Differential regulation of p65 and c-Rel NF-κB transactivating activity by Cot, protein kinase C ζ and NIK protein kinases in CD3/CD28 activated T cells

It has been shown that phosphorylation of p65/RelA and c-Rel plays a role in the regulation of transcriptional activity of NF-κB independent on IκB degradation. In this study, we show that anti CD3/CD28 activation induces the transactivation activity of both p65/RelA and c-Rel in T cells using Gal4 dependent assays. Moreover, protein kinase C (PKC)ζ, Cot kinase and NF-κB-inducing kinase (NIK) seem to be involved in those processes in a different manner. Thus, transfection of dominant negative forms of Cot and PKCζ inhibits CD3/CD28 induction of Gal4-p65 transactivation, whereas the kinase inactive versions of the 3 kinases inhibit induction of Gal4-c-Rel. Cot induction of Gal4-c-Rel transactivating activity seems to be mediated sequentially through PKCζ and NIK activation, since dominant negative form of NIK blocks Cot and PKCζ induction, whereas kinase inactive PKCζ only blocks Cot activity. In contrast, the contribution of NIK to the transactivation function of p65/RelA seems to be negligible and more importantly NIK-KD did not inhibit induction by Cot and PKCζ. Besides, the enhancing effect of Cot on Gal4-p65 was not decreased in mouse embryo fibroblasts from NIK deficient aly/aly mice in contrast with a greatest reduction on Gal4-c-Rel. By using Ser to Ala mutants in p65 and c-Rel transactivation domains, PKCζ and NIK activities seem to be dependent of a restricted set of Ser in both proteins. In contrast, the enhancing effect of Cot seems to be less dependent of a particular set of Ser residues being partially abrogated by mutation of several Ser residues.