Modulation of Immune Cell Functions by the E3 Ligase Cbl-b.

Maintenance of immunological tolerance is a critical hallmark of the immune system. Several signaling checkpoints necessary to balance activating and inhibitory input to immune cells have been described so far, among which the E3 ligase Cbl-b appears to be a central player. Cbl-b is expressed in all leukocyte subsets and regulates several signaling pathways in T cells, NK cells, B cells, and different types of myeloid cells.

The role of the e3 ligase cbl-B in murine dendritic cells.

Dendritic cells (DCs) are potent antigen-presenting cells with a promising potential in cancer immunotherapy. Cbl proteins are E3 ubiquitin ligases and have been implicated in regulating the functional activity of various immune cells. As an example, c-Cbl negatively affects DC activation.

PKCα and PKCβ cooperate functionally in CD3-induced de novo IL-2 mRNA transcription.

The physiological functions of PKCα and PKCθ isotypes downstream of the antigen receptor have been defined in CD3(+) T cells. In contrast, no function of the second conventional PKC member, PKCβ, has been described yet in T cell antigen receptor signalling. To investigate the hypothesis that both conventional PKCα and PKCβ isotypes may have overlapping functions in T cell activation signalling, we generated mice that lacked the genes for both isotypes.

PKCθ/β and CYLD are antagonistic partners in the NFκB and NFAT transactivation pathways in primary mouse CD3+ T lymphocytes.

In T cells PKCθ mediates the activation of critical signals downstream of TCR/CD28 stimulation. We investigated the molecular mechanisms by which PKCθ regulates NFκB transactivation by examining PKCθ/β single and double knockout mice and observed a redundant involvement of PKCθ and PKCβ in this signaling pathway. Mechanistically, we define a PKCθ-CYLD protein complex and an interaction between the positive PKCθ/β and the negative CYLD signaling pathways that both converge at the level of TAK1/IKK/I-κBα/NFκB and NFAT transactivation.

Reinforcement of cancer immunotherapy by adoptive transfer of cblb-deficient CD8+ T cells combined with a DC vaccine.

The success of cancer immunotherapy is limited by potent endogenous immune-evasion mechanisms, which are at least in part mediated by transforming growth factor-β (TGF-β). The E3 ubiquitin ligase Cbl-b is a key regulator of T cell activation and is established to regulate TGF-β sensitivity. cblb-deficient animals reject tumors via CD8(+) T cells, which make Cbl-b an ideal target for improvement of adoptive T-cell transfer (ATC) therapy.

PKCtheta and Itk functionally interact during primary mouse CD3+ T cell activation.

PKCtheta serine/threonine and Itk tyrosine protein kinases have been implicated in T lymphocyte signal transmission. We observed a PKCtheta/Itk complex after T cell activation, raising the possibility that PKCtheta and Itk might interact functionally during T cell development and response. To address this question PKCtheta/Itk double knockout mice were generated and T cell activation responses were compared to single deficiencies as well as to wild type controls.

The potent protein kinase C-selective inhibitor AEB071 (sotrastaurin) represents a new class of immunosuppressive agents affecting early T-cell activation.

There is a pressing need for immunosuppressants with an improved safety profile. The search for novel approaches to blocking T-cell activation led to the development of the selective protein kinase C (PKC) inhibitor AEB071 (sotrastaurin). In cell-free kinase assays AEB071 inhibited PKC, with K(i) values in the subnanomolar to low nanomolar range.

PKC theta cooperates with PKC alpha in alloimmune responses of T cells in vivo.

The physiological roles of PKC alpha and PKC theta were defined in T cell immune functions downstream of the antigen receptor. To investigate the hypothesis that both PKC isotypes may have overlapping functions, we generated mice lacking both genes. We find that PKC alpha(-/-)/theta(-/-) animals have additive T cell response defects in comparison to animals carrying single mutations in these genes.

PKC-theta selectively controls the adhesion-stimulating molecule Rap1.

The antigen-specific interaction of a T cell with an antigen-presenting cell (APC) results in the formation of an immunologic synapse (IS) between the membranes of the 2 cells. beta(2) integrins on the T cell, namely, leukocyte function-associated antigen 1 (LFA-1) and its counter ligand, namely, immunoglobulin-like cell adhesion molecule 1 (ICAM-1) on the APC, critically stabilize this intercellular interaction. The small GTPase Rap1 controls T-cell adhesion through modulating the affinity and/or spatial organization of LFA-1; however, the upstream regulatory components triggered by the T-cell receptor (TCR) have not been resolved.

The nuclear orphan receptor NR2F6 suppresses lymphocyte activation and T helper 17-dependent autoimmunity.

The protein kinase C (PKC) family of serine-threonine kinases plays a central role in T lymphocyte activation. Here, we identify NR2F6, a nuclear zinc-finger orphan receptor, as a critical PKC substrate and essential regulator of CD4(+) T cell activation responses. NR2F6 potently antagonized the ability of T helper 0 (Th0) and Th17 CD4(+) T cells to induce expression of key cytokine genes such as interleukin-2 (IL-2) and IL-17.

Defective IgG2a/2b class switching in PKC alpha-/- mice.

Using model tumor T cell lines, protein kinase C (PKC) alpha has been implicated in IL-2 cytokine promoter activation in response to Ag receptor stimulation. In this study, for the first time, PKCalpha null mutant mice are analyzed and display normal T and B lymphocyte development. Peripheral CD3(+) PKCalpha-deficient T cells show unimpaired activation-induced IL-2 cytokine secretion, surface expression of CD25, CD44, and CD69, as well as transactivation of the critical transcription factors NF-AT, NF-kappaB, AP-1, and STAT5 in vitro.