Stimulation of actin synthesis in phalloidin-treated cells. Evidence for autoregulatory control

We used the technique of scrape loading to introduce phalloidin into mouse embryo fibroblasts in mass culture. Phalloidin almost completely destroyed actin microfilament bundles, but the amount of polymerized cytoskeleton-associated actin was increased approximately two-fold and the amount of monomeric (Triton X-100 extractable) actin was significantly reduced. The major result of the present study is that the rate of actin synthesis in the phalloidin-treated cells was 2-3 times higher than in the control cells. Northern blot and translation in a cell-free system from rabbit reticulocytes showed that the actin mRNA level significantly increased as a result of phalloidin treatment.