Induction of p2z pnrinoreceptor-mediated phoipholipase d activity by lipopolyraccharide or interferon-gamma in a human monocytic cell line

The P_2z-purinoreceptor is a member of the ligand-gated ion channel family of ATP receptors and is expressed almost exclusively in myeloid cells. Several reports have demonstrated that in human monocytes and a human monocytic cell line (THP-1) inteiferon-gamma (Ifn) upregulates P_2z-mediated channel function and cytolysis. The Pz receptor has been shown in mouse macrophages to couple to phospholipase D (PLD) but the ability of immunomodulatory agents to regulate this activity has not been examined. We now show that in THP-1 cells bacterial lipopolysaccharide (LPS) or Ifn can upregulate Pz-mediated PLD activity. Either LPS or Ifn alone is sufficient for this effect but LPS plus Ifn are synergistic. With two days of treatment, Ifn alone induces this P_2z-mediated PLD activity at either 100 or 1000 μ/ml while LPS alone maximally induces at 1 μg/ml. In the presence of Ifn, however, P_2z-mediated PLD activity is maximally induced at 1 ng/ml LPS. LPS also upregulates ATP induced membrane depolarization in differentiated THP-1 cells, suggesting that the induced PLD activity may result from increased receptor expression. Interestingly, the CAMK-II inhibitor KN-62 completely inhibits P2Z-mediated PLD activity without affecting depolarization, indicating that CAMK-II may mediate PLD activation by ATP. Further studies will address agonist selectivity and other pharmacological inhibitors. The induction of P2z-mediated PLD by LPS or Ifn suggests that this PLD activity plays a role in activated macrophage function.