PHOSPHATIDIC-ACID GENERATION THROUGH INTERLEUKIN-2 (IL-2)-INDUCED ALPHA-DIACYLGLYCEROL KINASE ACTIVATION IS AN ESSENTIAL STEP IN IL-2-MEDIATED LYMPHOCYTE-PROLIFERATION

Proliferation of T lymphocytes is triggered by the interaction of inte rleukin 2 (IL-2) with its high affinity specific receptor that is expr essed on the cell surface following T lymphocyte activation. Significa nt advances have recently been made in identifying the multiple signal s that follow IL-2 receptor occupancy, although the exact mechanism re sponsible for IL-2-induced proliferation remains an enigma. It has bee n shown previously that unique species of phosphatidic acid are rapidl y produced in vivo following IL-2 binding. It was then suggested that, in contrast to other eukaryotic growth factor systems, phosphatidic a cid was at least in part generated through IL-2-induced diacylglycerol (DG) kinase activation. In the present study me demonstrate IL-2-depe ndent activation of the alpha isoform of DG kinase. Confocal microscop y studies reveal that the enzyme is located in the cytosol and nuclei of resting T cells. Interleukin 2 stimulation induces translocation of the enzyme to the perinuclear region. Furthermore, our results indica te that inhibition of the alpha isoform of DG kinase has a profound ef fect on IL-2-induced T cell growth. Studies on cell cycle distribution demonstrate that the inhibition of IL-2-induced phosphatidic acid pro duction induces arrest in late G1 phase of IL-2 dependent cells. Altog ether, these results link previous observations of interleukin 2 and p hosphatidic acid production to activation of an specific isoform of DG kinase and suggest that activation of this enzyme is part of a novel signaling cascade that utilizes phosphatidic acid as an effector molec ule.