THE CYTOPLASMIC DOMAINS OF E-SELECTIN AND P-SELECTIN DO NOT CONSTITUTIVELY INTERACT WITH ALPHA-ACTININ AND ARE NOT ESSENTIAL FOR LEUKOCYTE ADHESION

The selectins are a family of carbohydrate-binding adhesion molecules involved in the regulation of leukocyte migration. Although there is s trong homology between different selectins in their extracellular regi ons, there is none in the cytoplasmic tails, suggesting selectin-speci fic functions for these domains. Our previous work showed that the cyt oplasmic tail of L-selectin interacts with the actin cytoskeleton via a-actinin and vinculin, and that truncation of the cytoplasmic tail of L-selectin blocked both association with alpha-actinin and vinculin a nd leukocyte adhesion. In the present study, the effects of truncation of the cytoplasmic tails of E- or P-selectin on cell adhesion and cel l surface expression were examined, and possible interactions between cr-actinin and the E- and P-selectin cytoplasmic tails were assessed. In contrast to previous observations demonstrating a requirement for t he L-selectin cytoplasmic tail, truncation of the E- or P-selectin cyt oplasmic domains had no effect on cell adhesion, or on cell surface ex pression, when assessed in transiently transfected COS cells. This lac k of effect on cell surface expression and adhesion was also observed when transfections were performed with lower amounts of cDNA, which le d to submaximal levels of expression. In addition, no interaction betw een a-actinin and the cytoplasmic tails of either E- or P-selectin cou ld be detected under conditions in which binding of alpha-actinin to t he L-selectin cytoplasmic tail could be readily demonstrated. Therefor e, interactions between the cytoplasmic tail of E- or P-selectin and l y-actinin or other cytoskeletal proteins are not necessary for leukocy te adhesion per se, but may facilitate downstream biologic events.