Structure, function, and regulation of group V phospholipase A(2).

Area of Science:

• Biochemistry and Molecular Biology
• Immunology
• Cell Biology

Background:

• Phospholipase A(2) (PLA(2)) hydrolysis of membrane phospholipids is crucial for inflammatory eicosanoid production.
• Secretory group V PLA(2) (gVPLA(2)) has been implicated in eicosanoid biosynthesis in various cell types.

Purpose of the Study:

• To investigate the role and mechanism of secretory group V PLA(2) (gVPLA(2)) in inflammatory responses.
• To elucidate the unique structural and enzymatic properties of gVPLA(2) that enable its interaction with cell membranes.

Main Methods:

• Utilized mutational studies to understand gVPLA(2) structure-function relationships.
• Performed cell-based assays using neutrophils, eosinophils, and other cell lines.
• Investigated the effects of exogenously added gVPLA(2) on inflammatory cell activation and eicosanoid synthesis.

Main Results:

• gVPLA(2) possesses unique structural features enabling effective hydrolysis of phosphatidylcholine (PC) vesicles and mammalian cell plasma membranes.
• Exogenous gVPLA(2) directly induces eicosanoid biosynthesis in unstimulated human neutrophils and eosinophils by acting on outer plasma membranes.
• gVPLA(2) triggers leukotriene synthesis via activation of downstream signaling pathways, including MAP kinase.
• Heparan sulfate proteoglycans in neutrophils internalize and degrade cell surface-bound gVPLA(2), offering protection from lipolytic damage.

Conclusions:

• gVPLA(2)'s distinct structure and membrane-lytic activity allow it to initiate inflammatory cascades.
• gVPLA(2) can directly trigger inflammatory responses in immune cells, suggesting a role in physiological inflammatory conditions.
• Neutrophil surface proteoglycans play a protective role against gVPLA(2)-induced damage.