Autocrine and paracrine transcriptional regulation of type IIA secretory phospholipase A2 gene in vascular smooth muscle cells

Objective - The inflammation that occurs during the development of atherosclerosis is characterized by a massive release of sPLA2-IIA ( group IIA secretory phospholipase A2) from vascular smooth muscle cells (VSMCs). We have investigated the autocrine function of sPLA2-IIA in rat aortic and human VSMCs. Methods and Results - We found that the transcription of the endogenous sPLA2-IIA gene increased by adding a cell supernatant containing human sPLA2-IIA proteins. We show that this effect was independent of the sPLA2 activity using sPLA2-IIA proteins lacking enzyme activity. Transient transfections with various sPLA2-IIA rat promoterluciferase constructs demonstrated that the C/EBP, NK-kappa B, and Ets transcription factors are involved in the increase in sPLA2-IIA gene transcription. We also found the M-type sPLA2 receptor mRNA in VSMCs, and we showed that the sPLA2-luciferase reporter gene was induced by the specific agonist of the sPLA2 receptor, aminophenylmannopyranoside ( APMP), and that this induction was mediated by the same transcription factor-binding sites. Finally, we used a sPLA2-IIA mutant unable to bind heparan-sulfate proteoglycans to show that the binding of wild-type sPLA2-IIA to proteoglycans is essential for the induction of an autocrine loop. Conclusions - We have thus identified new autocrine and paracrine pathways activating sPLA2-IIA gene expression in rat and human VSMCs.