Dynamic aspects of cytoskeletal protein distribution in T lymphocytes: involvement of calcium in spectrin reorganization.

Our studies on the lymphocyte cytoskeleton have revealed a significant heterogeneity in the subcellular distribution of lymphocyte spectrin in vivo. Two model systems have been characterized in which this protein exhibits dynamic properties in response to activation signals. In this study, we have investigated the role of calcium in the activation-induced reorganization of spectrin in one of these systems, the DO-11.10 T cell hybridoma. DO-11.10 cells, as well as several other in vitro T cell models, can homogeneously and constitutively express a distinct cytoplasmic aggregate of spectrin that is rapidly fragmented upon activation. The reversible dissipation of the aggregate of spectrin is accompanied by an increase in the levels of spectrin diffusely distributed throughout the cytoplasm and at the plasma membrane. Pretreatment of cells with calcium-free medium, or with medium containing ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetraacetic acid (EGTA) or verapamil, significantly blocked the reorganization of spectrin induced by Concanavalin A or the calcium ionophore A23187, and also prevented the release of IL-2 from these cells. Further, immunofluorescent and ultrastructural analyses revealed abnormalities in the organization of spectrin induced by these treatments. These findings are discussed in light of our other studies, indicating a role for spectrin in early events associated with activation of T lymphocytes in vivo and in vitro.