Primary human CD4(+) T cells contain heterogeneous I kappa B kinase complexes: Role in activation of the IL-2 promoter

NF-kappa B transcription factors play an important role in the activation o f the IL-2 gene in response to TCR ligation, The release of NF-kappa B fact ors to the nucleus requires phosphorylation and degradation of the inhibito ry kappa-B proteins (I kappa Bs). I kappa B alpha and I kappa B beta phosph orylation is dependent on dual signaling by the TCR and the CD28 accessory receptor, This pathway involves a multisubunit I kappa B kinase (IKK) compl ex, which includes the IKK alpha (IKK-1) and IKK beta (IKK-2) kinases. We d emonstrate that stimulation of primary human CD4(+) T cells by CD3/CD28 act ivates two distinct endogenous IKK complexes, a heterodimeric IKK alpha/bet a and a homodimeric IKK beta complex, IKK beta overexpression in ct Jurkat cell line resulted in the formation of a constitutively active IKK complex, which was CD3/CD28 inducible, In contrast, ectopic expression of IKK-alpha assembled into a complex with negligible I kappa B kinase activity. Moreov er, IKK beta but not IKK alpha, overexpression enhanced transcriptional act ivation of the CD28 response element in the IL-2 promoter. Conversely, only kinase-inactive IKK beta interfered in the activation of the IL-2 promoter , Sodium salicylate, an inhibitor of IKK beta, but not IKK alpha activity, inhibited IL-2 promoter activation as well as IL-2 secretion and interfered in activation of both the heterodimeric as wed as the homodimeric IKK comp lexes in primary CD4(+) T cells. Taken together, these data demonstrate the presence of an IKK beta-mediated signaling pathway that is activated by TC R and CD28 coligation and regulates IL-2 promoter activity.