Divergent effects of co‐carcinogenic phorbol esters and a synthetic diacylglycerol on human neutrophil chemokinesis and granular enzyme secretion

Abstract

The effects of two co‐carcinogenic phorbol esters (phorbol myristate acetate (PMA) and phorbol dibutyrate (PDBu)) and a synthetic diacylglycerol (OAG, 1‐oleoyl‐2‐acetyl‐glycerol), which all stimulate protein kinase C, were compared with two inactive phorbol compounds (4α‐phorbol and 4α‐phorbol didecanoate (4α‐PDD)) on three functional properties of stimulated human polymorphonuclear leukocytes (PMNs): release of granular enzymes lysozyme and β‐glucuronidase, chemokinesis, and changes in cytoplasmic free calcium [Ca2+]i. PMA, PDBu and the diacylglycerol, OAG, all caused a dose‐dependent and slow (max by 15 min) release of small amounts of lysozyme with much less β‐glucuronidase and no release of cytoplasmic lactate dehydrogenase. Release was unaffected by removal of extracellular Ca2+. PMA, PDBu and OAG inhibited random movement of the cells, did not cause chemokinesis and induced a slow reduction in the basal [Ca2+]i, as measured by the quin‐2 method. PMA, PDBu and OAG increased the capacity of five independently‐acting stimulants (N‐formyl‐Met‐Leu‐Phe, leukotriene B4, C5a des‐Arg, platelet activating factor and A23187) to cause release of lysozyme and β‐glucuronidase but strongly inhibited PMN chemokinesis induced by the same five agents and reduced the stimulant‐induced increases in [Ca2+]i. PMA was always more potent than PDBu and much more potent than OAG in eliciting these stimulatory or inhibitory effects on human PMNs. In all tests, 4α‐phorbol and 4α‐PDD were inactive. The results confirm that stimulation of the diacylglycerol/protein kinase C system in human PMN, either by active phorbol esters or the synthetic diacylglycerol, causes bidirectional effects on human PMN function. In particular, activation of the C‐kinase causes inhibition of stimulated neutrophil motility, whereas the secretory functions of the cells are enhanced.

Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle

“…Another plausible explanation is that the aforementioned study used PDBu, whereas we utilized the PKC activator PMA. PMA and PDBu are phorbol esters that mimic DAG, the natural activator of PKC; however, differences in pharmacological properties of PDBu and PMA were reported, and the results showed that PMA is a more potent PKC activator (30). We should also consider that there are 11 different PKC isoforms, classified into 3 major groups (18,23,28,29).…”

A Molecular Defect in Intracellular Lipid Signaling in Human Neutrophils in Localized Aggressive Periodontal Tissue Damage

“…27. Moreover, DAGK inhibition or treatment with synthetic DAG species leads to alterations in normal PMN motility (35)(36)(37). Therefore, defective DAGK expression provides a potential molecular basis that may explain disparate functional responses in PMN from patients with LAP, namely, agonist-specific reduced motility and enhanced production of superoxide anions and related reactive oxygen species.…”

Hyperglycemia in vitro attenuates insulin-stimulated chemokinesis in normal human neutrophils. Role of protein kinase C activation

“…Also, the fMet-Leu-Phe-induced change of neutrophil shape to a polarized, locomotory cell shape in suspension was counteracted by the addition of PMA [21]. The PMA concentrations that efficiently decreased neutrophil locomotion and shape changes are found to be in the nanomolar range (this study) [21,30,31]. In this context, it is important to recall that in order to activate secretion of superoxide anions from the NADPH-oxidase, at least 10 times higher PMA concentrations are needed.…”

“…PKC activation by phorbol esters, like PMA, is known to inhibit random locomotion of neutrophils (this study) [21] and of Walker carcinosarcoma cells [30], as well as inhibiting neutrophil chemokinesis stimulated by several agonists (i.e., fMet-Leu-Phe, leukotriene B 4 , C5a, platelet-activating factor) [31]. Also, the fMet-Leu-Phe-induced change of neutrophil shape to a polarized, locomotory cell shape in suspension was counteracted by the addition of PMA [21].…”