Calcineurin activation is only one calcium-dependent step in cytotoxic T lymphocyte granule exocytosis.
We have tested the idea that calcineurin, a calcium-dependent phosphatase that is critical for activating cytokine gene expression in helper T cells, plays a role in lytic granule exocytosis in cytotoxic T lymphocytes (CTLs). We used TALL-104 human leukemic CTLs as a model. Our results confirm an earlier report (Dutz, J. P., Fruman, D. A., Burakoff, S. J., and Bierer, B. E. (1993) J. Immunol. 150, 2591-2598) that immunosuppressive drugs inhibit exocytosis in CTLs stimulated either via the T cell receptor (TCR) or via TCR-independent soluble agents. Of the two recently reported alternate targets of immunosuppressive drugs (Matsuda, S., Shibasaki, F., Takehana, K., Mori, H., Nishida, E., and Koyasu, S. (2000) EMBO Rep. 1, 428-434 and Matsuda, S., and Koyasu, S. (2000) Immunopharmacology 47, 119-125), JNK is not required for lytic granule exocytosis, but we were not able to exclude a role for P38. Exocytosis could be inhibited by expressing GFP fused to a C-terminal fragment of CAIN (cabin 1), but not by expressing VIVIT-GFP. Finally, expressing either full-length or truncated constitutively active mutant calcineurin A enhanced lytic granule exocytosis. However, the mutant calcineurin was unable to support exocytosis when cells were stimulated in the absence of Ca2+ influx. Taken together, our results support the idea that activation of calcineurin is required for lytic granule exocytosis but suggest that it is not the sole Ca2+-dependent step.
Grybko
Michael J
MJ
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06268-3125.
Bartnik
Jakub P
JP
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06268-3125.
Wurth
Georjeana A
GA
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06268-3125.
Pores-Fernando
Arun T
AT
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06268-3125.
Zweifach
Adam
A
Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut 06268-3125. Electronic address: adam.zweifach@uconn.edu.
D019703:Calcineurin / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D005089:Exocytosis; D053804:Granzymes / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D019169:Jurkat Cells; D007938:Leukemia / Q000378:metabolism; D008213:Lymphocyte Activation; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D008954:Models, Biological; D015398:Signal Transduction; D013602:T-Lymphocytes, Cytotoxic / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D007166:Immunosuppressive Agents; D049452:Green Fluorescent Proteins; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4; D019703:Calcineurin; D053804:Granzymes; D002118:Calcium