Implication of three isoforms of PLA2 in human T-cell proliferation

We observed that human (Jurkat) T-cells constitutively expressed the mRNA, encoding for the four isoforms of phospholipase A(2) (PLA(2)), i.e. two secretory (type IB and type V), and two cytosolic (type IV, Ca2+-dependent and type VI, Ca2+-independent). In order to assess whether these PLA2 isoforms are active, we labeled Jurkat T-cells with [H-3]arachidonic acid ([H-3]AA) and determined its release into the extracellular medium in the presence of phorbol 12-myristate 13-acetate (PMA) and ionomycin. The three PLA(2) isoforms seem functional as aristolochic acid and bromoenol lactone (BEL), the respective inhibitors of type IB/type V and type VI PLA(2)s, significantly inhibited the release of free [H-3]AA. On the other hand, arachidonyl trifluoromethyl ketone (AACOCFA an inhibitor of type IV PLA(2), failed to curtail significantly the release of free [H-3]AA into the extracellular medium. We assessed the implication of these PLA(2) isoforms in transcription of the interleukin-2 (IL-2) gene, involved in T-cell proliferation. Hence, aristolochic acid and BEL, but not AACOCF(3), significantly inhibited the PMA and ionomycin-induced induction of mRNA of IL-2. Similarly, aristolochic acid and BEL, but not AACOCF3, significantly inhibited the PMA and ionomycin-induced secretion of IL-2 in the culture supernatants. Together these results suggest that human Jurkat T-cells possess two secretory and two cytosolic PLA(2) isoforms and only three of them (type IB, type V and type VI) are implicated in T-cell proliferation. (C) 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.