Amino-terminal fragments of laminin γ2 chain retract vascular endothelial cells and increase vascular permeability

Laminin 2 (Lm2) chain, a subunit of laminin-332, is a typical molecular marker of invading cancer cells, and its expression correlates with poor prognosis of cancer patients. It was previously found that forced expression of Lm2 in cancer cells promotes their invasive growth in nude mice. However, the mechanism of the tumor-promoting activity of Lm2 remains unknown. Here we investigated the interaction between Lm2 and vascular endothelial cells. When treated with an N-terminal proteolytic fragment of 2 (2pf), HUVECs became markedly retracted or shrunken. The overexpression of Lm2 or treatment with 2pf stimulated T-24 bladder carcinoma cells to invade into the HUVEC monolayer and enhanced their transendothelial migration in vitro. Moreover, 2pf increased endothelial permeability in vitro and in vivo. As the possible mechanisms, 2pf activated ERK and p38 MAPK but inactivated Akt in HUVECs. Such effects of 2pf led to prominent actin stress fiber formation in HUVECs, which was blocked by a ROCK inhibitor. In addition, 2pf induced delocalization of VE-cadherin and -catenin from the intercellular junction. As possible receptors, 2pf interacted with heparan sulfate proteoglycans on the surface of HUVECs. Moreover, we localized the active site of 2pf to the N-terminal epidermal growth factor-like repeat. These data suggest that the interaction between 2pf and heparan sulfate proteoglycans induces cytoskeletal changes of endothelial cells, leading to the loss of endothelial barrier function and the enhanced transendothelial migration of cancer cells. These activities of Lm2 seem to support the aberrant growth of cancer cells.