Increased apoptosis in U937 cells over-expressing lipocortin 1 (annexin I)

The potential involvement of endogenous lipocortin 1 in the process of cell ular apoptosis, particularly in cells of the myelo-monocytic lineage, has b een investigated. U937 cells were transfected either with an antisense or a sense DNA for Lipocortin 1 and the stable clones 36.4AS clone (20-40% lowe r Lipocortin 1 levels) and 15S (30% higher lipocortin 1 levels) were obtain ed. Cell apoptosis was induced by incubation with tumor necrosis factor-a: optimal responses were observed within a 24 h incubation period at a 5 ng/m l concentration. Apoptosis was assessed both morphologically, by annexin V binding and cell cycle analysis with propidium iodide. Whilst no consistent difference was seen between wild type cells and clone 36.4AS, a higher inc idence of apoptosis (ranging from +30% to +60%) was observed in the 15S clo ne. Release of arachidonic acid from loaded cells was promoted by 24 h incu bation with the cytokine, and a higher degree of release was measured in th e 15S clone. These data indicate that endogenous intracellular lipocortin 1 is involved in the promotion of apoptosis in cells of the myelo-monocytic derivation. (C) 2000 Elsevier Science Inc.