Redistribution of Fodrin (a Component of the Cortical Cytoplasm) Accompanying Capping of Cell Surface Molecules

Fodrin, a protein composed of two polypeptides with molecular weights of 250,000 and 240,000, is concentrated in the cortical cytoplasm of neurons, and moves down the axons by the process of axonal transport. We have used immunofluorescence techniques to determine whether fodrin antigens also move in non-neuronal cells when cell surface ligands are induced to redistribute by crosslinking them. A redistribution of fodrin antigens occurred in the following instances: (i) when 3T3 cells were incubated with concanavalin A and anti-concanavalin A, surface concanavalin A receptors formed aggregates and fodrin antigens formed corresponding intracellular aggregates; (ii) when B lymphocytes were incubated with anti-Ig, the surface Ig formed caps and fodrin antigens formed intracellular subcaps; (iii) when T lymphocytes were treated with anti-H-2 followed by a secondary antibody, the H-2 antigen formed caps and fodrin formed corresponding subcaps. These observations show that fodrin antigens can move within non-neuronal cells, as well as in axons, and that their organization can be regulated by interaction between surface proteins and environmental stimuli. They also raise the possibility that fodrin, together with other proteins that form subcaps in lymphocytes (e.g., actin, myosin, and alpha-actinin) is a component of the cellular machinery responsible for the capping process. We consider whether the similarities between the movements of fodrin in lymphocyte capping and axonal transport may indicate that certain aspects of these two processes are related.