Implication of three isoforms of PLA 2 in human T-cell proliferation

Abstract

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, Ca 2+-dependent and type VI, Ca 2+-independent). In order to assess whether these PLA 2 isoforms are active, we labeled Jurkat T-cells with [ 3H]arachidonic acid ([ 3H]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 2s, significantly inhibited the release of free [ 3H]AA. On the other hand, arachidonyl trifluoromethyl ketone (AACOCF 3), an inhibitor of type IV PLA 2, failed to curtail significantly the release of free [ 3H]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 AACOCF 3, 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.