Pertussis toxin activates T lymphocytes by a mechanism that is independent of its ADP-ribosylation activity. The toxin stimulates increases in diacylglycerol and intracellular calcium apparently by interacting with a cell surface receptor. Consistent with the production of these second messengers we have found that pertussis toxin activates protein kinase C in the Jurkat cell line. The toxin was also found to activate a tyrosine protein kinase in these cells in a manner similar to that observed with phytohemagluttinin. These results provide evidence that the mechanism of activation of T cells by pertussis toxin involves stimulating the activity of protein kinase C and a tyrosine protein kinase.
The cysteine S conjugate of 1,2-dichloroethane, S-(2-chloroethyl)-DL-cysteine (CEC), is hepatotoxic, nephrotoxic, and mutagenic. To determine the cellular and chemical mechanisms involved in CEC-induced toxicity and to assess the role of an episulfonium ion, the effect of CEC on the viability of isolated rat hepatocytes was studied. CEC addition resulted in both a time- and concentration-dependent loss of cell viability. Depletion of intracellular glutathione concentrations (greater than 70%) and inhibition of microsomal Ca2+ transport and Ca2+-ATPase activity preceded the loss of cell viability, and initiation of lipid peroxidation paralleled the loss of viability. The depletion of glutathione concentrations was partially attributable to a reaction between glutathione and CEC to form S-[2-(DL-cysteinyl)ethyl]glutathione, which was identified by NMR and mass spectrometry. N-Acetyl-L-cysteine, vitamin E, and N,N'-diphenyl-p-phenylenediamine protected against the loss of cell viability. N,N'-Diphenyl-p-phenylenediamine inhibited CEC-initiated lipid peroxidation but did not protect against cell death at 4 h, indicating that lipid peroxidation was not the cause of cell death. The analogues S-ethyl-L-cysteine, S-(3-chloropropyl)-DL-cysteine, and S-(2-hydroxyethyl)-L-cysteine, which cannot form an episulfonium ion, were not cytotoxic, thus demonstrating a role for an episulfonium ion in the cytotoxicity associated with exposure to CEC and, possibly, 1,2-dichloroethane. These results show that an alteration in Ca2+ homeostasis and the generation of an electrophilic intermediate may be involved in the mechanism of cell death.
The LSTRA cell line has been shown to have an exceptionally high level of a tyrosine protein kinase (pp56rck). We now report that LSTRA cells also have a much higher level of proteins phosphorylated on tyrosine residues in comparison to several other cell lines with normal levels of pp56kk. The level of phosphotyrosine-containing proteins in LSTRA cells was comparable to that seen in K562 cells, a cell line known to have a constitutively active tyrosine protein kinase. These results provide evidence that LSTRA cells have an elevated level of in vivo tyrosine protein kinase activity, probably due to the overexpression and activation of pp56tck.Tyrosine protein kinase; Phosphotyrosine antibody; (Lymphoid cell)
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