Capping and mitogenesis: a model implicating microfilaments in lymphocyte activation.

In lymphocytes cap formation induced by concanavalin A (con A) was found to be concentration dependent on the mitogen in the presence of colchicine, a microtubule disrupting agent. The dose-respone of cap formation under these conditions was similar to mitogen dose-response. In addition, a direct correlation was found between con A capping induced in the presence of colchicine and mitogenic responses with con A alone. Agents such as dibutyryl cyclic AMP, which suppress mitogenic responses, decrease capping. Zinc increases capping when it causes enhancement of mitogenesis and decreases capping when it suppresses mitogenic response. These observations are interpreted on the basis of a model in which binding of con A to surface receptors leads to formation of microfilaments, which might be essential for capping as well as the initiation of DNA synthesis. Thus, the experimental observations in this report lend support to a model implicating the formation of microfilaments as a crucial event in triggering a variety of cellular responses following ligand binding.