In vitro studies evaluating the activity of imipenem in combination with relebactam against Pseudomonas aeruginosa

BACKGROUND

The prevalence of antibiotic resistance is increasing, and multidrug-resistant Pseudomonas aeruginosa has been identified as a serious threat to human health. The production of β-lactamase is a key mechanism contributing to imipenem resistance in P. aeruginosa. Relebactam is a novel β-lactamase inhibitor, active against class A and C β-lactamases, that has been shown to restore imipenem susceptibility. In a series of studies, we assessed the interaction of relebactam with key mechanisms involved in carbapenem resistance in P. aeruginosa and to what extent relebactam might overcome imipenem non-susceptibility.

RESULTS

Relebactam demonstrated no intrinsic antibacterial activity against P. aeruginosa, had no inoculum effect, and was not subject to efflux. Enzymology studies showed relebactam is a potent (overall inhibition constant: 27 nM), practically irreversible inhibitor of P. aeruginosa AmpC. Among P. aeruginosa clinical isolates from the SMART global surveillance program (2009, n = 993; 2011, n = 1702; 2015, n = 5953; 2016, n = 6165), imipenem susceptibility rates were 68.4% in 2009, 67.4% in 2011, 70.4% in 2015, and 67.3% in 2016. With the addition of 4 μg/mL relebactam, imipenem susceptibility rates increased to 87.6, 86.0, 91.7, and 89.8%, respectively. When all imipenem-non-susceptible isolates were pooled, the addition of 4 μg/mL relebactam reduced the mode imipenem minimum inhibitory concentration (MIC) 8-fold (from 16 μg/mL to 2 μg/mL) among all imipenem-non-susceptible isolates. Of 3747 imipenem-non-susceptible isolates that underwent molecular profiling, 1200 (32%) remained non-susceptible to the combination imipenem/relebactam (IMI/REL); 42% of these encoded class B metallo-β-lactamases, 11% encoded a class A GES enzyme, and no class D enzymes were detected. No relationship was observed between alleles of the chromosomally-encoded P. aeruginosa AmpC and IMI/REL MIC.

CONCLUSIONS

IMI/REL exhibited potential in the treatment of carbapenem-resistant P. aeruginosa infections, with the exception of isolates encoding class B, some GES alleles, and class D carbapenemases.

Systemic pan-AMPK activator MK-8722 improves glucose homeostasis but induces cardiac hypertrophy

5'-Adenosine monophosphate-activated protein kinase (AMPK) is a master regulator of energy homeostasis in eukaryotes. Despite three decades of investigation, the biological roles of AMPK and its potential as a drug target remain incompletely understood, largely because of a lack of optimized pharmacological tools. We developed MK-8722, a potent, direct, allosteric activator of all 12 mammalian AMPK complexes. In rodents and rhesus monkeys, MK-8722-mediated AMPK activation in skeletal muscle induced robust, durable, insulin-independent glucose uptake and glycogen synthesis, with resultant improvements in glycemia and no evidence of hypoglycemia. These effects translated across species, including diabetic rhesus monkeys, but manifested with concomitant cardiac hypertrophy and increased cardiac glycogen without apparent functional sequelae.

Elucidation of DnaE as the Antibacterial Target of the Natural Product, Nargenicin

Resistance to existing classes of antibiotics drives the need for discovery of novel compounds with unique mechanisms of action. Nargenicin A1, a natural product with limited antibacterial spectrum, was rediscovered in a whole-cell antisense assay. Macromolecular labeling in both Staphylococcus aureus and an Escherichia coli tolC efflux mutant revealed selective inhibition of DNA replication not due to gyrase or topoisomerase IV inhibition. S. aureus nargenicin-resistant mutants were selected at a frequency of ∼1 × 10(-9), and whole-genome resequencing found a single base-pair change in the dnaE gene, a homolog of the E. coli holoenzyme α subunit. A DnaE single-enzyme assay was exquisitely sensitive to inhibition by nargenicin, and other in vitro characterization studies corroborated DnaE as the target. Medicinal chemistry efforts may expand the spectrum of this novel mechanism antibiotic.

Utilizing HaloTag Technology to Track the Fate of PCSK9 from Intracellular vs. Extracellular Sources

The function of a particular protein is dependent upon its localization and milieu. The ability to track the "fate" of a protein is a valuable tool to elucidate its function. We present the use of HaloTag technology to study the localization and fate of human Proprotein Convertase Subtilisin-like Kexin type 9 (PCSK9).

The role of PCSK9 in the regulation of circulating low density lipoprotein-cholesterol (LDL-c) levels is ascribed to binding of circulating PCSK9 to the LDL receptor (LDLR) and subsequent lysosomal degradation of LDLR. However, hints in the literature indicate that intracellular PCSK9 may act on the LDLR, possibly during processing of newly synthesized protein. To address this question, the source and fate of intracellular PCSK9 requires further investigation.

We applied HaloTag technology to distinguish the source of intracellular PCSK9 and showed that newly synthesized intracellular PCSK9 has unique localization from the PCSK9 after re-uptake. This suggests different functions of PCSK9 while interacting with the LDLR.

An anti-PCSK9 antibody reduces LDL-cholesterol on top of a statin and suppresses hepatocyte SREBP-regulated genes

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a promising therapeutic target for treating coronary heart disease. We report a novel antibody 1B20 that binds to PCSK9 with sub-nanomolar affinity and antagonizes PCSK9 function in-vitro. In CETP/LDLR-hemi mice two successive doses of 1B20, administered 14 days apart at 3 or 10 mpk, induced dose dependent reductions in LDL-cholesterol (≥ 25% for 7-14 days) that correlated well with the extent of PCSK9 occupancy by the antibody. In addition, 1B20 induces increases in total plasma antibody-bound PCSK9 levels and decreases in liver mRNA levels of SREBP-regulated genes PCSK9 and LDLR, with a time course that parallels decreases in plasma LDL-cholesterol (LDL-C). Consistent with this observation in mice, in statin-responsive human primary hepatocytes, 1B20 lowers PCSK9 and LDLR mRNA levels and raises serum steady-state levels of antibody-bound PCSK9. In addition, mRNA levels of several SREBP regulated genes involved in cholesterol and fatty-acid synthesis including ACSS2, FDPS, IDI1, MVD, HMGCR, and CYP51A1 were decreased significantly with antibody treatment of primary human hepatocytes. In rhesus monkeys, subcutaneous (SC) dosing of 1B20 dose-dependently induces robust LDL-C lowering (maximal ~70%), which is correlated with increases in target engagement and total antibody-bound PCSK9 levels. Importantly, a combination of 1B20 and Simvastatin in dyslipidemic rhesus monkeys reduced LDL-C more than either agent alone, consistent with a mechanism of action that predicts additive effects of anti-PCSK9 agents with statins. Our results suggest that antibodies targeting PCSK9 could provide patients powerful LDL lowering efficacy on top of statins, and lower cardiovascular risk.

Cerium-Doped Orthophosphate Scintillators

Cerium-doped lutetium orthophosphate (LuPO4:Ce) is one of the most promising new scintillator materials. In this paper we report on the effects of total or partial replacement of Lu by Yb. When not doped with Ce, crystals of YbxLu1-xPO4 scintillate rather poorly, the emission being due to the Yb charge transfer transition. Activation with Ce reduces the light output from Yb even further, while correspondingly the addition of Yb to LuPO4:Ce also degrades that material's scintillation performance. We suggest that the nonradiative decay of the (Yb2+-Ce4+) charge transfer state is responsible for the mutual quenching of these ions. The differences in performance of LuPO4:Yb and LuPO4:Ce indicate that energy transfer mechanisms ordinarily associated with materials containing molecular anionic groups may not be quite sufficient to explain the results. Suggestions are presented that under γ-excitation the lattice-to-ion energy transfer in orthophosphates is accomplished by sequential capture of charge carriers rather than the more conventional mechanism of exciton hopping between molecular groups.

A PCSK9-binding antibody that structurally mimics the EGF(A) domain of LDL-receptor reduces LDL cholesterol in vivo

Proprotein convertase subtilisin-like/kexin type 9 (PCSK9) regulates LDL cholesterol levels by inhibiting LDL receptor (LDLr)-mediated cellular LDL uptake. We have identified a fragment antigen-binding (Fab) 1D05 which binds PCSK9 with nanomolar affinity. The fully human antibody 1D05-IgG2 completely blocks the inhibitory effects of wild-type PCSK9 and two gain-of-function human PCSK9 mutants, S127R and D374Y. The crystal structure of 1D05-Fab bound to PCSK9 reveals that 1D05-Fab binds to an epitope on the PCSK9 catalytic domain which includes the entire LDLr EGF(A) binding site. Notably, the 1D05-Fab CDR-H3 and CDR-H2 loops structurally mimic the EGF(A) domain of LDLr. In a transgenic mouse model (CETP/LDLr-hemi), in which plasma lipid and PCSK9 profiles are comparable to those of humans, 1D05-IgG2 reduces plasma LDL cholesterol to 40% and raises hepatic LDLr protein levels approximately fivefold. Similarly, in healthy rhesus monkeys, 1D05-IgG2 effectively reduced LDL cholesterol 20%-50% for over 2 weeks, despite its relatively short terminal half-life (t(1/2) = 3.2 days). Importantly, the decrease in circulating LDL cholesterol corresponds closely to the reduction in free PCSK9 levels. Together these results clearly demonstrate that the LDL-lowering effect of the neutralizing anti-PCSK9 1D05-IgG2 antibody is mediated by reducing the amount of PCSK9 that can bind to the LDLr.

A proprotein convertase subtilisin-like/kexin type 9 (PCSK9) C-terminal domain antibody antigen-binding fragment inhibits PCSK9 internalization and restores low density lipoprotein uptake

PCSK9 binds to the low density lipoprotein receptor (LDLR) and leads to LDLR degradation and inhibition of plasma LDL cholesterol clearance. Consequently, the role of PCSK9 in modulating circulating LDL makes it a promising therapeutic target for treating hypercholesterolemia and coronary heart disease. Although the C-terminal domain of PCSK9 is not involved in LDLR binding, the location of several naturally occurring mutations within this region suggests that it has an important role for PCSK9 function. Using a phage display library, we identified an anti-PCSK9 Fab (fragment antigen binding), 1G08, with subnanomolar affinity for PCSK9. In an assay measuring LDL uptake in HEK293 and HepG2 cells, 1G08 Fab reduced 50% the PCSK9-dependent inhibitory effects on LDL uptake. Importantly, we found that 1G08 did not affect the PCSK9-LDLR interaction but inhibited the internalization of PCSK9 in these cells. Furthermore, proteolysis and site-directed mutagenesis studies demonstrated that 1G08 Fab binds a region of beta-strands encompassing Arg-549, Arg-580, Arg-582, Glu-607, Lys-609, and Glu-612 in the PCSK9 C-terminal domain. Consistent with these results, 1G08 fails to bind PCSK9DeltaC, a truncated form of PCSK9 lacking the C-terminal domain. Additional studies revealed that lack of the C-terminal domain compromised the ability of PCSK9 to internalize into cells, and to inhibit LDL uptake. Together, the present study demonstrate that the PCSK9 C-terminal domain contribute to its inhibition of LDLR function mainly through its role in the cellular uptake of PCSK9 and LDLR complex. 1G08 Fab represents a useful new tool for delineating the mechanism of PCSK9 uptake and LDLR degradation.

Expression, purification and crystallization of human 5-lipoxygenase-activating protein with leukotriene-biosynthesis inhibitors

The nuclear membrane protein 5-lipoxygenase-activating protein (FLAP) plays an essential role in leukotriene synthesis. Recombinant full-length human FLAP with a C-terminal hexahistidine tag has been expressed and purified from the cytoplasmic membrane of Escherichia coli. Diffraction-quality crystals of FLAP in complex with leukotriene-synthesis inhibitor MK-591 and with an iodinated analogue of MK-591 have been grown using the sitting-drop vapor-diffusion method. The crystals exhibit tetragonal symmetry (P42(1)2) and diffracted to a resolution limit of 4 A.

Crystal Structure of Inhibitor-Bound Human 5-Lipoxygenase-Activating Protein

Leukotrienes are proinflammatory products of arachidonic acid oxidation by 5-lipoxygenase that have been shown to be involved in respiratory and cardiovascular diseases. The integral membrane protein FLAP is essential for leukotriene biosynthesis. We describe the x-ray crystal structures of human FLAP in complex with two leukotriene biosynthesis inhibitors at 4.0 and 4.2 angstrom resolution, respectively. The structures show that inhibitors bind in membrane-embedded pockets of FLAP, which suggests how these inhibitors prevent arachidonic acid from binding to FLAP and subsequently being transferred to 5-lipoxygenase, thereby preventing leukotriene biosynthesis. This structural information provides a platform for the development of therapeutics for respiratory and cardiovascular diseases.

Time-resolved Forster resonance energy transfer assays for the binding of nucleotide and protein substrates to p38alpha protein kinase

We have developed assays for the binding of nucleotide and protein substrates to p38alpha protein kinase based on time-resolved Forster resonance energy transfer. p38alpha was biotinylated by addition of a sequence that targets biotin to a single lysine when coexpressed with biotin ligase in Escherichia coli, allowing formation of a complex between a streptavidin "LANCE" europium chelate conjugate and p38alpha. When this reagent was combined with M39AF, a p38 inhibitor containing a fluorescent moiety whose excitation wavelengths match the emission wavelengths of the europium chelate, a change in ratio of light emitted at 665 nm/615 nm is detected. Less than 100pM complex was detected with a signal/background ratio of >30-fold. The complex exhibits slow, tight binding kinetics where the apparent K(d) decreases with a relaxation time of 21 min at 125 pM biotin-p38alpha. Preincubating inhibitors or ATP with biotin-p38alpha and adding M39AF as a competitor yielded IC(50)s consistent with those measured by enzyme assay for the activated form of biotin-p38alpha. The same technique was also used to measure affinity of inhibitors for the unphosphorylated and catalytically inactive form of biotin-p38alpha. To measure affinity of p38alpha for its protein substrate MK2, we incubated biotin-p38alpha with a glutathione S-transferase MK2 fusion protein. Detection of the complex after incubation with streptavidin-allophycocyanin and a LANCE-conjugated anti-GST allowed measurement of affinity of MK2 for biotin-p38alpha and detection of 0.5 nM p38alpha.MK2 complex with signal/background ratio >5-fold. Competition with unbiotinylated p38alpha yielded an IC(50) value of 5 nM. Activation of either p38alpha or MK2 had no effect on the measured K(d). M39AF was found to bind in a ternary complex with p38alpha.MK2 with lower affinity than that observed in the binary complex with p38alpha alone.

Cell-based assays to detect inhibitors of fungal mRNA capping enzymes and characterization of sinefungin as a cap methyltransferase inhibitor

The m7GpppN cap at the 5' end of eukaryotic mRNAs is important for transcript stability and translation. Three enzymatic activities that generate the mRNA cap include an RNA 5'-triphosphatase, an RNA guanylyltransferase, and an RNA (guanine-7-) -methyltransferase. The physical organization of the genes encoding these enzymes differs between mammalian cells and yeast, fungi, or viruses. The catalytic mechanism used by the RNA triphosphatases of mammalian cells also differs from that used by the yeast, fungal, or viral enzymes. These structural and functional differences suggest that inhibitors of mRNA capping might be useful antifungal or antiviral agents. The authors describe several whole-cell yeast-based assays developed to identify and characterize inhibitors of fungal mRNA capping. They also report the identification and characterization of the natural product sinefungin in the assays. Their characterization of this S-adenosylmethionine analog suggests that it inhibits mRNA cap methyltransferases and exhibits approximately 5- to 10-fold specificity for the yeast ABD1 and fungal CCM1 enzymes over the human Hcm1 enzyme expressed in yeast cells.

Anthrax lethal factor inhibition

The primary virulence factor of Bacillus anthracis is a secreted zinc-dependent metalloprotease toxin known as lethal factor (LF) that is lethal to the host through disruption of signaling pathways, cell destruction, and circulatory shock. Inhibition of this proteolytic-based LF toxemia could be expected to provide therapeutic value in combination with an antibiotic during and immediately after an active anthrax infection. Herein is shown the crystal structure of an intimate complex between a hydroxamate, (2R)-2-[(4-fluoro-3-methylphenyl)sulfonylamino]-N-hydroxy-2-(tetrahydro-2H-pyran-4-yl)acetamide, and LF at the LF-active site. Most importantly, this molecular interaction between the hydroxamate and the LF active site resulted in (i) inhibited LF protease activity in an enzyme assay and protected macrophages against recombinant LF and protective antigen in a cell-based assay, (ii) 100% protection in a lethal mouse toxemia model against recombinant LF and protective antigen, (iii) approximately 50% survival advantage to mice given a lethal challenge of B. anthracis Sterne vegetative cells and to rabbits given a lethal challenge of B. anthracis Ames spores and doubled the mean time to death in those that died in both species, and (iv) 100% protection against B. anthracis spore challenge when used in combination therapy with ciprofloxacin in a rabbit "point of no return" model for which ciprofloxacin alone provided 50% protection. These results indicate that a small molecule, hydroxamate LF inhibitor, as revealed herein, can ameliorate the toxemia characteristic of an active B. anthracis infection and could be a vital adjunct to our ability to combat anthrax.

The membrane organization of leukotriene synthesis

Cell signaling leading to the formation of leukotriene (LT)C(4) requires the localization of the four key biosynthetic enzymes on the outer nuclear membrane and endoplasmic reticulum. Whether any macromolecular organization of these proteins exists is unknown. By using fluorescence lifetime imaging microscopy and biochemical analysis, we demonstrate the presence of two distinct multimeric complexes that regulate the formation of LTs in RBL-2H3 cells. One complex consists of multimers of LTC(4) synthase and the 5-lipoxygenase activating protein (FLAP). The second complex consists of multimers of FLAP. Surprisingly, all LTC(4) synthase was found to be in association with FLAP. The results indicate that the formation of LTC(4) and LTB(4) may be determined by the compartmentalization of biosynthetic enzymes in discrete molecular complexes.

Chronic myelogenous leukemia as a paradigm of early cancer and possible curative strategies

The chronological history of the important discoveries leading to our present understanding of the essential clinical, biological, biochemical, and molecular features of chronic myelogenous leukemia (CML) are first reviewed, focusing in particular on abnormalities that are responsible for the massive myeloid expansion. CML is an excellent target for the development of selective treatment because of its highly consistent genetic abnormality and qualitatively different fusion gene product, p210(bcr-abl). It is likely that the multiple signaling pathways dysregulated by p210(bcr-abl) are sufficient to explain all the initial manifestations of the chronic phase of the disease, although understanding of the circuitry is still very incomplete. Evidence is presented that the signaling pathways that are constitutively activated in CML stem cells and primitive progenitors cooperate with cytokines to increase the proportion of stem cells that are activated and thereby increase recruitment into the committed progenitor cell pool, and that this increased activation is probably the primary cause of the massive myeloid expansion in CML. The cooperative interactions between Bcr-Abl and cytokine-activated pathways interfere with the synergistic interactions between multiple cytokines that are normally required for the activation of stem cells, while at the same time causing numerous subtle biochemical and functional abnormalities in the later progenitors and precursor cells. The committed CML progenitors have discordant maturation and reduced proliferative capacity compared to normal committed progenitors, and like them, are destined to die after a limited number of divisions. Thus, the primary goal of any curative strategy must be to eliminate all Philadelphia positive (Ph+) primitive cells that are capable of symmetric division and thereby able to expand the Ph+ stem cell pool and recreate the disease. Several highly potent and moderately selective inhibitors of Bcr-Abl kinase have recently been discovered that are capable of killing the majority of actively proliferating early CML progenitors with minimal effects on normal progenitors. However, like their normal counterparts, most of the CML primitive stem cells are quiescent at any given time and are relatively invulnerable to the Bcr-Abl kinase inhibitors as well as other drugs. We propose that survival of dormant Ph+ stem cells may be the most important reason for the inability to cure the disease during initial treatment, while resistance to the inhibitors and other drugs becomes increasingly important later. An outline of a possible curative strategy is presented that attempts to take advantage of the subtle differences in the proliferative behavior of normal and Ph+ stem cells and the newly discovered selective inhibitors of Bcr-Abl. Leukemia (2003) 17, 1211-1262. doi:10.1038/sj.leu.2402912

A peptide-based fluorescence resonance energy transfer assay for Bacillus anthracis lethal factor protease

A fluorescence resonance energy transfer assay has been developed for monitoring Bacillus anthracis lethal factor (LF) protease activity. A fluorogenic 16-mer peptide based on the known LF protease substrate MEK1 was synthesized and found to be cleaved by the enzyme at the anticipated site. Extension of this work to a fluorogenic 19-mer peptide, derived, in part, from a consensus sequence of known LF protease targets, produced a much better substrate, cleaving approximately 100 times more efficiently. This peptide sequence was modified further on resin to incorporate donor/quencher pairs to generate substrates for use in fluorescence resonance energy transfer-based appearance assays. All peptides cleaved at similar rates with signal/background ranging from 9-16 at 100% turnover. One of these substrates, denoted (Cou)Consensus(K(QSY-35)GG)-NH(2), was selected for additional assay optimization. A plate-based assay requiring only low nanomolar levels of enzyme was developed for screening and inhibitor characterization.

The phosphatidylinositol polyphosphate 5-phosphatase SHIP1 associates with the dok1 phosphoprotein in bcr-Abl transformed cells

The initial phase of chronic myelogenous leukemia (CML) is triggered by constitutive protein tyrosine kinase activity of the chimeric kinase p210(bcr-abl) (Bcr-Abl). A major substrate of Bcr-Abl was recently identified as the RasGAP-associated 62 kDa docking protein Dok1. Here, we report complex formation between endogenous Dok1 and the SH2 domain-containing phosphatidylinositol polyphosphate 5-phosphatase SHIP1 in hematopoietic cells expressing Bcr-Abl. Expression of Bcr-Abl induced tyrosine phosphorylation of both Dok1 and SHIP1 and the formation of a Dok1/SHIP1 complex. Tyr(P) SHIP1 was also bound to Shc in Bcr-Abl expressing cells. A small amount of Shc/SHIP1/Dok1 trimolecular complex was detected and this was due to binding of Dok1 to SHIP1 that was bound to Shc. In contrast, association of Dok1 with SHIP1 or RasGAP was mutually exclusive. Both the SH2 domain of SHIP1 and the PTB domain of Dok1 were required for complex formation between the two proteins. Neither the specific activity of SHIP1 as an inositol phosphate 5-phosphatase nor the subcellular localization of SHIP1 appeared to be altered by tyrosine phosphorylation. However, the Dok1/SHIP1 complex was only detected in the cytosolic fraction of Bcr-Abl transformed hematopoietic cells. We propose that interaction between Dok1 and SHIP1 modulates the ability of these two proteins to interact with other cytosolic binding partners.

Characterization of two novel sublines established from a human megakaryoblastic leukemia cell line transfected with p210(BCR-ABL)

Disease progression in chronic myelogenous leukemia (CML) is usually accompanied by chromosomal abnormalities such as an additional Ph chromosome, trisomies of chromosome 8 or 19, or i(17) in addition to the standard translocation t(9;22) (q34;q11). However, detailed studies of the various steps involved during this evolution are difficult to perform, thereby making the study of cell lines that contain the transposed genes BCR-ABL, especially those of human origin, an important focus. In this analysis we investigated the human megakaryoblastic cell line MO7e and its subline transfected with BCR-ABL, MO7e/p210. Initial studies demonstrated that the phenotype of the MO7e line was consistent with a megakaryocytic lineage as originally described and was growth factor dependent in liquid culture. The MO7e/p210 subline, however, was growth factor independent and could be further separated into two distinct sublines based on expression of glycophorin A using the monoclonal antibody R10. The subline R10 negative (R10-) was similar to the parent line MO7e but R10 positive (R10+) cells had a distinct erythroid phenotype. In addition, the R10- and R10+ sublines demonstrated strikingly different colony morphology when cultured in semisolid medium. Furthermore, R10+ cells had additional chromosomal abnormalities not detected in the R10- population. These results demonstrate that the insertion of the BCR-ABL in this human leukemia cell line resulted in two distinct subpopulations of cells, each now growth factor independent, but one with a phenotype and karyotype identical to the parent cell line and the other with a different phenotype and additional chromosomal abnormalities. These two subpopulations derived from the MO7e/p210 transfected cell line may prove useful in further understanding the multistep events that occur in the progression of this disease.

Assay for IkappaB kinases using an in vivo biotinylated IkappaB protein substrate

IkappaB kinases (IKK)-1 and -2 are related kinases that are induced by stimuli such as TNF or IL-1 to phosphorylate serines 32 and 36 of IkappaBalpha, the regulatory subunit of the transcription factor NF-kappaB. A procedure for an IKK protein kinase assay is described that uses an in vivo biotinylated IkappaB protein substrate, [gamma-(33)P]ATP, and capture onto a streptavidin membrane. Residues 1-54 of the IkappaBalpha substrate were expressed as a fusion with glutathione S-transferase (GST) and a short (22 amino acid) biotinylation sequence that allowed modification during bacterial expression. Using the streptavidin capture assay the phosphorylation activities of recombinant IKK-1 and -2 were characterized. The assay provided a convenient way to compare IKK protein and peptide substrate preferences; biotinylated GST-IkappaBalpha(1-54) was more readily phosphorylated by both IKK-1 and IKK-2 compared to biotinylated myelin basic protein or a 20-mer biotinylated peptide containing serines 32 and 36 of IkappaBalpha. IKK-1 had 83-fold less activity than IKK-2, and the IKK-1+2 complex had approximately 2-fold more activity than IKK-2. IKK-1+2 and IKK-2 had similar K(m) values for ATP and GST-biotin-IkappaB(1-54) and were similarly inhibited by staurosporine and two of its analogues K252a and K252b, suggesting that most of the IkappaBalpha kinase activity in the IKK-1+2 complex may be attributed to IKK-2. Several features of the assay including the broad linear binding range of the streptavidin membranes for the protein substrate GST-biotin-IkappaB(1-54) (1-4000 pmol of protein/cm(2)), the low background, and its capacity for both biotinylated peptides and proteins make it a useful tool for quantitating IKK activity. These factors and the ease of expressing in vivo biotinylated GST fusions will make this assay approach suitable for a wide variety of protein kinases.

A novel SH2-containing phosphatidylinositol 3,4,5-trisphosphate 5-phosphatase (SHIP2) is constitutively tyrosine phosphorylated and associated with src homologous and collagen gene (SHC) in chronic myelogenous leukemia progenitor cells

Because of the probable causal relationship between constitutive p210(bcr/abl) protein tyrosine kinase activity and manifestations of chronic-phase chronic myelogenous leukemia (CML; myeloid expansion), a key goal is to identify relevant p210 substrates in primary chronic-phase CML hematopoietic progenitor cells. We describe here the purification and mass spectrometric identification of a 155-kD tyrosine phosphorylated protein associated with src homologous and collagen gene (SHC) from p210(bcr/abl)-expressing hematopoietic cells as SHIP2, a recently reported, unique SH2-domain-containing protein closely related to phosphatidylinositol polyphosphate 5-phosphatase SHIP. In addition to an N-terminal SH2 domain and a central catalytic region, SHIP2 (like SHIP1) possesses both potential PTB(NPXY) and SH3 domain (PXXP) binding motifs. Thus, two unique 5-ptases with striking structural homology are coexpressed in hematopoietic progenitor cells. Stimulation of human hematopoietic growth factor responsive cell lines with stem cell factor (SCF), interleukin-3 (IL-3), and granulocyte-macrophage colony-stimulating factor (GM-CSF) demonstrate the rapid tyrosine phosphorylation of SHIP2 and its resulting association with SHC. This finding suggests that SHIP2, like that reported for SHIP1 previously, is linked to downstream signaling events after activation of hematopoietic growth factor receptors. However, using antibodies specific to these two proteins, we demonstrate that, whereas SHIP1 and SHIP2 selectively hydrolyze PtdIns(3,4,5)P3 in vitro, only SHIP1 hydrolyzes soluble Ins(1,3,4,5)P4. Such an enzymatic difference raises the possibility that SHIP1 and SHIP2 may serve different functions. Preliminary binding studies using lysates from p210(bcr/abl)-expressing cells indicate that both Ptyr SHIP2 and Ptyr SHIP1 bind to the PTB domain of SHC but not to its SH2 domain. Interestingly, SHIP2 was found to selectively bind to the SH3 domain of ABL, whereas SHIP1 selectively binds to the SH3 domain of Src. Furthermore, in contrast to SHIP1, SHIP2 did not bind to either the N-terminal or C-terminal SH3 domains of GRB2. These observations suggest (1) that SHIP1 and SHIP2 may have a different hierarchy of binding SH3 containing proteins and therefore may modulate different signaling pathways and/or localize to different cellular compartments and (2) that they may be substrates for tyrosine phosphorylation by different tyrosine kinases. Because recent evidence has clearly implicated both PI(3,4, 5)P3 and PI(3,4)P2 in growth factor-mediated signaling, our finding that both SHIP1 and SHIP2 are constitutively tyrosine phosphorylated in CML primary hematopoietic progenitor cells may thus have important implications in p210(bcr/abl)-mediated myeloid expansion.

Molecular cloning and characterization of p56dok-2 defines a new family of RasGAP-binding proteins

Chronic myelogenous leukemia (CML) is a disease characterized by the presence of p210(bcr-abl), a chimeric protein with tyrosine kinase activity. Substrates for p210(bcr-abl) are likely to be involved in the pathogenesis of CML. Here we describe the purification, cDNA cloning, and characterization of a 56-kDa tyrosine phosphorylated protein, p56(dok-2) (Dok-2), from p210(bcr-abl) expressing cells. The human dok-2 cDNA encodes a 412-amino acid protein with a predicted N-terminal pleckstrin homology domain as well as several other features of a signaling molecule, including 13 potential tyrosine phosphorylation sites, six PXXP motifs, and the ability to bind to p120(RasGAP). Dok-2 was shown to be 35% identical to p62(dok-1), a recently identified RasGAP binding protein from CML cells, and analysis of the expressed sequence tag data base revealed the presence of at least four additional proteins containing a Dok homology sequence motif. Dok mRNAs were primarily expressed in tissues of hematopoietic origin. These findings strongly suggest that a family of Dok-related proteins exists that bind to RasGAP and may mediate the effects of p210(bcr-abl) in CML.

New understanding of the pathogenesis of CML: a prototype of early neoplasia

The 9;22 chromosomal translocation characteristic of CML results in a fused bcr/abl gene and an abnormal fusion protein, p210bcr/abl. Relative to normal c-abl, p210bc1/abl has elevated tyrosine kinase activity that is essential for its transforming activity. We recently reported a prominent 62 kDa GAP-associated P-tyr protein and five additional consistent but less prominent P-tyr proteins as well as five more minor P-tyr proteins that are constitutively tyrosine phosphorylated in primary primitive lineage negative (lin-) chronic phase CML blasts but not in comparable primary lin- normal blasts. The GAP-associated p62 protein has now been purified, sequenced and its gene has been cloned; it is a previously unidentified protein and is currently being characterized. In analyzing P-tyr proteins in primary lin- normal blasts in response to various hematopoietic cytokines, we found a striking similarity in the tyrosine phosphorylation of four major and three minor proteins after stimulation with c-kit ligand (KL) and the P-tyr proteins that are constitutively phosphorylated in primary primitive lin- chronic phase CML blasts. Other cytokines tested (ie GM-CSF, G-CSF, IL-3, FLT3 ligand, TPO, EPO) were much less active or stimulated phosphorylation of other proteins. KL/c-kit and bcr/abl have some similar activities including enhancing survival and expansion of hematopoietic progenitor cells, probably acting primarily on early progenitors at the time of lineage commitment rather than on self-renewing stem cells. Activation of growth factor receptors promote a cascade of protein phosphorylations that can ultimately result in a wide range of cellular responses. Sustained activation of discrete signaling pathways in some types of cells results in differentiation, whereas transient activation instead causes a proliferative response; in other cell types, the converse is true. It may be postulated that stem cells and primitive progenitors are at a particularly susceptible stage of development that renders them especially responsive to sustained bcr/abl-induced phorphorylation of a number of signaling proteins that are components of critical regulatory pathways, including c-kit. The affected pathways control and coordinate multiple diverse cell processes including proliferation, differentiation, maturation and apoptosis, processes that are normally tightly regulated and integrated. Perturbation of these key pathways in primitive progenitors would be expected to seriously disrupt orderly hematopoiesis and could also explain the multiple subtle pleiotropic biological abnormalities characteristically observed in later maturing CML compartments that we have collectively designated 'discordant maturation'. The true situation is undoubtedly very complex and involves interaction of multiple cytokines and signaling pathways that we are now trying to define. Constitutive downstream activation of critical pathways in susceptible early progenitors that normally require KL or other factors for activation could explain most if not all features of the disease.

p62(dok): a constitutively tyrosine-phosphorylated, GAP-associated protein in chronic myelogenous leukemia progenitor cells

Characteristic of chronic myelogenous leukemia (CML) is the presence of the chimeric p210(bcr-abl) protein possessing elevated protein tyrosine kinase activity relative to normal c-abl tyrosine kinase. Hematopoietic progenitors isolated from CML patients in the chronic phase contain a constitutively tyrosine-phosphorylated protein that migrates at 62 kDa by SDS-PAGE and associates with the p120 ras GTPase-activating protein (GAP). We have purified p62(dok) from a hematopoietic cell line expressing p210(bcr-abl). p62(dok) is a novel protein with features of a signaling molecule. Association of p62(dok) with GAP correlates with its tyrosine phosphorylation. p62(dok) is rapidly tyrosine-phosphorylated upon activation of the c-Kit receptor, implicating it as a component of a signal transduction pathway downstream of receptor tyrosine kinases.

Variable subcellular localization of a neuron-specific protein during NTera 2 differentiation into post-mitotic human neurons

The current report describes the molecular characterization of the human (the D4S234 locus) and mouse (the m234) homologs of a gene that was isolated during our genomic analysis of the Huntington disease gene region. Sequence comparisons of full-length cDNA clones revealed that the mouse and human homologs encoded evolutionarily conserved 21-kDa proteins with greater than 90% amino acid sequence identity. Extensive sequence identity between the D4S234 gene and the rat p1A75 gene (a previously identified rat neuron-specific gene) showed that these genes are interspecies homologs. Furthermore, the D4S234 protein exhibited significant amino acid similarity to a 19-kDa mouse protein that localizes to the Golgi apparatus of embryonic neurons. However, nonconservative sequence differences suggested that these genes are independent members of a multigene family. Northern analyses revealed that rodent D4S234 expression occurred predominantly in the brain and included all brain regions. Neuron-specific expression was demonstrated using Northern analysis of cultured glial cells and quinolinic acid-treated rat brain samples. Minimal amounts of the rodent D4S234 mRNA were detected prenatally; however, elevated adult levels were detected within 1 month of birth. Sequence analyses of the human and mouse D4S234 proteins identified an evolutionarily conserved hydrophobic sequence and a consensus nuclear localization signal in both genes. Immunofluorescence microscopy, using an antipeptide antibody, established that the human D4S234 protein preferentially localized to the nucleus of mitotic cultured cells. Since the rat p1A75 protein was previously mapped to the neuronal cytoplasm by in situ hybridization, the subcellular localization of the D4S234 protein was subsequently examined during differentiation of the NTera 2 (NT2) cell line. Following differentiation into postmitotic NT2-N neurons, the D4S234 protein demonstrated cytoplasmic staining and reduced or undetectable nuclear staining in many cells. The variation in the intracellular localization of the D4S234 protein in mitotic and nonmitotic cells suggests that the subcellular localization of this protein is developmentally regulated and provides clues about the biochemical function of this protein.

Mechanism of activation for Zap-70 catalytic activity

There is a growing body of evidence, including data from human genetic and T-cell receptor function studies, which implicate a zeta-associated protein of M(r) 70,000 (Zap-70) as a critical protein tyrosine kinase in T-cell activation and development. During T-cell activation, Zap-70 becomes associated via its src homology type 2 (SH2) domains with tyrosine-phosphorylated immune-receptor tyrosine activating motif (ITAM) sequences in the cytoplasmic zeta chain of the T-cell receptor. An intriguing conundrum is how Zap-70 is catalytically activated for downstream phosphorylation events. To address this question, we have used purified Zap-70, tyrosine phosphorylated glutathione S-transferase (GST)-Zeta, and GST-Zeta-1 cytoplasmic domains, and various forms of ITAM-containing peptides to see what effect binding of zeta had upon Zap-70 tyrosine kinase activity. The catalytic activity of Zap-70 with respect to autophosphorylation increased approximately 5-fold in the presence of 125 nM phosphorylated GST-Zeta or GST-Zeta-1 cytoplasmic domain. A 20-fold activity increase was observed for phosphorylation of an exogenous substrate. Both activity increases showed a GST-Zeta concentration dependence. The increase in activity was not produced with nonphosphorylated GST-Zeta, phosphorylated zeta, or phosphorylated ITAM-containing peptides. The increase in Zap-70 activity was SH2 mediated and was inhibited by phenylphosphate, Zap-70 SH2, and an antibody specific for Zap-70 SH2 domains. Since GST-Zeta and GST-Zeta-1 exist as dimers, the data suggest Zap-70 is activated upon binding a dimeric form of phosphorylated zeta and not by peptide fragments containing a single phosphorylated ITAM. Taken together, these data indicate that the catalytic activity of Zap-70 is most likely activated by a trans-phosphorylation mechanism.

The utility of FK506-binding protein as a fusion partner in scintillation proximity assays: application to SH2 domains

Methodology has been developed which gives a specific measure of the interaction of an SH2 domain with a phosphopeptide ligand using scintillation proximity assay (SPA) technology. Recombinant SH2 domains were expressed from a T7 RNA polymerase-based vector in Escherichia coli as fusions to the C-terminus of the FK506-binding protein (FKBP) and purified from freeze-thaw lysates in high yield by affinity chromatography using immobilized phosphopeptides. For binding assays the phosphopeptide ligands were synthesized with a biotin tag and the FKBP fusion proteins were noncovalently radiolabeled with commercially available [3H]dihydroFK506. Complexes of tritiated SH2 fusion protein and biotinyl-phosphopeptide were then captured on streptavidin-coated SPA beads and counted. The modular protocol is an equilibrium technique that does not employ washing steps or specialized radiochemical syntheses required in other binding assays. The utility of the assay has been demonstrated in an examination of the ligand specificity of the SH2 domains of the tyrosine kinases ZAP70, Syk, and Lck. The methodology is potentially generalizable to any receptor-ligand interaction in which one component can be expressed as a fusion partner with FKBP and the other component can be captured on a SPA bead.

c-kit ligand stimulates tyrosine phosphorylation of the c-Cbl protein in human hematopoietic cells

c-kit ligand (KL) is a hematopoietic growth factor that plays a major role in the survival, expansion and differentiation of hematopoietic progenitor cells of various lineages. The biological actions elicited by KL are initiated by binding to its cognate receptor, c-kit, which is a transmembrane tyrosine kinase. The resulting ligand/receptor complex rapidly activates the intrinsic kit receptor tyrosine kinase and subsequent phosphorylation of specific intracellular substrates that are involved in downstream signaling events. In the present studies, we demonstrate that KL stimulates the rapid tyrosine phosphorylation of the proto-oncogene, c-Cbl, in two KL-responsive human hematopoietic cell lines, MO7e and TF-1. In both these cell lines we found a constitutive in vivo association between c-Cbl and the adaptor protein Grb2 and demonstrate (in vitro) that c-Cbl binds primarily to the N-terminal SH3 domain of Grb2. Furthermore, the stoichiometry of this association was not significantly affected upon c-kit receptor activation. We also provide evidence that c-Cbl is not stably associated with the kit receptor either prior to or following KL stimulation. Our findings suggest that c-Cbl is an important component in the KL signaling pathway in human hematopoietic progenitor cells.

c-kit ligand stimulates tyrosine phosphorylation of a similar pattern of phosphotyrosyl proteins in primary primitive normal hematopoietic progenitors that are constitutively phosphorylated in comparable primitive progenitors in chronic phase chronic myelogenous leukemia

Characteristic of Philadelphia (Ph)+ chronic myelogenous leukemia (CML) is the presence of the chimeric BCR/ABL (p210) protein possessing elevated protein tyrosine kinase activity relative to the normal c-abl tyrosine kinase. Our previous studies demonstrated subtle differences in the growth, phenotypic and morphologic characteristics of the most primitive subpopulations of primary lin-Ph+ chronic phase CML blasts and comparable primary lin- normal blasts. Recently, in comparing proteins phosphorylated on tyrosine in these cell populations, we reported a prominent 62 kDa phosphotyrosyl (P-tyr) protein constitutively present in primary primitive lin- CML chronic phase blasts which was virtually undetectable in primary primitive lin- normal blasts. In the present studies, we demonstrate that this P-tyr p62 from primary primitive lin- chronic phase CML blasts co-immunoprecipitates with ras-GAP. Furthermore, in addition to the p210 protein, we show in whole cell lysates the presence of other clearly consistent but less prominent P-tyr proteins with molecular weights of approximately 155, 140, 110, 55 and 45 kDa as well as more minor P-tyr proteins of approximately 190, 85, 52, 42 and 39 kDa constitutively present in primary primitive lin- chronic phase CML blasts. In analyzing proteins tyrosine phosphorylated in primary primitive lin- normal blasts in response to various hematopoietic growth factors, we found a striking similarity in the phosphorylation of four major (approximately 140, 110, 62 and 56 kDa) and three minor (approximately 51, 45 and 42 kDa) P-tyr proteins after stimulation with c-kit ligand and the P-tyr proteins constitutively phosphorylated in primary primitive lin- chronic phase CML blasts. Other growth factors tested (ie GM-CSF, G-CSF, IL-3, FLT3 ligand and EPO) were much less active or stimulated phosphorylation of other proteins. It is provocative that at least seven proteins rapidly and transiently phosphorylated on tyrosine in the c-kit ligand signal transduction pathway in lin- normal blasts may be constitutive substrates for the p210 activated tyrosine kinase in comparable lin- chronic phase CML blasts. In addition, it is intriguing that some of the biological effects on hematopoietic progenitors attributed to the c-kit ligand may be similar to some of the observed biological consequences of the p210 protein, including survival and expansion of a more mature stem cell population, probably at the time of lineage commitment rather than at the level of the earliest self-renewing stem cell.

High-yield expression, refolding, and purification of penicillin-binding protein 2a from methicillin-resistant Staphylococcus aureus strain 27R

The mecA-27R gene, which encodes PBP2a from methicillin-resistant Staphylococcus aureus strain 27R, was modified to remove the putative N-terminal membrane-spanning region, cloned into the T7 RNA polymerase expression vector pET11d, and used to transform Escherichia coli strain BL21(DE3). The majority of PBP2a was expressed in the form of inclusion bodies, which were extracted, denatured, and refolded. The protein was then purified by anion-exchange and size-exclusion chromatography. A 6-liter culture of induced E. coli provided 37 mg of purified PBP2a which was greater than 99% pure. Binding affinities for [3H]benzylpenicillin, imipenem, and L-695,256 (a beta-lactam with high affinity for PBP2a) were shown to be comparable to PBP2a found in membrane preparations of S. aureus strain 27R. A direct binding assay, using 14C-labeled L-695,256 was developed and used to show stoichiometric binding to the refolded, soluble PBP2a. In addition, electrospray mass spectrometry showed that 100% of the refolded PBP2a was covalently bound to the beta-lactam in a stoichiometric fashion. Finally, two mutations of the putative active-site serine showed the predicted loss of covalent binding of the beta-lactam to the PBP2a, demonstrating the high specificity of the soluble binding assay.

A 62-kilodalton tyrosine phosphoprotein constitutively present in primary chronic phase chronic myelogenous leukemia enriched lineage negative blast populations

Ph+ chronic myelogenous leukemia (CML) is associated with the reciprocal translocation between chromosomes 9 and 22 culminating in the production of the chimeric p210bcr/abl protein possessing elevated protein tyrosine kinase activity relative to the normal c-abl tyrosine kinase. Our recent studies have revealed subtle differences in the growth, phenotypic and morphologic characteristics of subpopulations of primary lin- Ph+ chronic phase CML blasts and comparable primary normal blasts. In an attempt to correlate these biologic abnormalities and the presence of the p210bcr/abl protein, we initiated studies to identify differences in proteins constitutively phosphorylated on tyrosine in whole cell lysates of comparable primary early blast subpopulations derived from normal and Ph+ chronic phase CML marrows. Immunoblotting with anti-P-tyr Abs demonstrated a prominent 62 kDa phosphotyrosyl protein (pp62) constitutively present in 11/11 Ph+ chronic phase linblasts while being virtually undetectable in equivalent amounts of protein derived from 15/15 and 2/2 comparable normal and Ph-negative chronic phase blast populations, respectively. Immunoblotting with an Ab reportedly specific for the ras GTPase activating protein (GAP) associated p62 protein revealed that the pp62 present in CML blasts is not immunologically related to the former protein. Although the identity of the pp62 is presently not known, its prominent presence in chronic phase CML blasts, in which the only known molecular abnormality is putatively the p210bcr/abl protein, strongly suggests that it may be a critical p210bcr/abl substrate involved in an early stage of expansion of the Ph+ clone.

Differences in the composition and in the efficiency of red cell production of normal and CML erythroid progenitor populations are highlighted by response to human c-kit ligand

Previous studies have suggested that erythroid progenitors derived from patients with chronic myelogenous leukemia (CML) in chronic phase may have reduced proliferative capacity. Considering recent evidence that mast cell growth factor (MGF) enhances the proliferative capacity of normal erythroid burst-forming units (BFU-E), we examined whether MGF could increase the proliferative potential of CML erythroid progenitors to normal capacity. To evaluate the total proliferative capacity achieved, the BFU-E were divided into four subpopulations (XL = extra large, L = large, M = medium, S = small) and colonies were aspirated to determine the cellularity of BFU-E from each subpopulation. MGF alone or in combination with MoT cell line conditioned medium (MoCM) or granulocyte-macrophage colony-stimulating factor (GM-CSF) + interleukin-3 (IL-3) significantly increased the proliferative capacity of erythropoietin (EPO) dependent CML and normal BFU-E. Although the total number of BFU-E generated were similar, the number of BFU-E with high proliferative potential were considerably less in CML BFU-E populations. BFU-E designated XL (129,000-431,000 cells) were only found in MGF cultures and only normal BFU-E had this proliferative capacity. BFU-E designated L were increased in both normal and CML BFU-E populations but less CML BFU-E had this proliferative capacity (mean number 25% of normal) and CML L BFU-E from 2/3 CML patients comprised fewer cells than normal L BFU-E. Normal BFU-E populations comprised 16-24% high proliferative BFU-E (XL + L) in contrast to 4-5% high proliferative BFU-E (L only) comprising CML BFU-E populations.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of lineage-negative blast subpopulations derived from normal and chronic myelogenous leukemia bone marrows and determination of their responsiveness to human c-kit ligand

Lineage-negative (lin-) normal and chronic myelogenous leukemia (CML) marrow blast populations were obtained by negative selection and subsequently separated on the basis of size by velocity sedimentation. The three subpopulations of lin- blasts obtained were enriched for F8 (the more primitive small blasts), F11 (blasts intermediate in size), and F13 (the more mature large blasts). We examined the morphological and phenotypic characteristics and cell cycle status of the subpopulations and determined the responsiveness of granulocyte-monocyte progenitors (colony-forming units/granulocyte-macrophage) derived from each subpopulation to mast cell growth factor in combination with granulocyte (G-CSF) or granulocyte-macrophage (GM-CSF) colony-stimulating factors alone and in combination. Morphological assessment revealed that an increased proportion of CML lin- blasts exhibited early cytoplasmic maturation as evidenced by the appearance of azurophilic (nonspecific) granules in the cytoplasm. Although the percentages of CML and normal small blasts expressing CD34 were similar, the proportion of CML lin- blasts expressing CD34 declined in the intermediate and more mature large lin- blast subpopulations by about 50%, whereas the percentage of CD34+ normal blasts remained essentially the same, indicating an earlier loss of CD34 expression by CML lin- blasts. In addition, the percentages of CML small blasts expressing CD33 were higher than normal (26-61% versus 0-16%, respectively), indicating that a higher proportion of CML small lin- blasts had a more mature phenotype. Mast cell growth factor addition to cultures stimulated by G-CSF, GM-CSF, or G-CSF plus GM-CSF, exerted the greatest synergistic effect (increased colony number and size) in the normal small and intermediate lin- blast cultures, but mast cell growth factor had considerably less effect, or no effect, in cultures of comparable CML subpopulations, indicating that CML lin- progenitors had a somewhat lower requirement for multiple growth factors. The findings suggest that the differences observed between normal and CML marrow subpopulations are proportional differences and that a greater proportion of CML lin- blast subpopulations exhibit characteristics associated with a more advanced stage of maturation than comparable normal lin- blast subpopulations.

Integration of molecular and biological abnormalities in quest for selective treatment of chronic myelogenous leukemia (CML)

CML is an excellent target for development of selective treatment because of its highly consistent genetic abnormality t(9;22) and unique fusion gene product, p210bcr/abl, although it is not yet clear what form of specific therapy might be effective. Several components of p210bcr/abl are thought to be essential for its transforming activity: These include the constitutive tyrosine kinase activity of abl and the ability of the first exon for bcr both to specifically bind to abl's SH2 binding domain and possibly also to function as a novel type of serine kinase. Relatively little is yet known about what specific abnormalities in the regulatory pathways are caused by the altered tyrosine kinase activity of p210bcr/abl and other bcr/abl oncoproteins, but whatever its precise mode of action proves to be, p210bcr/abl presumably somehow changes the normal pattern of phosphorylation of key regulatory proteins in the signaling pathways so that the genes which normally direct the orderly sequence of proliferation and maturation of the myeloid progenitors are not properly regulated. The end results of this 'disregulation' are that there is asynchronous or discordant maturation; relative to comparable normal progenitors, a higher proportion of CML progenitors exhibit earlier cytoplasmic and delayed nuclear maturation. The leukemic progenitors do not proliferate more rapidly than comparable normal progenitors or have increased ultimate proliferative potential, but they go through one or more additional divisions during passage through the later maturation compartments and also live longer, resulting in overexpansion of the leukemic population. It is important to recognize the close linkage between maturation and proliferation in designing experiments to correlate the molecular and biological abnormalities and in seeking novel therapies to selectively affect the leukemic progenitors.

An estimate of the number of genes in the Huntington disease gene region and the identification of 13 transcripts in the 4p16.3 segment

Physical mapping and genetic linkage studies have positioned the Huntington disease (HD) gene to a relatively large genomic region in the distal portion of the short arm of human chromosome 4 (4p16.3). To estimate the number of genes present in this region and to identify candidate disease genes, several clones that map to the 4p16.3 segment have been examined for clusters of CpG-rich restriction sites and transcribed sequences. Thirteen expressed sequences were identified and were shown by pulsed-field gel electrophoresis not to cluster into a small segment of the 4p16.3 band. The frequency of transcripts in these clones suggests that the putative HD gene region contains about 100 genes.

Constitutive expression of p53 protein in enriched normal human marrow blast cell populations

Previous studies by others using metabolic labeling, cell lysis, and immunoprecipitation have reported elevated levels of p53 protein in blast cells derived from patients with acute lymphoblastic leukemia (ALL) and acute myeloblastic leukemia (AML), whereas p53 protein was not detected in normal light-density bone marrow cells. In this report, using the same detection methods, we confirm the negligible expression of p53 protein in normal light density marrow cells. However, we find clearly significant levels of p53 protein expression in enriched normal human marrow blast populations. Furthermore, using a panel of p53 specific monoclonal antibodies, we find the p53 protein constitutively synthesized by normal marrow blasts has the immunologic phenotype identified by PAb240 that reportedly recognizes a common conformational-dependent epitope on mutant p53. We have also found that the p53 immunologic subclass identified by PAb240 exists in normal human circulating lymphocytes either resting, serum starved, or PHA activated. In summary, it is clear that (1) normal marrow blast populations provide the appropriate control for assessing the levels of p53 protein expression in leukemic blast cells; and (2) PAb240 cannot be used to distinguish p53 mutated at the DNA level from normal p53 in fresh human hematopoietic cells.

Duration of the preclinical phase of chronic myelogenous leukemia: a case report

The molecular events that allow for clonal expansion of the malignant population in chronic myelogenous leukemia (CML) are poorly understood. Recent experiments in transgenic mice suggest a close temporal relationship between expression of the aberrant protein and manifestation of a hematologic neoplasm that resembles CML; tracing the same phenomenon in humans has not been possible. We studied a patient who underwent autologous bone marrow harvest after completion of chemotherapy and radiation therapy for advanced stage Hodgkin's disease. At the time of harvest his peripheral blood counts and bone marrow were morphologically normal. Sixteen months later he developed the clinical manifestations of CML. Detailed molecular evaluation of the harvested marrow showed that a small number of cells contained the Philadelphia chromosome. The time interval required for expansion of the malignant clone, as suggested by this particular patient, was at least 16 months although it is recognized that this figure may be variable.

Co-detection of chimeric bcr/abl (target) and beta-actin (control) messenger RNA in individual CFU-GM colonies derived from CML patients using the polymerase chain reaction

In order to quantitate the magnitude of the normal and Philadelphia (Ph') chromosome-positive(+) progenitor cells for various research and clinical settings/studies, we have applied the highly sensitive polymerase chain reaction (PCR) for examining the cells contained in individual hematopoietic colonies for chimeric bcr/abl mRNA, a specific molecular marker for chronic myelogenous leukemia (CML). Thus, individual 14-day CFU-GM colonies, obtained by growth of bone marrow cells from CML patients were removed from methylcellulose cultures and total RNA from each colony was isolated. First-strand complementary DNAs (cDNA) corresponding to all mRNAs in the sample were obtained by using random hexamers in a reverse transcription (RT) reaction. cDNA then served as the substrate in the PCR. To ensure the integrity of the RNA extracted from each colony, beta-actin and bcr/abl cDNA sequences were amplified in the same reaction vessel. Using this method, we have examined the colonies grown from three CML patients and found that 5 out of 5, 9 out of 9 and 8 out of 9 colonies contained a bcr/abl transcript. This method is simple, highly sensitive and should facilitate studies comparing the expression of various oncogenes in normal and leukemic hematopoietic progenitor cells.

Analysis of the individual and combined reactivities of monoclonal antibodies H25, H366, and MY9 with normal progenitor cells and blast cells from patients with acute myeloblastic leukemia

Recently we reported that two monoclonal antibodies (MoAbs), H25 and H366, which react with human natural killer cells and monocytes, also react with normal in vitro colony-forming cells including granulocyte-monocyte colony-forming units (CFU-GM), erythroid burst-forming units (BFU-E), and erythroid colony-forming units and with leukemic blasts in preliminary testing of cells from patients with myeloid leukemias and T cell acute lymphocytic leukemia. In the present studies we examined the reactivities of MoAbs H25, H366, and MY9 (singly or combined) with the total leukemic cell population and the leukemic clonogenic cells (L-CFC) from 28 patients with acute myeloblastic leukemia. Using cytofluorography, we found the extent of expression of antigen H25 comparable to MY9 in the majority of patients, and both were more highly expressed than antigen H366. Incubation with H25 and H366 MoAbs simultaneously did not increase the number of positive cells over that seen when stained with H25 alone; however, the amount of antibody fluorescence intensity (FI) was increased. Leukemic cells simultaneously stained with MoAbs H25, H366, and MY9 displayed the highest number of positive cells and FI. Using magnetic beads coated with sheep anti-mouse IgG for depleting antibody-binding cells, greater than or equal to 90% of L-CFC were depleted by a combination of H25 and H366 MoAbs in 76% of AML cases tested as compared to 41% of the cases with MoAb MY9. Using a MoAb cocktail of H25, H366, and MY9, greater than or equal to 90% of L-CFC were depleted in 94% of cases tested, and greater than or equal to 99% of L-CFC were removed in 76% of the cases. Using the same depletion methods for normal bone marrow cells, a combination of anti-H25 and anti-H366 removed 90%, 98%, and 84% of CFU-GM, BFU-E, and multipotent colony-forming units (CFU-GEM), respectively, whereas the cocktail of H25, H366, and MY9 MoAbs removed 98%, 99.5%, and 97% of CFU-GM, BFU-E, and CFU-GEM, respectively. Incubation of H25 and H366-depleted bone marrow cells for 2 weeks in the presence of irradiated adherent cell layers from long-term marrow cultures generated CFU-GM and some BFU-E, as did H25, H366, and MY9-depleted marrow cells, although to a much lesser extent. Based on the overall data, combinations of H25, H366, and MY9 MoAbs and immunomagnetic beads conceivably might have therapeutic potential for ex vivo elimination of leukemic cells from AML remission marrows prior to autologous transplantation.

Immunophenotypic demonstration of two natural killer surface markers, H25 and H366, on fresh human leukemic cells

Using a modified alkaline-phosphatase/antialkaline-phosphatase method for phenotyping fresh human leukemias, we could demonstrate peripheral blood and bone marrow-derived blast cells to specifically react with two monoclonal antibodies (MoAbs), H25 and H366, previously shown to recognize natural killer cells, activated T lymphocytes and a proportion of normal hematopoietic precursor cells. MoAbs H25 and H366 were found to identify the majority of leukemic cells in patients presenting with T-ALL, LGL leukemia, pre-B-ALL, CML, and AML, respectively.

Elimination of myeloma cells from bone marrow by using monoclonal antibodies and magnetic immunobeads

The efficacy of immunomagnetic beads to purge human myeloma cells from bone marrow ex vivo was evaluated. The optimal conditions for purging were studied first by using three myeloma cell lines: RPMI-8226, SKO-007, and SKMM-2. Myeloma cells labeled with the vital fluorescent dye Hoechst 33342 were admixed with normal bone marrow cells, and two monoclonal antibodies reactive with the myeloma cells (PCA-1 and BL-3) were added alone or in combination with the cells. Magnetic beads coated with goat antimouse immunoglobulin G were then added, and the tumor cells to which beads were attached were separated from the mixture with a magnet. The efficacy of tumor cell removal was dependent on the bead-to-tumor ratio; a ratio of more than 500 was optimal in the presence of excess normal marrow cells. The combination of monoclonal antibodies PCA-1 and BL-3 increased the tumor cell removal as compared with either antibody alone. Two cycles of treatment were more effective than one cycle was. Under optimal conditions, 2.3 to 4 logs of tumor cells could be removed from the mixture containing 10% myeloma cells without a significant loss of normal hematopoietic progenitors as measured by CFU-GM, CFU-GEM, and BFU-E. When the efficacy of this procedure was tested on fresh bone marrow from patients with multiple myeloma (MM) by using the combination of PCA-1, BL-3, and J-5, 1.6 to 2.5 logs of tumor cells could be removed by one cycle of treatment, even from marrows containing less than 10% myeloma cells. These observations support the use of monoclonal antibody combinations and immunobeads as a reliable and nontoxic method to eliminate contaminating myeloma cells ex vivo in preparation for autologous bone marrow transplantation in patients with MM.

Discordant maturation as the primary biological defect in chronic myelogenous leukemia

Comparative studies of the in vitro growth characteristics of normal and chronic myelogenous leukemic (CML) progenitor cells have provided further evidence that discordant maturation is the primary biological defect in CML. The in vitro growth of total normal and CML granulocyte/macrophage colony forming unit (CFU-GM) populations were compared with early and intermediate (HLA-DR positive) CFU-GM derived from the same marrows. The absolute number of total CML CFU-GM exceeded the number generated by normal marrow through 7 days of culture due entirely to an excess of CML CFU-GM with limited proliferative capacity. Unlike normal colonies, relatively few of the leukemic colonies grew to a large size; the early and intermediate (HLA-DR positive) CML progenitors also exhibited limited proliferative capacity compared to normal. Highly enriched progenitor populations were prepared, and it was observed that the primitive (small) CML CFU-GM also had greatly reduced proliferative potential compared to primitive normal progenitors, but rather behaved similarly to normal mature (large) CFU-GM. Similarly, CML erythroid burst forming units were at a more advanced stage of maturation than normal erythroid burst forming units as evidenced by their reduced proliferative capacity, the observation that a reduced proportion required burst promoting activity to enable them to respond to erythropoietin and the observation that a larger fraction than normal could sustain a limited period of erythropoietin deprivation in the absence of burst promoting activity. Based on these findings and supporting evidence from our previous studies and those reported by other investigators, it is concluded that the dominance of the leukemic population is not due to unregulated proliferation but rather to discordant maturation resulting in expansion in the later maturational compartments which are not under strict regulatory control.

Cell-mediated toxicity of interleukin-2-activated lymphocytes against autologous and allogeneic human myeloma cells

We studied the sensitivity of human myeloma (plasma cell leukemia) toward autologous and allogeneic lymphokine-activated killer (LAK) cells. Fresh plasma cell leukemia (PCL)-derived peripheral blood mononuclear cells (PBMC) and PBMC from 3 normal donors were cultured in the presence of recombinant interleukin-2 (rIL2; 1,000 U/ml) for subsequent use as cytotoxic effectors against fresh and continuously cultured myeloma cells. Target cell lysis was measured in a 4-hour 51Cr radioisotope release assay. At an effector to target (E:T) ratio of 50:1, rIL2-induced PCL-PBMC lysed 48 +/- 19% (mean +/- 1 SD) of autologous myeloma targets, as compared to 89 +/- 5, 95 +/- 15, and 100 +/- 9% lysis of standard LAK-sensitive Daudi cells and allogeneic myeloma cell lines SKO-007, and RPMI-8226, respectively. Normal PBMC-derived rIL2-induced (LAK) cells exhibited a slightly lower cytotoxic reactivity against allogeneic targets (61 +/- 9, 60 +/- 6, and 81 +/- 8% cytolysis of SKO-007, RPMI-8226, and Daudi cells, respectively, at a 50:1 E:T ratio). Cytotoxicity against myeloma (PCL) of autologous PCL-derived killer cells could be significantly (at least 2-fold) enhanced when rIL-2-induced effector cells were preincubated for 18 h in the presence of recombinant Interferon-alpha rIFN-alpha; 1,000 U/ml). In summary, our results indicate the potential antitumor efficacy of rIL2- and rIL2 + rIFN-alpha-activated killer cells in human myeloma (PCL).

Effects of recombinant human tumor necrosis factor on highly enriched hematopoietic progenitor cell populations from normal human bone marrow and peripheral blood and bone marrow from patients with chronic myeloid leukemia

Previous studies using unseparated normal human bone marrow cells have indicated that recombinant tumor necrosis factor alpha (rTNF-alpha) can inhibit the in vitro colony growth by normal granulocyte/macrophage (CFU-GM) and erythroid (BFU-E) progenitor cells in a dose-dependent manner. In the present studies, by using very low numbers of highly enriched normal bone marrow progenitor cell populations as target cells, we have extended these previous findings to provide convincing evidence that erythroid and myeloid colony growth suppression by rTNF-alpha is manifested by a direct interaction between rTNF-alpha and CFU-GM and BFU-E progenitor cells. In addition, the sensitivity of normal peripheral blood and chronic myeloid leukemia bone marrow CFU-GM and BFU-E colony growth to inhibition by rTNF-alpha was examined and found to be comparable with that of normal bone marrow CFU-GM and BFU-E. Although the continuous presence of high doses of rTNF-alpha (5000 units/ml) was required in methylcellulose cultures for maximal CFU-GM (90%) and BFU-E (70%) colony suppression, short-term exposure (24 to 72 hr) of normal bone marrow-enriched progenitor cells to rTNF-alpha, in the absence of hematopoietic growth factors, was sufficient to irreversibly suppress up to 50 to 65% of CFU-GM colony growth. In contrast, the number of BFU-E colonies was increased under these conditions. If, however, hematopoietic growth factors (Mo-T-cell-conditioned medium and erythropoietin) were present during preincubation of the cells with rTNF-alpha, BFU-E were then slightly suppressed while the extent of CFU-GM inhibition remained essentially the same. The suppressive effect of rTNF-alpha on erythroid and myeloid progenitor cell growth appears to be most pronounced on the more primative stages of committed progenitor cell development, since inhibition of CFU-GM- and BFU-E-derived colony growth progressively decreased with the delayed addition of rTNF-alpha to methylcellulose cultures. [3H]Thymidine incorporation was also inhibited by rTNF-alpha in normal bone marrow-enriched progenitor cell populations stimulated to proliferate in liquid culture by colony-stimulating factors. This effect was transient, however, since the activity of rTNF-alpha declined after the first 24 h of culture at 37 degrees C, particularly at low doses of rTNF-alpha where the activity was completely lost after 48 h of culture. This loss of activity appeared to be due to a decreased sensitivity of progenitor cells to the antiproliferative effects of tumor necrosis factor (TNF) after an initial exposure rather than a lack of available TNF.(ABSTRACT TRUNCATED AT 400 WORDS)

Activities of four purified growth factors on highly enriched human hematopoietic progenitor cells

The activities of four purified human growth factors: biosynthetic (recombinant) granulocyte-macrophage colony-stimulating factor (GM-CSF); recombinant erythroid-potentiating activity (EPA); natural and recombinant pluripoietin (Ppo); and natural pluripoietin alpha (Ppo alpha), were compared on the growth of hematopoietic colonies from enriched populations of human marrow and blood progenitor cells. Conditioned medium from the Mo T cell line (MoCM) was used as a standard positive control. We found that activities of GM-CSF and Ppo alpha on the growth of hematopoietic colonies were indistinguishable; Ppo alpha is now believed to be identical to GM-CSF. Both factors were able to promote the growth of colonies derived from subpopulations of CFU-GM, BFU-E, and CFU-GEM. Colonies derived from CFU-GM and CFU-GEM in cultures stimulated by GM-CSF and Ppo alpha were much smaller than in cultures stimulated by MoCM. In contrast to previous reports in which less highly enriched progenitors were used as target cells, Ppo had no detectable activity on the growth of colonies derived from BFU-E or CFU-GEM but promoted the growth of a subpopulation of CFU-GM derived colonies. Ppo is now recognized to be identical to G-CSF. The GM colonies in cultures stimulated by G-CSF (Ppo) were much smaller than in cultures stimulated by MoCM. EPA had no detectable activity on either the size or number of colonies derived from CFU-GM, BFU-E, or CFU-GEM. Results from experiments using target cell populations of marrow fractions separated by velocity sedimentation and marrow populations following freezing suggested that GM-CSF (Ppo alpha) and G-CSF (Ppo) primarily affect the growth of relatively mature subpopulations of progenitor cells. It is clear from these results that additional factor(s) are present in MoCM that are necessary to stimulate CFU-GM, BFU-E, and CFU-GEM maximally in vitro.

Expression of two natural killer cell antigens, H-25 and H-366, by human immature myeloid cells and by erythroid and granulocytic/monocytic colony-forming units

Two monoclonal antibodies (MoAbs), H-25 and H-366, shown previously to react with human peripheral blood large granular lymphocytes with natural killer (NK) cell activity and some peripheral blood monocytes, have now been shown to also react with a significant proportion of the myeloid and erythroid precursor cells in human bone marrow and peripheral blood. In FACS IV cell sorting and immune rosetting of bone marrow cells, the antigens recognized by H-25 and H-366 were found to be expressed on most blasts and promyelocytes but sequentially fewer of the more mature cells of the myeloid lineage. Both antigens were also found on most monocytes but only a minor proportion of lymphoid and nucleated red cells in the bone marrow. In vitro assays detecting hematopoietic colony-forming units revealed that these antigens are expressed by virtually all mature erythroid colony-forming units (day-7 CFU-E), and the majority of the more primitive erythroid burst forming units (day-14 BFU-E). H-25 but not H-366 was also found on a variable proportion of the day-7 and day-14 granulocytic/monocytic colony-forming units (CFU-GM) in the bone marrow. The same type of precursor cells are also found in the H-25 and H-366 positive cell populations isolated from peripheral blood. In preliminary testing of cells from acute leukemic patients, FACS analysis showed that both antigens are also expressed on leukemic cells from patients with T cell acute lymphocytic leukemia and with myeloid leukemias. These studies demonstrate that the H-25 and H-366 positive NK cells in the peripheral blood retain some of the cell surface properties of early hematopoietic precursor cells, thus providing further evidence supporting the bone marrow origin of NK cells.