Calcium-triggered selective intermembrane exchange of phospholipids by the lung surfactant protein SP-A

It is shown that human lung surfactant protein (SP-A) mediates selective exchange of phospholipid probes with unlabeled phospholipid in excess vesicles in the presence of calcium and NaCl. The exchange occurs without leakage of vesicle contents, or transbilayer movement (flip-flop) of the phospholipid probes, or fusion of vesicles. Individual steps preceding the exchange are dissected by a combination of protocols, and the results are operationally interpreted in terms of a model where a calcium-dependent change in SP-A triggers aggregation of vesicles followed by probe exchange between the vesicles in contact through SP-A. The contacts remain stable in the presence of calcium; i.e., the vesicles in contact do not change their partners on the time scale of several minutes. The binding of SP-A to vesicles and the aggregation of vesicles are rapid, and the aggregation is rapidly reversed by EGTA; i.e., both the forward and reverse aggregation reactions are complete in about 1 min. The exchange rate of the various probes between aggregated vesicles below 1 mM calcium in the presence of NaCl shows selectivity, i.e., a modest dependence on the net anionic charge on vesicles and for the headgroup of the probe. Exchange with lower selectivity is seen at >2 mM Ca in the absence of NaCl. SP-A binding to vesicles does not show an absolute specificity for the phospholipid structure, but the time course of the subsequent changes does. The results suggest that SP-A contacts between phospholipid interfaces could mediate the exchange of phospholipid species (trafficking and sorting) between lung surfactant pools in the hypophase and all accessible phospholipid interfaces of the alveolar space.

Cationic residues 53 and 56 control the anion-induced interfacial k*cat activation of pancreatic phospholipase A2

Added NaCl or anionic amphiphiles increase the rate of hydrolysis of dispersions of zwitterionic phospholipid by pancreatic phospholipase A2 (PLA2). Two effects of the negative charge at the interface have been dissected: enhanced binding of the enzyme to the interface, and k*cat activation of the enzyme at the interface [Berg et al. (1997) Biochemistry 36, 14512-14530]. Results reported here show that the structural basis for the k*cat activation is predominantly through cationic K53 and K56 in bovine pancreatic PLA2 with the anionic interface. The maximum rate at saturating diheptanoylphosphatidylcholine micelles, VMapp, for WT, K56M, and K53M in 4 M NaCl is in the 800-1300 s-1 range. In contrast, VMapp at 0.1 M NaCl is considerably higher for K56M (400 s-1) and K53M (230 s-1) compared to the rate with WT (30 s-1) or K56E (45 s-1). The rate of hydrolysis of anionic dimyristoylphosphatidylmethanol vesicles is virtually the same with all these mutants (200-300 s-1) and it is not affected by added NaCl. The chemical step for the hydrolysis of anionic and zwitterionic substrates remains rate-limiting in the presence or absence of added NaCl. A modest (approximately 10-fold) effect of K56M substitution or of added NaCl is seen on the binding of the enzyme to the interface; however, the binding of the substrate or a substrate mimic to the active site of the enzyme at the interface is not affected by more than a factor of 2. Magnitudes of the primary rate and equilibrium parameters at the zwitterionic and anionic interfaces show that the effect of mutation or of added NaCl is primarily on k*cat at the zwitterionic interface. These results are interpreted in terms of a two-state model for the interfacial allosteric activation, where the enzyme-substrate complex at the zwitterionic interface becomes catalytically active only after the positive charge on cationic K56 and K53 has been removed by mutation or neutralized by anionic charges in the interface.

Aortic carboxypeptidase-like protein, a novel protein with discoidin and carboxypeptidase-like domains, is up-regulated during vascular smooth muscle cell differentiation

Phenotypic modulation of vascular smooth muscle cells plays an important role in the pathogenesis of arteriosclerosis. In a screen of proteins expressed in human aortic smooth muscle cells, we identified a novel gene product designated aortic carboxypeptidase-like protein (ACLP). The approximately 4-kilobase human cDNA and its mouse homologue encode 1158 and 1128 amino acid proteins, respectively, that are 85% identical. ACLP is a nonnuclear protein that contains a signal peptide, a lysine- and proline-rich 11-amino acid repeating motif, a discoidin-like domain, and a C-terminal domain with 39% identity to carboxypeptidase E. By Western blot analysis and in situ hybridization, we detected abundant ACLP expression in the adult aorta. ACLP was expressed predominantly in the smooth muscle cells of the adult mouse aorta but not in the adventitia or in several other tissues. In cultured mouse aortic smooth muscle cells, ACLP mRNA and protein were up-regulated 2-3-fold after serum starvation. Using a recently developed neural crest cell to smooth muscle cell in vitro differentiation system, we found that ACLP mRNA and protein were not expressed in neural crest cells but were up-regulated dramatically with the differentiation of these cells. These results indicate that ACLP may play a role in differentiated vascular smooth muscle cells.

Osmotic stress in viable Escherichia coli as the basis for the antibiotic response by polymyxin B

Cationic antimicrobial peptides, such as polymyxin B (PxB), below growth inhibitory concentration induce expression of osmY gene in viable E. coli without leakage of solutes and protons. osmY expression is also a locus of hyperosmotic stress response induced by common food preservatives, such as hypertonic NaCl or sucrose. High selectivity of PxB against Gram-negative organisms and the basis for the hyperosmotic stress response at sublethal PxB concentrations is attributed to PxB-induced mixing of anionic phospholipid between the outer layer of the cytoplasmic membrane with phospholipids in the inner layer of the outer membrane. This explanation is supported by PxB-mediated rapid and direct exchange of anionic phospholipid between vesicles. This mechanism is consistent with the observation that genetically stable resistance against PxB could not be induced by mutagenesis.

Interfacial recognition by bee venom phospholipase A2: insights into nonelectrostatic molecular determinants by charge reversal mutagenesis

The basis for tight binding of bee venom phospholipase A2 (bvPLA2) to anionic versus zwitterionic phospholipid interfaces is explored by charge reversal mutagenesis of basic residues (lysines/arginines to glutamates) on the putative membrane binding surface. Single-site mutants and, surprisingly, multisite mutants (2-5 of the 6 basic residues mutated) are fully functional on anionic vesicles. Mutants bind tightly to anionic vesicles, and active-site substrate and Ca2+ binding are not impaired. Multisite mutants undergo intervesicle exchange slightly faster than wild type, especially in the presence of salt. It is estimated that electrostatic contribution to interfacial binding is modest, perhaps 2-3 kcal/mol of the estimated 15 kcal/mol. Elution properties of bvPLA2 from HPLC columns containing solid phases of tightly packed monolayers of phosphocholine amphiphiles suggest that ionic effects provide a modest portion of the interfacial binding energy and that this contribution decreases as the number of cationic residues mutated is increased. These results are consistent with the observation that Gila monster venom PLA2 (Pa2), which is homologous to bvPLA2, has high activity on anionic vesicles despite the fact that it has only a single basic residue on its putative interfacial recognition face. Results with bvPLA2 mutants show that manoalogue and 12-epi-scalaradial inactivate bvPLA2 by modification of K94. Also, deletion of the large beta-loop (residues 99-118) is without consequence for interfacial binding and catalysis of bvPLA2. All together, the preferential binding of bvPLA2 to anionic vesicles versus phosphatidylcholine vesicles is mainly due to factors other than electrostatics. Therefore hydrogen-bonding and hydrophobic interactions must provide a major portion of the interfacial binding energy, and this is consistent with recent spectroscopic studies.

Interfacial activation of triglyceride lipase from Thermomyces (Humicola) lanuginosa: kinetic parameters and a basis for control of the lid

A strategy is developed to analyze steady-state kinetics for the hydrolysis of a soluble substrate partitioned into the interface by an enzyme at the interface. The feasibility of this approach to obtain interfacial primary kinetic and equilibrium parameters is demonstrated for a triglyceride lipase. Analysis for phospholipase A2 catalyzed hydrolysis of rapidly exchanging micellar (Berg et al. (1997) Biochemistry 36, 14512-14530) and nonexchangeable vesicular (Berg et al., (1991) Biochemistry 30, 7283-7291) phospholipids is extended to include the case of a substrate that does not form the interface. The triglyceride lipase (tlTGL) from Thermomyces (formerly Humicola) lanuginosa hydrolyzes p-nitrophenylbutyrate or tributyrin partitioned in the interface of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG) vesicles at a rate that is more than 100-fold higher than that for the monodispersed substrate or for the substrate partitioned into zwitterionic vesicles. Catalysis and activation is not seen with the S146A mutant without the catalytic serine-146; however, it binds to the POPG interface with the same affinity as the WT. Thus POPG acts as a diluent surface to which the lipase binds in an active, or "open", form for the catalytic turnover; however, the diluent molecules have poor affinity for the active site. Analysis of the substrate and the diluent concentration dependence of the rate of hydrolysis provides a basis for the determination of the primary interfacial catalytic parameters. As a competitive substrate, tributyrin provided a check for the apparent affinity parameters. Nonidealities from the fractional difference in the molecular areas in interfaces are expressed as the area correction factor and can be interpreted as a first-order approximation for the interfacial activity coefficient. The basis for the interfacial activation of tlTGL on anionic interface is attributed to cationic R81, R84, and K98 in the "hinge" around the 86-93 "lid" segment of tlTGL.

Thy-1, a novel marker for angiogenesis upregulated by inflammatory cytokines

We identified the cell surface glycoprotein Thy-1 on the endothelium of newly formed blood vessels in four models of angiogenesis in adult rats. Anti-Thy-1 staining showed that Thy-1 was upregulated in adventitial blood vessels after balloon injury to the carotid artery. Preabsorption with a rat Thy-1-Ig fusion construct eliminated all immunoreactivity and thus confirmed the specificity of the Thy-1 staining. Thy-1 was also expressed in the endothelium of small blood vessels formed after tumor implantation in the cornea, in periureteral vessels formed after ligation of the renal artery, and in small blood vessels of the uterus formed during pregnancy. In contrast with its expression during adult angiogenesis, Thy-1 was not expressed in the endothelium of blood vessels during embryonic angiogenesis. In vitro, the inflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha upregulated Thy-1 mRNA by 8- and 14-fold, respectively. Vascular endothelial growth factor, basic fibroblast growth factor, transforming growth factor-beta, and platelet-derived growth factor-BB had no effect on Thy-1 mRNA. Thus, Thy-1 appears to be a marker of adult but not embryonic angiogenesis. The upregulation of Thy-1 by cytokines but not growth factors indicates the importance of inflammation in the pathogenesis of adult angiogenesis.

Reductive dechlorination of DDE to DDMU in marine sediment microcosms

DDT is reductively dechlorinated to DDD and dehydrochlorinated to DDE; it has been thought that DDE is not degraded further in the environment. Laboratory experiments with DDE-containing marine sediments showed that DDE is dechlorinated to DDMU in both methanogenic and sulfidogenic microcosms and that DDD is dehydrochlorinated to DDMU three orders of magnitude more slowly. Thus, DDD does not appear to be an important precursor of the DDMU found in these sediments. These results imply that remediation decisions and risk assessments based on the recalcitrance of DDE in marine and estuarine sediments should be reevaluated.

Molecular cloning, characterization, and promoter analysis of the mouse Crp2/SmLim gene. Preferential expression of its promoter in the vascular smooth muscle cells of transgenic mice

Several members of the LIM protein family have important roles in development and differentiation. We recently isolated a rat cDNA encoding a new member of this family, CRP2/SmLIM, that contains two LIM domains and is expressed preferentially in vascular smooth muscle cells (VSMC). To study the molecular mechanisms that regulate VSMC-specific transcription of the Crp2/SmLim gene, we cloned the cDNA and gene of mouse Crp2/SmLim. Mouse Crp2/SmLim is a single copy gene of six exons and five introns spanning approximately 20 kilobases of genomic DNA. By 5'-rapid amplification of cDNA ends and S1 nuclease protection assay, we determined that the transcription start site is an A residue 80 base pairs 5' of the translation initiation codon. A TATA-like sequence is located 27 base pairs 5' of the transcription start site, and there are potential cis-acting elements (GATA, Sp1, AP-2, E box, CCAC box, and GArC motif) in the 5'-flanking sequence. In transient transfection assays in rat aortic smooth muscle cells in primary culture, 5 kilobases of the Crp2/SmLim 5'-flanking sequence generated a high level of luciferase reporter gene activity. By deletion analysis and gel mobility shift assay, we found that the region between bases -74 and -39 of this 5 kilobase DNA fragment binds Sp1 and confers basal promoter activity in the Crp2/SmLim gene. In vitro, the 5-kilobase fragment was active in multiple cell types. In vivo, however, the 5-kilobase fragment directed high level expression of the lacZ reporter gene preferentially in the VSMC of transgenic mice, indicating the presence of VSMC-specific element(s) in this fragment.

Enhancement of serum-response factor-dependent transcription and DNA binding by the architectural transcription factor HMG-I(Y)

The mechanisms by which HMG-I proteins regulate cell growth are unknown, and their effects on gene expression have only been partially elucidated. We explored the potential interaction between HMG-I proteins and serum-response factor (SRF), a member of the MADS-box family of transcription factors. In cotransfection experiments, HMG-I(Y) potentiated SRF-dependent activation (by more than 5-fold) of two distinct SRF-responsive promoters, c-fos and the smooth muscle-specific gene SM22alpha. This effect was also observed with a heterologous promoter containing multiple copies of the CC(A/T)6GG (CArG) box. HMG-I proteins bound specifically to the CArG boxes of c-fos and SM22alpha in gel mobility shift analysis and enhanced binding of SRF to these CArG boxes. By chelating peptide-immobilized metal affinity chromatography, we mapped the domain of HMG-I(Y) that interacts with SRF to amino acids 50-81, a region that does not bind specifically to DNA in electrophoretic mobility shift assays even though it includes the third AT-hook DNA-binding domain. Surprisingly, HMG-I(Y) mutants that failed to bind DNA still enhanced SRF binding to DNA and SRF-dependent transcription. In contrast, deletion of the HMG-I(Y) 50-81 domain that bound SRF prevented enhancement of transcription. To our knowledge, this is the first report of an HMG-I protein interacting with a MADS-box transcription factor. Our observations suggest that members of the HMG-I family play an important role in SRF-dependent transcription and that their effect is mediated primarily by a protein-protein interaction.

Role of TGF-beta in vascular development and vascular reactivity

Transforming growth factor-beta (TGF-beta) is the prototypic member of a large family of structurally related proteins. Three vertebrate TGF-beta isoforms have been identified and termed TGF-beta1, TGF-beta2, and TGF-beta3, respectively. In addition, two receptors of the serine/threonine kinase family termed type I and II have also been identified. In this review, we focused our attention on the effects of TGF-beta on vascular development and vascular reactivity. The critical role of the TGF-beta1 and the TGF-beta type II receptor in blood vessel formation in the yolk sac has been demonstrated by gene deletion experiments. Recent investigations have also shown that isoforms of TGF-beta play a critical role in smooth muscle cell differentiation. And, finally, a role for TGF-beta1 in the regulation of vascular tone and reactivity has been suggested by studies demonstrating that TGF-beta1 can inhibit the production of potent vasodilators (such as nitric oxide) and stimulate the production of potent vasoconstrictors (such as endothelin). Taken together, these studies suggest that TGF-beta plays a critical role in blood vessel development and vascular function.

In vitro system for differentiating pluripotent neural crest cells into smooth muscle cells

The change in vascular smooth muscle cells (SMC) from a differentiated to a dedifferentiated state is the critical phenotypic response that promotes occlusive arteriosclerotic disease. Despite its importance, research into molecular mechanisms regulating smooth muscle differentiation has been hindered by the lack of an in vitro cell differentiation system. We identified culture conditions that promote efficient differentiation of Monc-1 pluripotent neural crest cells into SMC. Exclusive Monc-1 to SMC differentiation was indicated by cellular morphology and time-dependent induction of the SMC markers smooth muscle alpha-actin, smooth muscle myosin heavy chain, calponin, SM22alpha, and APEG-1. The activity of the SM22alpha promoter was low in Monc-1 cells. Differentiation of these cells into SMC caused a 20-30-fold increase in the activity of the wild-type SM22alpha promoter and that of a hybrid promoter containing three copies of the CArG element. By gel mobility shift analysis, we identified new DNA-protein complexes in nuclear extracts prepared from differentiated Monc-1 cells. One of the new complexes contained serum response factor. This Monc-1 to SMC model should facilitate the identification of nodal regulators of smooth muscle development and differentiation.

Human EZF, a Krüppel-like zinc finger protein, is expressed in vascular endothelial cells and contains transcriptional activation and repression domains

Members of the erythroid Krüppel-like factor (EKLF) multigene family contain three C-terminal zinc fingers, and they are typically expressed in a limited number of tissues. EKLF, the founding member, transactivates the beta-globin promoter by binding to the CACCC motif. EKLF is essential for expression of the beta-globin gene as demonstrated by gene deletion experiments in mice. Using a DNA probe from the zinc finger region of EKLF, we cloned a cDNA encoding a member of this family from a human vascular endothelial cell cDNA library. Sequence analysis indicated that our clone, hEZF, is the human homologue of the recently reported mouse EZF and GKLF. hEZF is a single-copy gene that maps to chromosome 9q31. By gel mobility shift analysis, purified recombinant hEZF protein bound specifically to a probe containing the CACCC core sequence. In co-transfection experiments, we found that sense but not antisense hEZF decreased the activity of a reporter plasmid containing the CACCC sequence upstream of the thymidine kinase promoter by 6-fold. In contrast, EKLF increased the activity of the reporter plasmid by 3-fold. By fusing hEZF to the DNA-binding domain of GAL4, we mapped a repression domain in hEZF to amino acids 181-388. We also found that amino acids 91-117 of hEZF confer an activation function on the GAL4 DNA-binding domain.

Thermodynamic and kinetic basis of interfacial activation: resolution of binding and allosteric effects on pancreatic phospholipase A2 at zwitterionic interfaces

A general kinetic model for catalysis by interfacial enzymes is developed. It couples the Michaelis-Menten catalytic turnover cycle at the interface with that in the aqueous phase through the distribution equilibria between the interface and the surrounding aqueous phase. Analysis under two limiting conditions fully describes the steady-state kinetics of hydrolysis and resolves the allosteric effects from apparent modes of interfacial activation in terms of the primary rate and equilibrium parameters for pig pancreatic phospholipase A2 (PLA2). One limit is observed in dispersions of anionic phospholipid vesicles, in which intervesicle exchange of enzyme, substrate, and hydrolysis products is absent and reaction occurs only on vesicles containing enzyme. A complete analysis at this highly processive limit, called kinetics in the scooting mode, has been published [Berg et al. (1991) Biochemistry 30, 7283]. Here is reported the analysis in the other limit, PLA2-catalyzed hydrolysis of zwitterionic micelles of short-chain phosphatidylcholines, at which substrate and products are in rapid exchange. Hydrolysis occurs either in bulk aqueous solution with phospholipid monomers or at the micellar interface. Above the critical micelle concentration (cmc), the hydrolysis rate shows a hyperbolic dependence on the bulk substrate concentration present as micelles. This dependence, characterized by the fitting parameters KMapp and VMapp, is analyzed in terms of the primary rate and equilibrium constants. The kinetic analysis is based on the assumption that the microscopic steady-state condition is satisfied because substrate replenishment in the micro-environment of the enzyme is fast relative to the catalytic turnover time. Added NaCl and anionic interface increase the hydrolysis rate in zwitterionic micelles dramatically. The overall interfacial rate enhancement is attributed to three factors: (a) promotion of PLA2 binding by net anionic charge of the interface, (b) enhancement of substrate affinity of PLA2 at the interface (Ks* allostery), and (c) stimulation of the rate-limiting chemical step (kcat* allostery).

Crystal structure of the complex of bovine pancreatic phospholipase A2 with the inhibitor 1-hexadecyl-3-(trifluoroethyl)-sn-glycero-2-phosphomethanol,

The structure of recombinant bovine pancreatic phospholipase A2 (PLA2) complexed with the competitive inhibitor 1-hexadecyl-3-(trifluoroethyl)-sn-glycero -2-phosphomethanol (hereafter MJ33), a phospholipid analogue without the sn-3 phosphodiester group, has been determined. The crystals are trigonal, space group P3121, a = b = 46.36 A and c = 102.56 A, and isomorphous to the recombinant PLA2 with one molecule in the asymmetric unit. The structure was refined using 8082 reflections between 8.0 and 1.91 A resolution to a final R-value of 18.4% [Rfree = 28.0%]. The model includes 957 protein atoms, 86 water molecules, one calcium ion, and 26 non-hydrogen atoms of the inhibitor MJ33. The overall tertiary fold of the complex is very similar to that of the inhibitor-free recombinant PLA2 with a root mean square deviation of 0.32 A for all the backbone atoms. The electron density of the surface loop residues 62-66 is clear and ordered, unlike the other trigonal bovine PLA2 structures done to date. This structural change could be responsible for the interfacial allosteric activation, which thermodynamically relates the enhanced binding of the substrate mimic to the active site of the enzyme. MJ33 is tightly bound in the active-site cleft, dislodging the equatorial coordinated calcium water (W5), the putative catalytic water W6, and the neighboring water W7. The axial coordinated calcium water is missing; thus the hexacoordinated calcium is a monocapped pentagonal pyramid. Although MJ33 is a sn-2 tetrahedral mimic, its phosphate binds to PLA2 differently from the sn-2 phosphonate analogue of phospholipids, another tetrahedral mimic. The knowledge of the active-site geometry of MJ33 would be useful in the design of more useful therapeutic agents for PLA2.

Gossypol modification of Ala-1 of secreted phospholipase A2: a probe for the kinetic effects of sulfate glycoconjugates

Gossypol is shown to covalently modify secreted phospholipase A2 (PLA2) in the aqueous phase, but not at the interface. A rapid initial noncovalent binding of gossypol is followed by a slow covalent modification of the alpha-amino group of Ala-1 by stoichiometric amounts of gossypol. The rate of modification increases in the presence of calcium, but occupancy of the substrate binding site does not alter the rate. Pancreatic PLA2 is modified at the alpha-amino group of the N terminus to form a Schiff base, which can be stabilized by reduction with borohydride. Residual activity of the gossypol-modified PLA2 from several different sources is about 10%, indicative of impaired catalytic turnover. The half-time for the inactivation is about 10 min, and it is more than 100-fold longer for PLA2 at the interface. Gossypol promotes binding of PLA2 to the interface, and the binding of PLA2 to the interface promotes only the noncovalent binding of gossypol, but not the covalent modification. Gossypol, in conjunction with spectroscopic and kinetic protocols, is used to characterize the kinetic effects of sulfated glycoconjugates, heparin and artery wall proteoglycans, with human inflammatory and pancreatic PLA2.1 The conjugates do not interfere with the binding of PLA2 to the interface or with the catalytic cycle at the interface. The conjugates do not influence the kinetics of modification of PLA2 by gossypol in the aqueous phase, and the enzyme at the interface is not modified in the presence of the conjugates. The conjugates bind to PLA2 at the interface with only a modest effect on the interfacial catalytic turnover without dislodging the bound enzyme. Complex kinetic effects induced by the conjugates are shown to be due to sequestration of PLA2 in the aqueous phase as a high-molecular mass complex, which dissociates with added NaCl.

Sacral chordoma--a case report

Chordoma, a rare malignant tumour of early adulthood, rarely presents in children. We report such a case of rare malignant tumour which was diagnosed in the first decade of life.

Effect of surgical experience on results of esophagectomy for esophageal carcinoma

BACKGROUND

Esophagectomy for esophageal cancer is associated with substantial operative morbidity and mortality. The effect of surgical experience on results of esophagectomy has received little attention in the medical literature.

METHODS

A retrospective review of esophagectomies for cancer was done.

RESULTS

Seventy-four patients underwent esophagectomy by 20 different surgeons. Three surgeons performed 6 or more esophagectomies per year ("frequent" surgeons), whereas the other 17 surgeons performed 5 or fewer esophagectomies per year ("occasional" surgeons). Forty-two patients were operated on by frequent surgeons. There were 3 (7%) anastomotic leaks and no deaths. In 32 patients operated on by occasional surgeons, there were 7 (22%) anastomotic leaks and 7 (22%) operative deaths. The anastomotic leak rates were not significantly different (P < .07), but frequent surgeons had a significantly lower operative mortality (P < .0014).

CONCLUSIONS

Esophagectomy for esophageal cancer should be performed by experienced esophageal surgeons with sufficient yearly volume of procedures to maintain competence.

Environmental and physiological factors affecting the succinate product ratio during carbohydrate fermentation by Actinobacillus sp. 130Z

Actinobacillus sp. 130Z fermented glucose to the major products succinate, acetate, and formate. Ethanol was formed as a minor fermentation product. Under CO2-limiting conditions, less succinate and more ethanol were formed. The fermentation product ratio remained constant at pH values from 6.0 to 7.4. More succinate was produced when hydrogen was present in the gas phase. Actinobacillus sp. 130Z grew at the expense of fumarate and l-malate reduction, with hydrogen as an electron donor. Other substrates such as more-reduced carbohydrates (e.g., d-sorbitol) resulted in higher succinate and/or ethanol production. Actinobacillus sp. 130Z contained the key enzymes involved in the Embden-Meyerhof-Parnas and the pentose-phosphate pathways and contained high levels of phosphoenolpyruvate (PEP) carboxykinase, malate dehydrogenase, fumarase, fumarate reductase, pyruvate kinase, pyruvate formate-lyase, phosphotransacetylase, acetate kinase, malic enzyme, and oxaloacetate decarboxylase. The levels of PEP carboxykinase, malate dehydrogenase, and fumarase were significantly higher in Actinobacillus sp. 130Z than in Escherichia coli K-12 and accounted for the differences in succinate production. Key enzymes in end product formation in Actinobacillus sp. 130Z were regulated by the energy substrates.

The polymyositis-scleroderma autoantigen interacts with the helix-loop-helix proteins E12 and E47

The basic helix-loop-helix (bHLH) transcription factors E12 and E47 regulate cellular differentiation and proliferation in diverse cell types. While looking for proteins that bind to E12 and E47 by the yeast interaction trap, we isolated the rat (r) homologue of the human (h) polymyositis-scleroderma autoantigen (PM-Scl), which has been localized to the granular layer of the nucleolus and to distinct nucleocytoplasmic foci. The rPM-Scl and hPM-Scl homologues are 96% similar and 91% identical. We found that rPM-Scl mRNA expression was regulated by growth factor stimulation in cultured rat aortic smooth muscle cells. rPM-Scl bound to E12 and E47 but not to Id3, Gax, Myb, OCT-1, or Max. The C terminus of rPM-Scl (amino acids 283-353) interacted specifically with a 54-amino acid domain in E12 that is distinct from the bHLH domain. Finally, cotransfection of rPM-Scl and E47 specifically increased the promoter activity of a luciferase reporter construct containing an E box and did not affect the basal activity of the reporter construct. rPM-Scl appears to be a novel non-HLH-interacting partner of E12/E47 that regulates E2A protein transcription.

Leukotrienes in acetylcholine-induced contraction of esophageal circular smooth muscle in experimental esophagitis

BACKGROUND & AIMS

Phospholipase A2 (PLA2) participates in acetylcholine (ACh)-induced contraction of esophageal circular smooth muscle. Because PLA2, arachidonic acid, and its metabolites are involved in inflammatory responses, their role after induction of experimental esophagitis was examined.

METHODS

Experiments were performed in esophageal smooth muscle cells (ESO) isolated by enzymatic digestion from the circular layer of normal and esophagitis animals. Content of peptidoleukotrienes (leukotriene [LT] C4, LTD4, and LTE4) was measured in esophageal circular muscle tissue.

RESULTS

The cytosolic PLA2 antagonist trifluoromethyl ketone analogue of arachidonic acid inhibited ACh-induced contraction of normal and esophagitis ESO. Inhibition by secreted PLA2 antagonists AM5 and MJ33 was significantly greater in esophagitis ESO. The lipoxygenase inhibitor nordihydro-guaiaretic acid and the LTD4 antagonist ICI 198,615 inhibited ACh-induced contraction of esophagitis but not of normal ESO. Secreted PLA2 and LTD4 contracted normal ESO more than esophagitis ESO. However, in esophagitis, ESO contraction was increased by threshold diacylglycerol concentration. Resting levels of LTs were greater in esophagitis than in normal circular esophageal muscle and increased in response to ACh in esophagitis but not in normal esophageal muscle.

CONCLUSIONS

Esophagitis shifts the signal transduction pathway activated by ACh. Esophagitis increased the contribution of secreted PLA2 and of LTs to ACh-induced contraction.

Effect of surgical experience on results of esophagectomy for esophageal carcinoma

BACKGROUND

Esophagectomy for esophageal cancer is associated with substantial operative morbidity and mortality. The effect of surgical experience on results of esophagectomy has received little attention in the medical literature.

METHODS

A retrospective review of esophagectomies for cancer was done.

RESULTS

Seventy-four patients underwent esophagectomy by 20 different surgeons. Three surgeons performed 6 or more esophagectomies per year ("frequent" surgeons), whereas the other 17 surgeons performed 5 or fewer esophagectomies per year ("occasional" surgeons). Forty-two patients were operated on by frequent surgeons. There were 3 (7%) anastomotic leaks and no deaths. In 32 patients operated on by occasional surgeons, there were 7 (22%) anastomotic leaks and 7 (22%) operative deaths. The anastomotic leak rates were not significantly different (P < .07), but frequent surgeons had a significantly lower operative mortality (P < .0014).

CONCLUSIONS

Esophagectomy for esophageal cancer should be performed by experienced esophageal surgeons with sufficient yearly volume of procedures to maintain competence.