Context-dependent antagonism between Akt inhibitors and topoisomerase poisons

Signaling through the phosphatidylinositol-3 kinase (PI3K)/Akt pathway, which is aberrantly activated in >50% of carcinomas, inhibits apoptosis and contributes to drug resistance. Accordingly, several Akt inhibitors are currently undergoing preclinical or early clinical testing. To examine the effect of Akt inhibition on the activity of multiple widely used classes of antineoplastic agents, human cancer cell lines were treated with the Akt inhibitor A-443654 [(2S)-1-(1H-indol-3-yl)-3-[5-(3-methyl-2H-indazol-5-yl)pyridin-3-yl]oxypropan-2-amine; ATP-competitive] or MK-2206 (8-[4-(1-aminocyclobutyl)phenyl]-9-phenyl-2H-[1,2,4]triazolo[3,4-f][1,6]naphthyridin-3-one;dihydrochloride; allosteric inhibitor) or with small interfering RNA (siRNA) targeting phosphoinositide-dependent kinase 1 (PDK1) along with cisplatin, melphalan, camptothecin, or etoposide and assayed for colony formation. Surprisingly different results were observed when Akt inhibitors were combined with different drugs. Synergistic effects were observed in multiple cell lines independent of PI3K pathway status when A-443654 or MK-2206 was combined with the DNA cross-linking agents cisplatin or melphalan. In contrast, effects of the Akt inhibitors in combination with camptothecin or etoposide were more complicated. In HCT116 and DLD1 cells, which harbor activating PI3KCA mutations, A-443654 over a broad concentration range enhanced the effects of camptothecin or etoposide. In contrast, in cell lines lacking activating PI3KCA mutations, partial inhibition of Akt signaling synergized with camptothecin or etoposide, but higher A-443654 or MK-2206 concentrations (>80% inhibition of Akt signaling) or PDK1 siRNA antagonized the topoisomerase poisons by diminishing DNA synthesis, a process that contributes to effective DNA damage and killing by these agents. These results indicate that the effects of combining inhibitors of the PI3K/Akt pathway with certain classes of chemotherapeutic agents might be more complicated than previously recognized.

Farnesyltransferase inhibitor tipifarnib inhibits Rheb prenylation and stabilizes Bax in acute myelogenous leukemia cells

Although farnesyltransferase inhibitors have shown promising activity in relapsed lymphoma and sporadic activity in acute myelogenous leukemia, their mechanism of cytotoxicity is incompletely understood, making development of predictive biomarkers difficult. In the present study, we examined the action of tipifarnib in human acute myelogenous leukemia cell lines and clinical samples. In contrast to the Ras/MEK/ERK pathway-mediated Bim upregulation that is responsible for tipifarnib-induced killing of malignant lymphoid cells, inhibition of Rheb-induced mTOR signaling followed by dose-dependent upregulation of Bax and Puma occurred in acute myelogenous leukemia cell lines undergoing tipifarnib-induced apoptosis. Similar Bax and Puma upregulation occurred in serial bone marrow samples harvested from a subset of acute myelogenous leukemia patients during tipifarnib treatment. Expression of FTI-resistant Rheb M184L, like knockdown of Bax or Puma, diminished tipifarnib-induced killing. Further analysis demonstrated that increased Bax and Puma levels reflect protein stabilization rather than increased gene expression. In U937 cells selected for tipifarnib resistance, neither inhibition of signaling downstream of Rheb nor Bax and Puma stabilization occurred. Collectively, these results not only identify a pathway downstream from Rheb that contributes to tipifarnib cytotoxicity in human acute myelogenous leukemia cells, but also demonstrate that FTI-induced killing of lymphoid versus myeloid cells reflects distinct biochemical mechanisms downstream of different farnesylated substrates. (ClinicalTrials.gov identifier NCT00602771).

Phosphatidylserine exposure during apoptosis reflects bidirectional trafficking between plasma membrane and cytoplasm

Phosphatidylserine (PS) exposure on the external leaflet of the plasma membrane is widely observed during apoptosis and forms the basis for the annexin V binding assay to detect apoptotic cell death. Current efforts to explain PS exposure focus on two potential mechanisms, activation of a phospholipid scramblase or calcium-mediated trafficking of lysosomes to the cell surface. Here, we provide evidence that apoptotic PS exposure instead reflects bidirectional trafficking of membrane between the cell surface and cytoplasm. Using a series of cell lines, some of which expose large amounts of PS during apoptosis and some of which do not, we demonstrate that accumulation of plasma membrane-derived cytoplasmic vesicles in a dynamin-, clathrin- and Cdc42-independent manner is a previously undescribed but widely occurring feature of apoptosis. The apoptotic exposure of PS occurs when these vesicles traffic back to cell surface in a calcium-dependent process that is deficient in a substantial fraction of human cancer cell lines. These observations provide a new model for PS externalization during apoptosis and simultaneously identify an altered step that accounts for the paucity of apoptotic PS exposure in many cell lines.

Phase I and pharmacological study of cytarabine and tanespimycin in relapsed and refractory acute leukemia

BACKGROUND

In preclinical studies the heat shock protein 90 (Hsp90) inhibitor tanespimycin induced down-regulation of checkpoint kinase 1 (Chk1) and other client proteins as well as increased sensitivity of acute leukemia cells to cytarabine. We report here the results of a phase I and pharmacological study of the cytarabine + tanespimycin combination in adults with recurrent or refractory acute leukemia.

DESIGN AND METHODS

Patients received cytarabine 400 mg/m(2)/day continuously for 5 days and tanespimycin infusions at escalating doses on days 3 and 6. Marrow mononuclear cells harvested before therapy, immediately prior to tanespimycin, and 24 hours later were examined by immunoblotting for Hsp70 and multiple Hsp90 clients.

RESULTS

Twenty-six patients were treated at five dose levels. The maximum tolerated dose was cytarabine 400 mg/m(2)/day for 5 days along with tanespimycin 300 mg/m(2) on days 3 and 6. Treatment-related adverse events included disseminated intravascular coagulation (grades 3 and 5), acute respiratory distress syndrome (grade 4), and myocardial infarction associated with prolonged exposure to tanespimycin and its active metabolite 17-aminogeldanamycin. Among 21 evaluable patients, there were two complete and four partial remissions. Elevations of Hsp70, a marker used to assess Hsp90 inhibition in other studies, were observed in more than 80% of samples harvested 24 hours after tanespimycin, but down-regulation of Chk1 and other Hsp90 client proteins was modest.

CONCLUSIONS

Because exposure to potentially effective concentrations occurs only for a brief time in vivo, at clinically tolerable doses tanespimycin has little effect on resistance-mediating client proteins in relapsed leukemia and exhibits limited activity in combination with cytarabine. (Clinicaltrials.gov identifier: NCT00098423).

Protein kinase Cbeta modulates ligand-induced cell surface death receptor accumulation: a mechanistic basis for enzastaurin-death ligand synergy

Although treatment with the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) is known to protect a subset of cells from induction of apoptosis by death ligands such as Fas ligand and tumor necrosis factor-alpha-related apoptosis-inducing ligand, the mechanism of this protection is unknown. This study demonstrated that protection in short term apoptosis assays and long term proliferation assays was maximal when Jurkat or HL-60 human leukemia cells were treated with 2-5 nm PMA. Immunoblotting demonstrated that multiple PKC isoforms, including PKCalpha, PKCbeta, PKCepsilon, and PKC, translocated from the cytosol to a membrane-bound fraction at these PMA concentrations. When the ability of short hairpin RNA (shRNA) constructs that specifically down-regulated each of these isoforms was examined, PKCbeta shRNA uniquely reversed PMA-induced protection against cell death. The PKCbeta-selective small molecule inhibitor enzastaurin had a similar effect. Although mass spectrometry suggested that Fas is phosphorylated on a number of serines and threonines, mutation of these sites individually or collectively had no effect on Fas-mediated death signaling or PMA protection. Further experiments demonstrated that PMA diminished ligand-induced cell surface accumulation of Fas and DR5, and PKCbeta shRNA or enzastaurin reversed this effect. Moreover, enzastaurin sensitized a variety of human tumor cell lines and clinical acute myelogenous leukemia isolates, which express abundant PKCbeta, to tumor necrosis factor-alpha related apoptosis-inducing ligand-induced death in the absence of PMA. Collectively, these results identify a specific PKC isoform that modulates death receptor-mediated cytotoxicity as well as a small molecule inhibitor that mitigates the inhibitory effects of PKC activation on ligand-induced death receptor trafficking and cell death.

Expression of insulin receptor isoform A and insulin-like growth factor-1 receptor in human acute myelogenous leukemia: effect of the dual-receptor inhibitor BMS-536924 in vitro

The insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF1R) are receptor tyrosine kinases that participate in mitogenic and antiapoptotic signaling in normal and neoplastic epithelia. In the present study, immunoblotting and reverse transcription-PCR demonstrated expression of IGF1R and IR isoform A in acute myelogenous leukemia (AML) cell lines as well as in >80% of clinical AML isolates. Treatment with insulin enhanced signaling through the Akt and MEK1/2 pathways as well as survival of serum-starved AML cell lines. Conversely, treatment with BMS-536924, a dual IGF1R/IR kinase inhibitor that is undergoing preclinical testing, inhibited constitutive receptor phosphorylation as well as downstream signaling through MEK1/2 and Akt. These changes inhibited proliferation and, in some AML cell lines, induced apoptosis at submicromolar concentrations. Likewise, BMS-536924 inhibited leukemic colony formation in CD34+ clinical AML samples in vitro. Collectively, these results not only indicate that expression of IGF1R and IR isoform A is common in AML but also show that interruption of signaling from these receptors inhibits proliferation in clinical AML isolates. Accordingly, further investigation of IGF1R/IR axis as a potential therapeutic target in AML appears warranted.

Mitotic phosphorylation stimulates DNA relaxation activity of human topoisomerase I

Human DNA topoisomerase I (topo I) is an essential mammalian enzyme that regulates DNA supercoiling during transcription and replication. In addition, topo I is specifically targeted by the anticancer compound camptothecin and its derivatives. Previous studies have indicated that topo I is a phosphoprotein and that phosphorylation stimulates its DNA relaxation activity. The locations of most topo I phosphorylation sites have not been identified, preventing a more detailed examination of this modification. To address this issue, mass spectrometry was used to identify four topo I residues that are phosphorylated in intact cells: Ser(10), Ser(21), Ser(112), and Ser(394). Immunoblotting using anti-phosphoepitope antibodies demonstrated that these sites are phosphorylated during mitosis. In vitro kinase assays demonstrated that Ser(10) can be phosphorylated by casein kinase II, Ser(21) can be phosphorylated by protein kinase Calpha, and Ser(112) and Ser(394) can be phosphorylated by Cdk1. When wild type topo I was pulled down from mitotic cells and dephosphorylated with alkaline phosphatase, topo I activity decreased 2-fold. Likewise, topo I polypeptide with all four phosphorylation sites mutated to alanine exhibited 2-fold lower DNA relaxation activity than wild type topo I after isolation from mitotic cells. Further mutational analysis demonstrated that Ser(21) phosphorylation was responsible for this change. Consistent with these results, wild type topo I (but not S21A topo I) exhibited increased sensitivity to camptothecin-induced trapping on DNA during mitosis. Collectively these results indicate that topo I is phosphorylated during mitosis at multiple sites, one of which enhances DNA relaxation activity in vitro and interaction with DNA in cells.

Overcoming S-phase checkpoint-mediated resistance: sequence-dependent synergy of gemcitabine and 7-ethyl-10-hydroxycamptothecin (SN-38) in human carcinoma cell lines

Although agents that inhibit DNA synthesis are widely used in the treatment of cancer, the optimal method for combining such agents and the mechanism of their synergy is poorly understood. The present study examined the effects of combining gemcitabine (2',2'-difluoro 2'-deoxycytidine) and 7-ethyl-10-hydroxycamptothecin (SN-38; the active metabolite of irinotecan), two S-phaseselective agents that individually have broad antitumor activity, in human cancer cells in vitro. Colony-forming assays revealed that simultaneous treatment of Ovcar-5 ovarian cancer cells or BxPC-3 pancreatic cancer cells with gemcitabine and SN-38 resulted in antagonistic effects. In contrast, sequential treatment with these two agents in either order resulted in synergistic anti-proliferative effects, although the mechanism of synergy varied with the sequence. In particular, SN-38 arrested cells in S phase, enhanced the accumulation of gemcitabine metabolites, and diminished checkpoint kinase 1, thereby sensitizing cells in the SN-38 --> gemcitabine sequence. Gemcitabine treatment followed by removal allowed prolonged progression through S phase, contributing to synergy of the gemcitabine --> SN-38 sequence. These results collectively suggest that S-phase-selective agents might exhibit more cytotoxicity when administered sequentially rather than simultaneously.

Apoptosis-associated caspase activation assays

Caspases are aspartate-directed cysteine proteases that cleave a diverse group of intracellular substrates to contribute to various manifestations of apoptosis. These proteases are synthesized as inactive precursors and are activated as a consequence of signaling induced by a wide range of physiological and pathological stimuli. Caspase activation can be detected by measurement of catalytic activity, immunoblotting for cleavage of their substrates, immunolabeling using conformation-sensitive antibodies or affinity labeling followed by flow cytometry or ligand blotting. Here we describe methods for each of these assays, identify recent improvements in these assays and outline the strengths and limitations of each approach.

Major basic protein homolog (MBP2): a specific human eosinophil marker

Human eosinophil granule major basic protein (MBP1) is an exceedingly basic (isoelectric point >11) 14-kDa protein, comprising the core of the secondary eosinophil granule. Recently, a less cationic homolog of MBP, termed MBPH or simply, MBP2, has been discovered. We prepared a panel of mAbs to MBP2 and used these Abs to localize and quantitate this molecule in leukocytes and biological fluids. Specific mAbs for MBP2 were selected using slot-blot analyses and used in a two-site immunoassay, Western blotting, and immunofluorescence microscopy. The sensitivity of the immunoassay was markedly improved by reduction and alkylation of MBP2. MBP1 is more abundant than MBP2 in lysates of eosinophils and their granules, as judged by immunoassay and Western blotting. By immunofluorescence, MBP1 is present in eosinophils, basophils, and a human mast cell line (HMC1), whereas MBP2 is only detected in eosinophils. Neither MBP1 nor MBP2 could be detected in any other peripheral blood leukocyte. MBP2 levels measured in plasma and serum were essentially identical. In contrast to past measurements for MBP1, MBP2 was not detected above normal levels in sera from pregnant donors. However, measurement of serum MBP2 discriminated patients with elevated eosinophils from normal subjects, and MBP2 was also detectable in other biological specimens, such as bronchoalveolar lavage, sputum, and stool. These results indicate that MBP2 is present only in eosinophils and that it may be a useful biomarker for eosinophil-associated diseases.

In vitro and In vivo Antitumor Effects of the Dual Insulin-Like Growth Factor-I/Insulin Receptor Inhibitor, BMS-554417

The insulin-like growth factor receptor (IGF-IR) and insulin receptor are either overactivated and/or overexpressed in a wide range of tumor types and contribute to tumorigenicity, proliferation, metastasis, and drug resistance. Here, we show that BMS-554417, a novel small molecule developed as an inhibitor of IGF-IR, inhibits IGF-IR and insulin receptor kinase activity and proliferation in vitro, and reduces tumor xenograft size in vivo. In a series of carcinoma cell lines, the IC50 for proliferation ranged from 120 nmol/L (Colo205) to >8.5 micromol/L (OV202). The addition of stimulatory ligands was unnecessary for the antiproliferative effect in MCF-7 and OV202 cells. BMS-554417 treatment inhibited IGF-IR and insulin receptor signaling through extracellular signal-related kinase as well as the phosphoinositide 3-kinase/Akt pathway, as evidenced by decreased Akt phosphorylation at Ser473. At doses that inhibited proliferation, the compound also caused a G0-G1 arrest and prevented nuclear accumulation of cyclin D1 in response to LR3 IGF-I. In Jurkat T-cell leukemia cells, this agent triggered apoptotic cell death via the mitochondrial pathway. BMS-554417 was orally bioavailable and significantly inhibited the growth of IGF1R-Sal tumor xenografts in vivo. BMS-554417 is a member of a novel class of IGF-IR/insulin receptor inhibitors that have potential clinical applications because of their antiproliferative and proapoptotic activity in vitro and in vivo.

Differential extraction of eosinophil granule proteins

Eosinophil granules contain several toxic cationic proteins that contribute to the pathophysiology of allergic diseases. These include eosinophil peroxidase, two ribonucleases, and two forms of the major basic protein (MBP). Extraction of eosinophil granules by exposure to acid solution and fractionation on Sephadex G-50 characteristically yields a distinctive profile of three discrete peaks, and these proteins are usually recovered in good quantities, except for the eosinophil major basic protein homolog (MBP2). We investigated the effect of multiple granule extractions by dilute HCl on the recovery of granule proteins. Isolated granules were repetitively extracted, up to 31 times, in 0.01 M HCl, and the extracts fractionated on Sephadex G-50. Whereas initial extracts yielded the characteristic three-peak fractionation pattern, later extracts yielded four discrete peaks. Characterization of the novel fourth peak showed that it contained MBP2. These results indicate that repetitive extraction of eosinophil granules yields an increased amount of all granule proteins, and that MBP2 can now be recovered in good quantities and in a relatively pure form.

Phase I and Pharmacologic Study of Infusional Topotecan and Carboplatin in Relapsed and Refractory Acute Leukemia

PURPOSE

To assess the maximum tolerated dose, toxicities, pharmacokinetics, and antileukemic activity of topotecan and carboplatin in adults with recurrent or refractory acute leukemias.

EXPERIMENTAL DESIGN

Patients received topotecan and carboplatin by 5-day continuous infusion at nine dose levels. Patients achieving a complete remission received up to two additional courses for consolidation. Plasma topotecan and ultrafilterable platinum were assayed on days 1 to 5. In addition, pretreatment levels of various polypeptides in leukemic cells were examined by immunoblotting to assess possible correlations with response.

RESULTS

Fifty-one patients received a total of 69 courses of therapy. Dose-limiting toxicity consisted of grade 4/5 typhlitis and grade 3/4 mucositis after one course of therapy or grade 4 neutropenia and thrombocytopenia lasting >50 days when a second course was administered on day 21. Among 45 evaluable patients, there were 7 complete remissions, 2 partial remissions, 1 incomplete complete remission, and 1 reversion to chronic-phase chronic myelogenous leukemia. Topotecan steady-state plasma concentrations increased with dose. No accumulation of topotecan or ultrafilterable platinum occurred between days 1 and 5 of therapy. Leukemic cell levels of topoisomerase I, checkpoint kinase 1, checkpoint kinase 2, and Mcl-1 correlated with proliferating cell nuclear antigen but not with response. In contrast, low Bcl-2 expression correlated with response (P = 0.014, Mann-Whitney U test).

CONCLUSIONS

The maximum tolerated dose was 1.6 mg/m(2)/d topotecan plus 150 mg/m(2)/d carboplatin. The complete remission rate in a heavily pretreated population was 16% (33% at the highest three dose levels). Responses seem to correlate with low pretreatment blast cell Bcl-2 expression.

Proteomic analysis of mantle-cell lymphoma by protein microarray

Mantle-cell lymphoma (MCL) is a unique subtype of B-cell non-Hodgkin lymphoma (NHL) that behaves aggressively and remains incurable. In order to understand the pathogenesis of MCL and design new therapies, it is important to accurately analyze molecular changes in pathways dysregulated in MCL. We used antibody microarrays to compare patterns of protein expression between CD19(+) purified B lymphocytes from normal tonsil and 7 cases of histologically confirmed MCL. Protein overexpression was defined as a higher than 1.3-fold or 2-fold increase in at least 67% of tumor samples compared with normal B-cell control. Of the polypeptides, 77 were overexpressed using the higher than 1.3-fold cutoff, and 13 were overexpressed using the 2-fold cutoff. These included cell cycle regulators (regulator of chromosome condensation 1 [RCC1], murine double minute 2 [MDM2]), a kinase (citron Rho-interacting kinase [CRIK]), chaperone proteins (heat shock 90-kDa protein [Hsp90], Hsp10), and phosphatase regulators (A-kinase anchor protein 1 [AKAP149], protein phosphatase 5 [PP5], and inhibitor 2). The elevated expression of some of these polypeptides was confirmed by immunoblotting and immunohistochemistry, whereas elevated expression of others could not be confirmed, illustrating the importance of confirmatory studies. This study describes a novel technique that identifies proteins dysregulated in MCL.

A modular on-line three-dimensional liquid chromatography-tandem mass spectrometry approach to characterization of organelle proteomes

In this work we describe the use of a modular multidimensional chromatography-tandem mass spectrometry approach for rapid identification of proteins. In particular we highlight the use of a strong cation exchange cartridge in conjunction with a membrane postconcentration cartridge and nano-HPLC on-line with tandem mass spectrometry to characterize the eosinophil granule organelle proteome. Details are provided of the analytical approach we have developed and we discuss some of the advantages compared with previously reported analyses, as well as providing some specific examples of novel proteins identified.

Crystal structure of the eosinophil major basic protein at 1.8 A. An atypical lectin with a paradigm shift in specificity

The eosinophil major basic protein (EMBP) is the predominant constituent of the crystalline core of the eosinophil primary granule. EMBP is directly implicated in epithelial cell damage, exfoliation, and bronchospasm in allergic diseases such as asthma. Here we report the crystal structure of EMBP at 1.8 A resolution, and show that it is similar to that of members of the C-type lectin superfamily with which it shares minimal amino acid sequence identity (approximately 15--28%). However, this protein lacks a Ca(2+)/carbohydrate-binding site. Our analysis suggests that EMBP specifically binds heparin. Based on our results, we propose a possible new function for this protein, which is likely to have implications for EMBP function.

Comparative structure, proximal promoter elements, and chromosome location of the human eosinophil major basic protein genes

Human eosinophil major basic protein (MBP) is strongly implicated as a mediator of disease, especially bronchial asthma. We recently isolated a highly divergent human homologue of MBP (MBPH). Given human MBP's importance in disease and the restricted expression of it and human MBPH, we isolated the 4.6-kb human MBPH gene (HGMW-approved symbol PRG3). Comparisons among the human MBP (PRG2), human MBPH, and murine MBP-1 (mMBP-1; Prg2) genes suggest that the human MBP and mMBP-1 genes are more closely related than either is to the human MBPH gene. Proximal promoters of these three genes show conservation of potential binding sites for IK2 and STAT and of a known GATA site. However, a known C/EBP site is altered in the human MBPH gene's proximal promoter. The human MBP and MBPH genes localized to chromosome 11 in the centromere to 11q12 region. Thus, the human MBP and MBPH genes have diverged considerably, probably following a gene duplication event. Furthermore, the identified conserved and distinct proximal promoter elements likely contribute to the eosinophil-restricted and relatively reduced transcription of the human MBPH gene.

Reactivity of monoclonal antibodies EG1 and EG2 with eosinophils and their granule proteins

Use of the murine monoclonal antibodies EG1 and EG2 has been based on the assumption that EG2 recognizes activated eosinophils. We examined the reactivity of EG1 and EG2 with eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN), and stimulated and nonstimulated eosinophils from normal donors. By radioimmunoassay, EG1 recognized only ECP, whereas EG2 recognized both ECP and EDN. By Western blot, EG1 reacted with ECP, EG2 reacted with both ECP and EDN, but EG2 could not distinguish between lysates of stimulated and nonstimulated eosinophils. By immunofluorescence, EG1 and EG2 at 20 microg/mL stained 95-100% of nonstimulated eosinophils, regardless of fixative; EG1 and EG2 at 0.1 microg/mL stained 61-90% of acetone- and paraformaldehyde-fixed and only 5-21% of methanol-fixed nonstimulated eosinophils. Thus, the reactivity of EG1 and EG2 with eosinophils depends on the method of fixation and antibody concentration; and EG2, in contrast to previous reports, cannot reliably discriminate between resting and activated eosinophils.

Discordant and anomalous results among cytotoxicity assays: the confounding properties of eosinophil granule major basic protein on cell viability assays

When five cytotoxicity methods compared the toxicity of eosinophil granule major basic protein (MBP) and melittin to K562 and HL-60 cells, strikingly discrepant results were noted. Trypan blue staining, propidium iodide/CellTrackerGreen staining and incorporation of 14C-leucine assays indicated MBP damages > 75% of cells by 1 h. In contrast, 51Cr and lactic dehydrogenase (LDH) release assays indicated MBP damages most cells only at 20 h. All methods indicated melittin damages nearly all cells by 1 h. Further studies showed that without cell transfer, dye staining methods indicated MBP produces < 10% cytotoxicity after 4 h. A modified 14C-leucine assay, employing sodium dodecyl sulfate solubilization and trichloroacetic acid precipitation, showed lower cytotoxicity, 48%, at 4 h. Modified 51Cr and LDH assays showed increased cytotoxicities at 4 h, 34% and 58%, respectively. Overall, MBP's ability to cause molecular and cellular adhesion systematically confounds standard cytotoxicity measurements. However, the modified 14C-leucine assay provides a valid measure of MBP's cytotoxicity and may be useful for analyses of 'sticky' cytotoxins.

A novel and highly divergent homolog of human eosinophil granule major basic protein

Eosinophils are important effector cells in defense against helminth infection and in allergic diseases. To identify novel eosinophil proteins, large scale sequencing of a cDNA library prepared from interleukin-5-stimulated umbilical cord precursor cells was performed, and the major genes expressed by maturing eosinophils were determined. This resulted in the identification of a cDNA with 64% identity to human prepro-major basic protein (hprepro-MBP). This cDNA was designated hprepro-MBP homolog (hprepro-MBPH). Interestingly, the calculated pI values for hMBPH and hMBP differed by >100-fold, with pI values of 8.7 and 11.4, respectively. Given this pronounced basicity difference, the homolog transcript's abundance (1.1%), and MBP's critical role in eosinophil biological activity, we further characterized the homolog. Reverse transcription-polymerase chain reaction detected transcription of hprepro-MBPH in bone marrow only, and this result was confirmed by analysis of a large cDNA data base (electronic Northern). hMBPH was isolated from human eosinophil granule lysates, and its identity was verified by amino acid sequencing and by mass spectrometry. Analyses of the biological activities showed that hMBPH had effects similar to hMBP in cell killing and neutrophil (superoxide anion production and interleukin-8 release) and basophil (histamine and leukotriene C4 release) stimulation assays, but usually with reduced potency. Overall, this novel homolog's unique physical properties indicated that the high net positive charge of hMBP is important but not essential for biological activity.

Cytotoxic properties of eosinophil granule major basic protein for tumor cells

BACKGROUND

Eosinophil granule major basic protein (MBP) mediates many eosinophil-associated immune functions and it adheres eosinophils to parasite targets.

METHODS

We compared the toxicities of MBP and melittin to K562 and HL-60 cells using five cytotoxicity methods.

RESULTS

Trypan blue staining, propidium iodide/ CellTrackertrade markGreen staining and incorporation of 14C-leucine assays indicated that MBP damages most cells by 1 h. In contrast, 51Cr and lactic dehydrogenase (LDH) release assays indicated that MBP damages most cells only at 20 h. All five methods indicated that melittin damages nearly all cells by 1 h. To resolve these discrepancies, the procedures were modified. Without cell transfer, dye staining methods showed that MBP produces very little cytotoxicity at 4 h. 51Cr and LDH assays, modified to mimic cell transfer, showed increased cytotoxicities at 4 h. The 14C-leucine assay modified by solubilization of cells with SDS and by trichloroacetic acid precipitation showed increased recovery of labeled protein and, thus, lower cytotoxicity, about 50%, at 4 h.

CONCLUSION

Overall, MBP's ability to cause molecular and cellular adhesion confounds cytotoxicity measurements. A modified 14C-leucine assay overcame MBP's adhesiveness and provided an accurate measure of cytotoxicity.

Sulfonylureas Inhibit Cytokine-Induced Eosinophil Survival and Activation

Eosinophils play a key role in the pathogenesis of asthma and other allergic inflammatory diseases. We have previously shown that treatment of eosinophils with lidocaine preferentially inhibits IL-5-induced survival. This inhibition cannot be overcome by increasing concentrations of IL-5 and is not due to the blocking of Na+ channels by lidocaine. Here we report that one class of K+ channel blockers, the sulfonylureas, inhibits eosinophil survival in a manner similar to lidocaine. The sulfonylurea glyburide inhibits eosinophil survival even at high concentrations of IL-5. In contrast, increasing concentrations of IL-3 or granulocyte-macrophage CSF overcome glyburide inhibition. Glyburide also blocks cytokine-induced eosinophil superoxide production. Similar results were seen with the sulfonylureas tolbutamide and glipizide. Interestingly, the effects of glyburide are not antagonized by the ATP-sensitive K+ channel openers cromakalim, pinacidil, or diazoxide. Although Scatchard analysis of [3H]glyburide binding to eosinophil membranes indicated that the high affinity sulfonylurea receptor (SUR1) is not present on eosinophils, human eosinophils do express mRNA homologous to the sulfonylurea receptor family, in keeping with the presence of a sulfonylurea receptor. Finally, coculture of eosinophils with combinations of glyburide, lidocaine, and dexamethasone resulted in synergistic inhibition of cytokine-mediated eosinophil survival and superoxide production. These results have intriguing clinical implications for the treatment of eosinophil-associated diseases.

Sulfonylureas inhibit cytokine-induced eosinophil survival and activation

Eosinophils play a key role in the pathogenesis of asthma and other allergic inflammatory diseases. We have previously shown that treatment of eosinophils with lidocaine preferentially inhibits IL-5-induced survival. This inhibition cannot be overcome by increasing concentrations of IL-5 and is not due to the blocking of Na+ channels by lidocaine. Here we report that one class of K+ channel blockers, the sulfonylureas, inhibits eosinophil survival in a manner similar to lidocaine. The sulfonylurea glyburide inhibits eosinophil survival even at high concentrations of IL-5. In contrast, increasing concentrations of IL-3 or granulocyte-macrophage CSF overcome glyburide inhibition. Glyburide also blocks cytokine-induced eosinophil superoxide production. Similar results were seen with the sulfonylureas tolbutamide and glipizide. Interestingly, the effects of glyburide are not antagonized by the ATP-sensitive K+ channel openers cromakalim, pinacidil, or diazoxide. Although Scatchard analysis of [3H]glyburide binding to eosinophil membranes indicated that the high affinity sulfonylurea receptor (SUR1) is not present on eosinophils, human eosinophils do express mRNA homologous to the sulfonylurea receptor family, in keeping with the presence of a sulfonylurea receptor. Finally, coculture of eosinophils with combinations of glyburide, lidocaine, and dexamethasone resulted in synergistic inhibition of cytokine-mediated eosinophil survival and superoxide production. These results have intriguing clinical implications for the treatment of eosinophil-associated diseases.

Expression, purification, and characterization of the recombinant proform of eosinophil granule major basic protein

The cDNA for the highly toxic eosinophil granule major basic protein (MBP) encodes a 25-kDa acidic precursor (proMBP) that is processed to form the 14-kDa mature MBP. To characterize the biochemical and biological properties of proMBP, and compare these to the known properties of MBP, we expressed recombinant proMBP in Chinese hamster ovary cells and purified the secreted form from supernatants. We developed a mAb specific for proMBP, J163-15E10, and by using a proMBP-specific RIA we found that recombinant proMBP was expressed quite efficiently at levels between 10 and 100 mg/l. By SDS-PAGE and immunoblotting analyses of bulk Chinese hamster ovary supernatants, recombinant proMBP was electrophoretically heterogeneous with an apparent molecular mass ranging from 3 x 10(4) to 1 x 10(5) daltons. Despite difficulties encountered because of the extreme molecular heterogeneity of the proform, two methods for purification of a predominant 33-kDa form of recombinant proMBP are presented. Glycosylation analysis of purified 33-kDa proMBP indicated that approximately 5 kDa is likely accounted for by the addition of one glycosaminoglycan group, three O-linked, and one N-linked complex type carbohydrate groups. Functional studies of purified recombinant proMBP were also conducted. Using amounts of proMBP determined to be optimal for MBP activity, it was shown that proMBP not only lacked the ability to inhibit protein synthesis in K562 cells, but it also lacked the ability to stimulate basophil histamine release or generate neutrophil superoxide anion release. Furthermore, proMBP inhibited in a dose-responsive manner the basophil histamine release and superoxide anion generation stimulated by MBP. The development of a mAb and RIA specific for proMBP will now make it possible to analyze biologic fluids for the presence of this protein, especially in pregnancy, when proMBP is increased.

Expression, purification, and characterization of the recombinant proform of eosinophil granule major basic protein

The cDNA for the highly toxic eosinophil granule major basic protein (MBP) encodes a 25-kDa acidic precursor (proMBP) that is processed to form the 14-kDa mature MBP. To characterize the biochemical and biological properties of proMBP, and compare these to the known properties of MBP, we expressed recombinant proMBP in Chinese hamster ovary cells and purified the secreted form from supernatants. We developed a mAb specific for proMBP, J163-15E10, and by using a proMBP-specific RIA we found that recombinant proMBP was expressed quite efficiently at levels between 10 and 100 mg/l. By SDS-PAGE and immunoblotting analyses of bulk Chinese hamster ovary supernatants, recombinant proMBP was electrophoretically heterogeneous with an apparent molecular mass ranging from 3 x 10(4) to 1 x 10(5) daltons. Despite difficulties encountered because of the extreme molecular heterogeneity of the proform, two methods for purification of a predominant 33-kDa form of recombinant proMBP are presented. Glycosylation analysis of purified 33-kDa proMBP indicated that approximately 5 kDa is likely accounted for by the addition of one glycosaminoglycan group, three O-linked, and one N-linked complex type carbohydrate groups. Functional studies of purified recombinant proMBP were also conducted. Using amounts of proMBP determined to be optimal for MBP activity, it was shown that proMBP not only lacked the ability to inhibit protein synthesis in K562 cells, but it also lacked the ability to stimulate basophil histamine release or generate neutrophil superoxide anion release. Furthermore, proMBP inhibited in a dose-responsive manner the basophil histamine release and superoxide anion generation stimulated by MBP. The development of a mAb and RIA specific for proMBP will now make it possible to analyze biologic fluids for the presence of this protein, especially in pregnancy, when proMBP is increased.

Expression of eosinophil-granule major basic protein messenger ribonucleic acid in placental X cells

BACKGROUND

The human eosinophil-granule major basic protein (MBP) is a 13.8-kilodalton cationic polypeptide constituting the core of the eosinophil granule. MBP is cytotoxic to parasites and numerous mammalian cells and is a potent secretagogue for platelets, basophils, mast cells, and neutrophils. Concentrations of a molecule immunochemically similar to eosinophil granule MBP are present in maternal plasma, and MBP has been localized by immunofluorescence to placental X cells.

EXPERIMENTAL DESIGN

To determine whether X cells produce MBP, the expression of MBP messenger RNA (mRNA) was investigated in placentas by Northern blot analyses and by in situ hybridization with 35S-labeled RNA probes.

RESULTS

Northern blot analyses of RNA from placental septa and villi showed the existence of a 1.0-kb RNA band that hybridized with the MBP anti-sense probe; no MBP mRNA was detected in whole blood of normal or pregnant women or in cord blood. Analyses of placentas by in situ hybridization showed MBP mRNA in X cells of placental septa and anchoring villi, but not in other cellular elements such as syncytiotrophoblasts, cytotrophoblasts, villous stromal cells, and fetal endothelial cells. RNase pretreatment abolished X-cell hybridization signals; treatment of sections with an excess of nonradiolabeled anti-sense RNA also blocked binding of the 35S-labeled anti-sense RNA probe. Additional evidence supporting the production of MBP by X cells was obtained using a combination of in situ hybridization and immunofluorescence, which showed colocalization of MBP and its mRNA.

CONCLUSIONS

The presence of MBP mRNA and MBP protein in placental X cells indicates that X cells synthesize this biologically active molecule.

Eosinophil granule proteins in peripheral blood granulocytes

Eosinophils contain four principal cationic proteins, major basic protein (MBP), eosinophil-derived neurotoxin (EDN), eosinophil cationic protein (ECP), and eosinophil peroxidase (EPO). To determine the quantities of these proteins in granulocytes and whether they are specific to eosinophils, their concentrations in lysates of human granulocytes were measured using specific radioimmunoassays. The effect of different methods for eosinophil lysis on the recovery of the proteins was also studied. Maximal recovery occurred at pH 2 for MBP and pH 5.6 for the other granule proteins. The proteins cosedimented with eosinophils and their concentrations (mean +/- SEM) in ng/10(6) eosinophils (and in nM/10(6) eosinophils) were: MBP, 8,982 +/- 611 (641.6); EDN, 3,283 +/- 116 (178.4); ECP, 5,269 +/- 283 (250.9); and EPO, 12,174 +/- 859 (171.5). Basophils from a normal person contained (in ng/10(6) cells) MBP, 2,374; EDN, 214; ECP, 77; and EPO, 17. Highly purified neutrophils contained (in ng/10(6) cells) MBP, 3 +/- 0.5; EDN, 72 +/- 9; and ECP, 50 +/- 12. Therefore we conclude that these proteins are mainly expressed in eosinophils, but that certain ones are present in basophils and neutrophils.

Eosinophil-derived neurotoxin and human liver ribonuclease. Identity of structure and linkage of neurotoxicity to nuclease activity

Eosinophil-derived neurotoxin (EDN) and human liver RNase were found to be indistinguishable from each other but distinct from the pancreatic ribonucleases in their nucleolytic activity on polynucleotides or small defined substrates. Antibodies to EDN and liver RNase showed identical cross-reactivities in assays of nuclease inhibition and in a radioimmunoassay. In each instance, EDN and liver RNase were easily distinguished from bovine or human pancreatic RNase. When injected intrathecally into rabbits, 5-10 micrograms of EDN or liver RNase each was neurotoxic as judged by induction of the Gordon phenomenon. Human pancreatic RNase was less neurotoxic, and up to 20-fold higher levels of bovine pancreatic RNase showed no effect. Treatment of EDN, liver RNase, and eosinophil cationic protein with iodoacetic acid at pH 5.5 resulted in inactivation of their RNase activity and also destroyed their neurotoxicity. EDN conformation was not greatly affected by iodoacetate treatment since interaction of the modified protein with antibodies was only slightly altered. We conclude that RNase activity is necessary but not sufficient to induce neurotoxic action.

Acidic polyamino acids inhibit human eosinophil granule major basic protein toxicity. Evidence of a functional role for ProMBP

Eosinophil granule major basic protein (MBP), a potent toxin for helminths and mammalian cells in vitro, is a single polypeptide chain rich in arginine. MBP has been localized on damaged helminths and tissues in hypersensitivity diseases including bronchial asthma. The MBP cDNA indicates that MBP is translated as a slightly acidic preproprotein with an acidic propart. To test the hypothesis that the acidic pro-part of proMBP inhibits the toxicity of mature MBP, acidic polyamino acids (aa) were used as antagonists of MBP toxicity to K562 cells and guinea pig tracheal epithelium and used as antagonists of MBP airway hyperresponsiveness in primates. The acidic poly aa inhibited MBP toxicity and MBP airway hyperresposiveness. The acidic poly aa inhibited MBP toxicity in a charge-dependent manner similar to that proposed for proMBP, suggesting that the acidic pro-part of proMBP functions to mask mature MBP toxicity. This inhibition was not limited to MBP, but also applied to polyarginine and eosinophil cationic protein. These acidic poly aa may be useful to inhibit the actions of a number of cationic toxins released by the eosinophil in numerous hypersensitivity diseases.

Characterization of "peak E," a novel amino acid associated with eosinophilia-myalgia syndrome

Epidemiologic studies strongly associate eosinophilia-myalgia syndrome (EMS) with ingestion of tryptophan containing a contaminant ("peak E"). Prior reports have suggested that peak E is the di-tryptophan N alpha-animal of acetaldehyde. Spectral and chemical studies now demonstrate that peak E is 1,1'-ethylidenebis[tryptophan]. This novel amino acid may be the etiological agent responsible for EMS, or it may be a marker of a still unidentified causal agent.

An investigation of the cause of the eosinophilia-myalgia syndrome associated with tryptophan use

BACKGROUND

The eosinophilia-myalgia syndrome is a newly recognized illness that has been associated with the consumption of tryptophan products. It is not known whether the cause is related to the tryptophan itself or to chemical constituents introduced by the manufacturing process.

METHODS

To describe the epidemiology of the eosinophilia-myalgia syndrome further and elucidate a possible association with the manufacturing process, we conducted surveillance for the syndrome in Minnesota, a community survey of tryptophan use in Minneapolis-St. Paul, and a case-control study to assess potential risk factors, including the use of tryptophan from different manufacturers. We performed high-performance liquid chromatography on tryptophan samples to identify other chemical constituents.

RESULTS

The prevalence of tryptophan use increased from 1980 to 1989 and was highest among women. Among the subjects for whom the source of the tryptophan was known, 29 of 30 case patients (97 percent) and 21 of 35 controls (60 percent) had consumed tryptophan manufactured by a single company (odds ratio, 19.3; 95 percent confidence interval, 2.5 to 844.9; P less than 0.001). This company used a fermentation process involving Bacillus amyloliquefaciens to manufacture tryptophan. Analysis of the manufacturing conditions according to the retail lot demonstrated an association between lots used by case patients and the use of reduced quantities of powdered carbon in a purification step (odds ratio, 9.0; 95 percent confidence interval, 1.1 to 84.6; P = 0.014), as well as the use of a new strain of B. amyloliquefaciens (Strain V) (odds ratio, 6.0; 95 percent confidence interval, 0.8 to 51.8; P = 0.04). There was a significant correlation (r = 0.78, P less than 0.001) between the reduced amount of powdered carbon used during manufacturing and the use of the new bacterial strain. High-performance liquid chromatography of this company's tryptophan demonstrated one absorbance peak (peak E) that was present in 9 of the 12 retail lots (75 percent) used by patients and 3 of 11 lots (27 percent) used by controls (odds ratio, 8.0; 95 percent confidence interval, 0.9 to 76.6; P = 0.022).

CONCLUSIONS

The outbreak of the eosinophilia-myalgia syndrome in 1989 resulted from the ingestion of a chemical constituent that was associated with specific tryptophan-manufacturing conditions at one company. The chemical constituent represented by peak E may contribute to the pathogenesis of the eosinophilia-myalgia syndrome, or it may be a surrogate for another chemical that induces the syndrome.

Structure and chromosome localization of the human eosinophil-derived neurotoxin and eosinophil cationic protein genes: evidence for intronless coding sequences in the ribonuclease gene superfamily

Human genomic DNAs for the eosinophil granule proteins, eosinophil-derived neurotoxin (EDN) and eosinophil cationic protein (ECP), were isolated from genomic libraries. Alignment of EDN (RNS2) and ECP (RNS3) gene sequences demonstrated remarkable nucleotide similarities in noncoding sequences, introns, and flanking regions, as well as in the previously known coding regions. Detailed examination of the 5'-noncoding regions yielded putative TATA and CAAT boxes, as well as similarities to promoter motifs from unrelated genes. A single intron of 230 bases was found in the 5' untranslated region and we suggest that a single intron in this region and an intronless coding region are features common to many members of the RNase gene superfamily. The RNS2 and RNS3 genes were localized to the q24-q31 region of human chromosome 14. It is likely that these two genes arose as a consequence of a gene duplication event that took place approximately 25-40 million years ago and that a subset of anthropoid primates possess both of these genes or closely related genes.

In vitro killing of microfilariae of Brugia pahangi and Brugia malayi by eosinophil granule proteins

Eosinophil infiltration and degranulation around the tissue-invasive stages of several species of helminths have been observed. Release of eosinophil granule contents upon the worms is supported by localization of two of the major granule proteins, major basic protein (MBP) and eosinophil peroxidase (EPO), on and around species of trematodes, nematodes, and cestodes. In the case of filarial worms, MBP is deposited on degenerating microfilariae (mf) of Onchocerca volvulus. Here, we performed in vitro assays of the toxicity of four purified eosinophil granule proteins, namely, MBP, EPO, eosinophil cationic protein (ECP), and eosinophil-derived neurotoxin (EDN), for the mf of Brugia pahangi and Brugia malayi. MBP, ECP, and EDN killed these worms in a dose-related manner although relatively high concentrations of EDN were necessary. EPO, in the presence of a H2O2-generating system and a halide, was the most potent toxin on a molar basis; here, the most potent halide was I- followed by Br- and Cl-. Surprisingly, EPO in the absence of H2O2 killed mf at concentrations comparable to those required for MBP and ECP. The toxicity of EPO + H2O2 + halide was inhibited by heparin, catalase, or 1% BSA, whereas the toxicity of EPO alone was inhibited only by heparin. Heparin also inhibited killing by both MBP and ECP. Despite the homology of ECP with certain RNases, placental RNasin, an RNase inhibitor, was unable to inhibit ECP-mediated toxicity. These results indicate that all of the eosinophil granule proteins are toxic to mf and they support the hypothesis that eosinophil degranulation causes death of mf in vivo.

In vitro killing of microfilariae of Brugia pahangi and Brugia malayi by eosinophil granule proteins

Eosinophil infiltration and degranulation around the tissue-invasive stages of several species of helminths have been observed. Release of eosinophil granule contents upon the worms is supported by localization of two of the major granule proteins, major basic protein (MBP) and eosinophil peroxidase (EPO), on and around species of trematodes, nematodes, and cestodes. In the case of filarial worms, MBP is deposited on degenerating microfilariae (mf) of Onchocerca volvulus. Here, we performed in vitro assays of the toxicity of four purified eosinophil granule proteins, namely, MBP, EPO, eosinophil cationic protein (ECP), and eosinophil-derived neurotoxin (EDN), for the mf of Brugia pahangi and Brugia malayi. MBP, ECP, and EDN killed these worms in a dose-related manner although relatively high concentrations of EDN were necessary. EPO, in the presence of a H2O2-generating system and a halide, was the most potent toxin on a molar basis; here, the most potent halide was I- followed by Br- and Cl-. Surprisingly, EPO in the absence of H2O2 killed mf at concentrations comparable to those required for MBP and ECP. The toxicity of EPO + H2O2 + halide was inhibited by heparin, catalase, or 1% BSA, whereas the toxicity of EPO alone was inhibited only by heparin. Heparin also inhibited killing by both MBP and ECP. Despite the homology of ECP with certain RNases, placental RNasin, an RNase inhibitor, was unable to inhibit ECP-mediated toxicity. These results indicate that all of the eosinophil granule proteins are toxic to mf and they support the hypothesis that eosinophil degranulation causes death of mf in vivo.

Cloning and sequence analysis of the human gene encoding eosinophil major basic protein

Eosinophil granule major basic protein (MBP), a potent toxin for helminths and mammalian cells, is a single polypeptide rich in arginine. The gene, mbp, was cloned and its nucleotide sequence determined. The 3.3-kb gene consists of six exons and five introns, one of which contains an Alu family repeat. The combined exon sequence is similar to previously reported mbp cDNA sequences. The gene is immediately preceded by a putative promoter containing typical TATA and CCAAT boxes. Southern blots indicate that mbp exhibits limited polymorphism.

Blood eosinophils and eosinophil-derived proteins in allergic asthma

The concentrations of the eosinophil (EOS)-derived proteins, major basic protein (MBP), EOS-derived neurotoxin (EDN), EOS peroxidase (EPO), and EOS cationic protein (ECP), and EOS counts were measured in the peripheral blood of 12 atopic subjects with asthma and 23 normal control subjects. The same measurements were performed in seven subjects with asthma with previously documented dual (early plus late) asthmatic responses after inhalation challenges with methacholine and allergen. EOSs (p less than 0.001), MBP (p less than 0.01), EDN (p less than 0.01), and ECP (p greater than 0.03) were elevated in the subjects with asthma compared with control subjects, whereas EPO (p less than 0.01) concentrations were reduced. There were no significant differences between baseline measurements of FEV1, EOSs, MBP, EDN, EPO, or ECP on the methacholine- and allergen-challenge days. When the changes in these variables after allergen challenge were compared with the corresponding changes after methacholine challenge, there were no significant differences at 0 to 60 minutes or at 3 hours, whereas EDN (p less than 0.025), EPO (p less than 0.05), and ECP (p less than 0.025) were relatively increased at 6 to 12 hours and accompanied the late falls in FEV1 (p less than 0.001). EOSs (p less than 0.025) were elevated at 24 hours when there was a small relative increase in MBP (p less than 0.05). EOSs appear to be "activated" in subjects with allergic asthma, and further activation may occur during late asthmatic responses.

Sequence of human eosinophil-derived neurotoxin cDNA: identity of deduced amino acid sequence with human nonsecretory ribonucleases

Several clones of human eosinophil-derived neurotoxin (EDN) cDNA have been isolated from a lambda gt10 cDNA library prepared from mRNA derived from noninduced HL-60 cells. The amino acid (aa) sequence deduced from the coding sequence of the EDN cDNA is identical to the aa sequence of urinary nonsecretory RNase. Comparison of the aa and/or nucleotide (nt) sequences of EDN and other proteins possessing ribonucleolytic activity, namely bovine seminal RNase, human and rat pancreatic RNases, eosinophil cationic protein (ECP), and human angiogenin, shows extensive identity at half-cystine residues and at aa of active sites. Differences in aa sequences at the active sites are often the result of single nt changes in the codons. The data presented here support the concept of a RNase gene superfamily containing secretory and nonsecretory RNases, angiogenin, EDN and ECP.

Eosinophil cationic protein cDNA. Comparison with other toxic cationic proteins and ribonucleases

Human eosinophil granules contain several basic proteins including eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN) and major basic protein (MBP). ECP and MBP are potent helminthotoxins while EDN is less so. Both ECP and EDN possess neurotoxic and ribonuclease activities. A clone representing ECP mRNA was isolated from an eosinophil lambda ZAP cDNA library. The cDNA sequence codes for a preprotein of 160 amino acids and a protein of 133 amino acids, the amino terminus of which is identical to the known partial amino acid sequence of ECP. The ECP nucleotide sequence shows similarity to EDN, rat pancreatic ribonuclease, and human angiogenin; all are members of the ribonuclease gene superfamily. Although the deduced amino acid sequence of ECP shares identical active site and substrate binding site residues with EDN, angiogenin, and human pancreatic ribonuclease, the ribonuclease activity of ECP is 50 to 100 times less than that of EDN possibly because of the lack of a positively charged residue at human pancreatic ribonuclease position 122. The calculated isoelectric point (10.8), electronic charge (14.5), and cationic charge distribution of ECP are different from those of EDN but similar to those of MBP, which may account in part for the greater helminthotoxic activity of ECP when compared to EDN. These data suggest that ECP and EDN are derived from a common ancestral ribonuclease gene and that ECP has evolved into a potent helminthotoxin similar in some respects to MBP, while losing much of its ribonuclease activity.

Eosinophil cationic protein cDNA. Comparison with other toxic cationic proteins and ribonucleases

Human eosinophil granules contain several basic proteins including eosinophil cationic protein (ECP), eosinophil-derived neurotoxin (EDN) and major basic protein (MBP). ECP and MBP are potent helminthotoxins while EDN is less so. Both ECP and EDN possess neurotoxic and ribonuclease activities. A clone representing ECP mRNA was isolated from an eosinophil lambda ZAP cDNA library. The cDNA sequence codes for a preprotein of 160 amino acids and a protein of 133 amino acids, the amino terminus of which is identical to the known partial amino acid sequence of ECP. The ECP nucleotide sequence shows similarity to EDN, rat pancreatic ribonuclease, and human angiogenin; all are members of the ribonuclease gene superfamily. Although the deduced amino acid sequence of ECP shares identical active site and substrate binding site residues with EDN, angiogenin, and human pancreatic ribonuclease, the ribonuclease activity of ECP is 50 to 100 times less than that of EDN possibly because of the lack of a positively charged residue at human pancreatic ribonuclease position 122. The calculated isoelectric point (10.8), electronic charge (14.5), and cationic charge distribution of ECP are different from those of EDN but similar to those of MBP, which may account in part for the greater helminthotoxic activity of ECP when compared to EDN. These data suggest that ECP and EDN are derived from a common ancestral ribonuclease gene and that ECP has evolved into a potent helminthotoxin similar in some respects to MBP, while losing much of its ribonuclease activity.

Injurious effect of the eosinophil peroxide-hydrogen peroxide-halide system and major basic protein on human nasal epithelium in vitro

Tissue injury is observed in allergic and nonallergic eosinophilic rhinitis, but the mechanism of this injury is unclear. Because eosinophils are prominent in biopsy specimens in these conditions, we hypothesized that they may participate in the injury process. Initially, we developed techniques to isolate and purify human nasal epithelial cells from turbinate biopsies to use as target cells for eosinophil granule products. Primary cultures from explants were characterized by electron microscopy and indirect immunofluorescence with a panel of primary monoclonal and polyclonal antibodies. These studies revealed the homogeneity of the cells and confirmed their epithelial nature. Cultured nasal epithelial cells were then exposed to either purified human eosinophil peroxidase, bromide, and glucose plus glucose oxidase, as a continuous source of hydrogen peroxide, or eosinophil major basic protein. Neither eosinophil peroxidase alone nor glucose plus glucose oxidase in the absence of eosinophil peroxidase were injurious, but the combined addition of eosinophil peroxidase, glucose/glucose oxidase, and bromide produced marked target cell lysis. This effect was time- and eosinophil peroxidase dose-dependent. Catalase and azide significantly inhibited the lysis of these cells, suggesting the eosinophil peroxidase-catalyzed products of halide oxidation mediated this form of injury. The addition of purified human eosinophil major basic protein also caused dose- and time-dependent lysis of the nasal epithelial cells but required longer incubation periods to effect injury. We hypothesize that the eosinophil peroxidase-hydrogen peroxide-halide system and major basic protein may injure the nasal epithelium in inflammatory conditions such as allergic and nonallergic eosinophilic rhinitis.

Toxicity of eosinophil cationic proteins for guinea pig tracheal epithelium in vitro

We tested the effects of four eosinophil granule cationic proteins: major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil peroxidase (EPO), and eosinophil-derived neurotoxin (EDN), on guinea pig tracheal epithelium in vitro. Examination by inverted microscopy revealed that MBP, both the form stabilized by alkylation of sulfhydryl groups as well as the native form of the molecule, ECP, EPO by itself, as well as EPO + H2O2 + halide, but not EDN, cause dose-related damage to the tracheal epithelium. The lowest concentrations of MBP and ECP causing damage were 10 and 100 micrograms/ml, respectively. In contrast, EDN, although biochemically similar to ECP, did not damage the tracheal epithelium in concentrations of up to 200 micrograms/ml. MBP caused exfoliation, as well as bleb formation and ciliostasis. EPO in the presence of the H2O2-producing enzyme glucose oxidase (GO), Cl-, 0.11 M, and iodide caused ciliostasis, bleb formation, and exfoliation of epithelial cells at concentrations as low as 1 U/ml (3.9 micrograms/ml). EPO + GO in the presence of Cl-, 0.11 M, alone or with Cl- and l-, 10(-4) M, or Cl- and Br-, 5 x 10(-5) M, were all toxic to epithelium. Surprisingly, EPO by itself caused partial ciliostasis, bleb formation, and exfoliation of epithelial cells in a dose-related manner at concentrations as low as 10 to 30 U/ml (39 to 121 micrograms/ml). These results confirm prior observations showing the toxicity of MBP to tracheal epithelium and indicate that ECP and EPO alone, as well as EPO + GO + halide, cause damage. Thus, several eosinophil granule proteins are able to damage respiratory epithelium.

Biochemical and amino acid sequence analysis of human eosinophil granule major basic protein

Eosinophil granule major basic protein (MBP) is a relatively low molecular weight cationic (pI greater than 10) protein present in the crystalloid core of the eosinophil granule. Amino acid sequence analysis of this protein was undertaken as part of an analysis of the structural basis of the potent cytotoxic activities of MBP on parasites and mammalian cells. Many conventional sequencing strategies were unworkable because of the unusual amino acid composition of MBP and its insolubility in solutions buffered at neutral pH. Less conventional chemical reactions, including cyanogen bromide-induced cleavage at tryptophan and acid-induced cleavage at aspartic acid, were used successfully to obtain peptides which allowed definition of the amino acid sequence of MBP. Characterization of MBP by reverse-phase high pressure liquid chromatography and two-dimensional gel analysis showed no microheterogeneity that might be attributed to post-translational modifications. Comparison of the MBP sequence with a protein sequence data base showed that MBP has no significant sequence homology with other characterized proteins. The basicity (pI 10.9) and hydrophobicity predicted from the MBP sequence are likely responsible for the observed affinity of this cytotoxic molecule for cell surfaces and some serum proteins.

Effect of human eosinophil major basic protein on ion transport in dog tracheal epithelium

Eosinophil major basic protein (MBP) is a granule-associated cytotoxic protein found in sputum and deposited on airway tissues of patients with acute asthma. We therefore studied the effect of human MBP on ion transport in dog tracheal epithelium. We mounted the posterior tracheal membranes of mongrel dogs in Ussing chambers and measured potential differences across the membranes and short-circuit current. Using 22Na+ and 36Cl- as tracers, we determined net ion movements. The addition of MBP (5 X 10(-6) M) to the mucosal, but not to the serosal, side of the membranes produced an increase in short-circuit current from 2.25 +/- 0.19 (mean +/- SE) to 2.78 +/- 0.23 muEq.cm-2h-1 (p less than 0.0001) and in net chloride secretion from 1.57 +/- 0.22 to 2.31 +/- 0.24 muEq.cm-2h-1 (p less than 0.01). There was no change in net sodium movement. Pretreatment with indomethacin (10(-5) M) attenuated, but did not abolish, the increase in short-circuit current. After exposure to MBP, prostaglandin E2 release into the serosal bathing solution increased from 10.0 +/- 4.2 to 17.0 +/- 6.9 ng.cm-2h-1 (p less than 0.05). The results of this study indicate that MBP simulates prostaglandin E2 production and chloride secretion by dog tracheal epithelium. Thus, eosinophils in the airways, through release of MBP, may affect mucociliary clearance by changing the volume and composition of respiratory tract fluid.

Comparative toxicity of purified human eosinophil granule proteins for newborn larvae of Trichinella spiralis

Eosinophils have been implicated in both in vivo and in vitro destruction of helminths. One approach toward elucidating the role of the eosinophil in parasite killing has been to test the toxicity of purified eosinophil granule proteins for parasites in vitro. Previously, major basic protein (MBP) and eosinophil cationic protein (ECP) were shown to be toxic for schistosomules of Schistosoma mansoni, while eosinophil-derived neurotoxin (EDN) was only marginally so. We tested the toxicity of MBP, ECP, and EDN over a range of concentrations (0.006-5 X 10(-4) M) for newborn larvae of Trichinella spiralis. Our observations confirm previous reports of toxicity of mildly reduced and alkylated (R & A) MBP. At concentrations of 5 X 10(-5) M and above, R & A MBP killed 75% or more of the larvae within the first hour of culture. ECP was an effective toxin for these larvae after 3 hr of culture, and by 12 hr, dose-related toxicity was evident. After 24 hr, 100% of the larvae were killed at 5 X 10(-5) M ECP. EDN was much less toxic; after 12 hr, 90% of the larvae survived at concentrations of 1 X 10(4) M, while 5 X 10(-4) M EDN killed all the larvae. At the optimal toxic concentrations of 5 X 10(-5) M ECP and 5 X 10(-4) M EDN, kinetics of killing by these 2 proteins were essentially the same. Thus, on a molecular basis, both MBP and ECP appear to be potent helminthotoxins whereas EDN is much less so.

The effect of purified human eosinophil major basic protein on mammalian ciliary activity

Eosinophil granulocyte infiltration in a variety of lung disorders may directly damage local tissue by release of granule contents. A principal constituent of eosinophil granules is the major basic protein (MBP). Previous light and electron microscopic observations have indicated that guinea pig and human MBP produce detachment of tracheal epithelial cells and cessation of ciliary activity. To quantitate the damage, selected regions of the epithelial surface of rabbit tracheal explants were videotaped before and after treatment with human MBP. Tapes were analyzed for ciliary beat frequency and the extent of zones along the epithelial surface displaying ciliary activity. The MBP at 0.1 mg/ml reduced beat frequency and significantly reduced the measured zones of ciliary activity. Also, MBP at 0.7 mg/ml significantly reduced beat frequency and the measured zone of ciliary activity on the epithelial surface. Beat frequency was lowered by 27% within 10 min, with only 1% further decrease by 60 min. The zones of ciliary activity on the epithelium were continuously decreased throughout the 60 min to 29% of the initially active zone. To examine whether MBP was capable of direct inhibition of ciliary activity, isolated porcine tracheal ciliary axonemes, the structural organelles of individual cilia, were treated with human MBP. Concentrations above 67 micrograms/ml of MBP were completely inhibitory to reactivated isolated axonemes, 67 micrograms/ml stopped activity within 10 min, and 27 micrograms/ml stopped activity within 15 min. Pretreatment of isolated axonemes with increasing concentrations of MBP resulted in decreasing ATPase activity. These effects were not attributable to pH alteration.(ABSTRACT TRUNCATED AT 250 WORDS)

The injurious effect of eosinophil peroxidase, hydrogen peroxide, and halides on pneumocytes in vitro

Recent data suggest that eosinophils may cause lung injury. To determine if the eosinophil peroxidase (EPO)-hydrogen peroxide (H2O2)-halide system could mediate this injury, we added human EPO, H2O2 (or glucose and glucose oxidase as a continuous source of H2O2), and various halides to monolayers of 51Cr-labeled human A549 and rat type II pneumocytes. Cell lysis was measured as soluble 51Cr release. In initial experiments, EPO in solution did not induce lysis under these conditions. Therefore, in subsequent experiments, pneumocytes were preincubated with EPO for 15 minutes, washed to remove unbound enzyme, and then glucose, glucose oxidase, and the halides were added. EPO alone was not injurious, nor was the addition of glucose and glucose oxidase in the absence of EPO. In contrast, the combined addition of EPO, glucose, glucose oxidase, and chloride produced marked target-cell lysis. This effect was time and EPO dose dependent and was enhanced by the addition of iodide. Catalase and azide substantially inhibited the lysis produced by the EPO-H2O2-halide system, suggesting that EPO-catalyzed products of halide oxidation mediated this form of injury. Finally, the addition of eosinophil major basic protein at 10(-5) mol/L to EPO-coated pneumocytes incubated with glucose, glucose oxidase, and halides failed to enhance or inhibit lysis. We hypothesize that the EPO-H2O2-halide system may injure the lung in asthma and eosinophilic pulmonary syndromes.

Ribonuclease activity associated with human eosinophil-derived neurotoxin and eosinophil cationic protein

The eosinophil granule contains a series of basic proteins, including major basic protein, eosinophil peroxidase, eosinophil-derived neurotoxin (EDN), and eosinophil cationic protein (ECP). Both EDN and ECP are neurotoxins and helminthotoxins. Comparison of the partial N-terminal amino acid sequences of EDN and ECP showed 67% identity; surprisingly, they also showed structural homology to pancreatic ribonuclease (RNase). Therefore, we determined whether EDN and ECP possess RNase enzymatic activity. By spectrophotometric assay of acid soluble nucleotides formed from yeast RNA, purified EDN showed RNase activity similar to bovine pancreatic RNase, whereas ECP was 50 to 100 times less active. The RNase activity associated with ECP was not significantly inhibited after exposure of ECP to polyclonal or monoclonal antibody to EDN. These results indicate that EDN and ECP both possess RNase activity, the RNase activity of EDN and ECP is specific, and EDN and ECP have maintained not only structural but also functional homology to pancreatic RNase.