Mechanisms of Cbl-Mediated Ubiquitination of Proteins in T and Natural Killer Cells and Effects on Immune Cell Functions.

Post-translational ubiquitination is an essential mechanism for the regulation of protein stability and function, which contributes to the regulation of the immune system. Cbl, an E3 ubiquitin ligase, is particularly well-characterized in the context of T and NK cell signaling, where it serves as a key regulator of receptor downstream signaling events and as a modulator of cell activation. Cbl promotes the proteasomal degradation of TCR/CD3 subunits as well as the protein kinases Fyn and Lck in T cells.

The Peptidyl-Prolyl isomerase, Pin1, associates with Protein Kinase C θ a critical Phospho-Thr-Pro motif in the V3 regulatory domain.

Protein kinase C-θ (PKCθ) is a member of the novel PKC subfamily known for its selective and predominant expression in T lymphocytes where it regulates essential functions required for T cell activation and proliferation. Our previous studies provided a mechanistic explanation for the recruitment of PKCθ to the center of the immunological synapse (IS) by demonstrating that a proline-rich (PR) motif within the V3 region in the regulatory domain of PKCθ is necessary and sufficient for PKCθ IS localization and function. Herein, we highlight the importance of Thr-Pro residue in the PR motif, the phosphorylation of which is key in the activation of PKCθ and its subsequent IS localization.

The role of AMPK in cancer metabolism and its impact on the immunomodulation of the tumor microenvironment.

Adenosine monophosphate-activated protein kinase (AMPK) is a key metabolic sensor that is pivotal for the maintenance of cellular energy homeostasis. AMPK contributes to diverse metabolic and physiological effects besides its fundamental role in glucose and lipid metabolism. Aberrancy in AMPK signaling is one of the determining factors which lead to the development of chronic diseases such as obesity, inflammation, diabetes, and cancer.

Termination of TCR-mediated activation signals is regulated by CrkII-dependent Cbl-mediated ubiquitination and degradation of C3G.

Crk adaptor proteins are key players in signal transduction from multiple cell surface receptors, including the T cell antigen receptor (TCR). The involvement of CrkII in the early stages of T cell activation is well documented, but little is known about its role during the termination of the activation response. We substantiated findings showing that CrkII utilizes its SH3N and SH2 domains to constitutively associate with C3G and transiently with Cbl in resting and TCR/CD3-stimulated T cells, respectively.

Cyclophilin A associates with and regulates the activity of ZAP70 in TCR/CD3-stimulated T cells.

The ZAP70 protein tyrosine kinase (PTK) couples stimulated T cell antigen receptors (TCRs) to their downstream signal transduction pathways and is sine qua non for T cell activation and differentiation. TCR engagement leads to activation-induced post-translational modifications of ZAP70, predominantly by kinases, which modulate its conformation, leading to activation of its catalytic domain. Here, we demonstrate that ZAP70 in TCR/CD3-activated mouse spleen and thymus cells, as well as human Jurkat T cells, is regulated by the peptidyl-prolyl cis-trans isomerase (PPIase), cyclophilin A (CypA) and that this regulation is abrogated by cyclosporin A (CsA), a CypA inhibitor.

Decoupling the role of RORγt in the differentiation and effector function of T17 cells.

RORγt is known to instruct the differentiation of T helper 17 (T17) cells that mediate the pathogenesis of autoimmune diseases. However, it remains unknown whether RORγt plays a distinct role in the differentiation and effector function of T17 cells. Here, we show that mutation of RORγt lysine-256, a ubiquitination site, to arginine (K256R) separates the RORγt role in these two functions.

Corrigendum: Blockade of uttroside B-induced autophagic pro-survival signals augments its chemotherapeutic efficacy against hepatocellular carcinoma.

[This corrects the article DOI: 10.3389/fonc.2022.

Steroid nuclear receptor coactivator 2 controls immune tolerance by promoting induced T differentiation via up-regulating Nr4a2.

Steroid nuclear receptor coactivator 2 (SRC2) is a member of a family of transcription coactivators. While SRC1 inhibits the differentiation of regulatory T cells (T) critical for establishing immune tolerance, we show here that SRC2 stimulates T differentiation. SRC2 is dispensable for the development of thymic T, whereas naive CD4 T cells from mice deficient of SRC2 specific in T () display defective T differentiation.

Blockade of Uttroside B-Induced Autophagic Pro-Survival Signals Augments Its Chemotherapeutic Efficacy Against Hepatocellular Carcinoma.

Our previous study has demonstrated that Uttroside B (Utt-B), a saponin isolated from the leaves of Linn induces apoptosis in hepatic cancer cells and exhibits a remarkable growth inhibition of Hepatocellular Carcinoma (HCC). Our innovation has been granted a patent from the US (US 2019/0160088A1), Canada (3,026,426.), Japan (JP2019520425) and South Korea (KR1020190008323) and the technology have been transferred commercially to Q Biomed, a leading US-based Biotech company.

Histocompatibility and Reproduction: Lessons from the Anglerfish.

Reproduction in certain deep-sea anglerfishes involves the permanent attachment of dwarf males to much larger females and fusion of their tissues leading to the establishment of a shared circulatory system. This unusual phenomenon of sexual parasitism enables anglerfishes to maximize reproductive success in the vast and deep oceans, where females and males otherwise rarely meet. An even more surprising phenomenon relates to the observation that joining of genetically disparate male and female anglerfishes does not evoke a strong anti-graft immune rejection response, which occurs in vertebrates following allogeneic parabiosis.

Unraveling the hidden role of a uORF-encoded peptide as a kinase inhibitor of PKCs.

Approximately 40% of human messenger RNAs (mRNAs) contain upstream open reading frames (uORFs) in their 5' untranslated regions. Some of these uORF sequences, thought to attenuate scanning ribosomes or lead to mRNA degradation, were recently shown to be translated, although the function of the encoded peptides remains unknown. Here, we show a uORF-encoded peptide that exhibits kinase inhibitory functions.

Protein kinase C eta is activated in reactive astrocytes of an Alzheimer's disease mouse model: Evidence for its immunoregulatory function in primary astrocytes.

Alzheimer's disease (AD) is the primary cause of age-related dementia. Pathologically, AD is characterized by synaptic loss, the accumulation of β-amyloid peptides and neurofibrillary tangles, glial activation, and neuroinflammation. Whereas extensive studies focused on neurons and activation of microglia in AD, the role of astrocytes has not been well-characterized.

PICOT binding to chromatin-associated EED negatively regulates cyclin D2 expression by increasing H3K27me3 at the CCND2 gene promoter.

Protein kinase C (PKC)-interacting cousin of thioredoxin (PICOT; also termed glutaredoxin 3 (Grx3; Glrx3)) is a ubiquitous protein that can interact with the embryonic ectoderm development (EED) protein via each of its two C-terminal PICOT/Grx homology domains. Since EED is a Polycomb-Group protein and a core component of the polycomb repressive complex 2 (PRC2), we tested the involvement of PICOT in the regulation of PRC2-mediated H3 lysine 27 trimethylation (H3K27me3), transcription and translation of selected PRC2 target genes. A fraction of the cellular PICOT protein was found in the nuclei of leukemia cell lines, where it was associated with the chromatin.

PICOT (GLRX3) is a positive regulator of stress-induced DNA-damage response.

Protein kinase C (PKC)-interacting cousin of thioredoxin (PICOT; also termed glutaredoxin 3 (Glrx3)) is a ubiquitously expressed protein that possesses an N-terminal monothiol thioredoxin (Trx) domain and two C-terminal tandem copies of a monothiol Glrx domain. It has an overall highly conserved amino acid sequence and is encoded by a unique gene, both in humans and mice, without having other functional gene homologs in the entire genome. Despite being discovered almost two decades ago, the biological function of PICOT remains largely ill-defined and its ramifications are underestimated considering the fact that PICOT-deficiency in mice results in embryonic lethality.

PICOT binding to the polycomb group protein, EED, alters H3K27 methylation at the MYT1 PRC2 target gene.

PICOT is a ubiquitous protein that has no functional redundant ortholog and is critical for mouse embryonic development. It is involved in the regulation of signal transduction in T lymphocytes and cardiac muscle, and in cellular iron metabolism and biogenesis of Fe/S proteins. However, very little is known about the physiological role of PICOT and its mechanism of action, and on its upstream regulators or downstream target molecules.

Dietary arachidonic acid affects immune function and fatty acid composition in cultured rabbitfish Siganus rivulatus.

The marbled spinefoot rabbitfish (Siganus rivulatus) is an economically valuable fish species that has potential for commercial production in aquaculture. To overcome challenges in its sustainable production, a formulated diet is required for imparting health and robustness. This study evaluates the effect of dietary supplementation with arachidonic acid (ARA; 20:4n-6) on growth, survival, immune function and fatty acid composition of red blood cells (RBCs) in rabbitfish.

Protein kinase C (PKC) isoforms in cancer, tumor promotion and tumor suppression.

The AGC family of serine/threonine kinases (PKA, PKG, PKC) includes more than 60 members that are critical regulators of numerous cellular functions, including cell cycle and differentiation, morphogenesis, and cell survival and death. Mutation and/or dysregulation of AGC kinases can lead to malignant cell transformation and contribute to the pathogenesis of many human diseases. Members of one subgroup of AGC kinases, the protein kinase C (PKC), have been singled out as critical players in carcinogenesis, following their identification as the intracellular receptors of phorbol esters, which exhibit tumor-promoting activities.

TCR crosslinking promotes Crk adaptor protein binding to tyrosine-phosphorylated CD3ζ chain.

T cell antigen receptor (TCR) binding of a peptide antigen presented by antigen-presenting cells (APCs) in the context of surface MHC molecules initiates signaling events that regulate T cell activation, proliferation and differentiation. A key event in the activation process is the phosphorylation of the conserved tyrosine residues within the CD3 chain immunoreceptor tyrosine-based activation motifs (ITAMs), which operate as docking sites for SH2 domain-containing effector proteins. Phosphorylation of the CD3ζ ITAMs renders the CD3 chain capable of binding the ζ-chain associated protein 70 kDa (ZAP70), a protein tyrosine kinase that is essential for T cell activation.

Crk adaptor proteins regulate CD3ζ chain phosphorylation and TCR/CD3 down-modulation in activated T cells.

T cell receptor (TCR) recognition of a peptide antigen in the context of MHC molecules initiates positive and negative cascades that regulate T cell activation, proliferation and differentiation, and culminate in the acquisition of effector T cell functions. These processes are a prerequisite for the induction of specific T cell-mediated adaptive immune responses. A key event in the activation of TCR-coupled signaling pathways is the phosphorylation of tyrosine residues within the cytoplasmic tails of the CD3 subunits, predominantly CD3ζ.

In vivo regulation of human CrkII by cyclophilin A and FK506-binding protein.

Members of the Crk family of adaptor proteins are key players in signal transduction from a variety of cell surface receptors. CrkI and CrkII are two alternative-spliced forms of a single gene which possess an N-terminal SH2 domain and an SH3 domain that mediate interaction with other proteins. CrkII possesses an additional C-terminal linker region plus an extra SH3 domain, which does not interact with other proteins, but operates as regulatory moiety.

The Role of Crk Adaptor Proteins in T-Cell Adhesion and Migration.

Crk adaptor proteins are key players in signal transduction from a variety of cell surface receptors. They are involved in early steps of lymphocyte activation through their SH2-mediated transient interaction with signal transducing effector molecules, such as Cbl, ZAP-70, CasL, and STAT5. In addition, they constitutively associate, via their SH3 domain, with effector molecules, such as C3G, that mediate cell adhesion and regulate lymphocyte extravasation and recruitment to sites of inflammation.

Insights into peptidyl-prolyl cis-trans isomerase structure and function in immunocytes.

Peptidyl-prolyl isomerase (PPIase) catalyzes the interconversion of a specific Pro-imide bond between the cis and trans conformations. Two families of PPIases, cyclophilins and FKBPs, have been extensively studied because of their high affinity for immunosuppressive drugs in particular cyclosporine A and FK506. Despite apparent differences, these protein families share conserved amino acid sequences in their catalytic domains and impose similar enzymatic functions to their substrates.

PKCθ-regulated signalling in health and disease.

Protein kinase Cθ (PKCθ) is a key enzyme in T-lymphocytes where it plays an important role in signal transduction downstream of the activated T-cell receptor (TCR) and the CD28 co-stimulatory receptor. Antigenic stimulation of T-cells triggers PKCθ translocation to the centre of the immunological synapse (IS) at the contact site between antigen-specific T-cells and antigen-presenting cells (APCs). The IS-residing PKCθ phosphorylates and activates effector molecules that transduce signals into distinct subcellular compartments and activate the transcription factors, nuclear factor κB (NF-κB), nuclear factor of activated T-cells (NFAT) and activating protein 1 (AP-1), which are essential for the induction of T-cell-mediated responses.

Immunophilins control T lymphocyte adhesion and migration by regulating CrkII binding to C3G.

Crk adaptor proteins are key players in signal transduction from a variety of cell surface receptors. CrkI and CrkII, the two alternative spliced forms of CRK, possess an N-terminal Src homology 2 domain, followed by a Src homology 3 (SH3) domain, whereas CrkII possesses in addition a C-terminal linker region plus a SH3 domain, which operate as regulatory moieties. In this study, we investigated the ability of immunophilins, which function as peptidyl-prolyl isomerases, to regulate Crk proteins in human T lymphocytes.