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S K Kong

Publications and source records attributed to S K Kong.

11 recordsLinked to original sources
PubMed1992

Protein ubiquitination is regulated by phosphorylation. An in vitro study.

Protein ubiquitination has been implicated in ATP-dependent protein turnover and in a number of biological processes in eukaryotic cells. The ubiquitination activating enzyme, E1, and ubiquitin carrier protein, E2, are two essential enzymes in the protein ubiquitination machinery. Using purified E1 and E2 from rabbit reticulocytes and various protein kinases, which include cAMP-dependent protein kinase, protein kinase C, and protein tyrosine kinase, we demonstrated that E1 is phosphorylated by protein kinase C, with a stoichiometry of 0.65 mol of phosphate/mol of E1, and one of the E2 isoforms, E2(32kDa), is phosphorylated by protein tyrosine kinase to 2 eq of phosphate/mol of protein. Phosphorylation of E1 causes a 2-fold enhancement of its activity as monitored by ubiquitin-dependent ATP in equilibrium PPi exchange. When 1 eq of phosphate was incorporated into E2(32kDa), a 2.4-fold activation was also observed for its activity to catalyze the ubiquitination of histone H2A. The regulatory significance of this finding is discussed.

Adenosine Triphosphate↗
PubMed1991

Changes in Schultz-Dale reaction in sensitized canine tracheal smooth muscle.

Tracheal smooth muscles from adult dogs 17 to 20 months of age sensitized with ragweed pollen demonstrated a Schultz-Dale phenomenon in response to specific antigen challenge. Seventy percent of the sensitized tracheal smooth muscles developed a Schultz-Dale reaction that consisted only of a phasic response, and the remaining 30% developed a Schultz-Dale reaction that consisted of a phasic component followed by a discrete tonic component. All the Schultz-Dale reactions were mediated only by histamine. The triggering of presynaptic acetylcholine release by histamine during the Schultz-Dale reaction from tracheal smooth muscles of ragweed-pollen-sensitized puppies 6 to 8 months of age was not detected in sensitized adult dogs. Hyperresponsiveness to acetylcholine was detected in tissues from sensitized puppies but not from sensitized adult dogs. Maximal active tension obtained from the sensitized adult canine trachealis during the Schultz-Dale reaction was lower than that obtained from trachealis from sensitized puppies. Dose-response studies showed that sensitized tissues used in the present studies were hyperresponsive to histamine when compared with their nonsensitized control littermates. These results suggest that the nature of the Schultz-Dale response and the identity of the transmitters is age-dependent.

Acetylcholine↗
PubMed1991

Membrane depolarization was required to induce DNA synthesis in murine macrophage cell line PU5-1.8.

The role of membrane potential (Em) on the initiation of DNA synthesis in murine macrophage cell line PU5-1.8 was investigated with fluorescent probes bis-oxonol and diS-C3-(5). Incubation of PU5-1.8 cells in high K(+)-HEPES buffer or with gramicidin at 37 degrees C for 1h that depolarized the membrane induced [3H]-thymidine incorporation and expression of early response gene such as c-myc and c-fos. When PU5-1.8 cells were treated with a number of agents including fetal calf serum (FCS), lipopolysaccharide (LPS), epidermal growth factor (EGF), N-formyl-methionyl-leucyl-phenylalanine (FMLP) and bradykinin (BK), only FCS caused DNA synthesis and membrane depolarization. Other agents had no effect on these events. The FCS-mediated DNA synthesis in PU5-1.8 cells was inhibited by clamping the membrane potential with valinomycin. Moreover, intracellular alkalinization induced by nigericin at pH 7.9, which is believed to be a permissive signal for mitogenesis, caused membrane depolarization. On the other hand, challenge of cells with phorbol 12-myristate 13 acetate (PMA) suppressed the K(+)-mediated DNA synthesis. However, the treatment of cells with PMA did not change the membrane potential but suppressed the gramicidin-mediated membrane depolarization. These observations suggest that there is a correlation between membrane depolarization and initiation of DNA synthesis in PU5-1.8 cells. PKC may be acting as a modulator in this transducing pathway.

Animals↗
PubMed1991

Membrane depolarization induces protein kinase C translocation and voltage operated calcium channel opening in PU5-1.8 cells. Protein kinase C as a negative feedback modulator for calcium signalling.

Incubation of the murine macrophage tumour cell line PU5-1.8 in K+ (140 mM)-HEPES buffer induced depolarization of the membrane and the translocation of protein kinase C (PKC) to the subnuclear region. Membrane depolarization also induced an increase of intracellular free Ca2+ levels ([Ca2+]i) which was due to the Ca2+ influx. The amount of K(+)-mediated Ca2+ uptake was dependent on the Ca2+ concentration gradient as measured by indo-1 fluorescence and 45Ca2+ fluxes. The depolarization-mediated Ca2+ influx was suppressed by voltage sensitive Ca2+ channel blockers such as nifedipine and verapamil. Furthermore, in Na(+)-HEPES buffer, incubation of cells with a dihydropyridine agonist [3H]PN200-110 produced a dose-dependent saturable binding. On the other hand, short-term incubation of cells with phorbol 12-myristate 13-acetate (PMA) abolished the early phase of 45Ca2+ influx and the rise of indo-1 fluorescence. Depleting cells of PKC or incubating them with PKC inhibitors, H7 and sphingosine, enhanced the uptake of 45Ca2+ and the rise of indo-1 fluorescence. These observations suggest that membrane depolarization caused an activation of PKC and induced Ca2+ influx through the activation of dihydropyridine-sensitive, voltage-operated Ca2+ channels. Data also show that PKC may act as a negative modulator in controlling the Ca2+ response by closing the voltage-operated Ca2+ channel and/or by enhancing the Ca(2+)-ATPase activity during membrane depolarization in PU5-1.8 cells.

Animals↗
PubMed1990

Vasectomy and cardiovascular deaths in Korean men: a community-based case-control study.

This community-based case-control study was carried out in four cities in South Korea to examine whether vasectomy is associated with a long-term increased risk of cardiovascular death in Korean men. Our results coincide with those from epidemiological studies conducted in Western countries as well as the one study conducted in China and do not support the vasectomy--atherosclerosis hypothesis originating from animal research.

Adult↗
PubMed1990

Induction of rhythmic contraction in canine tracheal smooth muscle.

Na(+)-K+ ATPase activity of the canine tracheal smooth muscle membrane is responsible for the electrogenic pumping of Na+ and K+ ions. It has been shown that this activity results in muscle relaxation. Based on the results of the current study, we suggest that prolonged electrical stimulation induces increased Na(+)-K+ ATPase activity in isolated tracheal smooth muscle. Tracheal smooth muscle pretreated with prolonged electrical stimulation developed graded mechanical activity when subsequently treated with histamine, serotonin, acetylcholine, or 80 mM K+. This increased isometric tension was interrupted by rhythmic activity, which was elicited by histamine or serotonin but not by acetylcholine or 80 mM K+ stimulation. The spontaneous phasic activity was not inhibited by atropine or propranolol but was totally inhibited by 10(-6) M ouabain. These results suggested that the relaxation phase of rhythmic contraction in response to histamine and serotonin stimulation could be the result of stimulated Na(+)-K+ ATPase activity.

Animals↗
PubMed1990

Increased myosin phosphorylation in sensitized canine tracheal smooth muscle.

We have reported that the maximal velocity of shortening and myofibrillar adenosine triphosphatase (ATPase) activity of antigen-sensitized airway smooth muscle are higher than that of nonsensitized airway smooth muscle (Kong, S. K., R. P. C. Shiu, and N. L. Stephens. J. Appl. Physiol. 60: 92-94, 1986). To extend these studies, we attempted to determine whether the increased myofibrillar ATPase activity from sensitized airway smooth muscle was associated with either a change in distribution of two myosin heavy chain isozymes or an increase in myosin light chain phosphorylation. Myosin heavy chain isozymes from both control and sensitized airway smooth muscle were separated by 4% sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gels were analyzed by densitometry, which indicated that isozyme band pattern of sensitized airway smooth muscle was not different from that of the control. The maximal levels of phosphorylated myosin light chain from whole cell homogenates of sensitized and control tracheal smooth muscles were 0.65 +/- 0.029 (n = 6) and 0.40 +/- 0.025 mol Pi/mol light chain (n = 6), respectively. The degree of phosphorylation of myosin light chain of sensitized airway smooth muscle was significantly higher than that of the control (P less than 0.05). This study also indicated that increased myofibrillar ATPase activity in sensitized tracheal smooth muscle was correlated with phosphorylation of myosin light chain.

Animals↗
PubMed1989

cAMP activates Na+/H+ antiporter in murine macrophages.

The role of cAMP in activating the Na+/H+ antiporter in murine macrophage (M phi) system was investigated. Incubation of PU5-1.8 macrophage tumour cells, peritoneal M phi and bone marrow derived macrophages (BMDM phi s) with dibutyryl-cAMP (db-cAMP) or cholera toxin (CT) led to an increase in intracellular pH (pHi). The magnitudes of these responses differed markedly in the three cell types, BMDM phi s being the most sensitive, PU5-1.8 cells the least so. These cells also differed in their responses to inhibitors of Na+/H+ exchange. In PU5-1.8 cells, the db-cAMP- or CT-triggered intracellular alkalinization was abolished by amiloride treatment which, however, was ineffective in BMDM phi s. The chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP), also caused a significant increase in cytoplasmic pH. However, its action was apparently not mediated by cAMP. The significance of these observations is discussed.

Amiloride↗
PubMedDate not supplied

Membrane depolarization induced DNA synthesis in PU5-1.8 cells. Role of voltage-operated Ca2+ channel and protein kinase C.

Incubation of non-excitable murine macrophage cell line PU5-1.8 in K+(140 mM)-Hepes buffer caused membrane depolarization as measured by bis-oxonol and 3,3'-dipropylthiodicarbocyanine. Depolarization of cell membrane produced an increase of intracellular free Ca2+ concentration ([Ca2+]i). Interestingly, short-term exogenously imposed membrane depolarization in PU5-1.8 cells in the absence of growth factors initiated the incorporation of [3H]thymidine or its analog, 5-bromo-2'-deoxyuridine, as well as the expression of early-response genes such as c-fos and c-myc. The expression of the proto-oncogene products seemed to be dependent on external Ca2+, and the [3H]thymidine incorporation was inhibited by nifedipine and verapamil at similar dosages as for Ca2+ inhibition. Calcium influx and [3H]thymidine incorporation could also be induced by Bay K 8644 or by gramicidin in the Na(+)-Hepes buffer. On the other hand, challenge of cells with sphingosine, staurosporine or 1-(5-isoquinolinesulfonyl)-2-methylpiperazine suppressed the K(+)-mediated DNA synthesis. Furthermore, preincubation of cells with phorbol 12-myristate 13-acetate (PMA) for 15 min in Na(+)-Hepes buffer enhanced the DNA synthesis. Yet, pre-incubation of cells with PMA or 1,2-dioctanoyl-sn-glycerol in K(+)-Hepes buffer suppressed the K(+)-mediated DNA synthesis and membrane depolarization. These observations suggest that a rise of [Ca2+]i is required for the initiation of DNA synthesis, and PKC may be functioning as a modulator with dual action at least on the level of ion conductance.

Animals↗