IKKbeta phosphorylates p65 at S468 in transactivaton domain 2

Area of Science:

• Molecular Biology
• Cell Signaling
• Immunology

Background:

• Nuclear factor-kappa B (NF-kappaB) is a crucial transcription factor regulating immune responses and inflammation.
• Phosphorylation of NF-kappaB subunit p65 by IkappaB kinase (IKK) is a key regulatory step.
• Previous studies identified S536 in TAD1 as an IKK phosphorylation site.

Purpose of the Study:

• To investigate potential IKK phosphorylation sites in the second transactivation domain (TAD2) of NF-kappaB p65.
• To determine the specific IKK isoform responsible for phosphorylating p65 in TAD2.
• To elucidate the functional consequences of p65 phosphorylation at this newly identified site.

Main Methods:

• Recombinant IKKalpha and IKKbeta kinase assays using GST-p65 substrates.
• Site-directed mutagenesis to identify specific phosphorylation sites (S468A).
• Co-immunoprecipitation to assess protein interactions.
• NF-kappaB-driven luciferase reporter assays and RANTES mRNA analysis in reconstituted p65-/- MEFs.
• Stimulation with TNF-alpha and IL-1beta in various cell lines and primary cells.

Main Results:

• IKKbeta, but not IKKalpha, phosphorylated a p65 substrate lacking TAD1, identifying S468 as the primary IKK site in TAD2.
• S468 phosphorylation was rapidly induced by TNF-alpha and IL-1beta across diverse cell types.
• Phosphorylation at S468 occurred within the IkappaBalpha-p65 complex and was dependent on IKKbeta activity.
• p65 with S468 mutated to alanine (p65S468A) showed slightly elevated NF-kappaB activity and RANTES expression compared to wild-type p65.
• Nuclear translocation of p65 was unaffected by S468 mutation.

Conclusions:

• IKKbeta phosphorylates multiple sites on p65, including S468 in TAD2.
• IKKbeta mediates p65 phosphorylation within the inhibitory IkappaBalpha-p65 complex.
• Phosphorylation of p65 at S468 exerts a modest inhibitory effect on TNF-alpha- and IL-1beta-induced NF-kappaB activation.