Comment on "PDK1 nucleates T cell receptor-induced signaling complex for NF-kappaB activation".

We observe that protein kinase C (PKC) is phosphorylated on the activation loop at threonine 538 (Thr-538) before T cell activation. Our results are inconsistent with the conclusions of Lee et al. (Reports, 1 April 2005, p. 114) that the Thr-538 phosphorylation of PKC is regulated by T cell receptor activation. Other mechanisms, such as autophosphorylation of Thr-219, might orchestrate the cellular function of PKC in T cells.