The overproduction and extracellular buildup of amyloid-beta peptide (A beta) is a critical step in the etiology of Alzheimer's disease. Recent data suggest that intracellular trafficking is of central importance in the production of A beta. Here we use a neuronal cell line to examine two structurally similar clathrin assembly proteins, AP180 and CALM. We show that RNA interference-mediated knockdown of AP180 reduces the generation of A beta 1-40 and AP1-42, whereas CALM knockdown has no effect on A beta generation. Thus AP180 is among the traffic controllers that oversee and regulate amyloid precursor protein processing pathways. Our results also suggest that AP180 and CALM, while similar in their domain structures and biochemical properties, are in fact dedicated to separate trafficking pathways in neurons.. Published by Elsevier Inc.