Targeted deletion of protein kinase C lambda reveals a distribution of functions between the two atypical protein kinase C isoforms.

Protein kinase C lambda (PKClambda) is an atypical member of the PKC family of serine/threonine kinases with high similarity to the other atypical family member, PKCzeta. This similarity has made it difficult to determine specific roles for the individual atypical isoforms. Both PKClambda and PKCzeta have been implicated in the signal transduction, initiated by mediators of innate immunity, that culminates in the activation of MAPKs and NF-kappaB. In addition, work from invertebrates shows that atypical PKC molecules play a role in embryo development and cell polarity. To determine the unique functions of PKClambda, mice deficient for PKClambda were generated by gene targeting. The ablation of PKClambda results in abnormalities early in gestation with lethality occurring by embryonic day 9. The role of PKClambda in cytokine-mediated cellular activation was studied by making mouse chimeras from PKClambda-deficient embryonic stem cells and C57BL/6 or Rag2-deficient blastocysts. Cell lines derived from these chimeric animals were then used to dissect the role of PKClambda in cytokine responses. Although the mutant cells exhibited alterations in actin stress fibers and focal adhesions, no other phenotypic differences were noted. Contrary to experiments using dominant interfering forms of PKClambda, mutant cells responded normally to TNF, serum, epidermal growth factor, IL-1, and LPS. In addition, no abnormalities were found in T cell development or T cell activation. These data establish that, in vertebrates, the two disparate functions of atypical PKC molecules have been segregated such that PKCzeta mediates signal transduction of the innate immune system and PKClambda is essential for early embryogenesis.