Morphological changes in the Golgi complex correlate with actin cytoskeleton rearrangements

In this report we have studied the morphological changes of the Golgi compl ex (GC) that specifically accompany F-actin reorganizations. In starved rat RBL-2H3 tumor mast cells, the GC, that was visualized at immunofluorescenc e level with antibodies raised against the Golgi-resident proteins giantin, mannosidase II, or TGN-38, showed a compacted morphology with a supranucle ar positioning. Concomitant to membrane ruffle formation induced by epiderm al growth factor (EGF) or phorbol 12-myristate 13-acetate (PMA), and stress fiber formation induced by lysophosphatidic acid (LPA), specific GC morpho logical changes were observed. When cells were stimulated with EGF or PMA, the compacted GC morphology was transformed into a reticular network that w as extended towards the cell periphery. When cells were incubated with LPA, the GC acquired a characteristic ring-shaped morphology. Brefeldin A (BFA) did not affect the PMA- or LPA-induced membrane ruffling and stress fiber formation, respectively, indicating that actin rearrangements occurred inde pendent of the presence of the GC. Upon BFA removal, the presence of PMA or LPA during the recovery process induced the GC to acquire the morphologica l appearance described above for each agent. Moreover, the PMA- but not the LPA-induced GC rearrangements were sensitive to the actin perturbing agent s cytochalasin D and jasplakinolide. When cells were preincubated with the phosphatidylinositide 3-kinase (PI3K) inhibitors wortmannin or LY294002, th e PMA-induced GC morphological changes were inhibited but not membrane ruff les. Finally, the PMA-induced increase in the post-Golgi transport of glyco saminoglycans to the cell surface was not altered by cytochalasin D or jasp lakinolide. Altogether, these data suggest that: (1) the shape of the GC is influenced by the 3D arrangement of actin microfilaments; (2) PI3K regulat es the association of the GC with actin microfilaments; and (3) actin micro filaments are not essential for the post-Golgi transport to the plasma memb rane. Cell Motil. Cytoskeleton 43:334-348, 1999. (C) 1999 Wiley-Liss, Inc.