Lactacystin is a microbial metabolite isolated from Streptomyces that is now widely used as a selective inhibitor of the 20S proteasome. Lactacystin was first characterized by its ability to induce differentiation and inhibit cell cycle progression in several tumor cell lines. At concentrations from 2 to 10 μM, lactacystin induces the outgrowth of neurites in the neuroblastoma cell line Neuro2a. Lactacystin irreversibly alkylates subunit X of the 20S proteasome. The concomitant inhibition of proteasome peptidase activity results in the accumulation of a variety of ubiquitinated proteins which would normally undergo rapid degradation. Thus, the effects of lactacystin are pleiotropic and depend substantially on the expression pattern of signalling proteins within the treated cell.
