Tumor cell–induced endothelial cell necroptosis promotes tumor cell extravasation and metastasis.
Major finding: Tumor cell–induced endothelial cell necroptosis promotes tumor cell extravasation and metastasis.
Mechanism: Transmembrane APP expressed by tumor cells binds to endothelial DR6 to trigger necroptosis.
Impact: Targeting DR6-mediated endothelial cell necroptosis may be a potential therapeutic strategy.
The metastatic potential of tumor cells (TC) during extravasation, which occurs in the intermediate stages of the invasion–metastasis cascade, is dependent upon the rapid exit of tumor cells through endothelium. Strilic and colleagues sought to elucidate the molecular mechanisms underlying TC–endothelium interactions during tumor cell extravasation. Co-cultures of TCs and endothelial cells (EC) resulted in necroptotic endothelial cell death and enhanced TC transendothelial migration. Knockdown of two mediators of necroptosis, receptor interacting serine/threonine kinase 3 (RIPK3) and mixed lineage kinase domain-like (MLKL), or treatment with necrostatin-1, which inhibits the necroptosis-related enzyme RIPK1, resulted in decreased EC necroptosis and TC migration over an EC layer. Similarly, intravenous injection of metastatic murine TCs resulted in necroptotic lung ECs and metastasis formation in wild-type mice, whereas endothelial cell-specific RIPK3 knockout mice and MLKL-deficient mice exhibited a reduction in necroptotic cells, TC extravasation, and metastases after TC injection. Inhibition of caspase-8, a negative regulator of necroptosis, resulted in increased EC necroptosis, TC extravasation, and metastatic burden in vivo. An siRNA screen of endothelial receptors showed that death receptor 6 (DR6; also known as tumor necrosis factor receptor superfamily member 21 and encoded by TNFRSF21), which is expressed on both murine and human ECs, promoted TC-induced necroptosis and transmigration. Consistent with these findings, DR6 knockout mice or mice injected with DR6-blocking antibodies which were injected with TCs exhibited decreased metastasis compared to control mice. Knockdown of amyloid precursor protein (APP), which is a ligand of DR6, in TCs reduced TC-mediated EC necroptosis, TC transendothelial migration, and the formation of metastases in vivo. Further, EC necroptosis was induced by co-culture with transmembrane APP–expressing TCs and not by soluble APP. Together, these results describe a mechanism by which tumor cells interact with endothelial cells during tumor cell extravasation and formation of metastases and identify a potential clinically translatable antimetastatic therapeutic approach.