Selective inhibition by rottlerin of macropinocytosis in monocyte‐derived dendritic cells

Summary We present here the analysis of fluid‐phase endocytosis (FPE) in human blood monocytes and monocyte‐derived dendritic cells (MDDC) facilitated by our serendipitous identification of rottlerin as an efficient inhibitor of dendritic cell FPE (IC50 of 0·4 µM). Rottlerin was found to be an excellent tool for FPE analysis: rapid‐acting, irreversible and selective for FPE (as opposed to receptor‐mediated endocytosis) at concentrations of 3 µM and below. The inhibitory effect was not due to toxicity or visible change in membrane ruffles, but affects on cytoskeletal reorganization were evident in MDDC treated with relevant rottlerin concentrations during adhesion. A marked increase in FPE was observed in 1 hr interleukin (IL)‐4 and granulocyte macrophage‐colony stimulating factor (GM‐CSF)‐stimulated monocytes. Moreover, rottlerin inhibited the augmented FPE of 1‐day cytokine treated monocytes and their augmented ability to induce T cell proliferative responses to tetanus toxoid. We conclude that rottlerin is a useful tool for investigating FPE and its functional importance.