The Golgi-associated COPI-coated buds and vesicles contain beta/gamma-actin

It has been shown previously that the morphology and subcellular positionin g of the Golgi complex is controlled by actin microfilaments. To further ch aracterize the association between actin microfilaments and the Golgi compl ex, we have used the Clostridium botolinum toxins C2 and C3, which specific ally inhibit actin polymerization and cause depolymerization of F-actin in intact cells by the ADP ribosylation of G-actin monomers and the Rho small CTP-binding protein, respectively. Normal rat kidney cells treated with C2 showed that disruption of the actin and the collapse of the Golgi complex o ccurred concomitantly, However, when cells were treated with C3, the actin disassembly was observed without any change in the organization of the Golg i complex. The absence of the involvement of Rho was further confirmed by t he treatment with lysophosphatidic acid or microinjection with the constitu tively activated form of RhoA, both of which induced the stress fiber forma tion without affecting the Golgi complex. Immunogold electron microscopy in normal rat kidney cells revealed that beta- and gamma-actin isoforms were found in Golgi-associated COPI-coated buds and vesicles. Taken together, th e results suggest that the Rho signaling pathway does not directly regulate Golgi-associated actin microfilaments, and that beta- and gamma-actins mig ht be involved in the formation and/or transport of Golgi-derived vesicular or tubular intermediates.