Cloning of a complementary DNA for a protein-tyrosine kinase that specifically phosphorylates a negative regulatory site of p60c-src

The protein-tyrosine kinase activity of the proto-oncogene product p60c-src is negatively regulated by the phosphorylation of a tyrosine residue close to the C terminus, tyrosine 527. The phosphorylation might be catalysed by a so-far-unidentified tyrosine kinase, distinct from p60c-src. Recently we purified a protein-tyrosine kinase that specifically phosphorylates tyrosine 527 of p60c-src from neonatal rat brain. We have now confirmed the specificity of this enzyme by using a mutant p60c-src that has a phenylalanine instead of tyrosine 527, and cloned a complementary DNA that encodes the enzyme. The enzyme is similar to kinases of the src family in that it has two conserved regions, Src-homology regions 2 and 3, upstream of a tyrosine kinase domain. The amino-acid identity of each region is no more than 47%, however, and the enzyme lacks phosphorylation sites corresponding to tyrosines 416 and 527 of p60c-src and has no myristylation signal. These results suggest that this protein-tyrosine kinase, which might negatively regulate p60c-src, represents a new type of tyrosine kinase.

Tyrosine phosphorylation and activation of homologous protein kinases during oocyte maturation and mitogenic activation of fibroblasts

Meiotic maturation of Xenopus and sea star oocytes involves the activation of a number of protein-serine/threonine kinase activities, including a myelin basic protein (MBP) kinase. A 44-kDa MBP kinase (p44mpk) purified from mature sea star oocytes is shown here to be phosphorylated at tyrosine. Antiserum to purified sea star p44mpk was used to identify antigenically related proteins in Xenopus oocytes. Two tyrosine-phosphorylated 42-kDa proteins (p42) were detected with this antiserum in Xenopus eggs. Xenopus p42 chromatographs with MBP kinase activity on a Mono Q ion-exchange column. Tyrosine phosphorylation of Xenopus p42 approximately parallels MBP kinase activity during meiotic maturation. These results suggest that related MBP kinases are activated during meiotic maturation of Xenopus and sea star oocytes. Previous studies have suggested that Xenopus p42 is related to the mitogen-activated protein (MAP) kinases of culture mammalian cells. We have cloned a MAP kinase relative from a Xenopus ovary cDNA library and demonstrate that this clone encodes the Xenopus p42 that is tyrosine phosphorylated during oocyte maturation. Comparison of the sequences of Xenopus p42 and a rat MAP kinase (ERK1) and peptide sequences from sea star p44mpk indicates that these proteins are close relatives. The family members appear to be tyrosine phosphorylated, and activated, in different contexts, with the murine MAP kinase active during the transition from quiescence to the G1 stage of the mitotic cell cycle and the sea star and Xenopus kinases being active during M phase of the meiotic cell cycle.

Comparison of 6 and 8 hourly tobramycin dosing intervals in treatment of pulmonary exacerbations in cystic fibrosis patients

The efficacy and toxicity of a shortened tobramycin dosing interval in the treatment of exacerbations of Pseudomonas aeruginosa pulmonary infection in cystic fibrosis patients were evaluated prospectively. Patients ages 13 to 30 years received 34 treatment courses and were randomized by pairs to receive tobramycin administered either every 6 or 8 hours. Peak serum concentrations were adjusted to 8 to 10 micrograms/ml; thus a larger total daily dosage was administered to patients receiving tobramycin every 6 hours. The shorter dosing interval was associated with better pulmonary function at follow-up and significantly longer time before next hospital admission for a pulmonary exacerbation. During the study hospitalization there were no differences in pulmonary function tests, clinical score, sputum carriage of P. aeruginosa, toxicity or necessary length of hospitalization. A 6-hour tobramycin dosing interval was more efficacious than an 8-hour dosing interval in the treatment of cystic fibrosis patients.

Lack of correlation between changes in polyphosphoinositide levels and actin/gelsolin complexes in A431 cells treated with epidermal growth factor

The polyphosphoinositides, PIP and PIP2, have been proposed to regulate actin polymerization in vivo because they dissociate actin/gelsolin complexes in vitro. We tested this hypothesis by comparing the ability of EGF and bradykinin to affect PI metabolism and the actin cytoskeleton in A431 cells. EGF, but not bradykinin, was found to induce ruffling and dissociation of actin/gelsolin complexes in these cells. However, both EGF and bradykinin stimulated the accumulation of inositol phosphates in [3H]inositol-labeled cells indicating that stimulation of PI turnover is not sufficient for the induction of changes in actin/gelsolin complex levels. EGF stimulated a twofold increase in the level of PIP in A431 cells. Other phosphoinositide levels were not markedly altered. Treatment of the cells with cholera toxin abrogated the EGF-induced rise in PIP levels without altering the dissociation of actin from gelsolin. These data indicate that increases in PIP and/or PIP2 are not necessary for dissociation of actin/gelsolin complexes. Overall, these experiments suggest that in A431 cells, the effects of EGF on the actin cytoskeleton are unlikely to be mediated through changes in PIP or PIP2 levels.

Plasma factor VII is activated by postprandial triglyceridaemia, irrespective of dietary fat composition

Nine adults took two 7-day diets of standardised energy and total fat content, but with a dietary polyunsaturated/saturated fat ratio of less than 0.3 and greater than 3.0 respectively, while adhering to their daily routine. Blood was drawn on 6 occasions between 09.00 and 22.45 h on the final day of each dietary period for factor VII activity (VIIc), factor VII antigen (VIIag) and lipoprotein lipid concentrations. Diurnal variation was described for each variable in terms of its deviation from the individual's daily mean value at each time point across the day. Plasma triglyceride remained low until after the midday meal, whereafter a marked rise was sustained into the later evening. Plasma VIIc declined until early afternoon, but showed a marked rise in the late afternoon. Plasma VIIag showed no significant diurnal variation. Changes in plasma triglyceride concentration during the day were related positively to changes in VIIc about 160 min later, but not to VIIc at other time points. This effect of postprandial triglyceridaemia on VIIc persisted after allowance for the effect of VIIag on VIIc. Dietary fat composition did not influence VIIc or VIIag. The results suggested an acute but evanescent effect of triglyceride-rich lipoproteins on the reactivity of factor VII, irrespective of their lipid core composition.

Variant cDNAs encoding proteins similar to the alpha subunit of chicken CapZ

Chicken adult muscle and liver cDNA libraries were screened with a cDNA, alpha 1, previously isolated from a chicken embryo library by screening with antibodies against the alpha subunit of chicken CapZ. cDNAs with a new coding region, called alpha 2, were found in addition to ones with the alpha 1 coding region. alpha 2 predicts a protein sequence that matches exactly the N-terminal sequence of 5 peptides prepared from CapZ alpha purified from chicken muscle, while the protein sequence predicted by alpha 1 matches the peptides well, but not exactly. The predicted protein sequences of alpha 1 and alpha 2 are very similar to each other, and they are similar to those of the alpha subunit of capping protein from Dictyostelium [Hartmann et al., J. Biol. Chem. 163:5254-5254, 1989] and an actin-binding protein from Xenopus [Ankenbauer et al., Nature 342:822-824, 1989]. Other conserved features of the predicted primary and secondary structures are noted. Chicken alpha 1 and alpha 2 are transcribed in all of 7 adult chicken muscle and non-muscle tissues in comparable amounts by Northern analysis. alpha 2 has four poly(A)+RNA transcripts, one of which is rare in liver. alpha 1 has two transcripts. alpha 1 and alpha 2 are encoded by different single-copy genes by Southern analysis of chicken genomic DNA.

Normal release from proactive interference in untreated patients with Parkinson's disease

The relationship of release from proactive interference (PI) to set-shifting, explicit free recall and language remains controversial. We tested 56 patients with Parkinson's disease (PD) who had never received medication and 37 matched normal control subjects on a test of PI release based on semantic category. The PD group showed normal PI release but impaired word recall. PI release was independent of impaired Wisconsin card-sorting test performance, language production, explicit memory, overall cognitive status and severity of depression. The results indicate dissociation between ability to benefit from semantic stimulus properties and processes of explicit memory, set-shifting and expressive language.

Atypical presentation of pulmonary embolism

Today we have discussed an interesting patient with an atypical presentation of pulmonary embolism. We have outlined a suggested algorithm to aid in the diagnosis and management of this disease. References 8 through 24 in the reference section are suggested readings that offer further insight into the diagnosis and management of this entity.

Phosphorylation of the PDGF receptor beta subunit creates a tight binding site for phosphatidylinositol 3 kinase

The beta subunit of the platelet derived growth factor receptor (PDGFR) coprecipitates with a phosphatidyl-inositol 3 kinase activity (PI3K) following stimulation of cells by PDGF. Mutagenesis of a tyrosine (Y) phosphorylation site, Y751, in the PDGFR, greatly reduces PI3K, consistent with the possibility that phosphorylation of Y751 signals association of PI3K. To test this we have reconstituted the binding of the PDGFR beta subunit and PI3K in vitro. Binding is rapid, saturable and requires phosphorylation of the PDGFR at Y751, but does not require PDGF-dependent phosphorylation of PI3K. To test which portions of the PDGFR are important for binding, we used an antibody to a small region of the receptor that includes Y751. This antibody blocked in vitro binding of PI3K to the receptor, while an antiserum to the C-terminus of the receptor had no effect on binding of PI3K. In addition, we found that PDGF stimulation of a cell results in the association of essentially all the PI3K activity with cellular PDGFRs. These data suggest that PI3K is a specific ligand for PDGF receptors that are phosphorylated at Y751.

Properties of tripartite chimeras between Src and Lck

To evaluate the possible regulatory effects of interactions between different domains of Src-family kinases, we have assembled five chimeric molecules containing parts of p60c-src (Src) and p56lck (Lck). Chimeras contained the N-terminal portion, kinase domain or C-terminal tail from either of the parent molecules. None of the four full-length hybrid proteins induced morphological transformation of NIH3T3 cells, nor stimulated phosphorylation of cell proteins on tyrosine residues, suggesting that their protein-tyrosine kinase activities were repressed appropriately in fibroblastic cells. However, two hybrid proteins, SLS and SLL, containing the Src N-terminal region, Lck kinase domain, and either Src or Lck tail, respectively, inefficiently induced anchorage-independent growth. Sites of phosphorylation in these molecules were determined by two-dimensional peptide mapping. SLS and SLL were both phosphorylated at their C-terminal tyrosine residues similarly to the parental molecules. Curiously, both proteins were also significantly phosphorylated at tyrosine 416, a feature of transforming variants of Src and Lck. A modified hybrid, SLO, containing the N-terminal region of Src, kinase domain of Lck and a truncated C-terminus, fully transformed cells and stimulated phosphorylation of cell proteins at tyrosine. Comparison of SLS, SLL and SLO suggests that the full-length hybrids are repressed by their C-terminal phosphorylated tyrosine residues in vivo. Consistent with this, SLO resembled activated Src in being cytoskeletal, and SLS and SLL resembled nontransforming Src and were not cytoskeletal. Hybrids with an Lck N-terminal region were cytoskeletal, like Lck itself, even though they were not transforming, suggesting that cytoskeletal localization of Lck is determined through its N terminus. Curiously, the hybrid molecules appeared not to be regulated in vitro. The specific activities of SLS, SLL and Src were approximately equal, but the specific activity of SLO was not increased, being much less than that of activated Src. Enzymatic dephosphorylation stimulated the in vitro kinase activity of parental Src, but not of SLS or SLL. These observations suggest that chimeric Src-Lck molecules are regulated in the cell, but not in vitro.

Acidic residues at the carboxyl terminus of p60c-src are required for regulation of tyrosine kinase activity and transformation

Protein phosphorylation sites act to transduce signals into changes in enzymatic activity, representing a point of interaction within a regulatory pathway. The amino acid sequence surrounding a phosphorylation site may well have several functions, including recognition by an appropriate kinase. By generating random mutations in its immediate vicinity, we have examined the sequence requirements of a regulatory tyrosine phosphorylation site, Tyr527, in the proto-oncogene product, p60c-src. The transforming and kinase activities of p60c-src are repressed by phosphorylation of Tyr527. Mutations were made around Tyr527 without changing Tyr527 or the kinase domain. Twenty-nine mutants were sequenced and classified as transforming or nontransforming for Rat-2 cells. Nontransforming mutants contained a surprising variety of COOH-terminal mutations, although acidic residues were present at positions 518 and 524 in all nontransforming mutants. Transforming mutants that contained single-residue changes at Asp518 and Ser522 demonstrated the importance of these residues. Other transforming mutants contained two or more substitutions, but the results are most simply explained if residues Glu524 and Thr523 are also important for normal regulation. Transforming mutations reduced the phosphorylation of Tyr527. We conclude that only a few of the residues in the COOH terminus other than Tyr527 are required to ensure normal phosphorylation and repression of activity in fibroblasts. Other residues may have been conserved during evolution to permit normal function and regulation in other cell types.

Macrophage colony-stimulating factor-induced tyrosine phosphorylation of c-fms proteins expressed in FDC-P1 and BALB/c 3T3 cells

The c-fms protein is a receptor for macrophage colony-stimulating factor (M-CSF) with intrinsic protein-tyrosine kinase activity. We investigated the tyrosine phosphorylation of murine c-fms proteins expressed from a retroviral vector in factor-dependent myeloid FDC-P1 cells and in BALB/c 3T3 fibroblasts transformed by the expression of the c-fms gene. FDC-P1 cells expressing c-fms were able to grow and differentiate in response to M-CSF. Their c-fms proteins were normally phosphorylated on serine and became phosphorylated on tyrosine residues contained in five tryptic peptides when the cells were exposed to M-CSF. A subset of these peptides was constitutively phosphorylated in BALB/c cells expressing c-fms, consistent with the production of M-CSF by these cells. All the peptides detected in vivo were also phosphorylated in vitro. These peptides were analyzed by susceptibility to proteases, comparison with synthetic peptides, and site-directed mutagenesis. The identities of four of the tryptic peptides were determined; they arise from three unique tyrosine phosphorylation sites. One major site of tyrosine phosphorylation at residue 697 accounted for two of the tryptic peptides. A second major site was identified at tyrosine residue 706. These two tyrosine phosphorylation sites are located within the tyrosine kinase insert region. Tyrosine 807, which has homology to the major autophosphorylation site of the p60v-src tyrosine kinase, is a minor autophosphorylation site. Possible functional roles for these phosphorylations of the c-fms protein include interactions with substrate proteins, catalytic activity, and ligand-induced degradation.

Oncogenes and anti-oncogenes

The study of oncogenes offers insights into many steps in signal transduction. Rapid progress is possible because of the combination of biochemistry and genetics--unique in vertebrate cell biology--the availability of specific clones and antibodies, sequence information, dominant mutants, and biochemical assays of function. The wealth of detail on oncogenes and proto-oncogenes continues to increase dramatically. Hopefully, in the next year or two some of the gaps will be filled in and all the steps along at least one pathway from the cell membrane to the nucleus will be understood.

Binding of GAP to activated PDGF receptors

The ras proto-oncogene products appear to relay intracellular signals via the Ras guanosine triphosphatase (GTPase) activator protein, GAP. In dog epithelial cells expressing human platelet-derived growth factor (PDGF) receptors, binding of PDGF caused approximately one-tenth of the total GAP molecules to complex with the receptor. Studies with mutant PDGF receptors showed that maximum association required both receptor kinase activity and phosphorylatable tyrosine residues at both the identified sites of receptor autophosphorylation.

Disruption of the actin cytoskeleton in yeast capping protein mutants

Capping protein controls the addition of actin subunits to the barbed end of actin filaments and nucleates actin polymerization in vitro. Capping protein has been identified in all eukaryotic cells examined so far; it is a heterodimer with subunits of relative molecular masses 32,000-36,000 (alpha-subunit) and 28,000-32,000 (beta-subunit). In skeletal muscle, capping protein (CapZ) probably binds the barbed ends of actin filaments at the Z line. The in vivo role of this protein in non-muscle cells is not known. We report here the characterization of CAP2, the single gene encoding the beta-subunit of capping protein in Saccharomyces cerevisiae. Yeast cells in which the CAP2 gene was disrupted by an insertion or a deletion had an abnormal actin distribution, including the loss of actin cables. The mutant cells were round and large, with a heterogeneous size distribution, and, although viable, grew more slowly than congenic wild-type cells. Chitin, a cell wall component restricted to the mother-bud junction in wild-type budding yeast, was found on the entire mother cell surface in the mutants. The phenotype of CAP2 disruption resembled that of temperature-sensitive mutations in the yeast actin gene ACT1, indicating that capping protein regulates actin-filament distribution in vivo.

Leukotriene B4 increases pulmonary transvascular filtration by a neutrophil-independent mechanism

We examined the role of circulating granulocytes in the pulmonary microvascular response to leukotriene B4 (LTB4) by prior depletion of circulating granulocytes using hydroxyurea. LTB4 (2 micrograms/kg injection followed by infusion of 2 micrograms/kg over 15 min) produced transient increases in pulmonary arterial pressure and pulmonary vascular resistance, indicating that neutrophils were not required for the pulmonary hemodynamic effects of LTB4. Infusion of LTB4 in granulocyte-depleted sheep also resulted in transient increases in pulmonary lymph flow (QL) with no significant change in the lymph-to-plasma protein concentration ratio (L/P), findings similar to those in control animals. In vitro studies indicated that LTB4 (10(-7) or 10(-9) M) produced a transient adherence of neutrophils to cultured pulmonary artery endothelial monolayers. Maximal responses occurred at 10 min after the addition of LTB4 to the endothelial cell-neutrophil coculture system, and the adherence decreased to base line within 60 min. LTB4 infusion in sheep also produced a transient uptake of autologous 111In-oxine-labeled neutrophils. The results indicate that LTB4-mediated increase in pulmonary transvascular protein clearance (QL x L/P) is independent of circulating granulocytes.

Hypoxia and hypercarbia of chronic lung disease: minimal effects on anterior pituitary function

Previous studies have suggested that the hypoxia and/or hypercapnia associated with chronic lung diseases may lead to pituitary and gonadal dysfunction, with destruction of the sella turcica. It is unclear, however, whether these abnormalities were due to lung disease or to confounding factors. We studied the relationships between hormonal levels (triiodothyronine, thyroxine, T3 resin uptake, thyrotropin, prolactin, cortisol, and testosterone) and PaO2, PaCO2, pH, and alveolar-arterial gradient in 25 patients with chronic lung disease. These patients were highly homogeneous for diagnosis, age, sex, ambulatory status, lack of other illnesses, and minimal use of medications unrelated to lung disease, but did have various degrees of hypoxia and hypercarbia at the time of study. We found no relationship between hormonal levels and lung function, or evidence of major pituitary involvement on lateral roentgenograms of the skull, CT of the sella turcica, or stimulation of the pituitary. An inverse correlation did occur between serum levels of thyroxine and the daily dose of oral prednisone. We conclude that most of the endocrine dysfunction ascribed to chronic lung diseases is probably due to factors other than hypoxia or hypercarbia.

Pulmonary disease due to antirheumatic agents

Drug-induced lung disease presents several diagnostic and therapeutic problems to the clinician. This is especially true in the case of lung disease associated with antirheumatic agents in which pulmonary disease may be due to the underlying disorder. Unfortunately, no specific markers exist to differentiate drug-induced lung disease from other pathologic processes. In addition, the numerous drugs often used simultaneously or in close sequence in rheumatic disorders make assignment of toxicity to a specific agent difficult. Six groups of drugs used as anti-inflammatory/antirheumatic agents have been discussed in association with pulmonary damage penicillamine, gold, methotrexate, salicylates, NSAIDs, and colchicine. The major clinical syndromes ascribed to these drugs include hypersensitivity pneumonitis and chronic alveolitis/fibrosis (penicillamine, gold, methotrexate, NSAIDs), pulmonary-renal syndrome (penicillamine), bronchiolitis obliterans (penicillamine, gold), and noncardiogenic pulmonary edema (salicylates, colchicine). Unfortunately, treatment options remain limited. Withdrawal of the offending drug and supportive care are the mainstays of therapy. In cases in which active inflammation causes significant derangement of gas exchange, corticosteroids are warranted. More aggressive management using immunosuppressive drugs has been recommended in cases of refractory PABO and PAGS, but these recommendations are at present based only on isolated case reports.

Plasmodium falciparum: two antigens of similar size are located in different compartments of the rhoptry

Two previously described antigens, AMA-1 and QF3, which are located in the rhoptries of Plasmodium falciparum merozoites have polypeptides of similar relative molecular masses. On immunoblots, antibodies to both antigens recognized polypeptides of relative molecular mass 80,000 and 62,000 in all isolates tested. Two-dimensional electrophoresis showed that the isoelectric points of the two antigens were different. QF3 being more basic than AMA-1. AMA-1 was soluble in Triton X-114 whereas QF3 partitioned into the aqueous phase after temperature-dependent phase separation. In immunoelectron microscopic studies. QF3 was found in the body of the rhoptry whereas AMA-1 was consistently found in the neck of the rhoptry. Both antigens gave a punctate double-dot pattern in mature schizonts and merozoites when visualized by fluorescence microscopy, but AMA-1 antibodies also appeared to label the merozoite surface. QF3 was also detected in ring-infected erythrocytes whereas AMA-1 was not. Synthesis of both antigens was first observed in mature trophozoites and immature schizonts. Pulse-chase experiments showed that the Mr 80,000 polypeptide of the AMA-1 gene was subject to immediate processing to the Mr 62,000 product. This cleavage pattern was not stage specific. The Mr 80,000 polypeptide of QF3 was derived from a short-lived Mr 84,000 precursor polypeptide. Processing of the Mr 80,000 polypeptide to an Mr 62,000 polypeptide was restricted to the period of merozoite maturation and reinvasion. Hence AMA-1 and QF3 are different antigens with polypeptides of similar size but located in different compartments of the merozoite rhoptries.

Identification of peptides from autolysates of Saccharomyces cerevisiae that exhibit glucose tolerance factor activity in a yeast assay

1. Cationic fractions were isolated from a low chromium (less than 0.2 ppm) commercial yeast extract in an attempt to purify the material responsible for glucose tolerance factor (GTF) activity observed in a standard yeast assay system. 2. Following previously described procedures a fraction with GTF activity but containing negligible chromium was isolated, which on further purification was found to be composed of many separate small basic peptides. 3. Much of the activity of the yeast GTF material in the yeast assay could be attributed to the presence of basic peptides and free amino acids acting as nitrogen sources for the yeast. 4. Additional activity was present in the yeast GTF sample, which was not due to a synergistic effect of the mixed amino acids and peptides although the component of the yeast extract responsible for this activity was not identified. 5. The results show that the GTF fractions isolated according to most previously published procedures are highly impure, and conclusions drawn about the nature of GTF based on these isolates must remain open to question. 6. The activity due to the presence of peptides and amino acids is a major cause of lack of specificity of the yeast systems as an assay for GTF.

Role of albumin arginyl sites in albumin-induced reduction of endothelial hydraulic conductivity

We determined the effect of albumin on endothelial hydraulic conductivity (Lp) and the contributions of the positively charged arginyl and lysinyl residues of albumin in mediating the effect. Studies were made using monolayers of cultured sheep pulmonary artery endothelial cells grown to confluence on polycarbonate filters. Water flux was measured as transendothelial hydrostatic pressure was varied from 5 to 20 cm H2O. Lp was calculated from the slope of the relationship of water flux versus pressure. The Lp of endothelial monolayers perfused with albumin-free Hanks Balanced Salt Solution (HBSS) was compared to perfusion with HBSS containing either native albumin, or albumin in which the arginyl residues were modified by a condensation reaction with 1,2-cyclohexanedione (CHD-albumin), or albumin in which the lysinyl residues were modified by a substitution reaction with succinic anhydride (SC-albumin). Baseline Lp at 2.5 mg/ml native albumin was 1.6 +/- 0.1 X 10(-6) cm/s/cm H2O compared to the filter Lp after removing cells of 3.0 +/- 0.3 X 10(-4) cm/s/cm H2O. Endothelial Lp increased by 60% when albumin concentration was decreased from 2.5 mg/ml to 0.5 mg/ml (P less than 0.05), but did not change with an increase in concentration to 10 mg/ml. Albumin-free buffer and CHD-albumin increased endothelial Lp by 2.2 +/- 0.3-fold and 1.9 +/- 0.3-fold, respectively (P less than 0.05). All endothelial Lp values were restored to baseline when the native albumin concentration was returned to 2.5 mg/ml. Excess l-arginine (2 X 10(-3) M) inhibited the effect of native albumin and increased endothelial Lp 1.5 +/- 0.02-fold (P less than 0.05), but excess l-lysine (4 X 10(-3) in the presence of native albumin had no effect on Lp. None of the perfusates altered the filter Lp value. Neutral dextran (70 kD), in contrast to native albumin, had no effect on endothelial Lp. These results indicate that albumin reduces the hydraulic conductivity of endothelial monolayers in a concentration-dependent fashion and that the arginyl residues of albumin are required for the response. The effect of albumin may be mediated by a charge interaction of albumin with the endothelium.

Modulation of endoperoxide product levels and cyclophosphamide-induced injury by glutathione repletion

Glutathione is a tripeptide important in a number of diverse cellular functions including enzymatic reactions involved in prostaglandin endoperoxide metabolism. We have previously reported that cyclophosphamide administration to rats results in acute lung injury manifested by increased bronchoalveolar lavage albumin concentrations. In the current study we examine whether cyclophosphamide treatment affects pulmonary glutathione stores or bronchoalveolar endoperoxide metabolic product levels and whether these effects may be related to acute lung injury caused by the drug. We show that cyclophosphamide treatment causes a dose-dependent reduction in pulmonary glutathione stores 4 h after drug administration. In addition, acute lung injury as the result of cyclophosphamide can be abrogated by coadministration of oxothiazolidine carboxylate, an intracellular cysteine delivery system that also reverses pulmonary glutathione depletion induced by cyclophosphamide in our study. Finally, cyclophosphamide treatment reduces prostaglandin E2 concentrations in bronchoalveolar lavage and alveolar macrophage culture supernatant in a dose-dependent fashion and increases bronchoalveolar thromboxane concentrations in low dose-treated animals. These effects are reversed to a variable degree by coadministration of oxothiazolidine carboxylate. Our study suggests in vivo pulmonary arachidonic acid metabolism and cyclophosphamide-induced acute lung injury are modulated by cellular glutathione stores. These findings may have important implications for the treatment of acute lung injury.