Doxycycline reduction of F-actin content of human neutrophils and fibroblasts

We and others have shown that tetracyclines inhibit leukocyte adherence, migration, and phagocytosis, functions presumed to involve actin microfilament metabolism. In this study we investigated the influence of a tetracycline (doxycycline, Dc) on neutrophil and fibroblast actin metabolism. Human neutrophils and fibroblasts were pretreated with Dc or cytochalasin B (cB), stimulated with either the chemotactic peptide FMLP or phorbol myristate acetate (PMA), and the changes in phalloidin conjugate, associated F-actin were followed microscopically or quantified fluorometrically. Doxycycline suppressed, in a dose-related manner, the rise in F-actin content of neutrophils that normally follows their activation with either FMLP or PMA. Cytochalasin B had a similar affect on actin microfilament synthesis. Incubation of fibroblasts in Dc led to a loss of actin microfilaments and caused flattened adherent cells to round up and detach. Both Dc and cB also inhibited Con A-induced acceptor capping on neutrophils, a phenomenon known to be dependent on the presence of intact actin microfilaments. The data show that both Dc and cB influence actin metabolism and suggest they do so by differing mechanisms.