PKC-theta is a member of the Protein Kinase C family of serine/threonine kinase activated by elevated levels of di-acyl-glycerol (DAG) and Calcium. In mammals, PKC-theta is only expressed in cells of the immune system and in skeletal muscles. When PKC-theta is activated in cells of the immune system, such as T and B cells, it mediates NF-Kappa B signaling in parallel to the kinase Akt.

PKC-theta Activation in T and B Cells. The elevated levels of DAG and calcium needed for PKC-theta activation are generated by the PI3K pathway. PI3K, phosphorylates phospho-inositol lipids in the membrane to generate DAG and PIP3, which activates Akt and opens Calcium channels in the membrane of the Endoplasmic/Sarcoplasmic Reticulum (ER or SR), as a result Calcium enters the cytoplasm.

PI3K is activated by active T-cell Receptor (TCR) or B-Cell Receptor (BCR) signaling, these receptors are multi-complexes on the cellular membrane of T and B cells that bind antigen with incredible specificity that is achieved by a process of DNA recombination during T and B cell development in the Thymus or bone marrow, respectively. This process of recombination and differentiation is astonishingly complex and a remarkable feat of evolution. These cells have evolved to protect us from any foreign-antigen carrying pathogen, even thous that we have never met or are yet to have evolved.

The Role of PKC-theta in Immunological Synapse Stability and Motility. The Immunological Synapse (IS) is structure of multi-protein complexes that forms on the membrane interface between two interacting cells of the immune system. The IS that forms between Antigen Presenting Cells (APC) and T cells is a key stage in the activation of almost any type of an immune response. This interaction takes place in the lymph nodes after an APC presenting a foreign pathogen peptide (a peptide is a short sequence of amino acids or a small protein molecule) is specifically recognized by a specific TCR carrying T cell, resulting in signaling events in both cells. This signaling process is a fundamental stage in the immune response, because the T cell needs to gather information about the type of pathogen the APC encountered, activate it self, make a molecular decision about what kind of immune response is needed, pass this information back to the APC and then proliferate and distribute the information so an immune response can be generated. All of the above communicative events happen in the IS, the interaction is both through direct binding and ligand-receptor binding. The ligands secreted by active T-cells and other immune cells are known as cytokines that very according to the type of cell and the type of immune response generated.

So, what does PKC-theta have to do with the IS, apart from activating T and B cells through NF-Kappa B signaling? It turns-out that the localization of PKC-theta in the IS determines whether the T-cells are going to be motile and form short-lived IS interactions or stable. In T-cells, if PKC-theta localization is surrounding the center of the IS, the cells or more motile and form less stable synapses. But, if PKC-theta is excluded from the IS, the T-cells form very stable IS. This is crucial because activated T-cells secret cytokines and if the IS is stable the T-cell will secret in a more directed manner as apposed to a more dispersed secretion. Effector T-cell that form unstable IS, known as Kinapses, secret in a dispersed manner and are more inflammatory then less motile cells. Contradictory to Effector T-cells, Regulatory T-cells (cells that regulate and inactivate effector T-cells) are more effective and better inhibit inflammation, when stable IS are formed.

By inhibiting PKC-theta, it is possible to inhibit Effector T-cell inflammatory effect both directly, through inhibiting NF-Kappa B activation and reduced motility, and indirectly, by improved Regulatory T-cell function. This is a promising unti-inflammatory drug development opportunity, that might help the treatment of Auto-immune diseases or graft vs host disease in the future

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Disease relevance of Prkcq

• This paper therefore suggests that PKC theta mediates the activation of NF-kappa B by pre-TCR in immature thymocytes and contributes to the development of Notch3-dependent T-cell lymphoma [3].
• Taken together these data demonstrate that over-expression of dominant negative PKC-theta in skeletal muscle causes obesity associated to insulin resistance, as demonstrated by defective receptor and post-receptorial activation of signaling cascade [4].
• Unlike comparable cells from wild type mice, CD45RBhi T cells harvested from PKC theta deficient mice failed to induce colitis in the SCID-CD45RB cell transfer model of IBD [5].
• In another T cell-dependent model of inflammatory disease, PKC theta deficient animals developed far less severe neurologic signs and reduced spinal cord inflammatory cell infiltrate compared to WT controls in the MOG-induced EAE model [5].
• Similar to that of PKC-alpha, PKC-theta overexpression in murine EL4 thymoma cells caused a significant increase in phorbol 12-myristate 13-acetate (PMA)-induced transcriptional activation of full-length IL-2-chloramphenicol acetyltransferase (CAT) and NF-AT-CAT but not of NF-IL2A-CAT or NF-kappaB promoter-CAT reporter gene constructs [6].
• PKC-theta regulates leukemia stem cell activity in T-cell acute lymphoblastic leukemia [7].

High impact information on Prkcq

• PKC-theta is required for TCR-induced NF-kappaB activation in mature but not immature T lymphocytes [8].
• Although studies in T-cell lines had suggested that PKC-theta regulates activation of the JNK signalling pathway, induction of JNK was normal in T cells from mutant mice [8].
• TCR-initiated NF-kappaB activation was absent from PKC-theta(-/-) mature T lymphocytes, but was intact in thymocytes [8].
• DOCK2 is essential for antigen-induced translocation of TCR and lipid rafts, but not PKC-theta and LFA-1, in T cells [9].
• This includes the ability of Akt, like antibodies to CD28, to synergize with protein kinase C theta (PKC-theta) in the induction of RE/AP [10].

Biological context of Prkcq

• To test this hypothesis, we examined whether mice with inactivation of PKC-theta are protected from fat-induced insulin resistance in skeletal muscle [11].
• The PKC-specific inhibitor GF 109203X (bisindolylmaleimide I) reduced MARCKS phosphorylation in intact cells at a similar dose-response as enzymatic activity of recombinant isoenzymes cPKC-alpha, nPKC-epsilon, and nPKC-theta in vitro [12].
• Protein kinase C theta (PKC-theta) is the PKC isoform predominantly expressed in skeletal muscle, and it is supposed to mediate many signals necessary for muscle histogenesis and homeostasis, such as TGFbeta, nerve-dependent signals and insulin [4].
• In addition, a time course study of the persistence of T cell molecules to the immunologic synapse indicated that PKC theta;, unlike TCR, persisted in the synapse for at least 4 h, a time that is sufficient for commitment of a T cell to cell division [13].
• Dominant negative mutant Ha-enRasS17N completely inhibited in the PKC-O A148E-induced signal, identifying PKC-theta as a specific constituent upstream of or parallel to Ras in the signaling cascade leading to AP transcriptional activation [6].

Anatomical context of Prkcq

• Skeletal muscle and hepatic insulin action as assessed during hyperinsulinemic-euglycemic clamps did not differ between WT and PKC-theta KO mice following saline infusion [11].
• PKC theta mediates pre-TCR signaling and contributes to Notch3-induced T-cell leukemia [3].
• We have examined the potential role of two representative PKC isoforms in the induction of the IL-2 gene, i.e., PKC-alpha and PKC-theta, the latter being expressed predominantly in hematopoietic cell lines, particularly T cells [6].
• In the methylated BSA model, cellular infiltrates and articular cartilage damage were mild in the PKC-theta-deficient mice as compared with wild-type mice [14].
• Similar to PKC-theta-deficient primary CD4+ T cells, small interfering RNA-mediated knockdown of PKC-theta in Jurkat cells also resulted in apoptosis upon TCR stimulation [15].

Associations of Prkcq with chemical compounds

• In contrast, PKC-theta inactivation prevented fat-induced defects in insulin signaling and glucose transport in skeletal muscle [11].
• Recent studies have suggested that local accumulation of fat metabolites inside skeletal muscle may activate a serine kinase cascade involving protein kinase C-theta (PKC-theta), leading to defects in insulin signaling and glucose transport in skeletal muscle [11].
• Autophosphorylation of immunoprecipitated nPKC theta was observed; it was enhanced by phosphatidylserine and 12-O-tetradecanoylphorbol-13-acetate but attenuated by the addition of Ca2+ [16].
• However, nPKC theta lacks a putative Ca2+ binding region (C2 region) that is seen only in the conventional PKC subfamily (cPKC alpha, -beta I, -beta II, and -gamma) but not in the novel PKC subfamily (nPKC delta, -epsilon, -zeta, and -eta) [16].
• The protein kinase C theta (PKC theta) serine/threonine kinase has been implicated in signaling of T cell activation, proliferation, and cytokine production [17].

Physical interactions of Prkcq

• Vav was found to bind constitutively to PKC-theta in thymocytes [18].

Regulatory relationships of Prkcq

• We showed that CD3 crosslinking alone was sufficient to induce PKC theta; capping in naive CD4(+) T cells [13].
• To examine whether nPKC theta activation by phorbol esters regulates agrin-induced nAChR clustering, we treated overexpressing myotubes overnight with maximal agrin concentrations followed by phorbol esters for 1 hr [19].
• RUNX1 positively regulates transcription of PRKCQ; RUNX3 represses RUNX1; NOTCH1 activates RUNX3. The net result is that NOTCH1 represses PRKCQ expression [7].

Other interactions of Prkcq

• SAP regulates T(H)2 differentiation and PKC-theta-mediated activation of NF-kappaB1 [20].
• Studies with pharmacologic inhibitors and knockout mice showed that the TCR-derived signaling that drives PKC theta; membrane translocation requires the Src family kinase, Lck, but not Fyn [13].
• In addition, PKC-theta(-/-) T cells displayed resistance to Fas-mediated apoptosis as well as activation-induced cell death (AICD) [21].
• Antigen receptor-mediated activation of NF-kappa B, required for proliferation of B and T cells, is disrupted in T cells lacking PKC theta and in B and T cells lacking Bcl10, a caspase recruitment domain (CARD)-containing adaptor protein [22].
• Taken together, our results reveal a central role for PKC-theta signaling during Th2 responses [23].

Analytical, diagnostic and therapeutic context of Prkcq

• In the type II collagen-induced arthritis model, we observed a significant reduction in clinical scores (p < 0.01) in three independent experiments and diminished joint pathology (p < 0.005) in PKC-theta-deficient compared with wild-type littermates [14].
• Immunoprecipitation studies combined with dual staining and protein overlay assays confirmed the association of PKC beta and PKC theta with spectrin following its reorganization [24].
• The intracellular localization of the PKC theta and alpha isoforms in rat skeletal muscle was examined by immunocytochemistry. nPKC theta was detected in association with the sarcolemma of skeletal muscle and was found to be localized in the neuromuscular junction [25].
• Staining for nPKC theta in the neuromuscular junction persisted after prolonged denervation, suggesting that the enzyme is distributed postsynaptically.(ABSTRACT TRUNCATED AT 400 WORDS)[25]
• By far the highest steady-state level of PKC-theta mRNA was found as a 2.8-kb transcript on a Northern blot of poly(A)+ RNA from testes [26].
• Enforced expression of PRKCQ in both mouse and human T-ALL antagonizes leukemia stem cell activity [7].

References