Yoshio Kanayama

Identification of mutations in the coding sequence of the proto-oncogene c-kit in a human mast cell leukemia cell line causing ligand-independent activation of c-kit product.

The c-kit proto-oncogene encodes a receptor tyrosine kinase. Binding of c-kit ligand, stem cell factor (SCF) to c-kit receptor (c-kitR) is known to activate c-kitR tyrosine kinase, thereby leading to autophosphorylation of c-kitR on tyrosine and to association of c-kitR with substrates such as phosphatidylinositol 3-kinase (PI3K). In a human mast cell leukemia cell line HMC-1, c-kitR was found to be constitutively phosphorylated on tyrosine, activated, and associated with PI3K without the addition of SCF. The expression of SCF mRNA transcript in HMC-1 cells was not detectable by means of PCR after reverse transcription (RT-PCR) analysis, suggesting that the constitutive activation of c-kitR was ligand independent. Sequencing of whole coding region of c-kit cDNA revealed that c-kit genes of HMC-1 cells were composed of a normal, wild-type allele and a mutant allele with two point mutations resulting in intracellular amino acid substitutions of Gly-560 for Val and Val-816 for Asp. Amino acid sequences in the regions of the two mutations are completely conserved in all of mouse, rat, and human c-kit. In order to determine the causal role of these mutations in the constitutive activation, murine c-kit mutants encoding Gly-559 and/or Val-814, corresponding to human Gly-560 and/or Val-816, were constructed by site-directed mutagenesis and expressed in a human embryonic kidney cell line, 293T cells. In the transfected cells, both c-kitR (Gly-559, Val-814) and c-kitR (Val-814) were abundantly phosphorylated on tyrosine and activated in immune complex kinase reaction in the absence of SCF, whereas tyrosine phosphorylation and activation of c-kitR (Gly-559) or wild-type c-kitR was modest or little, respectively. These results suggest that conversion of Asp-816 to Val in human c-kitR may be an activating mutation and responsible for the constitutive activation of c-kitR in HMC-1 cells.

Substitution of an aspartic acid results in constitutive activation of c-kit receptor tyrosine kinase in a rat tumor mast cell line RBL-2H3

The c-kit protooncogene encodes a receptor tyrosine kinase that mediates signals required for differentiation, proliferation and survival of mast cells. We have already shown the constitutive activation of c-kit receptor tyrosine kinase (KIT) in a human mast cell leukemia line (HMC-1) and a murine mastocytoma cell line (P-815). We here examined whether such constitutive activation of KIT occurred in the rat tumor mast cell line RBL-2H3 as well, which is frequently used as a tool for studying functions of mast cells. In RBL-2H3 cells, KIT was constitutively phosphorylated on tyrosine and activated in the absence of autocrine production of its ligand, stem cell factor (SCF). Sequencing analysis revealed that one of c-kit genes of RBL-2H3 cells had a point mutation, resulting in amino acid substitution of Tyr for Asp in codon 817. When rat wild-type c-kit cDNA and mutant-type c-kit cDNA encoding KITTyr817 were transfected into cells of a human embryonic kidney cell line (293T), only mutant form KITTyr817 was constitutively phosphorylated on tyrosine and activated in the absence of SCF. Since mutations at the same Asp codon constitutively activated KIT in all the human HMC-1, murine P-815, and rat RBL-2H3 cell lines, and since the incorporation of antisense oligonucleotides of c-kit messenger RNA significantly suppressed the proliferation of RBL-2H3 cells, the activating mutations in the Asp codon of the c-kit gene appeared to be involved in neoplastic growth of mast cells.

Molecular basis of CD36 deficiency. Evidence that a 478C-->T substitution (proline90-->serine) in CD36 cDNA accounts for CD36 deficiency.

CD36 deficiency is divided into two subgroups: neither platelets nor monocytes express CD36 (type I deficiency), and monocytes express CD36 in spite of the lack of platelet CD36 (type II deficiency). We have already demonstrated that a 478C-->T substitution (proline90-->serine) in platelet CD36 cDNA predominates in type II deficiency (Kashiwagi, H., S. Honda, Y. Tomiyama, H. Mizutani, H. Take, Y. Honda, S. Kosugi, Y. Kanayama, Y. Kurata, and Y. Matsuzawa. 1993. Thromb. Haemostasis. 69:481-484). In this study, we revealed that monocyte CD36 cDNA from two type II deficient subjects was heterozygous for C478 and T478 form, while platelet CD36 cDNA of these subjects consisted of only T478 form. In a type I deficient subject, both platelet and monocyte CD36 cDNA showed only T478 form. Expression assay using C478 or T478 form of CD36 cDNA transfected cells revealed that there was an 81-kD precursor form of CD36, and that the maturation of the 81-kD precursor form to the 88-kD mature form of CD36 was markedly impaired by the substitution. The mutated precursor form of CD36 was subsequently degraded in the cytoplasm. These results indicate that the 478C-->T substitution directly leads to CD36 deficiency via defects in posttranslational modification, and that this substitution is the major defects underlying CD36 deficiency.

Elevated serum manganese superoxide dismutase in acute leukemias

We measured the serum levels of manganese-superoxide dismutase (Mn-SOD) in acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL). Serum Mn-SOD level for normal subjects was 94.1 +/- 23.5 ng/ml (mean +/- S.D.), the levels for AML and ALL patients were 159.6 +/- 77.1 ng/ml and 154.4 +/- 77.0 ng/ml, respectively. The serum Mn-SOD levels were unrelated to individual intracellular Mn-SOD levels, but correlated well with serum lactate dehydrogenase values. Regression of the leukemia was accompanied by decrease in the serum level of Mn-SOD. Serum Mn-SOD may thus serve as a measure of the activity of the disease.

Modulation of N-acetylglucosaminyltransferase III, IV and V activities and alteration of the surface oligosaccharide structure of a myeloma cell line by interleukin 6

The activity of N-acetylglucosaminyltransferase (GnT) III, IV and V on a myeloma cell line, OPM-1, was examined after incubation with interleukin 6 (IL-6). While augmenting cell proliferation, IL-6 resulted in a decrease of GnT III activity and an increase of GnT IV and V activities. Consistent with this, OPM-1 cultured with IL-6 showed an increased affinity to Datura stramonium lectin, which recognizes asialo-tri- and asialo-tetraantenary N-linked oligosaccharides. These results indicate that IL-6 modulates glycosyltransferase activity and the oligosaccharide structure of target cells.

Hypogalactosylation of immunoglobulin G sugar chains and elevated serum interleukin 6 in Castleman's disease

Immunoglobulin G (IgG) molecule has two N-linked complex type oligosaccharides, consisting of a mixture of at least 12 different structures. The pattern of these oligosaccharides is fairly constant in healthy individuals. In three patients with Castlemans disease, in whom serum interleukin 6 (IL-6) levels were elevated, agalactosyl species of serum IgG oligosaccharides were markedly increased as compared to those of normal healthy controls. A close relationship between increased IL-6 and altered IgG oligosaccharide structure is suggested.

Surface expression of human myeloma cells: an analysis using a panel of monoclonal antibodies

Neoplastic cells of 18 patients with multiple myeloma were studied using a panel of 6 monoclonal antibodies to B cells and monospecific antisera against the light chain types of immunoglobulin. OKT10 bound to the myeloma cells of all the patients, although only a small percentage of the cells reacted in 3 instances. Monoclonal sIg was present in 5 patients. HLA-DR antigen detected with OKIa-1 was found in 5 patients. B1 bound to a small percentage of the myeloma cells only in 2 patients who had received treatment. The B1+ cells were always sIg+. In 3 patients, BA-2 reacted with the myeloma cells. BA-1 and BA-3 invariably did not react with the cells. Myeloma cells with B cell markers were found more frequently in treated patients than in untreated patients. The RPMI8226 line was also studied and found to react with OKT10 and BA-2. The results of this study show the presence of phenotypic variety in myeloma cells.

Disappearance of intraglomerular lipoprotein thrombi and marked improvement of nephrotic syndrome by bezafibrate treatment in a patient with lipoprotein glomerulopathy

Lipoprotein glomerulopathy (LPG) is a hereditary disorder characterized by intraglomerular lipoprotein thrombi and increased serum apolipoprotein (apo) E. Patients with LPG usually manifest with nephrotic syndrome, and some progress to renal failure; however, no effective therapeutic regimen has been established for this disease. We experienced a patient with LPG for whom bezafibrate treatment was very effective. This 30-year-old Japanese woman had nephrotic syndrome and type III hyperlipoproteinemia. Renal biopsy showed markedly dilated capillary lumina containing massive lipoprotein thrombi. Plasma apo E concentration was elevated to twice that of normal controls. She was proved to be a heterozygote of apo E2 Kyoto (Arg25Cys). After 2 years treatment with bezafibrate (400 mg/day), her plasma albumin gradually increased from 2.1 to 4.0 mg/dl, and intraglomerular lipoprotein thrombi disappeared almost completely. Bezafibrate decreased plasma apo E and dramatically increased high density lipoprotein (HDL)-cholesterol. The decrease in apo E was observed mainly in the pre-beta-fraction, not in the alpha fraction. Lipidological analyses of our patient suggest that the origin her lipoprotein thrombi may be mainly from pre-beta-lipoproteins and that HDL might be involved in resolving lipoprotein thrombi. Our case suggests that administration of fibrates such as bezafibrate may be a novel therapeutic strategy for resolving intraglomerular thrombi and improving nephrotic syndrome in patients with LPG.

Elevated platelet-associated IgG in SLE patients due to anti-platelet autoantibody: differentiation between autoantibodies and immune complexes by ether elution

Summary The level of platelet‐associated IgG (PAIgG) is reported to be elevated in patients with systemic lupus erythematosus (SLE). However. the nature of PAIgG is unclear. We have investigated whether the PAIgG of SLE consists of anti‐platelet autoantibodies or immune complexes (IC). The PAIgG values measured by flow cytonietry were elevated in 11/25 patients with SLE. 3/6 SLE patients with thrombocytopenia had a high level of PAIgG (the mean fluorescence intensity >10). We used an ether elution technique to determine whether elevated PAIgG consists of anti‐platelet antibodies or IC. Preliminary experiments showed that the eluates prepared from platelets sensitized with anti‐HPA‐4a antibody reacted with normal platelets. while the eluates prepared from platelets sensitized with heat‐aggregated IgG or model IC failed to react with normal platelets. These results indicate that the reactivity of eluates can distinguish between platelet‐bound antibody and IC. We applied this technique to analysis of the PAIgG of SLE platelets. The eluates from SLE platelets (the mean fluorescence intensity > 10) reacted with normal platelets. indicating that the PAIgG of SLE platelets has the nature of anti‐platelet autoantibodies. Furthermore, we investigated the target antigens which bind PAIgGs of SLE, using the direct immunoprecipitation procedure and modified antigen capture ELISA (MACE). Both methods identified GPIIb/IIIa as the target antigens. We conclude that the ether elution technique can distinguish between anti‐platelet antibodies and TC. and that the PAIgGs of SLE with a high PAIgG value and thrombocytopenia have the nature of anti‐platelet autoantibodies.

A case of T‐cell chronic lymphocytic leukemia (T‐CLL) expressing a peculiar phenotype (E+, OKM1+, leu 1+, OKT3− and IgG EA−)

A case of chronic leukemia is reported. Malignant cells had the morphology of lymphocytes and an affinity for skin. Cytochemically, they were peroxidase negative, and NaF‐resistant α‐naphthyl esterase positive. The peripheral mononuclear cells formed E‐rosettes and reacted with Leu 1 and OKM1. They were unreactive with OKT3, OKT4, OKT6, OKT8, and OKIa1. The cells did not possess surface IG, C3b receptors, or IgG Fc receptors (EAIgG). They responded weakly to phytohemagglutinin, and did not respond to concanavalin A. The cells did not adhere to Petri dishes or phagocytose latex beads. It is concluded that it was a case of OKT3−, OKM1+, EAIgG− T‐cell chronic lymphocytic leukemia. This suggests that OKT3 does not recognize all peripheral T‐cells, and that OKM1 is not specific for the monocyte—myeloid lineage. These cells may be useful in the characterization of E+, OKM1+ subset of peripheral mononuclear cells.