Protein Kinase C-θ Is Required for Efficient Positive Selection

Abstract

Protein kinase C-θ (PKCθ) is critical for TCR-initiated signaling in mature T cells, but initial reports found no requirement for PKCθ in thymocyte development. Thymocytes and peripheral T cells utilize many of the same signaling components and, given the significant role of PKCθ in peripheral T cells, it was surprising that it was not involved at all in TCR signaling in thymocytes. We decided to re-evaluate the role of PKCθ in thymocyte development using the well-characterized class II-restricted n3.L2 TCR-transgenic TCR model. Analysis of n3.L2 PKCθ−/− mice revealed a defect in thymocyte-positive selection, resulting in a 50% reduction in the generation of n3.L2 CD4 single-positive thymocytes and n3.L2 CD4 mature T cells. Competition between n3.L2 WT and n3.L2 PKCθ−/− thymocytes in bone marrow chimeras revealed a more dramatic defect, with a >80% reduction in generation of n3.L2 CD4 single-positive thymocytes derived from PKCθ−/− mice. Inefficient positive selection of n3.L2 PKCθ−/− CD4 single-positive cells resulted from “weaker” signaling through the TCR and correlated with diminished ERK activation. The defect in positive selection was not complete in the PKCθ−/− mice, most likely accounted for by compensation by other PKC isoforms not evident in peripheral cells. Similar decreased positive selection of both CD4 and CD8 single-positive thymocytes was also seen in nontransgenic PKCθ−/− mice. These findings now place PKCθ as a key signaling molecule in the positive selection of thymocytes as well as in the activation of mature T cells.

Gene Targeting RhoA Reveals Its Essential Role in Coordinating Mitochondrial Function and Thymocyte Development

“…Positive selection is accompanied by cell survival and proliferation (36). It is thus logical to postulate that an impaired survival and proliferation could contribute to the decreased DP, CD4 + SP and CD8 + SP thymocytes in RhoA −/− mice.…”

Roles of the NF- B Pathway in Lymphocyte Development and Function

“…Regardless of this finding, the conventional pathway is likely to contribute to NF-kB activation during pre-TCR signaling (Sun et al 2000;Lin and Wang 2004;Thome 2004;Felli et al 2005;Jost et al 2007). Obligate components of the conventional pathways include PKCu and "CBM" complex components Carma1, Bcl-10, and Malt1 (PKCu may have an NF-kB-independent role though [Morley et al 2008]). Interestingly, a recent study reports the existence of an unconventional signaling path for TCR-mediated activation of NF-kB in mature CD8, but not CD4 T cells (Kingeter and Schaefer 2008); if such a pathway was also functional during selection of CD8 thymocytes, it would be consistent with the role for NF-kB in the development of these cells as discussed previously.…”

Protein kinase Cη, an emerging player in T-cell biology

“…4,5 Interestingly, the defects in T-cell development in PKCθ-knockout mice are so mild as to have been overlooked until recently. 7 To test whether PKCθ functions in place of PKCη or vice versa in T-cell development, we analyzed PKCη -/-, PKCθ -/and double-knockout mice, and confirmed that redundancy indeed exists between the two PKCs. For example, development of mature thymocytes and peripheral T cells is unchanged or mildly changed in PKCη -/and PKCθ -/mice, respectively, but is severely impaired in double-knockout mice.…”