Inactivation of Galpha(z) causes disassembly of the Golgi apparatus.

We showed previously that overexpression of the alpha subunit of G(z) or G(i2) suppresses nordihydroguaiaretic acid-induced Golgi disassembly. To determine whether the active form of Galpha is required to maintain the structure of the Golgi apparatus, we examined the effects of a series of Galpha GAPs, regulators of G protein signaling (RGS) proteins, on the Golgi structure. Expression of RGSZ1 or RGSZ2, both of which exhibit high selectivity for Galpha(z), markedly induced dispersal of the Golgi apparatus, whereas expression of RGS proteins that are rather selective for Galpha(q) or other Galpha(i) species did not. A mutated RGSZ1, which is deficient in the interaction with Galpha(z), did not induce Golgi disassembly. These results suggest that the active form of Galpha(z), but not Galpha(i2), is crucial for maintenance of the structure of the Golgi apparatus. Consistent with this idea, Golgi disruption also took place in cells transfected with a dominant-negative Galpha(z) mutant. Although previous studies showed that the expression of Galpha(z) is confined to neuronal cells and platelets, immunofluorescence and mRNA expression analyses revealed that it is also expressed, albeit at low levels, in non-neuronal cells, and is located in the Golgi apparatus. These results taken together suggest a general regulatory role for Galpha(z) in the control of the Golgi structure.

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