Golgi-disturbing Agents

Pharmacological agents have proven useful for gaining fundamental insights into the biology of the Golgi apparatus. This review summarizes pertinent and recent work on the effects on this organelle of monensin, brefeldin A, bafilomycin, ilimaquinone, okadaic acid, retinoic acid, and nocodazole. The molecular targets of monensin, brefeldin A, ilimaquinone, and retinoic acid remain to be elucidated whereas those for bafilomycin (vacuolar H+-ATPase), okadaic acid (serine/threonine phosphatases types 1, 2a, and 2b), and nocodazole (microtubules) are reasonably well understood. The molecular target of brefeldin has not been defined, but has been suggested to involve guanine nucleotide exchange proteins acting on ADP-ribosylation factor 1. Whether a defined molecular target can be found for monensin must be questioned since its main action consists in exchanging protons for Na+ which leads to osmotic swelling of post-Golgi endosomal structures and Golgi subcompartments by virtue of its membrane-associated effect as a cationophore. Brefeldin A was one of the most thoroughly investigated Golgi-disturbing agents and proved instrumental in unraveling retrograde flow mechanisms in the secretory pathways. Okadaic acid attracted interest for its properties mimicking mitotic fragmentation of the Golgi apparatus. Nocodazole was instrumental in establishing the cytoskeletal anchoring of the Golgi apparatus close to the microtubular organizing center.