Regulation of the NF-kappaB activation pathway by isolated domains of FIP3/IKKgamma, a component of the IkappaB-alpha kinase complex.
FIP3, isolated as a type 2 adenovirus E3-14.7-kDa interacting protein, is an essential component of the multimeric IkappaB-alpha kinase (IKK) complex and has been shown to interact with various components (Fas receptor-interacting protein, NF-kappaB-inducing kinase, IKKbeta) of the NF-kappaB activation pathway. FIP3 has also been shown to repress basal and tumor necrosis factor (TNF) alpha-induced NF-kappaB activity as well as to induce cell death when overexpressed. The adenovirus E3-14.7-kDa protein (E3-14.7K) is an inhibitor of TNFalpha-induced cell death. In the current study, we generated deletion mutants to map the domains of FIP3, which are responsible for its various functions. The NF-kappaB inhibitory activity and the E3-14.7K binding domains were mapped at the carboxyl half of the FIP3 protein. We also found that the carboxyl-terminal half of FIP3 blocked TNFalpha-induced IkappaB-alpha phosphorylation and subsequent degradation, which suggests that the stabilization of the cytoplasmic inhibitor of NF-kappaB underlies the FIP3 inhibition of NF-kappaB activity. The amino-terminal 119 amino acids were responsible for the FIP3-IKKbeta and FIP3-IKKalpha interaction, and the middle of the protein (amino acids 201-300) appeared to be both the FIP3 self-association domain as well as the FIP3-Fas receptor-interacting protein interaction domain. Thus, FIP3 might serve as a scaffold protein to organize the various components of the IkappaB-alpha kinase complex. Whereas the full-length protein is required for efficient cell death, the amino-terminal 200 amino acids are sufficient to cause rounding and detachment of the cells from the monolayer.
Ye
J
J
Albert Einstein College of Medicine, Department of Microbiology and Immunology, Bronx, New York 10461, USA.
Xie
X
X
Tarassishin
L
L
Horwitz
M S
MS
D000596:Amino Acids / Q000737:chemistry; D015536:Down-Regulation; D051550:I-kappa B Kinase; D016328:NF-kappa B / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors / Q000378:metabolism; D014764:Viral Proteins / Q000737:chemistry / Q000378:metabolism*
D000596:Amino Acids; D016328:NF-kappa B; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D017346:Protein Serine-Threonine Kinases; D051550:I-kappa B Kinase