Melanoma cell adhesion to injured arterioles: mechanisms of stabilized tethering

An isolated perfused vessel model was used to examine the mechanisms underlying the adhesive interactions between circulating tumor cells and subendothelial matrix in denuded arterioles. Arterioles ranging from 70 to 100 microm in diameter were isolated from rat mesentery, transferred to an isolated vessel chamber, cannulated on both ends with glass micropipettes, and perfused with media containing 10(6) hamster melanoma (RPMI 1856) cells/ml. In a second group of arterioles, the endothelium was denuded by running 2 ml of air through the vessel lumen. Since the tumor cells did not adhere to the vessel wall when perfused at physiologically relevant shear rates, perfusate flow was stopped and the tumor cells were allowed to settle onto the vessel wall for 20 min. After counting the number of tumor cells that settled onto the arteriolar wall, perfusate flow was re-initiated and unattached cells were washed away. The number of cells remaining adherent were counted and the percentage of adherent cells (relative to the total number of cells that settled on to the vessel wall during the period of no-flow) were calculated and compared among different groups. We observed that tumor cells are much more adhesive to denuded arterioles than to intact arterioles. To determine the mechanisms responsible for the adhesive interactions that become established and stabilized during the period of flow reduction, denuded arterioles were treated with fibronectin antiserum or Arg-Gly-Asp (RGD) peptides. Both treatments significantly reduced tumor cell adhesion to denuded arterioles. In subsequent studies, melanoma cells were treated with a transglutaminase inhibitor, monodansylcadaverine (MDC), which reduced the ability of adherent tumor cells to withstand the anti-adhesive effects of a subsequent increase in perfusate flow rate after the period of no-flow. Our data suggest that tumor cells adhere to fibronectin in the subendothelial matrix in denuded arterioles by an RGD-dependent mechanism. Moreover, our observations are consistent with the concept that a transglutaminase-catalysed reaction acts to stabilize the adhesive interactions between subendothelial matrix components and melanoma cells during the period of flow stasis such that the cells are able to withstand subsequent substantial increases in wall shear rate and remain adherent.