Padilla PI, Pacheco-Rodriguez G, Moss J, Vaughan M.
Nuclear localization and molecular partners
of BIG1, a brefeldin A -inhibited guanine nucleotide-exchange
protein for ADP-ribosylation factors.
Proc Natl Acad Sci U S A. 2004 Mar
2;101(9):2752-7.
Pulmonary-Critical Care Medicine Branch,
National Heart, Lung, and Blood Institute, National Institutes
of Health, Bethesda, MD 20892, USA. padillap@nhlbi.nih.gov
Brefeldin A-inhibited guanine nucleotide-exchange protein 1
(BIG1) is an approximately 200-kDa brefeldin A- inhibited
guanine nucleotide-exchange protein that preferentially
activates ADP-ribosylation factor 1 (ARF1) and ARF3. BIG1 was
found in cytosol in a multiprotein complex with a similar
ARF-activating protein, BIG2, which is also an A
kinase-anchoring protein. In HepG2 cells growing with serum,
BIG1 was primarily cytosolic and Golgi-associated. After
incubation overnight without serum, a large fraction of
endogenous BIG1 was in the nuclei. By confocal
immunofluorescence microscopy, BIG1 was localized with
nucleoporin p62 at the nuclear envelope (probably during
nucleocytoplasmic transport) and also in nucleoli, clearly
visible against the less concentrated overall matrix staining.
BIG1 was also identified by Western blot analyses in purified
subnuclear fractions (e.g., nucleoli and nuclear matrix).
Antibodies against BIG1, nucleoporin, or nucleolin
coimmunoprecipitated the other two proteins from purified
nuclei. In contrast, BIG2 was not associated with nuclear BIG1.
Also of note, ARF was never detected among proteins precipitated
from purified nuclei by anti-BIG1 antibodies, although
microscopically the two proteins do appear sometimes to be
colocalized in the nucleus. These data are consistent with
independent intracellular movements and actions of BIG1 and
BIG2, and they are also evidence of the participation of BIG1 in
both Golgi and nuclear functions.
PMID: 14973189 |
