Hematopoietic prostaglandin D synthase suppresses intestinal adenomas in ApcMin/+ mice

Aspirin and other nonsteroidal anti-inflammatory drugs prevent some cases of colon cancer by inhibiting prostaglandin (PG) synthesis. PGE(2) promotes colon neoplasia, as shown by knockout mouse studies on enzymes and receptors in the PG cascade. A few experiments 20 to 30 years ago suggested that PGD(2) may suppress tumors, but a role for biosynthetic enzymes for PGD(2) in tumor development has not been studied. We report here that disruption of the gene for hematopoietic PGD synthase in Apc(Min/+) mice led to approximately 50% more intestinal adenomas compared with controls. Tumor size was not affected. By immunohistochemistry, we detected hematopoietic PGD synthase mainly in macrophages and monocytes of the gut mucosa. The mean number of tumors did not increase with knockout of the gene for the lipocalin type of the enzyme, which is not produced in the intestine. On the other hand, Apc(Min/+) mice with transgenic human hematopoietic PGD synthase tended to have 80% fewer intestinal adenomas. The transgene produced high mRNA levels (375-fold over endogenous). There was a suggestion of higher urinary excretion of 11beta-PGF(2alpha) and a lower excretion of a PGE(2) metabolite in transgenic mice, but differences (30-40%) were not statistically significant. The results support an interpretation that hematopoietic PGD synthase controls an inhibitory effect on intestinal tumors. Further studies will be needed to prove possible mechanisms, such as routing of PG production away from protumorigenic PGE(2) or inhibition of the nuclear factor-kappaB cascade by PGD(2) metabolites.

c-Kit--a hematopoietic cell essential receptor tyrosine kinase

The receptor tyrosine kinase c-Kit is expressed in hematopoietic stem and progenitor cells and in several non-hematopoietic tissues. In the hematopoietic system, c-Kit is critical for proliferation, survival and differentiation. During recent years exploration of the signalling pathways downstream of this receptor has yielded significant new insights in the field. In this review, we will summarise the c-Kit background, structure, downstream signalling and medical significance with particular focus on its role in hematopoietic progenitor cells and mast cells.

Structural and Functional Characterization of HQL-79, an Orally Selective Inhibitor of Human Hematopoietic Prostaglandin D Synthase

We determined the crystal structure of human hematopoietic prostaglandin (PG) D synthase (H-PGDS) as the quaternary complex with glutathione (GSH), Mg2+, and an inhibitor, HQL-79, having anti-inflammatory activities in vivo, at a 1.45-A resolution. In the quaternary complex, HQL-79 was found to reside within the catalytic cleft between Trp104 and GSH. HQL-79 was stabilized by interaction of a phenyl ring of its diphenyl group with Trp104 and by its piperidine group with GSH and Arg14 through water molecules, which form a network with hydrogen bonding and salt bridges linked to Mg2+. HQL-79 inhibited human H-PGDS competitively against the substrate PGH2 and non-competitively against GSH with Ki of 5 and 3 microm, respectively. Surface plasmon resonance analysis revealed that HQL-79 bound to H-PGDS with an affinity that was 12-fold higher in the presence of GSH and Mg2+ (Kd, 0.8 microm) than in their absence. Mutational studies revealed that Arg14 was important for the Mg2+-mediated increase in the binding affinity of H-PGDS for HQL-79, and that Trp104, Lys112, and Lys198 were important for maintaining the HQL-binding pocket. HQL-79 selectively inhibited PGD2 production by H-PGDS-expressing human megakaryocytes and rat mastocytoma cells with an IC50 value of about 100 microm but only marginally affected the production of other prostanoids, suggesting the tight functional engagement between H-PGDS and cyclooxygenase. Orally administered HQL-79 (30 mg/kg body weight) inhibited antigen-induced production of PGD2, without affecting the production of PGE2 and PGF2alpha, and ameliorated airway inflammation in wild-type and human H-PGDS-overexpressing mice. Knowledge about this structure of quaternary complex is useful for understanding the inhibitory mechanism of HQL-79 and should accelerate the structure-based development of novel anti-inflammatory drugs that inhibit PGD2 production specifically.

Rho GTPases in hematopoietic cells

The ubiquitous Rho GTPases are instrumental in the organization of the actin cytoskeleton, but also for the control of gene expression. Here we review the role of the major members of this family, i.e., RhoA, Rac1, Rac2, and Cdc42, and their intracellular signaling in hematopoietic cells. Although these proteins have been classically implicated in chemotaxis, there are now clear indications on how differential signaling toward other, more specific functions, such as phagocytosis or the production of reactive oxygen species, is regulated by relatively small differences in primary sequence. The identification of mutations in these GTPases or their regulators has provided novel insights in their function as well as their relevance for the development of hematological diseases.

Molecular Determinants of Substrate Recognition in Hematopoietic Protein-tyrosine Phosphatase

The extracellular signal-regulated protein kinase 2 (ERK2) plays a central role in cellular proliferation and differentiation. Full activation of ERK2 requires dual phosphorylation of Thr183 and Tyr185 in the activation loop. Tyr185 dephosphorylation by the hematopoietic protein-tyrosine phosphatase (HePTP) represents an important mechanism for down-regulating ERK2 activity. The bisphosphorylated ERK2 is a highly efficient substrate for HePTP with a kcat/Km of 2.6 x 10(6) m(-1) s(-1). In contrast, the kcat/Km values for the HePTP-catalyzed hydrolysis of Tyr(P) peptides are 3 orders of magnitude lower. To gain insight into the molecular basis for HePTP substrate specificity, we analyzed the effects of altering structural features unique to HePTP on the HePTP-catalyzed hydrolysis of p-nitrophenyl phosphate, Tyr(P) peptides, and its physiological substrate ERK2. Our results suggest that substrate specificity is conferred upon HePTP by both negative and positive selections. To avoid nonspecific tyrosine dephosphorylation, HePTP employs Thr106 in the substrate recognition loop as a key negative determinant to restrain its protein-tyrosine phosphatase activity. The extremely high efficiency and fidelity of ERK2 dephosphorylation by HePTP is achieved by a bipartite protein-protein interaction mechanism, in which docking interactions between the kinase interaction motif in HePTP and the common docking site in ERK2 promote the HePTP-catalyzed ERK2 dephosphorylation (approximately 20-fold increase in kcat/Km) by increasing the local substrate concentration, and second site interactions between the HePTP catalytic site and the ERK2 substrate-binding region enhance catalysis (approximately 20-fold increase in kcat/Km) by organizing the catalytic residues with respect to Tyr(P)185 for optimal phosphoryl transfer.

First Determination of the Inhibitor Complex Structure of Human Hematopoietic Prostaglandin D Synthase

Hematopoietic prostaglandin (PG) D synthase (H-PGDS) is responsible for the production of PGD(2) as an allergy or inflammation mediator in mast and Th2 cells. We determined the X-ray structure of human H-PGDS complexed with an inhibitor, 2-(2'-benzothiazolyl)-5-styryl-3-(4'-phthalhydrazidyl) tetrazolium chloride (BSPT) at 1.9 A resolution in the presence of Mg(2+). The styryl group of the inhibitor penetrated to the bottom of the active site cleft, and the tetrazole ring was stabilized by the stacking interaction with Trp104, inducing large movement around the alpha5-helix, which caused the space group of the complex crystal to change from P2(1) to P1 upon binding of BSPT. The phthalhydrazidyl group of BSPT exhibited steric hindrance due to the cofactor, glutathione (GSH), increasing the IC(50) value of BSPT for human H-PGDS from 36.2 micro M to 98.1 micro M upon binding of Mg(2+), because the K(m) value of GSH for human H-PGDS was decreased from 0.60 micro M in the presence of EDTA to 0.14 micro M in the presence of Mg(2+). We have to avoid steric hindrance of the GSH molecule that was stabilized by intracellular Mg(2+) in the mM range in the cytosol for further development of structure-based anti-allergic drugs.

Hematopoietic prostaglandin D synthase

The biological actions of prostaglandin (PG) D(2) include vasodilatation, bronchoconstriction, inhibition of platelet aggregation, and recruitment of inflammatory cells. Characterization of DP receptor null mice in which antigen-induced airway and inflammatory responses are attenuated and identification of CRTH2 as a novel PGD(2) receptor have shed light on the role of PGD(2) in the immune and inflammatory responses. Hematopoietic PGD synthase (H-PGDS) is a cytosolic enzyme that isomerizes PGH(2), a common precursor for all PGs and thromboxanes, to PGD(2) in a glutathione-dependent manner. H-PGDS is expressed in mast cells, antigen-presenting cells, and Th2 cells, and is the only mammalian member of the Sigma class of cytosolic glutathione S-transferases. In this review, we focus on the molecular biology of H-PGDS, the determination of its three-dimensional structure, characterization of the regulation of its gene expression, and information gleaned from transgenic animals.

Dipeptidyl peptidase IV (CD26) activity in the hematopoietic system: differences between the membrane-anchored and the released enzyme activity

Dipeptidyl peptidase IV (DPP-IV; CD26) (EC 3.4.14.5) is a membrane-anchored ectoenzyme with N-terminal exopeptidase activity that preferentially cleaves X-Pro-dipeptides. It can also be spontaneously released to act in the extracellular environment or associated with the extracellular matrix. Many hematopoietic cytokines and chemokines contain DPP-IV-susceptible N-terminal sequences. We monitored DPP-IV expression and activity in murine bone marrow and liver stroma cells which sustain hematopoiesis, myeloid precursors, skin fibroblasts, and myoblasts. RT-PCR analysis showed that all these cells produced mRNA for DPP-IV. Partially purified protein reacted with a commercial antibody to CD26. The K M values for Gly-Pro-p-nitroanilide ranged from 0.43 to 0.98 mM for the membrane-associated enzyme of connective tissue stromas, and from 6.76 to 8.86 mM for the enzyme released from the membrane, corresponding to a ten-fold difference, but only a two-fold difference in K M was found in myoblasts. K M of the released soluble enzyme decreased in the presence of glycosaminoglycans, nonsulfated polysaccharide polymers (0.8-10 micro g/ml) or simple sugars (320-350 micro g/ml). Purified membrane lipid rafts contained nearly 3/4 of the total cell enzyme activity, whose K M was three-fold decreased as compared to the total cell membrane pool, indicating that, in the hematopoietic environment, DPP-IV activity is essentially located in the lipid rafts. This is compatible with membrane-associated events and direct cell-cell interactions, whilst the long-range activity depending upon soluble enzyme is less probable in view of the low affinity of this form.

Evaluating function of transmembrane protein tyrosine phosphatase CD148 in lymphocyte biology

The transmembrane protein tyrosine phosphatase CD148 is expressed on numerous cell types, including most cells of the hematopoietic lineage. CD148 has been shown to regulate density-dependent inhibition of cell growth as well as cellular differentiation in nonhematopoietic cells and has been shown to regulate signal transduction processes in several nonlymphoid hematopoietic cell types. Analysis of CD148 expression on lymphoid cells has demonstrated that CD148 is expressed at low levels on T cells and that it is upregulated in response to activation. Several groups have observed that CD148 negatively regulates T cell activation in response to crosslinking of the T cell antigen receptor, suggesting that it may play a role in feedback inhibition of the T cell immune response. In the B cell compartment, CD 148 expression appears to be restricted to the memory subpopulation, raising the possibility that it serves a unique function in these cells, which has yet to be determined. Recent studies have shown that CD148 interacts with the PDZ domain-containing protein syntenin, raising the possibility that its function or its localization with substrates in T and B cells may be controlled through this or a related interaction with another PDZ domain protein.

Mechanism of metal activation of human hematopoietic prostaglandin D synthase

Here we report the crystal structures of human hematopoietic prostaglandin (PG) D synthase bound to glutathione (GSH) and Ca2+ or Mg2+. Using GSH as a cofactor, prostaglandin D synthase catalyzes the isomerization of PGH2 to PGD2, a mediator for allergy response. The enzyme is a homodimer, and Ca2+ or Mg2+ increases its activity to approximately 150% of the basal level, with half maximum effective concentrations of 400 microM for Ca2+ and 50 microM for Mg2+. In the Mg2+-bound form, the ion is octahedrally coordinated by six water molecules at the dimer interface. The water molecules are surrounded by pairs of Asp93, Asp96 and Asp97 from each subunit. Ca(2+) is coordinated by five water molecules and an Asp96 from one subunit. The Asp96 residue in the Ca2+-bound form makes hydrogen bonds with two guanidium nitrogen atoms of Arg14 in the GSH-binding pocket. Mg2+ alters the coordinating water structure and reduces one hydrogen bond between Asp96 and Arg14, thereby changing the interaction between Arg14 and GSH. This effect explains a four-fold reduction in the K(m) of the enzyme for GSH. The structure provides insights into how Ca2+ or Mg2+ binding activates human hematopoietic PGD synthase.

[Gene therapy of Gaucher's and Fabry's diseases: current status and prospects]

Gaucher disease and Fabry disease are lysosomal storage disorders characterized by the accumulation of sphingolipids. In both cases, the goal of gene therapy is to permanently provide tissues with enzyme levels allowing to avoid storage of the undigested substrates. Different gene therapy strategies must however be designed as Gaucher disease is due to a deficiency in the membrane-associated enzyme glucocerebrosidase, whereas Fabry disease is caused by a deficiency in the soluble enzyme alpha-galactosidase. Indeed, a soluble enzyme can be provided to tissues is trans by gene-modified cells whereas gene transfer has to target the most affected cells in the case of membrane-bound enzymes. Thus, in non-neurological Gaucher disease (type 1), the hematopoietic tissue has to be targeted as the deficiency affects the monocyte/macrophage lineage. Following promising preclinical studies, clinical protocols have been initiated to explore the feasibility and safety of retroviral transfer of the glucocerebrosidase gene into CD34+ cells from patients with type 1 Gaucher disease. Although gene-marked cells were detected in vivo, the level of corrected cells was very low, a finding indicating that improved vectors along with partial myeloablation may be necessary. Here, lentiviral vectors should enable more gene transduction into the hematopoietic target cells. As concerns the diffuse neurological lesions in types 2 and 3 of Gaucher disease, they will probably be especially difficult to target by gene therapy because of the non soluble nature of glucocerebrosidase. Finally, over the last few years, Fabry disease has become a compelling target for gene therapy as an etiology-based treatment strategy. Indeed, several recent studies aiming at creating a large in vivo source of alpha-galactosidase have yielded positive long-term results in the Fabry knock-out mouse model.

Subcellular localization of intracellular protein tyrosine phosphatases in T cells

A high protein tyrosine phosphatase (PTPase) activity is required to maintain circulating T lymphocytes in a resting phenotype, and to limit the initiation of T cell activation. We report that 15 of the currently known 24 intracellular PTPases are expressed in T cells, namely HePTP, TCPTP, SHP1, SHP2, PEP, PTP-PEST, PTP-MEG2, PTEN, PTPH1, PTP-MEG1, PTP36, PTP-BAS, LMPTP, PRL-1 and OV-1. Most were found in the cytosol and many were enriched at the plasma membrane. Only TCPTP and PTP-MEG2 had subcellular localizations that essentially excludes them from a direct role in early T cell antigen receptor signaling events. Overexpression of 6 of the PTPases reduced IL-2 gene activation, 3 of them thereby identified as novel candidates for negative regulators of TCR signaling. Our findings expand the repertoire of PTPases that should be considered for a regulatory role in T cell activation.

Structure and chromosomal localization of human and mouse genes for hematopoietic prostaglandin D synthase. Conservation of the ancestral genomic structure of sigma-class glutathione S-transferase

Hematopoietic prostaglandin D synthase (H-PGDS) is the key enzyme for the production of the D and J series of prostanoids, and the first recognized vertebrate homolog of sigma-class glutathione S-transferase (GST). We isolated the genes and cDNAs for human and mouse H-PGDSs. The human and mouse cDNAs contained a coding region corresponding to 199 amino-acid residues with calculated molecular masses of 23 343 and 23 226, respectively. Both H-PGDS proteins recombinantly expressed in Escherichia coli showed bifunctional activities for PGDS and GST, and had almost the same catalytic properties as the rat enzyme. Northern analyses demonstrated that the H-PGDS genes were expressed in a highly species-specific manner. Whereas the human gene was widely distributed, in contrast, the mouse gene was detected only in samples from oviduct and skin. By fluorescence in situ hybridization, the chromosomal localization of the human and mouse H-PGDS genes were mapped to 4q21-22 and 3D-E, respectively. The human and mouse H-PGDS genes spanned approximately 41 and 28 kb, respectively, and consisted of six exons divided by five introns. The exon/intron boundaries of both genes were completely identical to those of the sigma-class GST subfamily, although the amino-acid sequences of the latter were only 17.0-21.5% identical to those of either H-PGDS. These findings suggest that the H-PGDS genes evolved from the same ancestral gene as the members of the sigma-class GST family.

Tissue specific expression of Yrk kinase: implications for differentiation and inflammation

The Src family of proto-oncogenes is a highly conserved group of non-receptor tyrosine kinases with very similar, but not identical, tissue distributions and functions. Yrk is a recently discovered new member of this family. Here we report the patterns of expression of this kinase in a variety of chicken tissues during development and after hatching, and experiments that correlate some of the observed patterns of expression with potential functions. The results show that the Yrk protein is primarily found in neuronal and epithelial cells and in monocyte/macrophages. In neuronal tissues of hatched chicks, Yrk is expressed in Purkinje cells, in the gigantocellularis of the brain-stem, and in retinal ganglion cells. In addition, staining for this kinase is also seen as thread-like and punctate patterns suggesting staining in neurites and growth cones. Epithelial cells express Yrk in the stomach during late developmental stages and after hatching but, in other epithelia such as in the peridermis, intestine and kidney, expression is high during development but low (skin) or undetectable (intestine and kidney) after hatching. These results suggest that Yrk may have several functional roles, specifically in cell migration and or differentiation during neuronal and epithelial cell development and in maintenance of the differentiated phenotype. In this study we also show that significant levels of Yrk are detected in monocytes of the blood and in tissue macrophages. Analysis of chicken hematopoietic cell lines confirmed the expression of Yrk in cells of monocyte/macrophage lineage and show for the first time in experimentally-induced inflammation that Yrk kinase activity is high during the period of monocyte infiltration, raising the possibility that this kinase plays a role in inflammation and/or response to injury.

Differential cytochemical staining characteristics of channel catfish leukocytes identify cell populations in lymphoid organs

This is one of the first characterizations of channel catfish (Ictalurus punctatus) leukocytes by enzyme cytochemistry. Leukocytes demonstrated cytoplasmic staining patterns very similar to mammalian leukocytes when stained with acid phosphatase, alpha-naphthyl butyrate esterase, beta-glucuronidase, alpha-naphthyl acetate esterase, Sudan Black B and anti-immunoglobulin specific immunohistochemistry. Lymphocytes, monocytes, macrophages, neutrophils, and surface immunoglobulin positive (surface Ig+) cells were present in channel catfish renal hematopoietic tissue and spleen and demonstrated distinctive cytoplasmic foci staining patterns, cytoplasmic blushing or cell membrane staining. Monocytes, macrophages, lymphocytes and surface Ig+ cells were present in the thymus. Thymic and splenic cellular organization appeared very similar to these same mammalian tissues. In the thymus, acid phosphatase positive cells were distributed throughout the parenchyma, while alpha-naphthyl butyrate esterase and beta-glucuronidase positive cells were concentrated in the cortex and the medulla, respectively. Surface immunoglobulin positive cells occurred in the cortex. In the spleen, acid phosphatase positive cells were scattered throughout the parenchyma, while alpha-naphthyl butyrate esterase positive cells were scattered throughout the parenchyma and adjacent to splenic arterioles. Beta-glucuronidase and surface immunoglobulin positive cells were restricted to immediately adjacent to splenic arterioles. Sudan Black B positive cells were scattered throughout the parenchyma, while alpha-naphthyl acetate esterase positive cells occurred adjacent to peri-arteriole lymphoid sheaths and appear very similar to mammalian metallophils.

Cellular source(s) of platelet-activating-factor acetylhydrolase activity in plasma

Platelet activating factor (PAF) is immediately degraded and inactivated in the bloodstream by plasma PAF acetylhydrolase (PAF-AH). Although plasma PAF-AH-like activity was secreted in vitro from various cell types such as macrophages and hepatocytes, the exact cellular source(s) of this enzyme activity in vivo remains unclear. There is a naturally-occurring missense mutation (V279F) in the plasma PAF-AH gene in the Japanese population which results in complete loss of the enzyme activity. We analyzed 52 Japanese who had received an allogeneic bone marrow transplant and maintained donor-derived hematopoiesis. Ten recipients had chimeric plasma PAF-AH genotypes between the donor-derived peripheral blood leukocytes and the recipient-derived epithelial cells of buccal mucosa. Multiple regression analysis demonstrated that PAF-AH activity in plasma depended on the donor's genotype (standardized regression coefficient = 0.68, P < 0.0001), but not on the recipient's genotype (p = 0.48). One recipient who was a V279F homozygote in leukocytes and wild type homozygote in buccal mucosa had undetectable PAF-AH activity in plasma. We conclude that most of the PAF-AH activity in human plasma originates from hematopoietic lineage cells.

Heart-specific activation of LTK results in cardiac hypertrophy, cardiomyocyte degeneration and gene reprogramming in transgenic mice

Leukocyte tyrosine kinase (LTK) is a receptor-type protein tyrosine kinase belonging to the insulin receptor superfamily. To elucidate its biological role, we generated transgenic mice expressing LTK under the control of cytomegarovirus enhancer and beta-actin promoter. The transgenic mice exhibited growth retardation and most of the transgenic mice died within several months after birth. Interestingly, although LTK was expressed in several major organs, the activation (tyrosine-phosphorylation, kinase activity, and multimerization) of LTK was observed selectively in the heart, where LTK was localized on intracellular membrane, presumably on endoplasmic reticulum. Echocardiography showed that the transgenic heart underwent severe concentric hypertrophy, which resulted in reduced cardiac output, low blood pressure, and increased heart rate. Histological examination of the heart exhibited focal degeneration of cardiomyocytes. These histological changes were considered to be due to apoptosis, based on the finding that the sarcolemmas of the degenerative cardiomyocytes were well preserved. In addition, expression of fetal genes, such as atrial natriuretic peptide and skeletal alpha-actin, was markedly induced in the transgenic heart. These results indicate that a certain tissue-specific mechanism of activating LTK exists in the heart and that the activated LTK resulted in cardiac hypertrophy, cardiomyocyte degeneration and gene reprogramming. These findings will provide novel insights into the activating mechanism and biological role of LTK in vivo.

Production and characterization of an antibody specific for a novel protein serine/threonine kinase, MPK38, highly expressed in hematopoietic cells

We report an antibody that selectively recognizes MPK38, a new protein serine/threonine kinase closely related to the SNF1 serine/threonine kinase family. This antibody recognized a region of the N-terminal kinase catalytic domain and part of the remaining C-terminal portion and was sensitive enough to detect a 72-kDa recombinant MPK38 in insect cells by Western blotting. Immunoblot analysis showed that the recombinant MPK38 was expressed in a time-dependent manner and reached a maximum after 48 h postinfection. In addition, the immune complex kinase assay revealed that the recombinant and endogenous MPK38 protein autophosphorylated in vitro. Phosphoamino acid analysis of autophosphorylated MPK38 protein showed that the phosphorylation was exclusively on serine and threonine residues, suggesting that MPK38 is a protein serine/threonine kinase. Thus, this antibody could be helpful for elucidating the biological functions of MPK38 in the MPK38-expressing cells.

Prostaglandin D2 and sleep regulation

Prostaglandin (PG) D2 is recognized as the most potent endogenous sleep-promoting substance whose action mechanism is the best characterized among the various sleep-substances thus far reported. The PGD2 concentration in rat cerebrospinal fluid (CSF) shows a circadian change coupled to the sleep-wake cycle and elevates with an increase in sleep propensity during sleep deprivation. Lipocalin-type PGD synthase is dominantly produced in the arachnoid membrane and choroid plexus of the brain, and is secreted into the CSF to become beta-trace, a major protein component of the CSF. The PGD synthase as well as the PGD2 thus produced circulates in the ventricular system, subarachnoidal space, and extracellular space in the brain system. PGD2 then interacts with DP receptors in the chemosensory region of the ventro-medial surface of the rostral basal forebrain to initiate the signal to promote sleep probably via the activation of adenosine A2A receptive neurons. The activation of DP receptors in the PGD2-sensitive chemosensory region results in activation of a cluster of neurons within the ventrolateral preoptic area, which may promote sleep by inhibiting tuberomammillary nucleus, the source of the ascending histaminergic arousal system.

Sharing of receptor subunits and signal transduction pathway between the IL-4 and IL-13 receptor system

In this review, we summarize the subunit structure of the interleukin (IL)-4 and IL-13 receptor system and the molecular mechanism of signals through the cytokine receptor systems. We have demonstrated that two different forms of IL-4R exist, classical and alternative. Classical IL-4R is predominantly expressed in hematopoietic cells and consists of IL-4R p140 (beta) and IL-2R gamma (gamma c) chains. The alternative form of IL-4R is predominantly expressed in nonhematopoietic cells and consists of IL-4R beta and IL-13R alpha' chains. Moreover, the alternative form of IL-4R is also used as a functional component in the IL-13R complex. For signal transduction through IL-4R and IL-13R, we have demonstrated that in nonhematopoietic cells, Janus protein tyrosine kinase (JAK) 2 is phosphorylated and activated instead of JAK3 tyrosine kinase. While JAK3 is required for signal transducer and activator of transcription-6 (STAT6) activation in hematopoietic cells, we recently demonstrated that in nonhematopoietic cells JAK2 is required for STAT6 activation for the alternative form of IL-4R. Thus, a major difference exists between hematopoietic and nonhematopoietic cells with regard to structure and signal transduction through the IL-4R and IL-13R systems.

ALK expression defines a distinct group of T/null lymphomas ("ALK lymphomas") with a wide morphological spectrum

The t(2;5)(p23;q35) translocation associated with CD30-positive anaplastic large cell lymphoma results in the production of a NPM-ALK chimeric protein, consisting of the N-terminal portion of the NPM protein joined to the entire cytoplasmic domain of the neural receptor tyrosine kinase ALK. The ALK gene products were identified in paraffm sections by using a new anti-ALK (cytoplasmic portion) monoclonal antibody (ALKc) that tends to react more strongly than a previously described ALK1 antibody with the nuclei of ALK-expressing tumor cells after microwave heating in 1 mmol/L ethylenediaminetetraacetic acid buffer, pH 8.0. The ALKc monoclonal antibody reacted selectively with 60% of anaplastic large cell lymphoma cases (60 of 100), which occurred mainly in the first three decades of life and consistently displayed a T/null phenotype. This group of ALK-positive tumors showed a wide morphological spectrum including cases with features of anaplastic large cell lymphoma "common" type (75%), "lymphohistiocytic" (10%), "small cell" (8.3%), "giant cell" (3.3%), and "Hodgkin's like" (3.3%). CD30-positive large anaplastic cells expressing the ALK protein both in the cytoplasm and nucleus represented the dominant tumor population in the common, Hodgkin's-like and giant cell types, but they were present at a smaller percentage (often with a perivascular distribution) also in cases with lymphohistiocytic and small cell features. In this study, the ALKc antibody also allowed us to identify small neoplastic cells (usually CD30 negative) with nucleus-restricted ALK positivity that were, by definition, more evident in the small cell variant but were also found in cases with lymphohistiocytic, common, and "Hodgkin's-like" features. These findings, which have not been previously emphasized, strongly suggest that the neoplastic lesion (the NPM-ALK gene) must be present both in the large anaplastic and small tumor cells, and that ALK-positive lymphomas lie on a spectrum, their position being defined by the ratio of small to large neoplastic cells. Notably, about 15% of all ALK-positive lymphomas (usually of the common or giant cell variant) showed a cytoplasm-restricted ALK positivity, which suggests that the ALK gene may have fused with a partner(s) other than NPM. From a diagnostic point of view, detection of the ALK protein was useful in distinguishing anaplastic large cell lymphoma cases of lymphohistiocytic and small cell variants from reactive conditions and other peripheral T-cell lymphoma subtypes, as well as for detecting a small number of tumor cells in lymphohemopoietic tissues. In conclusion, ALK positivity appears to define a clinicopathological entity with a T/null phenotype ("ALK lymphomas"), but one that shows a wider spectrum of morphological patterns than has been appreciated in the past.

Expression of the RNA component of telomerase during human development and differentiation

We used a radioactive in situ method to study expression of the RNA component of human telomerase (hTR) during normal human development and differentiation using archival tissues. In embryonic tissues, the highest and most uniform expression was present in undifferentiated neuroepithelium. Expression was stronger in immature epithelium than in accompanying immature mesenchyme. Differentiation of most tissues was accompanied by decreased or absent expression. Except for testis and adrenal, the adult pattern of expression was present by the 10th postnatal week. In adult tissues, high expression was present in the testis (primary spermatocytes and Sertoli cells), moderate expression was present in lymphoid follicles (germinal centers), and weak expression was present in epithelia (regenerative cells) but was absent in the nervous system and mesenchymal derived tissues. Expression in adult tissues was predominantly limited to dividing cells, although certain differentiated postmitotic cells expressed the hTR. Our studies demonstrate the complex interrelationship of hTR expression with human development, differentiation, and cell division.

ErbB-4 ribozymes abolish neuregulin-induced mitogenesis

The epidermal growth factor-like receptor tyrosine kinase (ErbB) family is frequently overexpressed in a variety of human carcinomas, including breast cancer. To assist in characterizing the role of ErbB-4 in breast cancer, we generated three specific hammerhead ribozymes targeted to the ErbB-4 mRNA. These ribozymes, Rz6, Rz21, and Rz29, efficiently catalyzed the specific cleavage of ErbB-4 message in a cell-free system. We demonstrated that the neuregulin-induced mitogenic effect was abolished in ribozyme Rz29- and Rz6-transfected 32D/ErbB-4 cells. Inhibition of mitogenesis was characterized by ribozyme-mediated down-regulation of ErbB-4 expression. In addition, we provide the first evidence that different threshold levels of ErbB-4 expression and activation correlate with different responses to neuregulin stimulation. High levels of ErbB-4 expression, phosphorylation, and homodimerization are necessary for neuregulin-stimulated, interleukin 3-independent cell proliferation in the 32D/E4 cells. In the case of Rz29-transfected 32D/E4 cells, low levels of ErbB-4 expression allowed neuregulin-induced phosphorylation but were insufficient to couple the activated receptor to cellular signaling. Furthermore, expression of the functional ErbB-4 ribozyme in T47D human breast carcinoma cells led to a down-regulation of endogenous ErbB-4 expression and a reduction of anchorage-independent colony formation. These studies support the use of ErbB-4 ribozymes to define the role of ErbB-4 receptors in human cancers.

Hematopoietic tissues, as a playground of receptor tyrosine kinases of the PDGF-receptor family

Three receptor tyrosine kinases of the PDGF receptor family (RTKP) that clustered within 1000 Kb of the mouse chromosome 5 constitute an interesting unit that are expressed in three distinct cell lineages essential for constructing hematopoietic tissues. Namely, the c-kit gene that is expressed in hematopoietic stem cells is flanked by pdgfr alpha and flk genes expressed respectively in stromal cells and vascular endothelial cells. In this article, we review our results on their expression in the embryonic hematopoietic tissues. We found that co-expression of Flkl and c-Kit was frequently detected either in vascular endothelial cells or hematopoietic cells in the early hematopoietic tissues. On the other hand, the three RTKPs are expressed in different cell lineages in the fetal liver. On the basis of this finding, we propose two modes of embryonic hematopoiesis; hematogenic angiopoiesis and hematopoiesis.

Hematopoietic cell protein-tyrosine phosphatase-deficient motheaten mice exhibit T cell apoptosis defect

We previously demonstrated that hematopoietic cell protein-tyrosine phosphatase is one of the molecules that can transduce Fas-mediated apoptosis signals in lymphoid cells. The present study analyzed the effect of defective Fas signaling on the T cell phenotype and apoptosis function in hematopoietic cell protein-tyrosine phosphatase-deficient motheaten mice. Viable motheaten (me(v)/me(v)) mice exhibited increased T cell proliferation and defective activation-induced apoptosis of Fas+ T cells in the lymph node, which was not ascribed to defective Fas ligand function. Furthermore, the Fas-mediated apoptosis defect in activated T cells from me(v)/me(v) mice was confirmed by their resistance to anti-Fas-induced apoptosis. No protein tyrosine dephosphorylation signal was delivered after anti-Fas cross-linking in the lymph node cells of me(v)/me(v) mice as revealed by 32Pi labeling of protein phosphatase substrates. The defective activation-induced apoptosis of Fas+ T cells in me(v)/me(v) mice led to lymphadenopathy with an accumulation of CD4- CD8- B220+ CD3+ T cells. Pneumonitis in me(v)/me(v) mice was associated with infiltration of cycling T cells detected by bromodeoxyuridine uptake in vivo. Thus, T cells from me(v)/me(v) mice are resistant to Fas-mediated apoptosis which results in lymphoproliferative disease and tissue infiltration.

Murine JAK3 is preferentially expressed in hematopoietic tissues and lymphocyte precursor cells

To elucidate the role of cytokine receptor signal transduction in T-cell development, we have investigated the expression pattern and biochemical characteristics of the murine Janus family tyrosine kinase, JAK3. Previous studies have shown that JAK3 is expressed in lymphoid and myeloid tumor cell lines and in a small number of lymphoid tissues. To further characterize JAK3 expression, we used a quantitative polymerase chain reaction approach to compare JAK3 mRNA levels at multiple stages of T-cell differentiation and in a broad range of mouse tissues. These studies, in conjunction with analyses of JAK3 protein expression, show that the highest levels of JAK3 are in adult, 2-week-old, and fetal thymus, followed by somewhat lower levels in bone marrow, spleen, fetal liver, and adult CD4-CD8- thymocytes. We also show that different forms of JAK3 mRNA arise by alternative splicing. Finally, our biochemical studies show that the JAK3 kinase domain, but not the pseudo-kinase domain, has tyrosine kinase activity and, furthermore, that JAK3 kinase activity is abolished by an amino acid substitution of the conserved lysine in the kinase domain (K851R). These studies show that JAK3 expression is profoundly skewed to hematopoietic and lymphoid precursor cells, strongly suggesting a role for JAK3 in hematopoiesis and T- and B-cell development.

A critical role of VLA-4 in erythropoiesis in vivo

Hematopoiesis requires specific interactions with the microenvironments, and VLA-4 has been implicated in these interactions based on in vitro studies. To study the role of VLA-4 in hematopoiesis in vivo, we performed in utero treatment of mice with an anti-VLA-4 monoclonal antibody. Although all hematopoietic cells in fetal liver expressed VLA-4, the treatment specifically induced anemia. It had no effect on the development of nonerythroid lineage cells, including lymphoids and myeloids. In the treated liver almost no erythroblast was detected, whereas the erythroid progenitors, which give rise to erythroid colonies in vitro, were present. These results indicate that VLA-4 plays a critical role in erythropoiesis, while it is not critical in lymphopoiesis in vivo.

The Dtk receptor tyrosine kinase, which binds protein S, is expressed during hematopoiesis

Dtk (Tyro 3/Sky/Rse/Brt/Tif) belongs to a recently recognized subfamily of receptor tyrosine kinases that also includes Ufo (Axl/Ark) and Mer (Eyk). Ligands for Dtk and Ufo have been identified as protein S and the related molecule Gas6, respectively. This study examined expression of Dtk during ontogeny of the hematopoietic system and compared the pattern of expression with that of Ufo. Both receptors were abundantly expressed in differentiating embryonic stem cells, yolk sac blood islands, para-aortic splanchnopleural mesoderm, fractionated AA4+ fetal liver cells, and fetal thymus from day 14 until birth. Although Ufo was expressed at moderate levels in adult bone marrow, expression of Dtk in this tissue was barely detectable. In adult bone marrow subpopulations fractionated using counterflow centrifugal elutriation, immunomagnetic bead selection for lineage-depletion and FACS sorting for c-kit expression, very low levels of Dtk and/or Ufo were detected in some cell fractions. These results suggest that Dtk and Ufo are likely to be involved in the regulation of hematopoiesis, particularly during the embryonic stages of blood cell development.

The ontogeny of key endoplasmic reticulum proteins in human embryonic and fetal red blood cells

Recently, using immunohistochemical methods, we surprisingly found that endoplasmic reticulum glucose-6-phosphatase is present in human embryonic and fetal red blood cells (RBCs) but not in adult RBCs. The fact that an endoplasmic reticulum enzyme, whose major site of expression in adults is the liver, is present in human embryonic and fetal RBCs, particularly nucleated cells, indicated that it would be sensible to determine whether these cells also contain other endoplasmic reticulum enzyme systems normally found in adult liver. Therefore, we have studied the expression of other endoplasmic reticulum proteins and found that human embryonic and fetal RBC precursors contain other protein components of the glucose-6-phosphatase system, ie, the phosphate and glucose transport proteins as well as other enzymes (eg, uridine diphosphate-glucuronosyltransferases, cytochrome P450 isozymes, nicotinamide adenine dinucleotide phosphate cytochrome P450 oxidoreductase, and prostaglandin H synthase). In addition, we also found the predominantly cytosolic markers 15-hydroxyprostaglandin dehydrogenase, prostaglandins PGE2 and 13,14-dihydro-15-keto-PGE2. The expression of key enzymes that control glucose production, detoxification of endobiotics and xenobiotics, and the regulation of prostaglandin levels in embryonic and early fetal RBCs means that these cells may have an important role in protecting the developing conceptus before it establishes an efficient circulation and before all tissues fully express their normal complement of these enzymes.

Mechanism of action of DNA topoisomerase inhibitors

DNA topoisomerases are enzymes that regulate DNA topology and are essential for the integrity of the genetic material during transcription, replication and recombination processes. Inhibitors of the mammalian enzymes are widely used antitumor drugs. They stabilize topoisomerase-DNA cleavable complexes by hindering the DNA relegating step of the catalytic reaction, thus resulting in DNA cleavage stimulation. Investigations on the sequence selectivity of DNA cleavage stimulated by chemically unrelated compounds established that specific nucleotides flanking strand cuts are required for drug action. Moreover, structure-activity relationship studies have identified structural determinants of drug sequence specificities, thus eventually allowing the design of new agents targeted at selected genomic regions. The initial cellular lesion, i.e., the drug-stabilized cleavable complex, is a reversible molecular event; however, how it may lead to cell death remains to be fully clarified. Several laboratories focused in past years on molecular and genetic aspects of drug-activated apoptosis. Irreversible double-stranded DNA breaks, generated from collisions between cleavable complexes and advancing replication forks, were suggested to increase p53 protein levels, thus triggering the cell death program. Other genes were also shown to cooperate in modulating the cell response to drug treatments. Recently, several groups have evaluated the possible prognostic value of topoisomerase II levels in solid tumors and hematopoietic neoplasms. Topoisomerase II inhibitors may also have genotoxic effects. Secondary leukemias, characterized by a translocation between chromosomes 11 and 9, have been reported in disease-free patients after treatments with drug regimens that included anti-topoisomerase II agents. It has been proposed that an impairment of topoisomerase activity may be involved in the molecular pathogenesis of secondary leukemias.

C-RAF-1 serine/threonine kinase is required in BCR/ABL-dependent and normal hematopoiesis

BCR/ABL oncogenic tyrosine kinase is responsible for initiating and maintaining the leukeic phenotype of Philadelphia chromosome-positive cells. c-RAF-1 serine/threonine kinase is known to be activated by receptor and nonreceptor tyrosine kinases. To determine whether c-RAF-1 plays a role in the growth of BCR/ABL-dependent cells, we examined whether c-RAF-1 associates with and/or is regulated by BCR/ABL and, if so, whether this interaction is functionally significant for BCR/ABL-dependent growth of chronic myelogenous leukemia cells and for growth factor-dependent proliferation of normal bone marrow cells. We show that c-RAF-1 enzymatic activity is regulated by BCR/ABL, although the protein does not associate with BCR/ABL. Downregulation of c-RAF-1 expression with antisense oligodeoxynucleotides or cDNA constructs, and inhibition of c-RAF-1 activity by its dominant negative mutants, inhibited both BCR/ABL-dependent growth of chronic myelogenous leukemia cells and growth factor-dependent proliferation of normal hematopoietic progenitors and the MO7 cell line without affecting the BCR/ABL-and growth factor-independent proliferation of HL-60 cells. These results indicate that c-RAF-1 plays an important role in Philadelphia chromosome-positive and normal hematopoiesis.

Isolation of tyrosine kinase related genes expressed in the early hematopoietic system

Transmembrane tyrosine kinase receptors are involved in cellular interactions which promote proliferation and differentiation of many cell types. To identify receptor tyrosine kinases important in embryonic hematopoietic cell development we have utilized the polymerase chain reaction (PCR) and degenerate oligonucleotides for isolation of such genes from mouse yolk sac and fetal liver. Sequence analysis of PCR amplified cDNAs from these hematopoietic sites of day 8 and 14 embryos, resulted in the isolation of nine tyrosine kinase and three serine/threonine kinase related clones. Two of these receptors, tek and flk-1, are expressed in both yolk sac and fetal liver and have been shown previously to be important for endothelial cell development. Two other clones, 9B4 and 9A2 appeared novel upon isolation but have been recently described as ryk and SK2 (rat homologue). Here we describe the twelve isolated kinases, the specific expression patterns of flk-1, tek and ryk kinases and their potential relationship to the development of the hematopoietic system.

bcr/abl expression in 32D cl3(G) cells inhibits apoptosis induced by protein tyrosine kinase inhibitors

Eight protein tyrosine kinase inhibitors with in vitro epidermal growth factor receptor kinase 50% inhibitory concentration values ranging from 0.043 to 22 microM were studied for their ability to inhibit the growth of the murine interleukin-3 (IL-3) dependent myeloid 32D cl3(G) cell line and, a subclone (LG7) transformed to IL-3 independent growth by retroviral transduction and expression of the chronic myelogenous leukemia-associated protein tyrosine kinase p210bcr/abl. Cell proliferation 50% inhibitory concentration values ranged from 4 to 250 microM, and one compound was not inhibitory at 500 microM. The dose-cell proliferation curves were remarkably similar for parental 32D cl3(G) cells + IL-3 and LG7 +/- IL-3, and reversion of LG7 cells to IL-3 dependence was not observed, suggesting that none of the compounds tested could selectively inhibit p210bcr/abl. However, 6 compounds induced the appearance of a 200-base pair nucleosomal DNA ladder characteristic of apoptosis at 24 h in parental 32D cl3(G) cells + IL-3, which mimicked the effects of IL-3 withdrawal alone, but not in similarly growth arrested LG7 cells that eventually developed a necrotic pattern of DNA fragmentation. These studies suggest that the expression of p210bcr/abl can suppress apoptotic signal transduction and that this may contribute to the development of the myeloid hyperplasia that occurs in chronic phase chronic myelogenous leukemia.

A hematopoietic protein tyrosine phosphatase (HePTP) gene that is amplified and overexpressed in myeloid malignancies maps to chromosome 1q32.1

Tyrosine phosphorylation is an important regulator of cell growth and differentiation reflecting the interaction of protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP). Although excessive PTK activity can result in hematopoietic cell transformation, perturbation of either of these two modulators may result in uncontrolled cell growth. Myeloid cells are responsive to growth factors and cytokines that induce tyrosine phosphorylation and can become ligand independent when endogenous PTKs become dysregulated. Specific PTPs, through mutation or altered expression, may enhance PTK activities and also cause myeloid ligand independence, though this has not yet been demonstrated. We have previously reported the isolation of a hematopoietic specific cytoplasmic PTP (HePTP). We now report that this gene maps to chromosome 1q32.1 utilizing fluorescent in situ chromosomal hybridization (FISH). This site is frequently amplified in preleukemic myeloproliferative diseases. FISH analysis of a patient with myelodysplastic syndrome characterized by myeloid hypoplasia and monocytosis reveals triplication of the HePTP gene on one allele with elevated protein expression in neoplastic myelomonocytic cells. Elevated expression is also identified in blasts from some patients with acute leukemia. These observations prompted us to examine the experimental effects on cell growth of HePTP overexpression. Though normal myeloid cells show minimal HePTP expression, all hematopoietic cell lines tested show high expression of HePTP. Gene transfer of HePTP into NIH 3T3 cells was therefore performed, which caused altered cell morphology, disorganized growth, anchorage independent colony formation and subtle differences in the pattern of tyrosine phosphoproteins compared to control cell lines. We conclude that amplification and overexpression of HePTP may be an important cofactor contributing to abnormal myeloid cell growth.

Expression of a novel form of Tec kinase in hematopoietic cells and mapping of the gene to chromosome 5 near Kit

The Tec kinase was initially identified as a novel cytoplasmic protein tyrosine kinase that is preferentially expressed in the liver and is highly homologous to the Drosophila Dsrc28C src-related tyrosine kinase. In screening of interleukin 3 (IL-3)-dependent myeloid leukemia cells for protein tyrosine kinases, we observed that all cell lines examined expressed high levels of Tec transcripts. However, characterization of Tec cDNAs indicated that they differed significantly from the published sequence. Most strikingly, an insertion of 41 bp in the 5' region affects the initiation codon and results in replacing the published 13 amino acid amino-terminal sequences with 94 amino acids. Using polymerase chain reaction (PCR) analysis, only the form containing the insertion was detected in hematopoietic cells. In addition, we found an in-frame insertion of 66 bp that introduces an additional 22 amino acids into the SH3 domain. This insertion restores conserved SH3 sequences that are found in the src gene family and in the Dsrc28C gene. By PCR analysis, approximately equal levels of Tec transcripts containing the intact SH3 domain and containing the 22 amino acid deletion were found in hematopoietic cells. Lastly, by interspecies backcross analysis, we show that the Tec gene is tightly linked to the c-Kit gene on mouse chromosome 5.

CD-13 ('gp150'; aminopeptidase-N): co-expression on endothelial and haemopoietic cells with conservation of functional activity

This report details experimental results which show the presence of enzymic aminopeptidase-N-like activity on endothelial cells, concomitant with cell surface expression previously detected by both ELISA and indirect immunofluorescence. This activity, detected using selected chromogenic substrates in 'functional' assays, is shown to be due (at least in part) to a molecule previously termed 'gp 150' and recognized by MoAb belonging to CD-13, since such antibodies can be shown to inhibit this activity. Activity, as detected on endothelial cells, is similar to that observed on various haemopoietic cells. These assays not only provide a functional basis to cell surface gp150 (CD-13) co-expression on haemopoietic and endothelial cells but have also been used to help define structural epitopes present on aminopeptidase-N/gp150, previously analysed using radiolabelled antibodies in competitive binding assays. Appraisal of these new data suggests that the number of distinct antibody binding sites on this molecule is greater than that previously demonstrated. This study is therefore an important first step in investigating the potential involvement of this selective peptidase molecule in the control of haemopoietic cell growth and differentiation and in haemostatic mechanisms.

Selective up-regulation of type II inosine 5'-monophosphate dehydrogenase messenger RNA expression in human leukemias

The discovery of isozymes (types I and II) of IMP dehydrogenase (IMPDH; EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, has attracted attention as a possible novel approach to cancer diagnosis and selective tumor cell chemotherapy. To elucidate differences in expression and regulation of the two IMPDH isozymes, we examined the steady-state levels of these mRNAs in various types of leukemic cells from patients. Northern blot analysis revealed that type II IMPDH was more active transcriptionally (1.5- to 5.1-fold) in all the leukemic cells examined than in normal lymphocytes, whereas type I expression was similar. The increased expression of type II mRNA in leukemic cells was closely linked with the increase in total IMPDH activity (r = 0.92). When leukemic cells from a patient with chronic granulocytic leukemia in blast crisis were separated into blast-rich and mature leukocyte-rich fractions, the expression of type II mRNA correlated positively with the population of immature leukemic cells, whereas type I expression was unchanged. Treatment of leukemic blasts with 12-O-tetradecanoyl-phorbol-13-acetate for 5 days resulted in a 90% decrease in the expression of type II mRNA with macrophage-like differentiation, while the expression of type I mRNA was relatively stable. These observations suggest that expression of type II IMPDH is stringently linked with immature characteristics of leukemic cells; thus, it should be a selective target for antileukemic chemotherapy.

Expression of human adenosine deaminase in mice after transplantation of genetically-modified bone marrow

A high titer retroviral vector was used to transfer a human adenosine deaminase (h-ADA) cDNA into murine bone marrow cells in vitro. The h-ADA cDNA was linked to the retroviral promoter, and the vector also contained a neomycin phosphotransferase gene as a selectable marker. Infected marrow was transplanted into syngeneic W/Wv recipients, and h-ADA expression was monitored for 5.5 months. Several weeks after transplantation, h-ADA was detected in the erythrocytes of all nine recipients, eight of which expressed levels equal to the endogenous enzyme. This level of expression persisted in two of six surviving mice, while expression in three others stabilized at lower, but readily detectable, levels. Only one mouse had no detectable h-ADA after 5.5 months. Vector DNA sequences with common integration sites were found in hematopoietic and lymphoid tissues of the mice at 5.5 months, providing evidence that hematopoietic stem cells had been infected. Furthermore, all mice transplanted with marrow that had been selected in G418 before infusion had multiple vector copies per genome. While this category included the two highest h-ADA expressors, it also included the negative mouse. Thus, multiple copies of the vector were not sufficient to guarantee long-term h-ADA expression. Mice were monitored for "helper virus" infections with an assay designed to detect a wide range of replication-competent retroviruses, including those endogenous to the mouse genome. No helper virus was detected in the two highest h-ADA expressors, ruling out helper-assisted vector spread as a cause of the high h-ADA expression. These results help provide a foundation for the development of somatic gene therapy techniques to be used in the treatment of human disease.

Expression of multiple Na+,K+-adenosine triphosphatase isoform genes in human hematopoietic cells. Behavior of the novel A3 isoform during induced maturation of HL60 cells

Multiple isoenzymes of the Na+,K+-ATPase (alpha, alpha+, and alpha 3) have been identified by molecular cloning (Shull, G. E., J. Greeb, and J. B. Lingrel. 1986. Biochemistry. 25:8125-8132; and Schneider, J. W., R. W. Mercer, and E. J. Benz, Jr. 1987. Clin. Res. 35:585A. [Abstr.]). At least one of these, the alpha 3 chain, represents a novel form for which protein products and enzymatic activities are just beginning to be defined in rodents. We have recently demonstrated that expression of alpha 3 is largely confined to neuromuscular tissues of fetal and adult rats (Schneider, J. W., R. W. Mercer, M. Gilmore-Hebert, M. F. Utset, C. Lai, A. Greene, and E. J. Benz, Jr. 1988. Proc. Natl. Acad. Sci. USA. 85:284-288). We now report that certain human leukemia cell lines including HL60, HEL, and Molt 4 express mRNA for both alpha and alpha 3 isoforms of Na+,K+-ATPase; mRNA was not detected in several other cell lines, including K562 and U937; no cell lines expressed alpha+ mRNA. In uninduced HL60 cells, alpha 3 mRNA comprised 20-30% of total Na+,K+-ATPase mRNA. Furthermore, in HL60 and HEL cells, both alpha and alpha 3 mRNA declined after induction of maturation by DMSO, retinoic acid, or hemin. However, the reduction in alpha 3 mRNA was far more dramatic. alpha 3 mRNA virtually disappeared, but alpha mRNA declined by only approximately 50%. In contrast, when maturation of HL60 cells along the monocyte/macrophage lineage was induced by exposure to phorbol esters, alpha 3 mRNA remained abundant. Moreover, mRNA for the beta subunit of the Na+,K+-ATPase increased dramatically. Our results demonstrate that the alpha 3 isoform, formerly thought to be confined to neuromuscular tissues, is expressed in restricted lineages of hematopoietic origin. These leukemia cell lines should provide a useful model for analyzing regulation of the alpha 3 isoform gene and characterization of alpha 3 isoform activities.

Ultrastructural localization of phenoloxidases in cuticle and haemopoietic tissue of the blowfly Lucilia cuprina

The ultrastructural localization of two types of biochemically characterized phenol oxidase activity is described in the larva of the sheep blowfly, Lucilia cuprina. Cuticular tyrosinase activity (enzyme A) is seen in epicuticular filaments and procuticle. Procuticle activity can be detected only after a presumed process of activation takes place in damaged cuticle. By using either the dopamine reaction or inducing melanization by hot-water treatment, tyrosinase is readily shown in haemopoietic tissue which, in L. cuprina, occurs subdermally as well as being associated with the dorsal vessel. The adaptation of the diaminobenzidine technique, used to stain laccase in electrophoretic gels, to ultrastructural cytochemistry has made it possible to demonstrate enzymic activity probably due to laccase (enzyme B). The laccase activity is present in the inner epicuticle of late wandering third instar larvae (about to pupariate) but is not present in the epicuticle of younger larvae.

Induction of (2'-5') oligoadenylate synthetase activity during granulocyte and monocyte differentiation

Variations in the (2'-5') oligoadenylate synthetase (2-5 A synthetase) level were examined prior to and during the differentiation in culture of the human monocyte cell line U937 and the promyelocytic cell line HL60 in an attempt to reveal whether the enzyme is actively involved in hematopoietic cell maturation. The basal level of this enzyme was much higher in U937 than in HL60 cells. The activity of 2-5 A synthetase was enhanced in both cell lines in response to alpha, beta interferons. During cell differentiation, ten markers were measured. The level of the enzyme rose during the process of cellular maturation in both cell lines. The 2-5 A synthetase activity observed in differentiated HL60 and U937 cells was comparable to that observed in mature normal granulocytes and monocytes respectively. Induction of U937 differentiation by chemicals was associated with detectable production of IFN. The increase in enzyme activity observed was mostly dependent on endogenous production of interferon, since it was inhibited by interferon antibodies. Kinetic studies showed that in U937 cells 2-5 A synthetase was expressed prior to several of the differentiation markers. The rise in the enzyme's level observed during the differentiation of HL60 cells was independent of endogenous production of interferon, since it was not inhibited by the addition of anti-interferon antibodies. These results suggest that different biochemical and molecular mechanisms are responsible for the induction of 2-5 A synthetase observed during the differentiation of hematopoietic cells. In any case, 2-5 A synthetase can be considered as a biochemical marker of cell status and differentiation in hematopoietic cells.

Some comparative properties of pyruvate kinase in haematopoietic cells and erythrocytes from rainbow trout (Salmo gairdneri R)

1. Temperature acts as a pyruvate kinase regulator in haematopoietic cells and erythrocytes. 2. Fructose-1,6-biphosphate and alanine act as allosteric modulators of pyruvate kinase in haematopoietic cells, while in erythrocytes although fructose-1,6-biphosphate exerts also allosteric effect, alanine appears to be a competitive inhibitor. ATP (1.0 mM) does not exert any clear effect on pyruvate kinase of both cellular populations. 3. The level of specific activity of pyruvate kinase in haematopoietic cells is 40-fold that of PK from erythrocytes.

Vitamin B12-dependent methyltetrahydrofolate: homocysteine methyltransferase activity in normal and leukemic human hematopoietic cells

The cyanogen bromide method was applied to the assay of vitamin B12-dependent methyltetrahydrofolate:homocysteine methyltransferase activity in normal and leukemic human hematopoietic cells. Normal peripheral lymphocytes and leukemia cells of lymphoid origin wuch as CLL and ALL, contained higher levels of enzyme activity than did normal human bone marrow cells. Normal granulocytes and leukemia cells of myeloid origin, such as CML in the chronic phase and AML, contained lower enzyme activity. Leukemia cells of CML in blast crisis showed higher mean activity than in the chronic phase of the disease.