Group VI phospholipases A2: homeostatic phospholipases with significant potential as targets for novel therapeutics.

Group VI phospholipase A2 (PLA2) is a family of acyl hydrolases that targets the sn-2 fatty acid on the glycerophospholipid (GPL) backbone. These enzymes are grouped together based on structural homologies and catalytic activities that are independent of calcium and hence are also called the iPLA(2)s. Although the best characterized of these enzymes, iPLA2beta and iPLA2gamma, have long been proposed as homeostatic enzymes involved in basal GPL metabolism, recent studies indicate roles for these enzymes in biomedically relevant processes as well. For example, iPLA2 modulates calcium homeostasis by promoting replenishment of intracellular calcium stores. This function is likely of importance in the pathogenesis of Duchenne muscular dystrophy and potentially allergy as well. iPLA2 has a variety of roles in bacterial pathogenesis and the host response against bacterial and fungal infections. These characteristics suggest that the enzyme as a potential target to control infectious diseases. iPLA2 is linked to both proliferation and chemotherapy-induced apoptosis of tumor cells. As such, the enzyme is a potential target for cancer chemotherapy. Recent studies indicate essential roles for iPLA2 in glucose homeostasis, maintenance of energy balance, adipocyte development, and hepatic lipogenesis. Thus, the enzyme is an attractive target for drugs to control type II diabetes, fatty liver disease, and other manifestations of the metabolic syndrome. Several recent studies have associated iPLA2 inactivation with neurodegenerative diseases, suggesting the possibility that products of the iPLA2 reaction as potential treatments for these disorders. Together, these observations suggest iPLA2 as a novel and important target for drug development. However given the ubiquitous expression of the enzyme and its roles in basal GPL metabolism, drug strategies targeting iPLA2 must exhibit exquisite selectivity to avoid undesired side effects. Furthermore, the cell-specific nature of many iPLA2 functions may present another challenge in the design and implementation of drugs targeted to the enzyme.