Comparative anatomy of phospholipase A2 structures

Activation of human granulocyte type 1-prophospholipase A2

Using an assay for measurement of released type 1-prophospholipase A2 (type 1-proPLA2) propeptides (PROP assay), we have shown that human granulocytes, but not lymphocytes or macrophages, abundantly express this 'pancreatic' type 1-proPLA2 zymogen. Stimulation with tumour necrosis factor-alpha (TNF-alpha) and other cytokines results in the immediate release from granulocytes of a mixture of free propeptides and type 1-proPLA2 precursor. We also found that granulocytes contain an approximately 29 kDa trypsin-like endogenous type 1-proPLA2 activator. PROP assay and TAP (trypsinogen activation peptide) assay of plasma samples accurately predicts the segregation of acute pancreatitis into three clearly defined categories of severity--mild, intermediate and severe--at the time of first hospital admission and over the next few hours of observation. Mild and intermediate pancreatitis are associated with a degree of granulocyte stimulation limited to the release of the unactivated type 1-proPLA2 precursor. Progression to severe disease is accompanied by the activation of granulocyte type 1-proPLA2, apparently carried to completion. This identifies the approximately 29 kDa endogenous activator of type 1-proPLA2 in granulocytes as a critical mediator at a threshold stage in acute pancreatitis, which marks the transition from uncomplicated pancreatitis to the potentially lethal disease. Specific inhibitors of this key regulatory enzyme modelled on the P3-P1 domain of the type 1-proPLA2 activation peptide would seem to be promising candidates for a new class of chemotherapeutic agents.

Regulation of extracellular phospholipase A2 activity: implications for inflammatory diseases

Phospholipases A2 (PLA2s; E.C.3.1.1.4) are a family of esterases that are involved in myriads of physiological and pathological processes. The involvement of these enzymes, especially the extracellular PLA2s, in the generation of proinflammatory lipid mediators makes them a very important target for investigation. These PLA2s have been suggested to be involved in the pathogenesis of several human inflammatory diseases. Thus, delineating the mechanism(s) of regulation of the activity of these enzymes may provide a better understanding of the pathophysiology of these diseases and allow the rational design and development of novel therapeutic agents. In this article, we provide a brief description of PLA2s in general with a special emphasis on extracellular enzymes, their mechanism(s) of action, and possible role in the pathogenesis of inflammatory diseases. Additionally, we describe: (i) a novel mechanism of activation of extracellular PLA2s by transglutaminases and (ii) the development of one class of antiinflammatory agents, antiflammins, derived from the active site structure of endogenous PLA2-inhibitory proteins.