The subunit RelA(p65) mediates NF-kB signal transduction in multiple ways

Thu, 03/31/2016 - 11:00

RelA (also known as p65) is an NF-kB family member and a subunit of the NF-kB transcription factor complex.  The mammalian NF-kB family has five members (NF-kB1, NF-kB2, RelA (p65), RelB, and c-Rel), each of which contains an N-terminal Rel homology domain. Active NF-kB protein complexes are dimeric (hetero- or homo-), and are made up of two family members. NF-kB signaling is activated in response to many different types of stimuli and modulates transcription of numerous downstream targets. NF-kB-mediated signaling plays known roles in inflammatory and immune responses (Hayden and Ghosh, 2008), as well as neuronal development and synaptogenesis (Boersma et al., 2011; Gutierrez et al., 2005).  Aberrant NF-kB activity has also been linked to various human diseases including a number of cancers (Perkins, 2012).

In the central nervous system, NF-kB activity is dependent on translocation to the nucleus, where the complex binds to DNA targets (Wellmann et al., 2001).  This relocation is often mediated by protein-protein interactions between NF-kB subunits and other transport proteins.  These interactions have been detected using antibody pairs (in the context of proximity ligation assays) as well as single antibodies for immunoprecipitation assays.  For instance one group has used these methods to show that RelA(p65) directly interacts with Heat Shock Cognate 70 (HSP70) in hippocampal neurons (Klenke et al., 2013), and that this interaction affects RelA(p65) subcellular localization.

NF-kB activity is also mediated via post-translational modification of its subunits (Huang et al., 2010). RelA(p65), for example, contains phosphorylation sites both in its C-terminal transactivation domain (O'Shea and Perkins, 2008) and Rel homology domain (Hochrainer et al., 2013). Individual and combinatorial phosphorylation at each of these sites can activate or repress NF-kB-mediated transcription in a cell type and disease state specific manner (Neumann and Naumann, 2007). Previous studies have used antibodies to detect RelA(p65) phosphorylation state and examine how different phosphorylation events affect activity (Hochrainer et al., 2013). One recent study found that mutation of the RelA(p65) phosphorylation site Thr505 leads to early onset of hepatocellular carcinoma and altered proliferative response to liver damage in mouse models (Moles et al., 2016). These results indicate that RelA(p65) phosphorylation at Thr505 is important for NF-kB tumor suppressor roles. Phospho-Thr505 specific antibodies can be used to detect this post translational modification in different experimental contexts.  Various other antibodies that detect other phosphorylation events on RelA(p65) (inducing Ser536, Ser529, Ser276, and Thr435) have also been used in a number of contexts to examine the functional significance of RelA(p65) post-translational modification. 


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