Background: The 14-3-3 family of proteins plays a key regulatory role in signal transduction, checkpoint control, apoptotic and nutrient-sensing pathways (1,2). 14-3-3 proteins are highly conserved and ubiquitously expressed. There are at least seven isoforms, β, γ, ε, σ, ζ, τ, and η that have been identified in mammals. The initially described α and δ isoforms are confirmed to be phosphorylated forms of β and ζ, respectively (3). Through their amino-terminal α helical region, 14-3-3 proteins form homo- or heterodimers that interact with a wide variety of proteins: transcription factors, metabolic enzymes, cytoskeletal proteins, kinases, phosphatases, and other signaling molecules (3,4). The interaction of 14-3-3 proteins with their targets is primarily through a phospho-Ser/Thr motif. However, binding to divergent phospho-Ser/Thr motifs, as well as phosphorylation independent interactions has been observed (4). 14-3-3 binding masks specific sequences of the target protein, and therefore, modulates target protein localization, phosphorylation state, stability, and molecular interactions (1-4). 14-3-3 proteins may also induce target protein conformational changes that modify target protein function (4,5). Distinct temporal and spatial expression patterns of 14-3-3 isoforms have been observed in development and in acute response to extracellular signals and drugs, suggesting that 14-3-3 isoforms may perform different functions despite their sequence similarities (4). Several studies suggest that 14-3-3 isoforms are differentially regulated in cancer and neurological syndromes (2,3).
Background: The transcriptional nuclear factor κB (NF-κB)/Rel transcription factors are present in the cytosol in an inactive state, complexed with the inhibitory IκB proteins. Activation occurs via phosphorylation of IκBα at Ser32 and Ser36, resulting in the ubiquitin-mediated proteasome-dependent degradation of IκBα and the release and nuclear translocation of active NF-κB dimers. The regulation of IκBβ and IκBε is similar to that of IκBα, however, the phosphorylation and degradation of these proteins occurs with much slower kinetics. Phosphorylation of IκBβ occurs at Ser/Thr19 and Ser23, while IκBε can be phosphorylated at Ser18 and Ser22. The key regulatory step in this pathway involves activation of a high molecular weight IkappaB kinase (IKK) complex, consisting of three tightly associated IKK subunits. IKKα and IKKβ serve as the catalytic subunits of the kinase. Activation of IKK depends on phosphorylation at Ser177 and Ser181 in the activation loop of IKKβ (176 and 180 in IKKα). NF-κB-inducing kinase (NIK), TANK-binding kinase 1 (TBK1), and its homolog IKKε (IKKi), phosphorylate and activate IKKα and IKKβ.