Activation of phospholipase D is tightly coupled to the phagocytosis of Mycobacterium tuberculosis or opsonized zymosan by human macrophages.

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Abstract
Phagocytosis of Mycobacterium tuberculosis by human mononuclear phagocytes is mediated primarily by complement receptors (CRs) but the transmembrane signaling mechanisms that regulate phagocytosis of the bacterium are unknown. We have analyzed the activation of phospholipase D (PLD) during phagocytosis of the virulent Erdman and attenuated H37Ra strains of M. tuberculosis by human monocyte-derived macrophages (MDMs), radiolabeled with [3H]-lyso-phosphatidylcholine. Phagocytosis of either Erdman or H37Ra M. tuberculosis in the presence of autologous non-immune serum was associated with a 2.5-3-fold increase in phosphatidic acid (PA). Definitive evidence for activation of PLD by M. tuberculosis was provided by markedly increased generation of the PLD-specific product phosphatidylethanol (PEt) (9.9-fold increases in [3H]-PEt for both Erdman and H37Ra strains compared to control, P < 0.001, n = 12), in the presence of 0.5% ethanol. Phagocytosis of opsonized zymosan (OZ), which is also mediated by CRs, was similarly associated with activation of PLD (12.2-fold increase in PEt, P < 0.001, n = 12). The competitive PLD inhibitor 2,3-diphosphoglycerate (2,3-DPG) produced concentration-dependent inhibition of PLD activity stimulated by either M. tuberculosis (-78 +/- 8%) or OZ (-73 +/- 6%). Inhibition of PLD by 2,3-DPG was associated with concentration-dependent reductions in phagocytosis of M. tuberculosis (-74 +/- 4%) and OZ (-68 +/- 5%). Addition of purified PLD from Streptomyces chromofuscus to 2,3-DPG-treated macrophages restored phagocytosis of M. tuberculosis to control levels. Inhibition of M. tuberculosis- or OZ-stimulated PA generation by ethanol was associated with concentration-dependent reductions in phagocytosis of both particles. Incubation of MDMs with either Erdman or H37Ra M. tuberculosis, or OZ, resulted in rapid (onset 1 min) and sustained (60 min) increases in the tyrosine phosphorylation (Tyr-P) of multiple MDM proteins. Prominent Tyr-P was noted in proteins of 150, 95, 72, 56, and 42 kD. The protein tyrosine kinase (PTK) inhibitors genistein and herbimycin A reduced M. tuberculosis-stimulated PLD activity by 66-84%. Inhibition of PLD activity by genistein or herbimycin A was associated with inhibition of phagocytosis of M. tuberculosis and OZ. These data demonstrate that PLD is activated during macrophage phagocytosis of M. tuberculosis or OZ, that PTKs are involved in this stimulation of PLD, and that the extent of phagocytosis of these particles is tightly coupled to activation of PLD.

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