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* Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud,
66030 Santa Maria Imbaro (Chieti), Italy; and We have investigated the role of the ADP-
ribosylation induced by brefeldin A (BFA) in the
mechanisms controlling the architecture of the Golgi
complex. BFA causes the rapid disassembly of this organelle into a network of tubules, prevents the association of coatomer and other proteins to Golgi membranes, and stimulates the ADP-ribosylation of two
cytosolic proteins of 38 and 50 kD (GAPDH and
BARS-50; De Matteis, M.A., M. DiGirolamo, A. Colanzi, M. Pallas, G. Di Tullio, L.J. McDonald, J. Moss,
G. Santini, S. Bannykh, D. Corda, and A. Luini. 1994. Proc. Natl. Acad. Sci. USA. 91:1114-1118; Di Girolamo,
M., M.G. Silletta, M.A. De Matteis, A. Braca, A. Colanzi, D. Pawlak, M.M. Rasenick, A. Luini, and D. Corda. 1995. Proc. Natl. Acad. Sci. USA. 92:7065-7069).
To study the role of ADP-ribosylation, this reaction
was inhibited by depletion of NAD+ (the ADP-ribose
donor) or by using selective pharmacological blockers
in permeabilized cells. In NAD+-depleted cells and in
the presence of dialized cytosol, BFA detached coat
proteins from Golgi membranes with normal potency
but failed to alter the organelle's structure. Readdition
of NAD+ triggered Golgi disassembly by BFA. This effect of NAD+ was mimicked by the use of pre-ADP-
ribosylated cytosol. The further addition of extracts enriched in native BARS-50 abolished the ability of
ADP-ribosylated cytosol to support the effect of BFA.
Pharmacological blockers of the BFA-dependent
ADP-ribosylation (Weigert, R., A. Colanzi, A. Mironov, R. Buccione, C. Cericola, M.G. Sciulli, G. Santini, S. Flati, A. Fusella, J. Donaldson, M. DiGirolamo, D. Corda, M.A. De Matteis, and A. Luini. 1997. J. Biol. Chem. 272:14200-14207) prevented Golgi disassembly by BFA in permeabilized cells. These inhibitors
became inactive in the presence of pre-ADP-ribosylated cytosol, and their activity was rescued by supplementing the cytosol with a native BARS-50-enriched fraction. These results indicate that ADP-ribosylation
plays a role in the Golgi disassembling activity of BFA,
and suggest that the ADP-ribosylated substrates are
components of the machinery controlling the structure
of the Golgi apparatus.
Department of Biology, University of California at San Diego, La Jolla,
California 92093
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