protein which reversibly blocks the "barbed" ends of actin filaments but does not sever them

A 41,000-dalton Ca2+-sensitive actin-modulating protein has been purified from rabbit alveolar macrophages using ion exchange and gel filtration chromatography. On sodium dodecyl-polyacrylamide gel electrophoresis, this macrophage protein migrates more rapidly than actin and fails to cross-react with polyclonal anti-actin antibody. It has a Stokes radius of 3.0 nm and an isoelectric point of 6.6. In the presence of micromolar Ca2+ this 41,000-Da protein: reduces the viscosity of polymerized actin, nucleates actin filament assembly, causes a nearly instantaneous increase in fluorescence intensity of subcritical concentrations of pyrenyl-actin (estimated KD of the pyrene actin-macrophage protein complex, 5 X 10(-8) M), increases the critical concentration of actin by 0.65 microM (molar ratios of protein/actin, 1/100-1/10), blocks actin monomer depolymerization from the "barbed" filament ends, and does not sever preformed actin filaments. The ability of this protein to block filament ends is rapidly and completely inhibited by lowering free calcium ion concentration below the micromolar range.

Septic thrombosis of the dural venous sinuses

From 1940 to 1984, 19 cases of septic dural-sinus thrombosis have been diagnosed at the Massachusetts General Hospital, and some 136 cases have been reported from other institutions. Septic thrombosis most frequently involves the cavernous sinuses (96 cases). Facial or sphenoid air sinus infection often precede cavernous-sinus disease. In addition to the classical signs of proptosis, chemosis, and oculomotor paralysis, isolated sixth-nerve palsy and hypo- or hyperesthesia of the fifth nerve may be found. The major pathogens associated with cavernous-sinus infection include Staphylococcus aureus, other gram-positive organisms, and anaerobes. Septic lateral-sinus thrombosis (64 cases) is almost exclusively a complication of otitis media and/or mastoid infection. Organisms causing this infection include Proteus species, Escherichia coli, S. aureus, and anaerobes. Septic thrombosis of the superior sagittal sinus (23 cases) most frequently accompanies bacterial meningitis or air sinus infection. Causative organisms include Streptococcus pneumoniae, S. aureus, other streptococci, and Klebsiella species. Because septic dural-sinus thrombosis is rare, this disease is frequently misdiagnosed. Evaluation should include lumbar puncture, air sinus films, and computed tomographic scan with contrast. Other helpful diagnostic tests may include carotid angiography, and dynamic brain scan. Orbital venography is the most definitive study in cases of chronic cavernous-sinus thrombosis. Therapy should include intravenous antibiotics and early surgical drainage of purulent exudate in the air sinuses or mastoid regions. Retrospective analysis suggests that treatment with heparin may reduce mortality in carefully selected cases of septic cavernous-sinus thrombosis. Anticoagulation is not recommended in other forms of septic dural-sinus thrombosis. Mortality in the antibiotic-era remains high, particularly in patients with septic thrombosis of the cavernous (30%) and superior sagittal (78%) sinuses.

Effects of macrophage profilin on actin in the presence and absence of acumentin and gelsolin

We purified profilin from rabbit alveolar macrophages and documented its structural and functional similarity to profilins isolated from other cells. The KD for formation of the macrophage profilin-actin complex was 3.0 +/- 0.8 microM (mean +/- S.D.). The affinity of this protein for actin did not change significantly in the presence of various concentrations of KCl and MgCl2, profilin-actin complex concentration being strictly dependent on the critical actin monomer concentration and free profilin concentration. We also examined profilin's interactions with actin in the presence of acumentin, a macrophage protein which inhibits actin monomer exchange at the "pointed" ends of actin filaments. Low concentrations of this protein caused substantial decreases in estimated profilin-actin complex concentration. The macrophage gelsolincalcium ion complex which blocks exchange at the "barbed" end of actin filaments, when added to profilin and actin solutions in substoichiometric concentrations, caused large increases in estimated profilin-actin complex concentration. The changes in calculated profilin-actin complex concentration induced by these two actin-modulating proteins were too large to be explained solely by their effects on critical actin monomer concentration.

The motor of leukocytes

The movements of leukocytes involve extension, flow, and contraction of a margin of organelle-excluding cytoplasm. Actin is the principal structural component of this region. This paper reviews evidence that the expansion of cortical cytoplasm can result from the growth of actin polymers into an orthogonal network in which actin fibers branch perpendicularly under the influence of actin-binding protein. Flow occurs when actin filaments are disassembled and severed. The assembly and fragmentation of actin are regulated by actin-modulating proteins such as profilin, which sequesters actin monomers, acumentin, which binds to the slow-growing end of actin fibers, and gelsolin, a calcium-regulated protein that binds to the fast-growing end of actin polymers and severs actin filaments. Contraction of the actin network is caused by myosin, the assembly and activity of which are regulated by its state of phosphorylation, which is in turn controlled by phosphorylating and dephosphorylating enzymes and by calmodulin and calcium. Present information leads to the prediction that intracellular calcium gradients guide cytoplasmic movement and that the direction of actin assembly and therefore of cytoplasmic extension is toward regions of low cytoplasmic free calcium.

An analogue of the erythroid membrane skeletal protein 4.1 in nonerythroid cells

Protein 4.1 is a crucial component of the erythrocyte membrane skeleton. Responsible for the amplification of the spectrin-actin interaction, its presence is required for the maintenance of erythrocyte integrity. We have demonstrated a 4.1-like protein in nonerythroid cells. An antibody was raised to erythrocyte protein 4.1 purified by KCl extraction (Tyler, J. M., W. R. Hargreaves, and D. Branton, 1979, Proc. Natl. Acad. Sci. USA, 76:5192-5196), and used to identify a serologically cross-reactive protein in polymorphonuclear leukocytes, platelets, and lymphoid cells. The cross-reactive protein(s) were localized to various regions of the cells by immunofluorescence microscopy. Quantitative adsorption studies indicated that at least 30-60% of the anti-4.1 antibodies reacted with this protein, demonstrating significant homology between the erythroid and nonerythroid species. A homologous peptide doublet was observed on immunopeptide maps, although there was not complete identity between the two proteins. When compared with erythrocyte protein 4.1, the nonerythroid protein(s) displayed a lower molecular weight--68,000 as compared with 78,000-and did not bind spectrin or the nonerythroid actin-binding protein filamin. There was no detectable cross-reactivity between human acumentin or human tropomyosin-binding protein, which are similarly sized actin-associated proteins, and erythrocyte protein 4.1. The possible origin and significance of 4.1-related protein(s) in nonerythroid cells are discussed.

Sphenoid sinusitis. A review of 30 cases

We studied 30 patients with infectious sphenoid sinusitis (15 acute cases and 15 chronic cases) in an effort to characterize the clinical presentation, bacteriology, and associated complications of this frequently misdiagnosed infection. Severe frontal, temporal, or retro-orbital headache that radiated to the occipital regions or pain in the trigeminal (V1 to V3) distribution or both were the most prominent presenting symptoms. In acute cases, purulent exudate was frequently seen in the middle and superior nasal turbinates. Computerized axial tomography or sinus tomography and cannulation of the sphenoid sinus proved to be the most useful diagnostic studies. Organisms detected in acute cases included streptococci other than Streptococcus pneumoniae (41 per cent), Staphylococcus aureus (29 per cent), and Str. pneumoniae (17 per cent). In chronic infections, gram-negative bacilli (43 per cent) and staphylococcal species (24 per cent) were the predominant organisms. In acute disease, early diagnosis and aggressive therapy, including surgical drainage, were important. Delay in treatment was always associated with serious morbidity or mortality. Fatal complications included cavernous sinus thrombosis and bacterial meningitis.