sPLA2s (secretory phospholipases A2) belong to a broad and structurally diverse family of enzymes that hydrolyse the sn-2 ester bond of glycerophospholipids. We previously showed that a secreted fungal 15 kDa protein, named p15, as well as its orthologue from Streptomyces coelicolor (named Scp15) induce neurite outgrowth in PC12 cells at nanomolar concentrations. We report here that both p15 and Scp15 are members of a newly identified group of fungal/bacterial sPLA2s. The phospholipid-hydrolysing activity of p15 is absolutely required for neurite outgrowth induction. Mutants with a reduced PLA2 activity exhibited a comparable reduction in neurite-inducing activity, and the ability to induce neurites closely matched the capacity of various p15 forms to promote fatty acid release from live PC12 cells. A structurally divergent member of the sPLA2 family, bee venom sPLA2, also induced neurites in a phospholipase activity-dependent manner, and the same effect was elicited by mouse group V and X sPLA2s, but not by group IB and IIA sPLA2s. Lysophosphatidylcholine, but not other lysophospholipids, nor arachidonic acid, elicited neurite outgrowth in an L-type Ca2+ channel activity-dependent manner. In addition, p15-induced neuritogenesis was unaffected by various inhibitors that block arachidonic acid conversion into bioactive eicosanoids. Altogether, these results delineate a novel, Ca2+- and lysophosphatidylcholine-dependent neurotrophin-like role of sPLA2s in the nervous system.
Abbreviations used: PLA2, phospholipase A2; bvPLA2, bee venom PLA2; CAM, cell adhesion molecule; COX, cyclo-oxygenase; HA, haemagglutinin; LOX, lipoxygenase; lysoPC, lysophosphatidylcholine; MAPK, mitogen-activated protein kinase; NDGA, nordihydroguaiaretic acid; NGF, nerve growth factor; PA, palmitic acid; PC, phosphatidylcholine; rbvPLA2, recombinant bvPLA2; sPLA2, secretory PLA2; mcPAF, methylcarbamyl platelet-activating factor C-16; DMEM, Dulbecco's modified Eagle's medium.