Kimihiko Sano

Synergistic functions of phorbol ester and calcium in serotonin release from human platelets

In human platelets, thrombin activates Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C) and mobilizes Ca2+ concomitantly, whereas 12-O-tetradecanoylphorbol-13-acetate (TPA) may be intercalated into membranes and directly activates protein kinase C without mobilization of Ca2+ in sufficient quantities. A series of experiments with TPA and Ca2+-ionophore (A23187) indicates that activation of protein kinase C is a prerequisite requirement for release of serotonin, and that this enzyme activation and Ca2+ mobilization act synergistically to elicit a full cellular response. Both cyclic AMP and cyclic GMP inhibit activation of protein kinase C by prohibiting the signal-dependent breakdown of inositol phospholipid to produce diacyl-glycerol, but none of these cyclic nucleotides prevents the TPA-induced activation of this enzyme.

Phospholipid turnover as a possible transmembrane signal for protein phosphorylation during human platelet activation by thrombin

Summary Human platelets contain a large amount of Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C). The activation of this enzyme is initiated by unsaturated diacylglycerol which results from the thrombin-induced phosphatidylinositol hydrolysis. Protein kinase C preferentially phosphorylates in vitro a polypeptide having a molecular weight of about 40,000 (40K protein). This protein is labelled rapidly in platelets stimulated by thrombin as well as by exogenous phospholipase C, and diacylglycerol formation always accompanies 40K protein phosphorylation. The phosphorylation of 40K protein in vivo induced by thrombin is selectively inhibited by chlorpromazine and dibucaine, which are potent inhibitors for protein kinase C. Thus, phosphatidylinositol turnover provoked by thrombin seems to serve as a transmembrane signal for protein phosphorylation during platelet activation.

PC-1 Nucleoside Triphosphate Pyrophosphohydrolase Deficiency in Idiopathic Infantile Arterial Calcification

Inogranic pyrophosphate (PPi) inhibits hydroxyapatite deposition, and mice deficient in the PPi-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH) Plasma cell membrane glycoprotein-1 (PC-1) develop peri-articular and arterial calcification in early life. In idiopathic infantile arterial calcification (IIAC), hydroxyapatite deposition and smooth muscle cell (SMC) proliferation occur, sometimes associated with peri-articular calcification. Thus, we assessed PC-1 expression and PPi metabolism in a 25-month-old boy with IIAC and peri-articular calcifications. Plasma PC-1 was <1 ng/ml by enzyme-linked immunosorbent assay in the proband, but 10 to 30 ng/ml in unaffected family members and controls. PC-1 functioned to raise extracellular PPi in cultured aortic SMCs. However, PC-1 was sparse in temporal artery lesion SMCs in the proband, unlike the case for SMCs in atherosclerotic carotid artery lesions of unrelated adults. Proband plasma and explant-cultured dermal fibroblast NTPPPH and PPi were markedly decreased. The proband was heterozygous at the PC-1 locus, and sizes of PC-1 mRNA and polypeptide, and the PC-1 mRNA-coding region sequence were normal in proband fibroblasts. However, immunoreactive PC-1 protein was relatively sparse in proband fibroblasts. In conclusion, deficient extracellular PPi and a deficiency of PC-1 NTPPPH activity can be associated with human infantile arterial and peri-articular calcification, and may help explain the sharing of certain phenotypic features between some IIAC patients and PC-1-deficient mice.

Phosphatidylinositol turnover in platelet activation; Calcium mobilization and protein phosphorylation

Ca2+-activated, phospholipid-dependent protein kinase (C-kinase) in platelets is normally activated by diacylglycerol, which is derived from phosphatidylinositol through its receptor-linked breakdown. Under appropriate conditions this enzyme can also be activated by synthetic diacylglycerol which is directly added to intact platelets. C-Kinase thus activated preferentially phosphorylates an endogenous platelet protein having a molecular weight of approximately 40,000. This protein phosphorylation is merely a prerequisite but not a sufficient requirement for the release of serotonin. Evidence is presented suggesting that Ca2+ mobilization and C-kinase activation are synergistically involved in the physiological response of platelets to extracellular messengers, such as thrombin, collagen and platelet-activating factor.

Differential mechanisms of inorganic pyrophosphate production by plasma cell membrane glycoprotein-1 and B10 in chondrocytes.

OBJECTIVE Increased nucleoside triphosphate pyrophosphohydrolase (NTPPPH) activity in chondrocytes is associated with cartilage matrix inorganic pyrophosphate (PPi) supersaturation in chondrocalcinosis. This study compared the roles of the transforming growth factor beta (TGFbeta)-inducible plasma cell membrane glycoprotein-1 (PC-1) and the closely related B10 NTPPPH activities in chondrocyte PPi metabolism. METHODS NTPPPH expression was studied using reverse transcriptase-polymerase chain reaction and Western blotting. Transmembrane PC-1 (tmPC-1), water-soluble secretory PC-1 (secPC-1), and transmembrane B10 were expressed by adenoviral gene transfer or plasmid transfection, and expression of PPi was assessed in cultured articular chondrocytes and immortalized NTPPPH-deficient costal chondrocytes (TC28 cells). RESULTS PC-1 and B10 messenger RNA were demonstrated in articular cartilages in situ, in untreated cultured normal articular chondrocytes, and in TC28 cells. Expression of tmPC-1 and secPC-1, but not B10, rendered the NTPPPH-deficient TC28 cells able to increase expression of extracellular PPi, with or without addition of TGFbeta (10 ng/ml) to the media. More plasma membrane NTPPPH activity was detected in cells transfected with tmPC-1 than in cells transfected with B10. Furthermore, confocal microscopy with immunofluorescent staining of articular chondrocytes confirmed preferential plasma membrane localization of PC-1, relative to B10. Finally, both PC-1 and B10 increased the levels of intracellular PPi, but PC-1 and B10 appeared to act principally in different intracellular compartments (Golgi and post-Golgi versus pre-Golgi, respectively). CONCLUSION PC-1 and B10 NTPPPH activities were not redundant in chondrocytes. Although increased PC-1 and B10 expression caused elevations in intracellular PPi, the major effects of PC-1 and B10 were exerted in distinct subcellular compartments. Moreover, PC-1 (transmembrane and secreted), but not B10, increased the levels of extracellular PPi. Differential expression of PC-1 and B10 could modulate cartilage mineralization in degenerative joint diseases.

Valproic acid induces apoptosis in human leukemia cells by stimulating both caspase-dependent and -independent apoptotic signaling pathways

We investigated the effects of valproic acid (VPA) on the growth and survival of human leukemia cell lines. VPA induced cell death in all of the nine cell lines tested in a dose dependent manner. VPA-treatment induced apoptotic changes in MV411 cells including DNA fragmentation, phosphatidylserine externalization, cytochrome c release from mitochondria, and activation of caspases-3, -8, and -9. A caspase inhibitor, zVAD-FMK, inhibited the DNA fragmentation induced by VPA but not cell death. These findings suggest that VPA exerts an anti-leukemic effect by both caspase-dependent and -independent apoptotic signaling pathways.

Isolation and sequence of a cDNA clone for the rat pulmonary surfactant-associated protein (PSP-A)

Pulmonary surfactant is composed mainly of phospholipid and two groups of apoproteins. One of these apoproteins is a family of glycoproteins (pulmonary surfactant-associated protein A, PSP-A). We have isolated and sequenced a cDNA clone encoding for rat PSP-A and the full amino acid sequence has been deduced from the nucleotide sequence. The sequence of 56 amino acids at the N-terminus of PSP-A isolated from rats treated with silica was determined independently, and there is complete agreement with the sequence deduced from the cDNA. Isolated rat alveolar type II cells contain two species of mRNA for this protein.

Double intratracheal instillation of keratinocyte growth factor prevents bleomycin-induced lung fibrosis in rats.

Alveolar re‐epithelialization is necessary in the repair of damaged alveolar epithelium after lung injury. Keratinocyte growth factor (KGF) has been shown to be a potent proliferation and differentiation factor for rat alveolar type II cells. The present study examined whether KGF would prevent bleomycin‐induced lung fibrosis. Adult rats were anaesthetized and recombinant human KGF (rhKGF) (150 μg/kg) or saline was injected intratracheally at 48 h before and 24 h after bleomycin (Bleo, 5 mg/kg) instillation. Seven and 14 days after the last administration, rat lungs were processed for lung physiology, immunohistochemistry, and in situhybridization. Double instillation of KGF prevented the loss of body weight and reduction in total lung capacity (TLC) due to Bleo, and markedly attenuated the protein accumulation and mRNA expression of collagen types I and III and the decreased expression of surfactant protein mRNAs in the fibrotic lesions of Bleo‐treated rats. KGF may play an important role in maintaining alveolar epithelium and repairing the damaged epithelium after lung injury.

Mode of Inhibitory Action of Bilirubin on Protein Kinase C

ABSTRACT: Ca2+-activated, phospholipid-dependent protein kinase (protein kinase C) is widely distributed in mammalian tissues. Accumulating evidence has revealed that protein kinase C as well as cAMP-dependent protein kinase plays important roles in various cellular functions. The purpose of this study is to examine the effect of bilirubin on protein kinase C and cAMP-dependent protein kinase activity in a cell-free system as a cause of bilirubin toxicity to the central nervous system. Bilirubin inhibited protein kinase C activity in a dose-dependent manner. This effect was markedly diminished by the addition of human serum albumin at a molar ratio of bilirubin to albumin of less than 1.0. Kinetic analysis revealed that bilirubin did not compete with phospholipid, diacylglycerol, or calcium. Bilirubin also inhibited cAMP-dependent protein kinase, but did not compete with cAMP. The inhibitory effect of bilirubin on protein kinase C seems to be irreversible because removal of bilirubin by Sephadex G-25 column chromatography did not restore the protein kinase C activity. Observations reported herein suggest that bilirubin, especially in its free form, induces an irreversible change to the catalytically active site of protein kinase C.

Effects of dexamethasone on the expression of myelin basic protein, proteolipid protein, and glial fibrillary acidic protein genes in developing rat brain

Effects of dexamethasone (DEX) on the relative abundance of myelin basic protein (MBP), proteolipid protein (PLP) and glial fibrillary acidic protein (GFAP) mRNAs in the developing rat brain were examined. After DEX (1.0 mg/kg body weight) or saline was administered intraperitoneally to 3-day-old rats for 7 consecutive days, wet weight, DNA content and the relative abundance of the glia-specific mRNAs in cerebrum and cerebellum were analyzed at postnatal days (P) 10, 20 and 30. DEX decreased both wet weight and DNA content in cerebellum more profoundly than in cerebrum. The appearance of MBP, PLP and GFAP mRNAs in cerebellum preceded that in cerebrum in the control group. In cerebrum, the relative abundance of MBP and PLP mRNAs was significantly less in the DEX group than that in the control group at P20 and P30. The relative abundance of the GFAP mRNA was significantly less in the DEX group than in the control group at P10 and P20, but there was no significant difference at P30. In cerebellum, a significant decrease in the abundance of MBP, PLP and GFAP mRNAs in the DEX group was observed only at P10 but not at P20 and P30. Our findings indicate that DEX suppresses expression of genes related to glial functions, especially myelination when administered in the early postnatal period.