Vacuolar H(+)-pyrophosphatase purified from pear fruit

A vacuolar H(+)-translocating inorganic pyrophosphatase was purified from pear fruit through selective detergent treatments, Superose 6 and Mono Q column chromatography. The specific activity of the purified enzyme was 850 mumol h-1 mg protein-1. The Mr of V-PPase was 66 kDa by SDS-PAGE and the polypeptide cross-reacted with the antiserum against V-PPase of mung bean. The purified V-PPase was stimulated by potassium and inhibited by calcium and N, N'-dicyclohexylcarbodiimide.

Decreased nitric oxide-mediated natural killer cell activation in chronic fatigue syndrome

BACKGROUND

L-Arginine (L-Arg), one of the essential amino acids, has been reported to have an immunomodulatory effect. The precise mechanism of the L-Arg-induced natural killer (NK) cell activation remains unresolved,and the effect of L-Arg on NK cells in chronic fatigue syndrome (CFS) patients has not been estimated.

METHODS

NK cell function was evaluated in 20 subjects with CFS and compared with that in 21 healthy individuals.

RESULTS

In healthy control subjects, NK activity was significantly increased after treatment with L-Arg, an NK function enhancer, for 24 h, whereas the same treatment failed to enhance NK activity in the CFS patients. We thus focused on L-Arg metabolism, which involves nitric oxide (NO) production through NO synthase (NOS). The expression of inducible NO synthase (iNOS) transcripts in peripheral blood mononuclear cells was not significantly different between healthy control subjects and CFS patients. The L-Arg-mediated NK cell activation was abolished by addition of NG-monomethyl-L-arginine, an inhibitor for iNOS. Furthermore, incubation with S-nitroso-N-acetyl-penicillamine, an NO donor, stimulated NK activity in healthy control subjects but not in CFS patients.

CONCLUSION

These results demonstrate that the L-Arg-induced activation of NK activity is mediated by NO and that a possible dysfunction exists in the NO-mediated NK cell activation in CFS patients.

Changes in phenytoin concentrations in blood and cerebrospinal fluid caused by direct hemoperfusion in a patient intoxicated with phenytoin

We performed direct hemoperfusion (DHP) 5 times on a patient with consciousness disorder and phenytoin intoxication. We then measured the phenytoin concentrations in her cerebrospinal fluid (CSF) and blood at various times. After the first DHP session, consciousness began to improve, and it normalized after the fourth DHP session when the blood concentration of phenytoin had decreased from 54.0 microg/ml to 16.5 microg/ml. The average plasma phenytoin elimination rate of DHP was 18.0% over 120-180 min. The concentration of phenytoin in the CSF decreased as that in the blood was lowered by DHP. The average reduction rate of phenytoin in the CSF after a DHP session was 23.7%, which was similar to the rate of elimination from the blood. The CSF/blood phenytoin ratio was 0.17, and no marked changes were detected before or after a DHP session.

Secondary aortoduodenal fistula complicating aortic grafting, as a cause of intermittent chronic intestinal bleeding

Intermittent intestinal bleeding persisted in a 77-year-old male, who had undergone grafting for abdominal aortic aneurysm. Each attack lasted for a few weeks and spontaneously resolved. Only a minute abnormality was found in the third portion of the duodenum; barium studies showed a segmental narrowing, but endoscopy disclosed only a small erosion in that portion. Massive and fatal gastrointestinal hemorrhage broke out 6 months after the onset of bleeding. Autopsy revealed an adhesion area with a small fistula formation between the duodenum and aorta. Even slight endoscopic findings should be considered suggestive of aortoenteric fistula in patients after aortic surgery.

Enhanced renal toxicity by inorganic mercury in metallothionein-null mice

To elucidate a protective role of metallothionein (MT) in the manifestation of inorganic mercury toxicity, we studied the susceptibility of MT-null mice to the renal toxicity of mercuric chloride. Because the MT-null (J) mice are a genetic background of 129/Sv strain, the 129/Sv mice were used as wild-type controls. Nine-week-old male MT-null (J) and 129/Sv mice were given subcutaneous injections of mercuric chloride at doses of 10 to 40 micromol/kg. The basal MT level in the kidney of MT-null (J) mice was undetectable (<0.2 microg/g of tissue) and approximately 2.5 microg/g of tissue in 129/Sv mice. The sensitivity to the renal toxicity of mercuric chloride was markedly enhanced in the MT-null (J) mice compared with the 129/Sv mice. The renal mercury level was similar for the MT-null (J) and 129/Sv mice at 4 hr after the injection of mercuric chloride (20 micromol/kg) but became significantly lower in MT-null (J) mice than in 129/Sv mice at 24 and 72 hr. Based on the present results, we conclude that MT is an important protective factor against the renal toxicity caused by inorganic mercury and that it may play a major role in the retention of mercury in the kidney.

Follicular dendritic cell tumor with histiocytic characteristics and fibroblastic antigen

A report is presented of a follicular dendritic cell (FDC) tumor arising in the lymph nodes and inguen of a 55-year-old Japanese female, who had suffered from schizophrenia for 25 years. The left submandibular lymph nodes had completely lost their normal architecture, except for the capsule, due to tumor cell infiltration. Occasional nodular structures resembling epithelioid granulomas, attributable, at least in part, to follicular involvement of tumor cells, were observed. These nodules were composed of epithelioid- or fibroblast-like tumor cells forming interwoven fascicles, to which small lymphocytes were attached. Tumor cells were also scattered in the internodular areas. For more atypical tumor cells, arranged in a sheet-like structure, were present in the inguinal specimen, the tumor cells of which expressed Ki-M4p, CD21, CD35 and other antigens known to be expressed on FDC. Furthermore, they also expressed the monocyte/macrophage antigens, alpha 1-antitrypsin, alpha 1-antichymotrypsin, lysozyme, CD14, CD33, CD68 and Mac387 and fibroblastic antigen. Ultrastructural studies demonstrated lysosomal granules as well as a few desmosomes, indicating the tumor cells possessed fibrohistiocytic and FDC characteristics.

Changes in H(+)-pumps and a tonoplast intrinsic protein of vacuolar membranes during the development of pear fruit

Vacuolar H(+)-ATPase (V-ATPase) was purified from pear fruit and antibodies were raised against the subunits of 55 and 33 kDa. Antibodies against mung bean H(+)-pyrophosphatase (V-PPase) and radish VM23, which is a tonoplast intrinsic protein (TIP) and a water channel, cross-reacted with the vacuolar membrane proteins of pear fruit. To clarify the roles of these proteins in development of pear fruit, we determined their levels relative to the total amount of protein by immunoblot analysis. The levels of subunits of the V-ATPase increased with fruit development. By contrast, the level of V-PPase was particularly high at the cell-division stage and remained almost the same at other stages. The changes in the activities of V-ATPase and V-PPase corresponded to those in their protein levels. The ratio of V-PPase activity to V-ATPase activity indicated that V-PPase is a major H(+)-pump of the vacuolar membranes of young fruit and that the contribution of V-ATPase increases with fruit development, finally, V-ATPase becomes the major H(+)-pump during the later stages of fruit development. The level of a protein analogous to VM23 (VM23P) was especially high during the active cell-expansion stage in young fruit, and VM23P might, therefore, play an important role in the rapid expansion of cells as a vacuolar water channel. Our results show that the levels of V-ATPase, V-PPase and VM23P change differently and reflect the roles of the respective protein in the development of pear fruit.

Anti-angiogenic compound (TNP-470) inhibits mesangial cell proliferation in vitro and in vivo

Growth factors, especially basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF), and transforming growth factor-beta (TGF-beta) are known to play key roles in the pathogenesis of mesangial proliferative glomerulonephritis. TNP-470 (AGM-1470), a potent anti-angiogenic compound, has anti-growth factor properties and inhibits the activation of cyclin-dependent kinase (cdk) 2 and phosphorylation of RB protein. We investigated whether TNP-470 could suppress growth factor induced mesangial cell proliferation in vitro and experimental model of mesangial proliferative glomerulonephritis in vivo. TNP-470 inhibited potently PDGF- and bFGF-stimulated proliferation of rat mesangial cells in vitro (IC50 = 50 pg/ml). In anti-Thy 1.1 glomerulonephritis, high dose use of TNP-470 (20 mg/kg/day) markedly suppressed mesangial cell proliferation and mesangial matrix expansion on day 6; however, mesangiolysis remained. Low dose use of TNP-470 (10 mg/kg/day) moderately inhibited mesangial cell proliferation and mesangial matrix synthesis, and induced appropriate glomerular healing on day 14 in anti-Thy 1.1 glomerulonephritis. Thus, TNP-470 potently inhibits growth factor-induced proliferation of mesangial cells in vitro, and mesangial cell proliferation and extracellular matrix expansion in anti-Thy 1.1 glomerulonephritis in vivo. These results suggest a novel therapeutic potential of TNP-470 in mesangial proliferative glomerulonephritis.

Enhanced gene expression of scavenger receptor in peripheral blood monocytes from patients on cuprophane haemodialysis

BACKGROUND

Macrophage scavenger receptor (SR) is implicated in playing a key role in macrophage-derived foam cell formation by taking up a large amount of modified low-density lipoproteins (LDL). It has also been postulated that alpha 2-macroglobulin receptor/LDL receptor-related protein (alpha 2MG/LRP) is involved in the development of foam cells by taking up apo E-enriched chylomicrons and VLDL remnants, and lipoprotein lipase-triglyceride-rich lipoprotein complexes. Accumulation of these lipid-loaded monocyte/ macrophages in the subendothelial space is considered to be an early event of atherogenesis. Since atherogenesis is considered to be accelerated in dialysis patients, we attempted to investigate whether gene expression of SR and alpha 2MG/LRP are altered in peripheral blood monocytes from patients on haemodialysis with a cuprophane (Cu) or polymethylmethacrylate (PMMA) membranes.

METHODS

Peripheral blood monocytes (PBM) were prepared from patients undergoing haemodialysis with a Cu membrane (n = 9), patients undergoing haemodialysis with a PMMA membrane (n = 9), and healthy controls (n = 7). In a separate experiment we examined SR gene expression in uraemic patients (n = 12) and healthy controls (n = 9). SR and alpha 2MG/LRP mRNA were semiquantitated using reverse-transcription polymerase chain reaction (RT-PCR) assay followed by Southern blotting.

RESULTS

SR mRNA expression in PBM from patients on chronic haemodialysis with a Cu membrane was about twofold higher than that in PBM from patients on chronic haemodialysis with a PMMA membrane or the controls (P < 0.05). alpha 2MG/LRP mRNA expression in PBM showed no difference among these, three groups. SR gene expression in monocytes from uraemic patients was not increased compared with that in the controls.

CONCLUSION

PBM from patients under Cu membrane dialysis showed higher gene expression of SR than patients under PMMA membrane dialysis, uraemic patients, or healthy controls. This increased gene expression of SR in monocytes may be associated with the pathogenesis of accelerated atherosclerosis in patients on dialysis with a Cu membrane.

Divergent fructokinase genes are differentially expressed in tomato

Two cDNA clones (Frk1 and Frk2) encoding fructokinase (EC 2.7.1.4) were isolated from tomato (Lycopersicon esculentum). The Frk2 cDNA encoded a deduced protein of 328 amino acids that was more than 90% identical with a previously characterized potato (Solanum tuberosum) fructokinase. In contrast, the Frk1 cDNA encoded a deduced protein of 347 amino acids that shared only 55% amino acid identity with Frk2. Both deduced proteins possessed and ATP-binding motif and putative substrate recognition site sequences identified in bacterial fructokinases. The Frk1 cDNA was expressed in a mutant yeast (Saccharomyces cerevisiae) line, which lacks the ability to phosphorylate glucose and fructose and is unable to grow on glucose or fructose. Mutant cells expressing Frk1 were complemented to grow on fructose but not glucose, indicating that Frk1 phosphorylates fructose but not glucose, and this activity was verified in extracts of transformed yeast. The mRNA corresponding to Frk2 accumulated to high levels in young, developing tomato fruit, whereas the Frk1 mRNA accumulated to higher levels late in fruit development. The results indicate that fructokinase in tomato is encoded by two divergent genes, which exhibit a differential pattern of expression during fruit development.

Follow-up after the Hanshin-Awaji earthquake: diverse influences on pneumonia, bronchial asthma, peptic ulcer and diabetes mellitus

We evaluated the influence of the Hanshin-Awaji earthquake on the patients in our internal medicine department. After the initial rush of patients with injury, the number of respiratory diseases, largely pneumonia, increased within one month. This same event, however, seemed to decrease attacks among asthma patients. During the following three months, the number of peptic ulcer patients increased: 39.5% had a giant gastric ulcer and 34.8% had bleeding complications. Diabetic control of outpatients became worse after the earthquake. It is important to recognize that various disorders involving physical and psychological problems develop at different stages after a large-scale disaster.

[Clinical evaluation of cefpirome sulfate for severe infections in patients with hematological disorders. Hanshin Study Group of Hematopoietic Disorders and Infections]

We investigated the therapeutic efficacy and safety of cefpirome sulfate (CPR) in treatment of hematopoietic disorder-associated infections. A total of 219 patients were admitted to 12 hospitals of Hanshin Study Group of hematopoietic disorders and infections between April 1994 and March 1996 and were enrolled in this study. Most patients received intravenously infused CPR at a dose of 1 or 2 g twice a day for 3 days or more. Twenty nine patients dropped out or were excluded and remaining 190 patients were adopted for the evaluation. A overall response rate was 58.4% (111/190). Among neutropenic patients, the response rate was 50% (8/16) in patients whose peripheral neutrophil counts (PNC) remained less than 100/microliter throughout the observation period and was 53.7% (22/41) in patients with PNC remained less than 500/microliter. In contrast, in patient whose PNC was below 500 before the treatment but exceeded 501/microliter during of at the end of the treatment, the response rate was as high as 78.4% (29/37). When G-CSF was combined, the response rate became significantly (P < 0.05) higher, 68.5% (50/73), as compared with that, 52.1% (61/117), in patients without it. In cases in which the causative organisms could be identified, the organisms were eliminated in 81.8% (9/11) of the patients infected with Gram-positive bacteria, whereas in 100% (12/12) in those infected with Gram-negative bacteria. Skin eruption developed in 6 patients during the treatment with CPR, and vascular pain and parosmia in one each other. These symptoms subsided soon after discontinuation or even without discontinuation of CPR. Abnormal laboratory findings, mainly liver dysfunction, i.e. elevation of slight degree of serum transaminase levels, were observed. The values, however, turned to normal immediately after the cessation or completion of the treatment. In conclusion, CPR is considered to be an antibiotic of value with high efficacy and safety in treatment of hematopoietic disorder-associated infections.

Functional role of cation-independent mannose 6-phosphate/insulin-like growth factor II receptor in cell adhesion and proliferation of a human myeloma cell line OPM-2

The molecular mechanism underlying the interaction between myeloma cells and stromal cells was investigated by using a human myeloma cell line (OPM-2) and human umbilical vein endothelial cells (HUVECs). Adhesion of OPM-2 cells to HUVECs was found to be significantly augmented with treatment of OPM-2 cells with an alpha-glycosidase inhibitor, castanospermine (CSP). The treatment of OPM-2 cells with CSP resulted in alteration of oligosaccharide structures of cell surface glycoproteins particularly at molecular weight of 220 kD (GP220). To determine if GP220 was involved in the adhesion of OPM-2 cells to HUVECs, cell surface glycoproteins of HUVECs were labeled by biotin and were incubated with the PVDF membrane to which cell surface glycoproteins of OPM-2 cells were blotted. The biotinylated glycoproteins at the plasma membrane of HUVECs specifically bound to GP220 of OPM-2 cells. Purification and partial amino acid sequencing of GP220 revealed that GP220 had a structure homologous to cation-independent mannose 6-phosphate/insulin-like growth factor-II (CIM6P/IGF-II) receptor. Furthermore, an antibody against CIM6P/IGF-II receptor was reactive with GP220, indicating that GP220 was a CIM6P/IGF-II receptor. The adhesion of OPM-2 cells to HUVECs was inhibited by mannose 6-phosphate. Moreover, M6P was found to suppress the adhesion of human myeloma cell lines, OPM-2 and RPMI 8226, to bone marrow stromal cells that was established from the patients with multiple myeloma. In addition, proliferation of OPM-2 was stimulated in response to IGF-II. These results suggest that CIM6P/IGF-II receptor may be functional in terms of supporting cell adhesion and proliferation of myeloma cells.

Lovastatin inhibits gene expression of type-I scavenger receptor in THP-1 human macrophages

Lovastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, inhibits the synthesis of mevalonic acid and is widely used as an anti-atherosclerotic drug. The macrophage scavenger receptor (SCR), a trimeric membrane glycoprotein, is postulated to play a key role in atheroma macrophage foam cell formation. HMG-CoA reductase is involved in the control of the synthesis of glycoproteins and farnesylated proteins, including ras proteins, which are involved in the transcriptional regulation of SCR gene expression. Accordingly, we examined whether lovastatin alters the gene expression of SCRs in THP-1 cell derived human macrophages. Lovastatin (5-15 microM) caused a significant dose-related reduction in steady state levels of type-I SCR mRNA in phorbol 12-myristate 13-acetate (PMA)-treated THP-1 cells. The addition of exogenous mevalonate (1 mM) completely restored the lovastatin-induced decrease of type-I SCR mRNA levels. While the addition of the isoprenoid end-product, isopentenyl adenine (50 microM), had little effect on the type-I SCR mRNA levels in lovastatin treated cells, the addition of isoprenoid farnesol (5 microM) largely restored the lovastatin-induced decrease of type-I SCR mRNA levels. Actinomycin D treatment showed that degradation rates of type-I SCR mRNA did not differ between the THP-1 derived cells with and without lovastatin treatment. Nuclear run-on assays showed that lovastatin markedly decreased the transcription of SCR gene in the cells. These results suggest that lovastatin inhibits the transcription of type-I SCR gene by affecting mevalonate metabolism, possibly through the farnesyl-pyrophosphate related end-product(s) in the THP-1-derived macrophages.

Calcium-binding protein regucalcin inhibits deoxyribonucleic acid synthesis in the nuclei of regenerating rat liver

The effect of regucalcin, a Ca(2+)-binding protein isolated from rat liver cytosol, on deoxyribonucleic acid (DNA) synthesis in the nuclei of regenerating rat liver was investigated. At 1 day after partial hepatectomy, the liver weight was increased about 50% of that of sham-operated rats, and it reached to the same levels as sham operation at 3 days after hepatectomy. Nuclear DNA synthesis was markedly increased at 1 day after hepatectomy, and this increase was also seen at 3 days. Nuclear DNA synthesis was clearly enhanced in the presence of EGTA (0.4 mM) in the incubation mixture. The presence of Ca2+ (1.0-25 microM) caused a significant decrease in the nuclear DNA synthesis of normal rat liver. Regucalcin (0.25 and 0.5 microM) clearly inhibited the nuclear DNA synthesis of normal rat liver. This inhibition was also seen in the presence of Ca2+ (1.0 microM). Moreover, in the liver nuclei obtained at 1 day after partial hepatectomy, the presence of regucalcin (0.05-0.5 microM) caused a remarkable inhibition of nuclear DNA synthesis. This effect was also revealed in the presence of EGTA (0.4 mM). Thus, the inhibitory effect of regucalcin was remarkable in regenerating rat liver nuclei in comparison with that of normal rat liver. The present results demonstrate that regucalcin can suppress nuclear DNA synthesis in regenerating rat liver. We suppose that regucalcin may have a role in the regulation of nuclear DNA synthesis in liver cell proliferation.

Reduced retention of cadmium in the liver of metallothionein-null mice

The distribution of cadmium (Cd) in the organs of mice was studied using metallothionein (MT)-null transgenic mice. When mice were administered with Cd chloride at a single subcutaneous dose of 1.0 mg Cd/kg body weight, Cd accumulated mainly in the liver and kidney by 6 h after injection without any significant difference between the MT-null mice and control (C57BL/6J) mice. MT was not detected in these organs of MT-null mice both before and after Cd administration whereas MT was induced mainly in these organs of the control mice. There was a marked elimination of Cd from the liver of MT-null mice by 21 days after administration, compared with a relatively slow Cd elimination in the C57BL/6J mice. Under the condition that no significant liver or kidney damage was observed, MT was considered to play a significant role in the retention of Cd in the liver but not in the uptake of this metal.

Myelodysplastic syndrome associated with erythrophagocytosis by blasts and myeloid cells

A 63-year-old man with refractory anemia with excess of blasts in transformation exhibited erythroid hyperplasia, dyserythropoiesis, a del(20q) abnormality, susceptibility to bacterial infections, and a relatively short survival. Phagocytosis of erythrocytes by blast cells was observed. Erythrophagocytosis was also seen in myeloid cells, including promyelocytes, myelocytes, metamyelocytes and neutrophils. Neither the monocytes nor the macrophages showed erythrophagocytosis. This is the first report of erythrophagocytosis by blasts and myeloid cells in a patient with myelodysplastic syndrome.

Gene expression of endothelin receptors in aortic cells from cyclosporine-induced hypertensive rats

1. We examined preproendothelin-1, ETA and ETB receptor mRNA levels in aortic endothelial and smooth muscle cells from cyclosporine (CyA)-induced hypertensive rats using the reverse transcription polymerase chain reaction method. 2. Aortic endothelial preproendothelin-1 mRNA expression was about 1.5-fold higher, while that of ETB receptor mRNA was markedly decreased in CyA-treated rats compared with those in controls. 3. The expression of ETA receptor mRNA in smooth muscle cells from CyA-induced hypertensive rats was increased about two-fold over that in cells from control animals. 4. Thus, increased endothelial preproendothelin-1, and ETA receptor mRNA levels in smooth muscle cells, which are concomitant with the decrease in ETB receptor mRNA levels in endothelium, may contribute to CyA-induced hypertension in rats.

Enhancement of nuclear Ca(2+)-ATPase activity in regenerating rat liver: involvement of nuclear DNA increase

The alteration of calcium content, Ca(2+)-ATPase activity, DNA content and DNA fragmentation in the nuclei of regenerating rat liver was investigated. Liver was surgically removed about 70% of that of sham-operated rats. The reduced liver weight by partial hepatectomy was completely restored at 3 days after the surgery. Regenerating liver significantly increased Ca(2+)-ATPase activity and DNA content in the nuclei between 1 and 5 days after hepatectomy. The nuclear calcium content was clearly increased from 2 days after hepatectomy. The increase of Ca(2+)-ATPase activity in regenerating liver was clearly inhibited by the presence of trifluoperazine (10 microM), staurosporine (2.5 microM) and dibucaine (10 microM), which are inhibitors of calmodulin and protein kinase, in the enzyme reaction mixture. However, the nuclear enzyme activity in normal rat liver was not significantly altered by these inhibitors. Meanwhile, the increase of nuclear DNA content in regenerating liver was completely blocked by the administration of trifluoperazine (2.5 mg/100 g body weight), suggesting an involvement of calmodulin. Now, the nuclear DNA fragmentation was significantly decreased in regenerating liver, suggesting that this decrease is partly contributed to the increase in nuclear DNA content. The present study clearly demonstrates that regenerating liver enhances nuclear Ca(2+)-ATPase activity and induces a corresponding elevation of nuclear calcium content. This Ca(2+)-signaling system may be involved in the regulation of nuclear DNA functions in regenerating rat liver.

Abnormal processing of the glycoprotein IIb transcript due to a nonsense mutation in exon 17 associated with Glanzmann's thrombasthenia

We analyzed the molecular genetic defect responsible for type I Glanzmann's thrombasthenia in a Japanese patient. In an immunoblot assay using polyclonal anti-GpIIb-IIIa antibodies, some GPIIIa (15% of normal amount) could be detected in the patient's platelets, whereas GPIIb could not (< 2% of normal amount). Nucleotide sequence analysis of platelet GPIIb mRNA-derived polymerase chain reaction (PCR) products revealed that patient's GPIIb cDNA had a 75-bp deletion in the 3' boundary of exon 17 resulting in an in-frame deletion of 25 amino acids. DNA analysis and family study revealed that the patient was a compound heterozygote of two GPIIb gene defects. One allele derived from her father was not expressed in platelets, and the other allele derived from her mother had a 9644C--> T mutation which was located at the position -3 of the splice donor junction of exon 17 and resulted in a termination codon (TGA). Moreover, quantitative analysis demonstrated that the amount of the abnormal GPIIb transcript in the patient's platelets was markedly reduced. Thus, the C --> T mutation resulting in the abnormal splicing of GPIIb transcript and the reduction in its amount is responsible for Glanzmann's thrombasthenia.

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.

Blood pressure regulates platelet-derived growth factor A-chain gene expression in vascular smooth muscle cells in vivo. An autocrine mechanism promoting hypertensive vascular hypertrophy

To clarify the role of PDGF A-chain in hypertensive vascular hypertrophy of spontaneously hypertensive rats (SHRs), we studied levels of PDGF A-chain gene expression and transcription factors related to the gene in vascular smooth muscle cells (VSMCs) of SHRs in vivo. RNase protection assay and in situ hybridization showed that PDGF A-chain mRNA levels in VSMCs of SHRs were twofold higher than in those of normotensive Wistar-Kyoto rats. Gel retardation assays showed that levels of Sp1 and AP-2 in VSMCs of SHRs were twofold more abundant than in those of Wistar-Kyoto rats. Treatment with four pharmacologically different species of antihypertensive drugs for 2 wk decreased the levels of both PDGF A-chain mRNA and Sp1, but not AP-2 level in VSMCs of SHRs with regression of aortic hypertrophy, indicating that increases in levels of both PDGF A-chain mRNA and Sp1 in VSMCs of SHRs were associated with high blood pressure. These results suggest that high blood pressure is a stimulus which upregulates PDGF A-chain gene expression in VSMCs of SHRs, resulting in an autocrine enhancement in hypertensive vascular hypertrophy, and that the activation of the gene may be mediated through increases in Sp1 in these cells.