NIH Research Festival
BIG1 and BIG2, brefeldin A-inhibited guanine nucleotide-exchange factors (GEFs) that activate ADP-ribosylation factors (Arfs) by accelerating the replacement of bound GDP with GTP, contain A kinase-anchoring protein (AKAP) sequences that act as scaffolds for multimolecular complexes. Multifunctional β-catenin, with critical roles in both cell-cell adhesion and Wnt-signaling pathways, was among HeLa cell proteins co-immunoprecipitated by antibodies against BIG1 or BIG2. Direct interaction of BIG1 N-terminal sequence with β-catenin, found in yeast two-hybrid studies, was confirmed using in vitro-synthesized proteins. Depletion of BIG1 and/or BIG2 or over-expression of GEF-inactive mutant, but not wild type, BIG1 or BIG2 interfered with β-catenin trafficking, leading to accumulation at perinuclear Golgi structures. Both phospholipase D activity and vesicular trafficking were required for effects of BIG1 and BIG2 on β-catenin activation. Levels of PKA (protein kinase A)-phosphorylated β-catenin S675 and β-catenin association with PKA, BIG1, and BIG2 were also diminished after BIG1/BIG2 depletion. In addition, transcriptional activity of β-catenin was lower in HeLa cells after BIG1 and/or BIG2 depletion, further consistent with their roles in regulating β-catenin action via S675 phosphorylation.
Scientific Focus Area: Cell Biology
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