The cytoplasmic domains of E- and P-selectin do not constitutively interact with α-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 strong homology between different selectins in their extracellular regions, there is none in the cytoplasmic tails, suggesting selectin-specific functions for these domains. Our previous work showed that the cytoplasmic tail of L- selectin interacts with the actin cytoskeleton via α-actinin and vinculin, and that truncation of the cytoplasmic tail of L-selectin blocked both association with α-actinin and vinculin and leukocyte adhesion. In the present study, the effects of truncation of the cytoplasmic tails of E- or P- selectin on cell adhesion and cell surface expression were examined, and possible interactions between α-actinin and the E- and P-selectin cytoplasmic tails were assessed. In contrast to previous observations demonstrating a requirement for the L-selectin cytoplasmic tail, truncation of the E- or P-selectin cytoplasmic domains had no effect on cell adhesion, or on cell surface expression, when assessed in transiently transfected COS cells. This lack of effect on cell surface expression and adhesion was also observed when transfections were performed with lower amounts of cDNA, which led to submaximal levels of expression. In addition, no interaction between α-actinin and the cytoplasmic tails of either E- or P-selectin could be detected under conditions in which binding of α-actinin to the L-selectin cytoplasmic tail could be readily demonstrated. Therefore, interactions between the cytoplasmic tail of E- or P-selectin and α-actinin or other cytoskeletal proteins are not necessary for leukocyte adhesion per se, but may facilitate downstream biologic events.