Biomedical subjects

M A Schwartz

Publications and source records attributed to M A Schwartz.

At least 19 recordsLinked to original sources

PubMed2002

Central venous catheter-related bacteremia due to Tsukamurella species in the immunocompromised host: a case series and review of the literature.

We report 6 cases of bacteremia due to Tsukamurella species, all of which were in immunosuppressed patients with indwelling central venous catheters (CVCs). Fewer than 20 cases of serious illness due to these gram-positive bacilli have been reported in the medical literature; these cases have mostly been ascribed to the species Tsukamurella paurometabola. Tsukamurella species are frequently misidentified as Rhodococcus or Corynebacterium species. We used high-performance liquid chromatography to identify these organisms to the genus level and 16S ribosomal RNA gene sequencing and DNA-DNA dot blots for species identification. Three of our isolates were identified as Tsukamurella pulmonis, 1 was identified as Tsukamurella tyrosinosolvans, and 1 was identified as a unique species. One isolate was not maintained long enough for species identification. All patients were successfully treated with antimicrobial therapy and CVC removal. Infection with this organism should be considered in the immunosuppressed patient with an indwelling CVC and gram-positive bacilli in the blood.

Actinomycetales↗

PubMed2001

Phase II trial of weekly docetaxel in second-line therapy for nonsmall cell lung carcinoma.

BACKGROUND: The authors conducted a Phase II study to evaluate the activity and toxicity of weekly docetaxel in second-line therapy for nonsmall cell lung carcinoma (NSCLC). METHODS: Patients with documented recurrent or refractory NSCLC, previously treated with no more than one chemotherapy regimen, were eligible if they had a performance status (PS) of 0-2, measurable or evaluable disease, and adequate organ function. Patients were treated with docetaxel 36 mg/m(2)/week for 6 consecutive weeks, administered intravenously with dexamethasone premedication. Cycles were repeated every 8 weeks. RESULTS: Thirty-one patients were enrolled. One patient was ineligible because of uncontrolled brain metastases. Hematologic toxicity was minimal. Nonhematologic toxicities were modest except for diarrhea and cumulative fatigue. There were no treatment-related deaths. The overall response rate was 10% (95% confidence interval [CI], 1.6-29%). The median survival time (MST) was 8.0 months. and the 1-year survival rate was 31% (95% CI, 17- 58%). Patients with PS 0-1 had a MST of 11.9 months with 1-year survival of 42%. CONCLUSIONS: Weekly docetaxel is very well tolerated as second-line therapy for NSCLC. The activity of this regimen appears to be comparable to the standard 3-week schedule. This regimen offers new opportunities for combination regimens, both as first- and second-line therapy for NSCLC.

Aged↗

PubMed2001

Ligation of integrin alpha 3beta 1 by laminin 5 at the wound edge activates Rho-dependent adhesion of leading keratinocytes on collagen.

Wounding of the epidermis signals the transition of keratinocytes from quiescent anchorage on endogenous basement membrane laminin 5 to migration on exposed dermal collagen. In this study, we attempt to characterize activation signals that transform quiescent keratinocytes into migratory leading cells at the wound edge. Previously, we reported that adhesion and spreading on collagen via integrin alpha(2)beta(1) by cultured human foreskin keratinocytes (HFKs) requires RhoGTP, a regulator of actin stress fibers. In contrast, adhesion and spreading on laminin 5 requires integrins alpha(3)beta(1) and alpha(6)beta(4) and is dependent on phosphoinositide 3-hydroxykinase (Nguyen, B. P., Gil, S. G., and Carter, W. G. (2000) J. Biol. Chem. 275, 31896-31907). Here, we report that quiescent HFKs do not adhere to collagen but adhere and spread on laminin 5. By using collagen adhesion as one criterion for conversion to a "leading wound cell," we found that activation of collagen adhesion requires elevation of RhoGTP. Adhesion of quiescent HFKs to laminin 5 via integrin alpha(3)beta(1) and alpha(6)beta(4) is sufficient to increase levels of RhoGTP required for adhesion and spreading on collagen. Consistently, adhesion of quiescent HFKs to laminin 5, but not collagen, also promotes expression of the precursor form of laminin 5, a characteristic of leading keratinocytes in the epidermal outgrowth. We suggest that wounding of quiescent epidermis initiates adhesion and spreading of keratinocytes at the wound edge on endogenous basement membrane laminin 5 via alpha(3)beta(1) and alpha(6)beta(4) in a Rho-independent mechanism. Spreading on endogenous laminin 5 via alpha(3)beta(1) is necessary but not sufficient to elevate expression of precursor laminin 5 and RhoGTP, allowing for subsequent collagen adhesion via alpha(2)beta(1), all characteristics of leading keratinocytes in the epidermal outgrowth.

Cell Adhesion↗

PubMed2001

Activation of integrins in endothelial cells by fluid shear stress mediates Rho-dependent cytoskeletal alignment.

Fluid shear stress is a critical determinant of vascular remodeling and atherogenesis. Both integrins and the small GTPase Rho are implicated in endothelial cell responses to shear but the mechanisms are poorly understood. We now show that shear stress rapidly stimulates conformational activation of integrin alpha(v)beta3 in bovine aortic endothelial cells, followed by an increase in its binding to extracellular cell matrix (ECM) proteins. The shear-induced new integrin binding to ECM induces a transient inactivation of Rho similar to that seen when suspended cells are plated on ECM proteins. This transient inhibition is necessary for cytoskeletal alignment in the direction of flow. The results therefore define the role of integrins and Rho in a pathway leading to endothelial cell adaptation to flow.

Animals↗

PubMed2001

c-Abl tyrosine kinase binds and phosphorylates phospholipid scramblase 1.

Phospholipid scramblase 1 (PLSCR1) is a plasma membrane protein that has been proposed to play a role in the transbilayer movement of plasma membrane phospholipids. PLSCR1 contains multiple proline-rich motifs resembling Src homology 3 (SH3) domain-binding sites. An initial screen against 13 different SH3 domains revealed a marked specificity of PLSCR1 for binding to the Abl SH3 domain. Binding between intracellular PLSCR1 and c-Abl was demonstrated by co-immunoprecipitation of both proteins from several cell lines. Deletion of the proline-rich segment in PLSCR1 (residues 1--118) abolished its binding to the Abl SH3 domain. PLSCR1 was Tyr-phosphorylated by c-Abl in vitro. Phosphorylation was abolished by mutation of Tyr residues Tyr(69)/Tyr(74) within the tandem repeat sequence (68)VYNQPVYNQP(77) of PLSCR1, implying that these residues are the likely sites of phosphorylation. Cellular PLSCR1 was found to be constitutively Tyr-phosphorylated in several cell lines. The Tyr phosphorylation of PLSCR1 was increased upon overexpression of c-Abl and significantly reduced either upon cell treatment with the Abl kinase inhibitor STI571, or in Abl-/- mouse fibroblasts, suggesting that cellular PLSCR1 is a normal substrate of c-Abl. Cell treatment with the DNA-damaging agent cisplatin activated c-Abl kinase and increased Tyr phosphorylation of PLSCR1. The cisplatin-induced phosphorylation of PLSCR1 was inhibited by STI571 and was not observed in Abl-/- fibroblasts. These findings indicate that c-Abl binds and phosphorylates PLSCR1, and raise the possibility that an interaction between c-Abl and plasma membrane PLSCR1 might contribute to the cellular response to genotoxic stress.

Amino Acid Sequence↗

PubMed2001

Integrin-mediated mechanotransduction requires its dynamic interaction with specific extracellular matrix (ECM) ligands.

The aim of this study is to elucidate the role of integrins in transducing fluid shear stress into intracellular signals in vascular endothelial cells, a fundamental process in vascular biology. We demonstrated that shear stress activates specific integrins in endothelial cells plated on substrates containing the cognate extracellular matrix (ECM) ligands. The shear stress-induced mechanotransduction, as manifested by integrin-Shc association, was abolished when new integrin-ECM ligand interactions were prevented by either blocking the integrin-binding sites of ECM ligands or conjugating the integrins to immobilized antibodies. Our results indicate that the dynamic formation of new connections between integrins and their specific ECM ligands is critical in relaying the signals induced by shear stress to intracellular pathways.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Coordinate signaling by integrins and receptor tyrosine kinases in the regulation of G1 phase cell-cycle progression.

Cell proliferation is dependent upon the activation of receptor tyrosine kinases and integrins by soluble growth factors and extracellular matrix proteins, respectively. It is now apparent that concerted, rather than individual, signaling by these receptors is the critical feature responsible for cell-cycle progression through G1 phase. ERK (extracellular signal-regulated kinase), Rho GTPases and G1-phase cyclin-dependent kinases are all regulated jointly by growth-factor receptors and integrins. Recent studies have begun to reveal how this regulated signaling in the cytoplasm is linked to activation of the G1-phase cyclin-dependent kinases in the nucleus.

Animals↗

PubMed2001

Integrin signaling revisited.

Adhesion to the extracellular matrix (ECM) is a crucial regulator of cell function, and it is now well established that signaling by integrins mediates many of these effects. Ten years of research has seen integrin signaling advance on many fronts towards a molecular understanding of the control mechanisms. Most striking is the merger with studies of other receptors, the cytoskeleton and mechanical forces within the general field of signaling networks.

Animals↗

PubMed2001

Rac recruits high-affinity integrin alphavbeta3 to lamellipodia in endothelial cell migration.

Integrin alphavbeta3 has an important role in the proliferation, survival, invasion and migration of vascular endothelial cells. Like other integrins, alphavbeta3 can exist in different functional states with respect to ligand binding. These changes involve both affinity modulation, by which conformational changes in the integrin heterodimer govern affinity for individual extracellular matrix proteins, and avidity modulation, by which changes in lateral mobility and integrin clustering affect the binding of cells to multivalent matrices. Here we have used an engineered monoclonal antibody Fab (antigen-binding fragment) named WOW-1, which binds to activated integrins alphavbeta3 and alphavbeta5 from several species, to investigate the role of alphavbeta3 activation in endothelial cell behaviour. Because WOW-1 is monovalent, it is insensitive to changes in integrin clustering and therefore reports only changes in affinity. WOW-1 contains an RGD tract in its variable region and binds only to unoccupied, high-affinity integrins. By using WOW-1, we have identified the selective recruitment of high-affinity integrins as a mechanism by which lamellipodia promote formation of new adhesions at the leading edge in cell migration.

Androstadienes↗

PubMed2001

Timing of cyclin D1 expression within G1 phase is controlled by Rho.

The expression of cyclin D1 in mid-G1 phase is associated with sustained ERK activity, and we show here that Rho is required for the sustained ERK signal. However, we also report that Rho inhibits an alternative Rac/Cdc42-dependent pathway, which results in a strikingly early G1-phase expression of cyclin D1. Thus, cyclin D1 is induced in mid-G1 phase because a Rho switch couples its expression to sustained ERK activity rather than Rac and Cdc42. Our results show that Rho is crucial for maintaining the correct timing of cyclin D1 expression in G1 phase and describe a new role for cytoskeletal integrity in the regulation of cell cycle progression.

3T3 Cells↗

PubMed2001

Increased filamin binding to beta-integrin cytoplasmic domains inhibits cell migration.

Multicellular animal development depends on integrins. These adhesion receptors link to the actin cytoskeleton, transmitting biochemical signals and force during cell migration and interactions with the extracellular matrix. Many integrin-cytoskeleton connections are formed by filamins and talin. The beta7 integrin tail binds strongly to filamin and supports less migration, fibronectin matrix assembly and focal adhesion formation than either the beta1D tail, which binds strongly to talin, or the beta1A tail, which binds modestly to both filamin and talin. To probe the role of filamin binding, we mapped the filamin-binding site of integrin tails and identified amino acid substitutions that led to selective loss of filamin binding to the beta7 tail and gain of filamin binding to the beta1A tail. These changes affected cell migration and membrane protrusions but not fibronectin matrix assembly or focal adhesion formation. Thus, tight filamin binding restricts integrin-dependent cell migration by inhibiting transient membrane protrusion and cell polarization.

Amino Acid Substitution↗

PubMed2001

Tsukamurella strandjordae sp. nov., a proposed new species causing sepsis.

We have isolated a gram-positive, weakly acid-alcohol-fast, irregular rod-shaped bacterium from cultures of blood from a 5-year-old girl with acute myelogenous leukemia. This isolate was compared with 14 other strains including reference strains of Tsukamurella species by a polyphasic approach based on physiological and biochemical properties, whole-cell short-chain fatty acid and mycolic acid analyses, DNA-DNA hybridization, and sequencing of the 16S rRNA gene. This isolate represents a new taxon within the genus Tsukamurella for which we propose the name Tsukamurella strandjordae sp. nov. Our study also revealed that Tsukamurella paurometabola ATCC 25938 represents a misnamed Tsukamurella inchonensis isolate and confirms that Tsukamurella wratislaviensis belongs to the genus Rhodococcus.

Actinomycetales↗

PubMed2001

Integrins and cell proliferation: regulation of cyclin-dependent kinases via cytoplasmic signaling pathways.

Cell cycle progression in mammalian cells is strictly regulated by both integrin-mediated adhesion to the extracellular matrix and by binding of growth factors to their receptors. This regulation is mediated by G1 phase cyclin-dependent kinases (CDKs), which are downstream of signaling pathways under the integrated control of both integrins and growth factor receptors. Recent advances demonstrate a surprisingly diverse array of integrin-dependent signals that are channeled into the regulation of the G1 phase CDKs. Regulation of cyclin D1 by the ERK pathway may provide a paradigm for understanding how cell adhesion can determine cell cycle progression.

Animals↗

PubMed2000

Association of Mycoplasma genitalium with nongonococcal urethritis in heterosexual men.

Chlamydia trachomatis and Neisseria gonorrhoeae are universally acknowledged as urethral pathogens, yet the etiology in the majority of cases of urethritis is unclear. Our case-control study assessed the association of Mycoplasma genitalium, Ureaplasma urealyticum, and other potential pathogens with acute nongonococcal urethritis (NGU) in heterosexual men presenting to an urban sexually transmitted diseases clinic. M. genitalium was detected in 27 (22%) of 121 NGU case patients and in 5 (4%) of 117 control subjects (P<.01). Although C. trachomatis was detected in 36 (30%) of 121 NGU case patients and in 4 (3%) of 117 control subjects (P<.01), only 3 men with NGU were infected with both C. trachomatis and M. genitalium. U. urealyticum was not associated with NGU. By multivariate analyses, controlling for age, race, history of prior urethritis, and chlamydial infection, M. genitalium was associated with a 6.5-fold increased risk of urethritis (95% confidence interval, 2.1-19.5), which supports a role of this organism in the etiology of NGU.

Adolescent↗

PubMed2000

The molecular adapter SLP-76 relays signals from platelet integrin alphaIIbbeta3 to the actin cytoskeleton.

Platelet adhesion to fibrinogen through integrin alpha(IIb)beta(3) triggers actin rearrangements and cell spreading. Mice deficient in the SLP-76 adapter molecule bleed excessively, and their platelets spread poorly on fibrinogen. Here we used human platelets and a Chinese hamster ovary (CHO) cell expression system to better define the role of SLP-76 in alpha(IIb)beta(3) signaling. CHO cell adhesion to fibrinogen required alpha(IIb)beta(3) and stimulated tyrosine phosphorylation of SLP-76. SLP-76 phosphorylation required coexpression of Syk tyrosine kinase and stimulated association of SLP-76 with the adapter, Nck, and with the Rac exchange factor, Vav1. SLP-76 expression increased lamellipodia formation induced by Syk and Vav1 in adherent CHO cells (p < 0.001). Although lamellipodia formation requires Rac, SLP-76 functioned downstream of Rac by potentiating adhesion-dependent activation of PAK kinase (p < 0.001), a Rac effector that associates with Nck. In platelets, adhesion to fibrinogen stimulated the association of SLP-76 with the SLAP-130 adapter and with VASP, a SLAP-130 binding partner implicated in actin reorganization. Furthermore, SLAP-130 colocalized with VASP at the periphery of spread platelets. Thus, SLP-76 functions to relay signals from alpha(IIb)beta(3) to effectors of cytoskeletal reorganization. Therefore, deficient recruitment of specific adapters and effectors to sites of adhesion may explain the integrin phenotype of SLP-76(-/-) platelets.

Actins↗

PubMed2000

Localized Rac activation dynamics visualized in living cells.

Signaling proteins are thought to be tightly regulated spatially and temporally in order to generate specific and localized effects. For Rac and other small guanosine triphosphatases, binding to guanosine triphosphate leads to interaction with downstream targets and regulates subcellular localization. A method called FLAIR (fluorescence activation indicator for Rho proteins) was developed to quantify the spatio-temporal dynamics of the Rac1 nucleotide state in living cells. FLAIR revealed precise spatial control of growth factor-induced Rac activation, in membrane ruffles and in a gradient of activation at the leading edge of motile cells. FLAIR exemplifies a generally applicable approach for examining spatio-temporal control of protein activity.

3T3 Cells↗

PubMed2000

Stimulation of fascin spikes by thrombospondin-1 is mediated by the GTPases Rac and Cdc42.

Cell adhesion to extracellular matrix is an important physiological stimulus for organization of the actin-based cytoskeleton. Adhesion to the matrix glycoprotein thrombospondin-1 (TSP-1) triggers the sustained formation of F-actin microspikes that contain the actin-bundling protein fascin. These structures are also implicated in cell migration, which may be an important function of TSP-1 in tissue remodelling and wound repair. To further understand the function of fascin microspikes, we examined whether their assembly is regulated by Rho family GTPases. We report that expression of constitutively active mutants of Rac or Cdc42 triggered localization of fascin to lamellipodia, filopodia, and cell edges in fibroblasts or myoblasts. Biochemical assays demonstrated prolonged activation of Rac and Cdc42 in C2C12 cells adherent to TSP-1 and activation of the downstream kinase p21-activated kinase (PAK). Expression of dominant-negative Rac or Cdc42 in C2C12 myoblasts blocked spreading and formation of fascin spikes on TSP-1. Spreading and spike assembly were also blocked by pharmacological inhibition of F-actin turnover. Shear-loading of monospecific anti-fascin immunoglobulins, which block the binding of fascin to actin into cytoplasm, strongly inhibited spreading, actin cytoskeletal organization and migration on TSP-1 and also affected the motility of cells on fibronectin. We conclude that fascin is a critical component downstream of Rac and Cdc42 that is needed for actin cytoskeletal organization and cell migration responses to thrombospondin-1.

3T3 Cells↗

PubMed2000

New thiol and sulfodiimine metalloproteinase inhibitors and their effect on human microvascular endothelial cell growth.

Matrix metalloproteinases (MMPs, matrixins) are a family of homologous zinc endopeptidases that may play a very important role in many physiological and pathological processes, e.g., the initiation of angiogenesis. Two new matrixin inhibitors were synthesized and characterized. A thiol inhibitor MAG-283 had IC(50) values of 480, 3, 280, 14, 1.1, and 2.3 nM against human interstitial collagenase (MMP-1), gelatinase A (MMP-2), stromelysin (MMP-3), matrilysin (MMP-7), neutrophil collagenase (MMP-8), and gelatinase B (MMP-9), respectively. A sulfodiimine inhibitor YLL-224 had IC(50) values of 180, 63, 4500, 210, 5.9, and 44 nM against MMP-1, -2, -3, -7, -8, and -9, respectively. Human skin microvascular endothelial cells were treated with these two compounds in culture. These inhibitors at very low micromolar concentrations suppressed proliferation of the endothelial cells stimulated by acidic fibroblast growth factor and vascular endothelial growth factor. They also partially blocked cell invasion through type IV collagen. These results suggested a correlation between the anti-metalloenzyme activity and the effects of these inhibitors on the growth and invasion of endothelial cells.

Amides↗