Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.1.1 (hexokinase)
 5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We recently proposed that extracellular ATP (ATPo) may be involved in CTL-mediated cytotoxicity by acting in concert with yet unidentified cellular components (ATPo receptors/ATPo-binding proteins, ectoprotein kinases). The TCR-triggered ATPo accumulation by CTL has been demonstrated, whereas the resistance of CTL to ATPo was explained by the action of highly active ecto-ATPases or by the absence of relevant ATP-binding proteins. However, no data were available to discriminate between the possibilities of: i) ATPo acting alone as a "hit" molecule because of the cell-permeabilizing properties of ATP4- or ii) ATPo acting as a "messenger" (as MgATP2-) in concert with other molecules. Comparing ATPo-induced and CTL-mediated cell lysis, we found that ATPo-induced lysis of some target cells is greatly decreased at neutral and acidic pH, whereas Ca(2+)-dependent CTL-mediated lysis of the same cells is barely affected. In agreement with the observed pH dependency, at low Mg2+ concentrations, which favor ATP4- over MgATP2-, maximal ATPo-induced lysis was observed. However, CTL-mediated cytotoxicity in both Ag-specific and retargeting assays was markedly reduced at low Mg2+ concentrations. These results suggest that ATPo acting alone as a "hit" molecule cannot fully account for the extracellular Ca(2+)-dependent lethal hit delivery by CTL or that ATP4- is active at very low concentrations. This conclusion was further supported by studying the lytic effect of ATPo and CTL on the anti-TCR mAb-coupled SRBC. CTL were efficient in the SRBC lysis, whereas no lysis of SRBC by ATPo was detected. The resistance of SRBC to ATPo is not caused by a high ATPo degradation, because the ecto-ATPase activity of SRBC was much lower than in ATPo-resistant CTL OE4 cells and comparable with EL4 tumor cells, which were easily lysed by ATPo. These data suggested the need for careful consideration of the pH and cation composition of the media used for studying ATPo effects. The caveats in the use of ATP-degrading enzymes to implicate the role of extracellular ATPo in the CTL-mediated cytotoxicity are described here. A clarification of the previously described cytotoxicity inhibition by hexokinase, which is caused by an inhibitory salt effect, is presented. It is suggested that if Ca(2+)-dependent lysis of SRBC and of other target cells by CTL does involve extracellular ATP, it may function as a "messenger" in concert with other extracellular molecules.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Comparative studies of the cytotoxic T lymphocyte-mediated cytotoxicity and of extracellular ATP-induced cell lysis. Different requirements in extracellular Mg2+ and pH. 194 Mar 62

Addition of 0.4-25 microM extracellular ATP results in transient, dose-dependent increases in cytosolic free calcium measured in Ehrlich ascites tumor cells. In cells incubated with 1 mM extracellular Ca2+, ATP induces a triphasic Ca2+ transient: an initial rapid increase (2-3 s), a second, slower phase of increase (60-90 s), and, finally, a gradual return to near resting [Ca2+]i (4-5 min). Several findings demonstrate that the initial, rapid phase of Ca2+ transient results from a mobilization of Ca2+ from a non-mitochondrial intracellular store, while the second, slow phase of increase is produced by enhanced influx of Ca2+ across the plasma membrane. Successive additions of extracellular ATP can elicit repetitive Ca2+ transients if the initially added ATP is removed either through the action of native ecto-ATPase activity or exogenous hexokinase. Other adenine nucleotides, including non-hydrolyzable ATP analogs, neither alter cytosolic [Ca2+] nor antagonize the ATP-induced effects. Conversely, other nucleotide triphosphates (ITP, UTP, and GTP) induce Ca2+ transients which are identical to those produced by ATP. A variety of experimental results indicate that these actions of ATP and other nucleotide triphosphates are not due to a generalized increase in plasma membrane permeability. The results suggest that, in these transformed cells, ATP may act in a manner similar to other Ca2+ mobilizing hormones and growth factors.
 ...
PMID:Intracellular Ca2+ mobilization activated by extracellular ATP in Ehrlich ascites tumor cells. 403 Jul 63