Phospholipase A2 antagonists inhibit nocodazole-induced Golgi ministack formation:: Evidence of an ER intermediate and constitutive cycling

Evidence has been presented both for and against: Obligate retrograde movement of resident Golgi proteins through the endoplasmic reticulum (ER) during nocodazole-induced Golgi ministack formation. Here, we studied the nocodazole-induced formation of ministacks using phospholipase A(2) (PLA(2)) antagonists, which have been shown previously to inhibit brefeldin A-stimulated Golgi-to-ER retrograde transport. Examination of clone; 9 rat;hepatocytes by immunofluorescence and immunoelectron microscopy revealed that a subset:of PLA, antagonists prevented nocodazole-induced ministack formation by inhibiting-two different trafficking pathways for resident Golgi enzymes; at 25 mu M, retrograde Golgi-to-ER transport was inhibited, whereas at 5 mu M, Golgi-to-ER trafficking was permitted, but resident Golgi enzymes accumulated in the ER. Moreover, resident Golgi enzymes gradually redistributed from the juxtanuclear Golgi or Golgi ministacks to the ER in cells treated with these PLA, antagonists alone. Not only was ER-to-Golgi transport of resident Golgi enzymes inhibited in cells treated with these PLA, antagonists, but transport of the vesicular stomatitis virus G protein out of the ER was also prevented. These results support a model of obligate retrograde recycle of Golgi resident enzymes during flocodazole-induced ministack formation and provide additional evidence that resident Golgi enzymes slowly and constitutively cycle between the Golgi and ER.