TRAF-3 interacts with p62 nucleoporin, a component of the nuclear pore central plug that binds classical NLS-containing import complexes

The TRAF-3 gene encodes a number of splice-variant isoforms that function as adapter molecules in NF-κB signaling, in part by associating with the cytoplasmic tails of CD40 or other TNF-receptor (TNF-R) family members. To identify downstream molecules in TRAF-3 signaling, a yeast two-hybrid library was screened with a full-length TRAF-3 construct. Nine independent TRAF-3 interacting clones encoded fragments of p62 Nucleoporin (p62), a 522 amino acid (aa) component of the nuclear pore central plug, that is known to bind karyopherin-β/classical-NLS import factor complexes. The interaction of p62 with TRAF-3 was specific, since p62 failed to interact with TRAF-2, -4, -5, or -6. Deletional analysis in yeast revealed that the p62:TRAF-3 interaction is mediated by a p62 carboxy (C)-terminal coiled-coil domain and TRAF-3’s fifth zinc (Zn) finger and coiled-coil domain. In human 293 T cells, recombinant TRAF-3 or p62 specifically co-immunoprecipitates the other species. In addition, endogenous p62 co-precipitates over-expressed TRAF-3. The functional effects of over-expressing a TRAF-3 binding fragment, p62(aa 336–522) were studied on NF-κB-dependent, or control STAT1-dependent reporter activity in 293 T cells, either resting or after stimulation by CD40 or IFN-γ, respectively. Over-expression of p62(aa 336–522) induces NF-κB activation in resting cells and augments CD40-induced NF-κB activation, but has no effect on control STAT1 reporter activity, either at baseline or after IFN-γ induction. The finding that TRAF-3 binds p62, suggests that TRAF-3 may serve as an adapter molecule at the nuclear membrane, in addition to its known adapter function at the plasma membrane.