Association of Serine Protease with the Rise of Intracellular Calcium in Cytotoxic T Lymphocytes

Abstract

The precise role of the granular enzyme A (granzyme A), a serine protease, in the lytic process of cytotoxic T lymphocytes (CTL) is not clear. We have recently constructed a CTL line transfected with the antisense gene of granzyme A (a-GrA). These a-GrA CTL had lower GrA activity as well as decreased lytic activities, as measured by51Cr and by DNA degradation assays. Furthermore, at low effector:target ratio (1:8) in prolonged lytic assays, they could not lyse targets as rapidly as the control CTL. When we examined their ability to exocytose BLT (CBZ-L-lys-thiobenzyl)-esterase in the presence of anti-CD3 antibody, the a-GrA CTL exocytosed poorly compared to the parental CTL or control transfectant with a CAT gene. Most strikingly, a-GrA cells could not release intracellular stores of Ca2+in response to anti-CD3 induction, although the Ca2+flux was normal when they were stimulated with ionomycin. When the parental CTL was treated with a specific benzyllactam inhibitor of BLT-esterase orN-tosyl-L-phenylalanylchloromethyl ketone, the Ca2+flux induced by anti-CD3 was also suppressed. We propose that granzyme A is involved in the signal transduction pathway that causes the rise of the intracellular calcium.