Protein Kinase C β Controls Nuclear Factor κB Activation in B Cells Through Selective Regulation of the IκB Kinase α

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Abstract
Activation of the nuclear factor (NF)-κB transcription complex by signals derived from the surface expressed B cell antigen receptor controls B cell development, survival, and antigenic responses. Activation of NF-κB is critically dependent on serine phosphorylation of the IκB protein by the multi-component IκB kinase (IKK) containing two catalytic subunits (IKKα and IKKβ) and one regulatory subunit (IKKγ). Using mice deficient for protein kinase C β (PKCβ) we show an essential role of PKCβ in the phosphorylation of IKKα and the subsequent activation of NF-κB in B cells. Defective IKKα phosphorylation correlates with impaired B cell antigen receptor–mediated induction of the pro-survival protein Bcl-xL. Lack of IKKα phosphorylation and defective NF-κB induction in the absence of PKCβ explains the similarity in immunodeficiencies caused by PKCβ or IKKα ablation in B cells. Furthermore, the well established functional cooperation between the protein tyrosine kinase Bruton's tyrosine kinase (Btk), which regulates the activity of NF-κB and PKCβ, suggests PKCβ as a likely serine/threonine kinase component of the Btk-dependent NF-κB activating signal transduction chain downstream of the BCR.