Constitutively Active Protein Kinase B Enhances Lck and Erk Activities and Influences Thymocyte Selection and Activation

Abstract

Protein kinase B (PKB), a serine threonine kinase is critically involved in cellular proliferation and survival. To characterize its role in T cell development in vivo, we have analyzed transgenic mice that express a membrane-targeted constitutively active version of PKB (myr PKB) in thymocytes and peripheral T cells. We report that myr PKB renders proliferative responses of thymocytes more sensitive to TCR signals by increased and sustained activation of Src kinase Lck and the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway. In addition, the proliferative response of myr PKB T cells is relatively independent of calcium mobilization and calcineurin activity. We also find that myr PKB enhances phosphorylation of glycogen synthase kinase 3, a negative regulator of NFAT and T cell activation, and the recruitment of the adapter protein Cbl-c. Interestingly, we demonstrate that upon TCR/CD3 stimulation of wild-type T cells PKB is translocated into lipid rafts, adding a new role for PKB in TCR-initiated signalosome formation in T cell activation. Localization of transgenic PKB in lipid rafts could contribute to the higher TCR sensitivity of myr PKB thymocytes which is reflected in an increase in positive selection toward the CD4 lineage and variable effects on negative selection depending on the model system analyzed. Thus, our observations clearly indicate a cross-talk between PKB and important signaling molecules downstream of TCR that modulate the thresholds of thymocyte selection and T cell activation.

γc cytokines provide multiple homeostatic signals to naive CD4+ T cells

“…In both these cases, the PKB expression in the peripheral compartment was not restricted to naive T cells. We therefore asked whether a PKB Tg expressed in developing and mature T cells [34] would modify the c c deficiency phenotypes that we had observed in naive Ml CD4 + T cells. We generated monoclonal Ml c c -female mice that were also Tg for Bcl-2 and/or activated PKB.…”

“…Mice Tg for an activated PKB [34] or human Bcl-2-Tg mice B6.Cg-Tg (BCL2)25Wehi/J [27] were backcrossed to Ml RAG2 -/-or RAG2 -/-/c c -/-mice to generate 'monoclonal' Ml Bcl-2 + mice with or without c c . CD122 -/-mice (B6 Il2rbtm1Mak/J , JAX) or CD127 -/-mice (B6.129S7 Il7ratm1Pes/J , JAX) were used to generate 'monoclonal' Ml CD122 -/-or CD127 -/-mice.…”

Constitutive Akt1 signals attenuate B‐cell receptor signaling and proliferation, but enhance B‐cell migration and effector function

“…In view of the fact that, in our mouse model, expression of Tg myristoylated Akt1 (Akt1 Tg) in T and B cells did not lead to B-cell expansion [18] and that enhanced Akt signaling is linked to autoimmunity and generation of tumors [19,20], we assessed the effects of constitutive Akt1 signals on B-cell function and development. We found a reduced BCR-induced proliferation of splenic B cells from Akt1 Tg mice, which correlated with reduced activation of several signaling cascades.…”

Thymic myoid cells protect thymocytes from apoptosis and modulate their differentiation: implication of the ERK and Akt signaling pathways

“…28,37 In coculture with MITC, we observed a prolonged activation of Akt and ERK1/2, which could thus favor DP thymocyte differentiation in CD4 þ SP instead of CD8 þ SP thymocytes. These observations suggest that MITC could modulate thymocyte differentiation in vitro.…”

“…Although the ERK1/2 and Akt signaling pathways are usually described as independent, recent reports suggest a certain degree of crosstalk between these two cascades. Na et al 28 described that Akt enhanced ERK activity modulating thymocyte selection and T-cell activation. The involvement of Akt in cell survival is well documented.…”