LL-37, the unique cathelicidin expressed in humans, in addition to acting as an endogenous antibiotic, is an important cell-signaling molecule upregulated in ovarian, breast, and lung tumors. However, the role of LL-37 in tumor microenvironment and its specific actions on the endothelial compartment remain elusive. Prostanoids are key regulators of inflammation, and cyclooxygenases (COXs) display proangiogenic activity in vitro and in vivo, mediated principally through prostaglandin E2 (PGE2). Here, we provide evidence for a novel proangiogenic role of LL-37, exerted via activation of endothelial cells and subsequent PGE2 biosynthesis.Approach and Results—
LL-37 triggers PGE2 synthesis in endothelial cells in a dose-dependent manner with maximal induction after 4 hours. Endothelial PGE2 biosynthesis was dependent on COX-1, rather than COX-2, as judged by pharmacological inhibition and gene silencing. In vitro matrigel assays supported these findings because LL-37–induced cord formation was abolished by COX-1, but not COX-2, small interfering RNA, and the angiogenic phenotype could be rescued by addition of exogenous PGE2. We find that LL-37 acts on endothelial cells as a potent calcium agonist, inducing phosphorylation and activation of cytosolic phospholipase A2 (cPLA2), promoting a cPLA2→COX-1→PGE2 biosynthetic pathway and subsequent signaling via PGE2 receptor EP3. Moreover, cathelicidin-related antimicrobial peptide, which is the murine ortholog of LL-37, induced prostaglandin-dependent angiogenesis in vivo, which could be blocked by aspirin.Conclusions—
Our results identify a novel proangiogenic role of LL-37, suggesting that the axis LL-37/COX-1/PGE2 followed by EP3 signaling is amenable to therapeutic intervention in pathological angiogenesis, for instance by aspirin.