Crucial importance of PKC-β(I) in LFA-1–mediated locomotion of activated T cells

Protein Kinase C at the Crossroad of Mutations, Cancer, Targeted Therapy and Immune Response

The frequent PKC dysregulations observed in many tumors have made these enzymes natural targets for anticancer applications. Nevertheless, this considerable interest in the development of PKC modulators has not led to the expected therapeutic benefits, likely due to the complex biological activities regulated by PKC isoenzymes, often playing ambiguous and protective functions, further driven by the occurrence of mutations. The structure, regulation and functions of PKCs have been extensively covered in other publications. Herein, we focused on PKC alterations mostly associated with complete functional loss. We also addressed the modest yet encouraging results obtained targeting PKC in selected malignancies and the more frequent negative clinical outcomes. The reported observations advocate the need for more selective molecules and a better understanding of the involved pathways. Furthermore, we underlined the most relevant immune mechanisms controlled by PKC isoforms potentially impacting the immune checkpoint inhibitor blockade-mediated immune recovery. We believe that a comprehensive examination of the molecular features of the tumor microenvironment might improve clinical outcomes by tailoring PKC modulation. This approach can be further supported by the identification of potential response biomarkers, which may indicate patients who may benefit from the manipulation of distinctive PKC isoforms.

The steroidal lactone withaferin A impedes T-cell motility by inhibiting the kinase ZAP70 and subsequent kinome signaling

The steroidal lactone withaferin A (WFA) is a dietary phytochemical, derived from Withania somnifera. It exhibits a wide range of biological properties, including immunomodulatory, anti-inflammatory, antistress, and anticancer activities. Here we investigated the effect of WFA on T-cell motility, which is crucial for adaptive immune responses as well as autoimmune reactions. We found that WFA dose-dependently (within the concentration range of 0.3–1.25 μM) inhibited the ability of human T-cells to migrate via cross-linking of the lymphocyte function-associated antigen-1 (LFA-1) integrin with its ligand, intercellular adhesion molecule 1 (ICAM-1). Coimmunoprecipitation of WFA interacting proteins and subsequent tandem mass spectrometry identified a WFA-interactome consisting of 273 proteins in motile T-cells. In particular, our data revealed significant enrichment of the zeta-chain-associated protein kinase 70 (ZAP70) and cytoskeletal actin protein interaction networks upon stimulation. Phospho-peptide mapping and kinome analysis substantiated kinase signaling downstream of ZAP70 as a key WFA target, which was further confirmed by bait-pulldown and Western immunoblotting assays. The WFA-ZAP70 interaction was disrupted by a disulfide reducing agent dithiothreitol, suggesting an involvement of cysteine covalent binding interface. In silico docking predicted WFA binding to ZAP70 at cystine 560 and 564 residues. These findings provide a mechanistic insight whereby WFA binds to and inhibits the ZAP70 kinase and impedes T-cell motility. We therefore conclude that WFA may be exploited to pharmacologically control host immune responses and potentially prevent autoimmune-mediated pathologies.

The role of activated leukocyte cell adhesion molecule (ALCAM) in cancer progression, invasion, metastasis and recurrence: A novel cancer stem cell marker and tumor-specific prognostic marker

Activated leukocyte cell adhesion molecule (ALCAM) or CD166 is a 100 to 105 KDa transmembrane immunoglobulin which is involved in activation of T-cells, hematopoiesis, neutrophils trans-endothelial migration, angiogenesis, inflammation and tumor propagation and invasiveness through formation of homophilic and heterophilic interactions. Recently, many studies have proposed that the expression pattern of ALCAM is highly associated with the grade, stage and invasiveness of tumors. Although ALCAM is a valuable prognostic marker in different carcinomas, similar expression patterns in different tumor types may be associated with completely different prognostic states, making it to be a tumor-type-dependent prognostic marker. In addition, ALCAM isoforms provide ways for primary detection of tumor cells with metastatic potential. More importantly, this prognostic marker has shown to be considerably dependent on the cytoplasmic and membranous expression, indirect and direct regulation of post-transcriptional molecules, pro-apoptotic proteins functionalities and several other oncogenic proteins or signalling pathways. This review mainly focuses on the pathways involved in expression of ALCAM and its prognostic value of in different types of cancers and the way in which it is regulated.

CG-NAP/Kinase Interactions Fine-Tune T Cell Functions

CG-NAP, also known as AKAP450, is an anchoring/adaptor protein that streamlines signal transduction in various cell types by localizing signaling proteins and enzymes with their substrates. Great efforts are being devoted to elucidating functional roles of this protein and associated macromolecular signaling complex. Increasing understanding of pathways involved in regulating T lymphocytes suggests that CG-NAP can facilitate dynamic interactions between kinases and their substrates and thus fine-tune T cell motility and effector functions. As a result, new binding partners of CG-NAP are continually being uncovered. Here, we review recent advances in CG-NAP research, focusing on its interactions with kinases in T cells with an emphasis on the possible role of this anchoring protein as a target for therapeutic intervention in immune-mediated diseases.

Frontline Science: Antagonism between regular and atypical Cxcr3 receptors regulates macrophage migration during infection and injury in zebrafish

The CXCR3‐CXCL11 chemokine‐signaling axis plays an essential role in infection and inflammation by orchestrating leukocyte trafficking in human and animal models, including zebrafish. Atypical chemokine receptors (ACKRs) play a fundamental regulatory function in signaling networks by shaping chemokine gradients through their ligand scavenging function, while being unable to signal in the classic G‐protein‐dependent manner. Two copies of the CXCR3 gene in zebrafish, cxcr3.2 and cxcr3.3, are expressed on macrophages and share a highly conserved ligand‐binding site. However, Cxcr3.3 has structural characteristics of ACKRs indicative of a ligand‐scavenging role. In contrast, we previously showed that Cxcr3.2 is an active CXCR3 receptor because it is required for macrophage motility and recruitment to sites of mycobacterial infection. In this study, we generated a cxcr3.3 CRISPR‐mutant to functionally dissect the antagonistic interplay among the cxcr3 paralogs in the immune response. We observed that cxcr3.3 mutants are more susceptible to mycobacterial infection, whereas cxcr3.2 mutants are more resistant. Furthermore, macrophages in the cxcr3.3 mutant are more motile, show higher activation status, and are recruited more efficiently to sites of infection or injury. Our results suggest that Cxcr3.3 is an ACKR that regulates the activity of Cxcr3.2 by scavenging common ligands and that silencing the scavenging function of Cxcr3.3 results in an exacerbated Cxcr3.2 signaling. In human, splice variants of CXCR3 have antagonistic functions and CXCR3 ligands also interact with ACKRs. Therefore, in zebrafish, an analogous regulatory mechanism appears to have evolved after the cxcr3 gene duplication event, through diversification of conventional and atypical receptor variants.

PKCβ1 regulates meiotic cell cycle in mouse oocyte

PKCβI, a member of the classical protein kinase C family, plays key roles in regulating cell cycle transition. Here, we report the expression, localization and functions of PKCβI in mouse oocyte meiotic maturation. PKCβI and p-PKCβI (phosphor-PKCβI) were expressed from germinal vesicle (GV) stage to metaphase II (MII) stage. Confocal microscopy revealed that PKCβI was localized in the GV and evenly distributed in the cytoplasm after GV breakdown (GVBD), and it was concentrated at the midbody at telophase in meiotic oocytes. While, p-PKCβI was concentrated at the spindle poles at the metaphase stages and associated with midbody at telophase. Depletion of PKCβI by specific siRNA injection resulted in defective spindles, accompanied with spindle assembly checkpoint activation, metaphase I arrest and failure of first polar body (PB1) extrusion. Live cell imaging analysis also revealed that knockdown of PKCβI resulted in abnormal spindles, misaligned chromosomes, and meiotic arrest of oocytes arrest at the Pro-MI/MI stage. PKCβI depletion did not affect the G2/M transition, but its overexpression delayed the G2/M transition through regulating Cyclin B1 level and Cdc2 activity. Our findings reveal that PKCβI is a critical regulator of meiotic cell cycle progression in oocytes. Abbreviations: PKC, protein kinase C; COC, cumulus-oocyte complexes; GV, germinal vesicle; GVBD, germinal vesicle breakdown; Pro-MI, first pro-metaphase; MI, first metaphase; Tel I, telophase I; MII, second metaphase; PB1, first polar body; SAC, spindle assembly checkpoint.

Immunometabolomic Phenotyping of Motile T-Cells

The immune system and its components defend our body against diverse pathogens and help in maintaining tissue homeostasis. Immune cells are highly dynamic in terms of their growth, migration, differentiation, and effector functions, and adopt diverse metabolic configurations to respond to varying immunological challenges. Growing body of evidence suggests that metabolic pathways fuel immune cells for their functioning, including T-cell migration to the site of infection. This chapter provides detailed methodology for the efficient extraction of T-cell metabolites for successful downstream immunometabolomic profiling of motile T-lymphocytes.

An Introduction to LFA-1/ICAM-1 Interactions in T-Cell Motility

The inherent ability of T-cells to migrate is critical for a fully functional immune system, both in normal immune surveillance and for mounting an adaptive immune response. At the same time, inappropriate trafficking of T-cells can be a pathological factor for immune-mediated or chronic inflammatory diseases. T-cell motility is critically dependent on a series of ligand-receptor interactions, a precisely regulated intracellular signaling, an involvement of adaptor proteins, and dynamic remodeling of the cytoskeletal systems. The leukocyte integrin LFA-1 receptor present on T-cells binds to the ligand intercellular adhesion molecule 1 (ICAM-1) and this LFA-1/ICAM-1 contact acts as a trigger for T-cell motility. In this book, we present a collection of methods and protocols that are frequently used by researchers to better understand T-cell motility in health and diseases.

Aggregatibacter actinomycetemcomitans leukotoxin causes activation of lymphocyte function-associated antigen 1

Repeats-in-toxin leukotoxin (LtxA) produced by the oral bacterium Aggregatibacter actinomycetemcomitans kills human leukocytes in a lymphocyte function-associated antigen 1 (LFA-1, integrin α_L /β₂ )-dependent manner, although the mechanism for this interaction has not been identified. The LtxA internalisation by LFA-1-expressing cells was explored with florescence resonance energy transfer (FRET) microscopy using a cell line that expresses LFA-1 with a cyan fluorescent protein-tagged cytosolic α_L domain and a yellow fluorescent protein-tagged β₂ domain. Phorbol 12-myristate 13-acetate activation of LFA-1 caused transient cytosolic domain separation. However, addition of LtxA resulted in an increase in FRET, indicating that LtxA brings the cytosolic domains closer together, compared with the inactive state. Unlike activation, this effect was not transient, lasting more than 30 min. Equilibrium constants of LtxA binding to the cytoplasmic domains of both α_L and β₂ were determined using surface plasmon resonance. LtxA has a strong affinity for the cytosolic domains of both the α_L and β₂ subunits (K_d  = 15 and 4.2 nM, respectively) and a significantly lower affinity for the cytoplasmic domains of other integrin α_M , α_X , and β₃ subunits (K_d  = 400, 180, and 230 nM, respectively), used as controls. Peptide fragments of α_L and β₂ show that LtxA binds membrane-proximal domain of α_L and intermediate domain of β₂ .

Centrosome- and Golgi-Localized Protein Kinase N-Associated Protein Serves As a Docking Platform for Protein Kinase A Signaling and Microtubule Nucleation in Migrating T-Cells

Centrosome- and Golgi-localized protein kinase N-associated protein (CG-NAP), also known as AKAP450, is a cytosolic scaffolding protein involved in the targeted positioning of multiple signaling molecules, which are critical for cellular functioning. Here, we show that CG-NAP is predominantly expressed in human primary T-lymphocytes, localizes in close proximity (<0.2 μm) with centrosomal and Golgi structures and serves as a docking platform for Protein Kinase A (PKA). GapmeR-mediated knockdown of CG-NAP inhibits LFA-1-induced T-cell migration and impairs T-cell chemotaxis toward the chemokine SDF-1α. Depletion of CG-NAP dislocates PKARIIα, disrupts centrosomal and non-centrosomal microtubule nucleation, causes Golgi fragmentation, and impedes α-tubulin tyrosination and acetylation, which are important for microtubule dynamics and stability in migrating T-cells. Furthermore, we show that CG-NAP coordinates PKA-mediated phosphorylation of pericentrin and dynein in T-cells. Overall, our findings provide critical insights into the roles of CG-NAP in regulating cytoskeletal architecture and T-cell migration.

Not Just an Adhesion Molecule: LFA-1 Contact Tunes the T Lymphocyte Program

The α_Lβ₂ integrin LFA-1 is known to play a key role in T lymphocyte migration, which is necessary to mount a local immune response, and is also the main driver of autoimmune diseases. This migration-triggering signaling process in T cells is tightly regulated to permit an immune response that is appropriate to the local trigger, as well as to prevent deleterious tissue-damaging bystander effects. Emerging evidence shows that, in addition to prompting a diverse range of downstream signaling cascades, LFA-1 stimulation in T lymphocytes modulates gene-transcription programs, including genetic signatures of TGF-β and Notch pathways, with multifactorial biological outcomes. This review highlights recent findings and discusses molecular mechanisms by which LFA-1 signaling influence T lymphocyte differentiation into the effector subsets Th1, Th17, and induced regulatory T cells. We argue that LFA-1 contact with a cognate ligand, such as ICAM-1, independent of the immune synapse activates a late divergence in T cells' effector phenotypes, hence fine-tuning their functioning.

G-CSF inhibits LFA-1-mediated CD4+ T cell functions by inhibiting Lck and ZAP-70

In this study, we showed that G-CSF mobilization increased the frequency of T cells, specifically CD3⁺CD4⁺ T cells. G-CSF mobilization decreased the secretion of inflammatory cytokines of CD4⁺ T cells through the LFA-1/ICAM-1 signaling pathway, whereas it did not alter the TH1/TH2 ratio. We found that G-CSF mobilization inhibited LFA-1-mediated CD4⁺ T cell polarization and motility. In vitro, G-CSF stimulation also attenuated the polarization and adhesiveness of CD4⁺ T cells through the LFA-1/ICAM-1 interaction. Further investigation revealed that G-CSF mobilization suppressed LFA-1 signaling by down-regulating Lck and ZAP-70 expression in CD4⁺ T cells, similar results was also confirmed by in-vitro studies. These findings suggested that G-CSF directly suppressed LFA-1-mediated CD4⁺ T cell functions through the down-regulation of Lck and ZAP-70. The immunosuppressive effect of G-CSF mobilization deepened our understanding about peripheral blood hematopoietic stem cell transplantation. LFA-1/ICMA-1 pathway may become a potential target for graft-versus-host disease prophylaxis.

Protein kinase C: a regulator of cytoskeleton remodelling and T-cell migration

Protein kinase C (PKC) is a family of ten serine/threonine kinases that have diverse roles in the signalling pathways regulating cellular proliferation, differentiation, apoptosis and immune responses. Elucidating roles for individual PKC isoforms in the immune responses of T-cells have long been a challenging prospect, because these cells are known to express nine of these isoforms. A variety of approaches including the use of knockout mice, overexpression of kinase-inactive mutants, cell-permeable peptides, pharmacological inhibitors and siRNAs have shown that PKCs regulate the production of inflammatory cytokines and the cytotoxic responses of various T-cell subsets. Central to the T-cell immune response is a requirement to migrate to various organs and tissues in search of pathogens and micro-organisms. T-cell migration is guided by specific sets of chemokines and integrin ligands that activate their cognate chemokine receptors and integrins on T-cells, resulting in remodelling of the cytoskeleton and the dynamic protrusive/contractile forces necessary for cell adhesion and motility. In the present article, we review the role of PKC in T-cell migration, with an emphasis on studies that have defined their roles in cytoskeletal remodelling, cell polarity and intracellular trafficking downstream of chemokine receptors and integrins.

RNAi Screening with Self-Delivering, Synthetic siRNAs for Identification of Genes That Regulate Primary Human T Cell Migration

Screening of RNA interference (RNAi) libraries in primary T cells is labor-intensive and technically challenging because these cells are hard to transfect. Chemically modified, self-delivering small interfering RNAs (siRNAs) offer a solution to this problem, because they enter hard-to-transfect cell types without needing a delivery reagent and are available in library format for RNAi screening. In this study, we have screened a library of chemically modified, self-delivering siRNAs targeting the expression of 72 distinct genes in conjunction with an image-based high-content-analysis platform as a proof-of-principle strategy to identify genes involved in lymphocyte function-associated antigen-1 (LFA-1)-mediated migration in primary human T cells. Our library-screening strategy identified the small GTPase RhoA as being crucial for T cell polarization and migration in response to LFA-1 stimulation and other migratory ligands. We also demonstrate that multiple downstream assays can be performed within an individual RNAi screen and have used the remainder of the cells for additional assays, including cell viability and adhesion to ICAM-1 (the physiological ligand for LFA-1) in the absence or presence of the chemokine SDF-1α. This study therefore demonstrates the ease and benefits of conducting siRNA library screens in primary human T cells using self-delivering, chemically modified siRNAs, and it emphasizes the feasibility and potential of this approach for elucidating the signaling pathways that regulate T cell function.

Immunostimulatory effects of RACK1 pseudosubstrate in human leukocytes obtained from young and old donors

Aims of this study were to investigate the ability of RACK1 pseudosubstrate alone or in combination with classical immune stimuli to activate human leukocytes, and to restore age-associated immune defects.A total of 25 donors (17 old donors, 77-79 yrs; 8 young donors, 25-34 yrs) were enrolled. To evaluate the effect of RACK1 pseudosubstrate on cytokine production and CD86 expression the whole blood assay was used. Cultures were treated with RACK1 pseudosubstrate in the presence or absence of lipopolysaccharide (LPS) or phytohaemagglutinin (PHA) and incubated for 24 h or 48 h for LPS-induced CD86 expression, TNF-α, IL-6, IL-8, IL-10 production, and PHA-induced IL-4, IL-10, IFN-γ, respectively. RACK1 pseudosubstrate alone induced IL-6, IL-8, and CD86 expression in both young and old donors, and IFN-γ in old donors. In combination with LPS an increase in IL-8, IL-10 and TNF-α was observed, also resulting in restoration of age-associated defective production, while no changes in the other parameters investigated were found.Even if based on a small sample size, these results suggest the possibility to by-pass some of age-associated immune alterations, which may be beneficial in situations were natural immune stimulation is required, and highlight a different role of PKCβ in immune cells activation.

Protein kinase C-δ and -β coordinate flow-induced directionality and deformation of migratory human blood T-lymphocytes

T-lymphocyte migration under flow is critical for immune responses, but the mechanisms by which flow modulates the migratory behaviors of T-lymphocytes remain unclear. Human peripheral blood T-lymphocytes (PBTLs), when stimulated with phorbol 12-myristate 13-acetate (PMA), stretched their cell bodies dramatically and moved along the flow direction. In contrast, stromal cell-derived factor-1α-stimulated PBTLs deformed and migrated in a random manner. Here we elucidated the molecular mechanisms underlying flow-induced directionality and deformation of PMA-stimulated PBTLs. PMA primed PBTLs for polarization under flow, with protein kinase C (PKC)-δ enriched in the leading edge, PKC-βI in the microtubule organizing center, and PKC-βII in the uropod and peripheral region. PKC-δ regulated cell protrusions in the leading edge through Tiam1/Rac1/calmodulin, whereas PKC-β regulated RhoA/Rho-associated kinase activity and microtubule stability to modulate uropod contractility and detachment. Our findings indicate that PKC-δ and -β coordinate in the cell leading edge and uropod, respectively, to modulate the directionality and deformability of migratory T-lymphocytes under flow.

Adaptor regulation of LFA-1 signaling in T lymphocyte migration: Potential druggable targets for immunotherapies?

The integrin lymphocyte function associated antigen-1 (LFA-1) plays a key role in leukocyte trafficking and in adaptive immune responses through interactions with adhesive ligands, such as ICAM-1. Specific blockade of these interactions has validated LFA-1 as a therapeutic target in many chronic inflammatory diseases, however LFA-1 antagonists have not been clinically successful due to the development of a general immunosuppression, causing fatal side effects. Growing evidence has now established that LFA-1 mediates an array of intracellular signaling pathways by triggering a number of downstream molecules. In this context, a class of multimodular domain-containing proteins capable of recruiting two or more effector molecules, collectively known as "adaptor proteins," has emerged as important mediators in LFA-1 signal transduction. Here, we provide an overview of the adaptor proteins involved in the intracellular signaling cascades by which LFA-1 regulates T-cell motility and immune responses. The complexity of the LFA-1-associated signaling delineated in this review suggests that it may be an important and challenging focus for future research, enabling the identification of "tunable" targets for the development of immunotherapies.

Combretastatin (CA)-4 and its novel analogue CA-432 impair T-cell migration through the Rho/ROCK signalling pathway

The capacity of T-lymphocytes to migrate and localise in tissues is important in their protective function against infectious agents, however, the ability of these cells to infiltrate the tumour microenvironment is a major contributing factor in the development of cancer. T-cell migration requires ligand (ICAM-1)/integrin (LFA-1) interaction, activating intracellular signalling pathways which result in a distinct polarised morphology, with an actin-rich lamellipodium and microtubule (MT)-rich uropod. Combretastatin (CA)-4 is a MT-destabilising agent that possesses potent anti-tumour properties. In this study, the effect of CA-4 and its novel analogue CA-432 on human T-cell migration was assessed. Cellular pretreatment with either of CA compounds inhibited the migration and chemotaxis of the T-cell line HuT-78 and primary peripheral blood lymphocyte (PBL) T-cells. This migration-inhibitory effect of CA compounds was due to the disruption of the MT network of T-cells through tubulin depolymerisation, reduced tubulin acetylation and decreased MT stability. In addition, both CA compounds induced the RhoA/RhoA associated kinase (ROCK) signalling pathway, leading to the phosphorylation of myosin light chain (MLC). Furthermore, the siRNA-mediated depletion of GEF-H1, a MT-associated nucleotide exchange factor that activates RhoA upon release from MTs, in T-cells prevented CA-induced phosphorylation of MLC and attenuated the formation of actin-rich membrane protrusions and cell contractility. These results suggest an important role for a GEF-H1/RhoA/ROCK/MLC signalling axis in mediating CA-induced contractility of T-cells. Therapeutic agents that target cytoskeletal proteins and are effective in inhibiting cell migration may open new avenues in the treatment of cancer and metastasis.

Phosphorylation of Rab5a protein by protein kinase Cϵ is crucial for T-cell migration

Rab GTPases control membrane traffic and receptor-mediated endocytosis. Within this context, Rab5a plays an important role in the spatial regulation of intracellular transport and signal transduction processes. Here, we report a previously uncharacterized role for Rab5a in the regulation of T-cell motility. We show that Rab5a physically associates with protein kinase Cϵ (PKCϵ) in migrating T-cells. After stimulation of T-cells through the integrin LFA-1 or the chemokine receptor CXCR4, Rab5a is phosphorylated on an N-terminal Thr-7 site by PKCϵ. Both Rab5a and PKCϵ dynamically interact at the centrosomal region of migrating cells, and PKCϵ-mediated phosphorylation on Thr-7 regulates Rab5a trafficking to the cell leading edge. Furthermore, we demonstrate that Rab5a Thr-7 phosphorylation is functionally necessary for Rac1 activation, actin rearrangement, and T-cell motility. We present a novel mechanism by which a PKCϵ-Rab5a-Rac1 axis regulates cytoskeleton remodeling and T-cell migration, both of which are central for the adaptive immune response.

Novel modulating effects of PKC family genes on the relationship between serum vitamin D and relapse in multiple sclerosis

BACKGROUND

The interplay between genes and environmental factors on multiple sclerosis (MS) clinical course has been little studied.

METHODS

We conducted a prospective cohort study of 141 participants with relapsing-remitting MS (RRMS) and genotype data followed from 2002 to 2005 and examined genes in the vitamin D metabolism and vitamin D receptor (VDR)/retinoid X receptor (RXR) transcription factor formation pathway. Gene-vitamin D interactions and the genetic predictors of relapse were assessed using survival analysis. Genetic predictors of 25-hydroxyvitamin D (25(OH)D) were evaluated by multilevel mixed-effects linear regression. Significance threshold was adjusted by Bonferroni correction for the number of genes evaluated.

RESULTS

The relationship between 25(OH)D and hazard of relapse was significantly different for different alleles of two intronic single nucleotide polymorphisms (SNPs) (rs908742 in PRKCZ and rs3783785 in PRKCH) in the protein kinase C (PKC) family genes (p(interaction)=0.001, p(adj)=0.021, respectively). Two other intronic SNPs (rs1993116 in CYP2R1and rs7404928 in PRKCB) were significantly associated with lower levels of 25(OH)D (p(interaction)=0.001, p(adj)=0.021, respectively). A cumulative effect of multiple 'risk' genotypes on 25(OH)D levels and hazard of relapse was observed for the significant SNPs (p(trend)=7.12×10(-6) for 25(OH)D levels, p(trend)=8.86×10(-6) for hazard of relapse).

CONCLUSIONS

Our data support the hypothesis that gene-vitamin D interactions may influence MS clinical course and that the PKC family genes may play a role in the pathogenesis of MS relapse through modulating the association between 25(OH)D and relapse.

PKCθ regulates T cell motility via ezrin-radixin-moesin localization to the uropod

Cell motility is a fundamental process crucial for function in many cell types, including T cells. T cell motility is critical for T cell-mediated immune responses, including initiation, activation, and effector function. While many extracellular receptors and cytoskeletal regulators have been shown to control T cell migration, relatively few signaling mediators have been identified that can modulate T cell motility. In this study, we find a previously unknown role for PKCθ in regulating T cell migration to lymph nodes. PKCθ localizes to the migrating T cell uropod and regulates localization of the MTOC, CD43 and ERM proteins to the uropod. Furthermore, PKCθ-deficient T cells are less responsive to chemokine induced migration and are defective in migration to lymph nodes. Our results reveal a novel role for PKCθ in regulating T cell migration and demonstrate that PKCθ signals downstream of CCR7 to regulate protein localization and uropod formation.

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. We found that PKCα(-/-)/β(-/-) animals are viable, live normal life spans and display normal T cell development. However, these animals possess additive defects in T cell responses in comparison to animals that carry single mutations in these genes. Our studies demonstrate that the activities of PKCα and PKCβ converge to regulate IL-2 cytokine responses in anti-CD3 stimulated primary mouse T cells. Here, we present genetic evidence that PKCα and PKCβ cooperate in IL-2 transcriptional transactivation in primary mouse T cells independently of the actions of PKCθ.

Protein kinase C signaling and cell cycle regulation

A link between T cell proliferation and the protein kinase C (PKC) family of serine/threonine kinases has been recognized for about 30 years. However, despite the wealth of information on PKC-mediated control of, T cell activation, understanding of the effects of PKCs on the cell cycle machinery in this cell type remains limited. Studies in other systems have revealed important cell cycle-specific effects of PKC signaling that can either positively or negatively impact proliferation. The outcome of PKC activation is highly context-dependent, with the precise cell cycle target(s) and overall effects determined by the specific isozyme involved, the timing of PKC activation, the cell type, and the signaling environment. Although PKCs can regulate all stages of the cell cycle, they appear to predominantly affect G0/G1 and G2. PKCs can modulate multiple cell cycle regulatory molecules, including cyclins, cyclin-dependent kinases (cdks), cdk inhibitors and cdc25 phosphatases; however, evidence points to Cip/Kip cdk inhibitors and D-type cyclins as key mediators of PKC-regulated cell cycle-specific effects. Several PKC isozymes can target Cip/Kip proteins to control G0/G1 → S and/or G2 → M transit, while effects on D-type cyclins regulate entry into and progression through G1. Analysis of PKC signaling in T cells has largely focused on its roles in T cell activation; thus, observed cell cycle effects are mainly positive. A prominent role is emerging for PKCθ, with non-redundant functions of other isozymes also described. Additional evidence points to PKCδ as a negative regulator of the cell cycle in these cells. As in other cell types, context-dependent effects of individual isozymes have been noted in T cells, and Cip/Kip cdk inhibitors and D-type cyclins appear to be major PKC targets. Future studies are anticipated to take advantage of the similarities between these various systems to enhance understanding of PKC-mediated cell cycle regulation in T cells.

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. In Jurkat leukemic T cells, CYLD is endoproteolytically processed in the initial minutes of stimulation by the paracaspase MALT1 in a PKC-dependent fashion, which is required for robust IL-2 transcription. However, in primary T cells, CYLD processing occurs with different kinetics and an altered dependence on PKC. The formation of a direct PKCθ/CYLD complex appears to regulate the short-term spatial distribution of CYLD, subsequently affecting NFκB and NFAT repressional activity of CYLD prior to its MALT1-dependent inactivation. Taken together, our study establishes CYLD as a new and critical PKCθ interactor in T cells and reveals that antagonistic PKCθ/β-CYLD crosstalk is crucial for the adjustment of immune thresholds in primary mouse CD3⁺ T cells.

The yin and yang of protein kinase C-theta (PKCθ): a novel drug target for selective immunosuppression

Protein kinase C-theta (PKCθ) is a protein kinase C (PKC) family member expressed predominantly in T lymphocytes, and extensive studies addressing its function have been conducted. PKCθ is the only T cell-expressed PKC that localizes selectively to the center of the immunological synapse (IS) following conventional T cell antigen stimulation, and this unique localization is essential for PKCθ-mediated downstream signaling. While playing a minor role in T cell development, early in vitro studies relying, among others, on the use of PKCθ-deficient (Prkcq(-/-)) T cells revealed that PKCθ is required for the activation and proliferation of mature T cells, reflecting its importance in activating the transcription factors nuclear factor kappa B, activator protein-1, and nuclear factor of activated T cells, as well as for the survival of activated T cells. Upon subsequent analysis of in vivo immune responses in Prkcq(-/-) mice, it became clear that PKCθ has a selective role in the immune system: it is required for experimental Th2- and Th17-mediated allergic and autoimmune diseases, respectively, and for alloimmune responses, but is dispensable for protective responses against pathogens and for graft-versus-leukemia responses. Surprisingly, PKCθ was recently found to be excluded from the IS of regulatory T cells and to negatively regulate their suppressive function. These attributes of PKCθ make it an attractive target for catalytic or allosteric inhibitors that are expected to selectively suppress harmful inflammatory and alloimmune responses without interfering with beneficial immunity to infections. Early progress in developing such drugs is being made, but additional studies on the role of PKCθ in the human immune system are urgently needed.

Cell division fidelity is altered during the vascular response to injury: its novel role in atherosclerosis progression

The rapid proliferation of smooth muscle cells (SMCs) contributes to atherosclerotic plaque formation and neointimal thickening in other occlusive vascular diseases. In cancer cells, rapid cell proliferation is often accompanied by DNA damage, division aberrations, elevated cell apoptosis, or accumulation of abnormal cells. However, little is known about division fidelity in vascular disorders. We have analyzed the cell division fidelity during the rapid SMC proliferation that occurs after balloon injury of the rat carotid artery using en face confocal microscopy of the full thickness of the vessel wall. SMCs newly migrated to the neointima had increased division defects and increased apoptosis compared with SMCs in the subjacent media, despite comparable mitosis rates. Protein kinase Cα and the receptor for hyaluronic acid-mediated motility (RHAMM) regulate division fidelity in cultured neointimal SMCs. The centrosomal targeting sequence of RHAMM was required for localization to the mitotic spindle and spindle organization. Dynein and RHAMM colocalized in the spindle area and were part of a complex. Dynein inhibition caused spindle defects similar to RHAMM or protein kinase C inhibition. Our study uncovered abnormalities in rapidly proliferating SMCs after arterial injury that could contribute to the growth of atherosclerotic plaques and reduce plaque stability by triggering apoptosis, and it described a mechanism by which RHAMM and dynein coordinate division fidelity in neointimal SMCs.

The high and low molecular weight forms of hyaluronan have distinct effects on CD44 clustering

CD44 is a major cell surface receptor for the glycosaminoglycan hyaluronan (HA). Native high molecular weight hyaluronan (nHA) and oligosaccharides of hyaluronan (oHA) provoke distinct biological effects upon binding to CD44. Despite the importance of such interactions, however, the feature of binding with CD44 at the cell surface and the molecular basis for functional distinction between different sizes of HA is still unclear. In this study we investigated the effects of high and low molecular weight hyaluronan on CD44 clustering. For the first time, we provided direct evidence for a strong relationship between HA size and CD44 clustering in vivo. In CD44-transfected COS-7 cells, we showed that exogenous nHA stimulated CD44 clustering, which was disrupted by oHA. Moreover, naturally expressed CD44 was distributed into clusters due to abundantly expressed nHA in HK-2 cells (human renal proximal tubule cells) and BT549 cells (human breast cancer cell line) without exogenous stimulation. Our results suggest that native HA binding to CD44 selectively induces CD44 clustering, which could be inhibited by oHA. Finally, we demonstrated that HA regulates cell adhesion in a manner specifically dependent on its size. oHA promoted cell adhesion while nHA showed no effects. Our results might elucidate a molecular- and/or cellular-based mechanism for the diverse biological activities of nHA and oHA.

Involvement of distinct PKC gene products in T cell functions

It is well established that members of the protein kinase C (PKC) family seem to have important roles in T cells. Focusing on the physiological and non-redundant PKC functions established in primary mouse T cells via germline gene-targeting approaches, our current knowledge defines two particularly critical PKC gene products, PKCθ and PKCα, as the "flavor of PKC" in T cells that appear to have a positive role in signaling pathways that are necessary for full antigen receptor-mediated T cell activation ex vivo and T cell-mediated immunity in vivo. Consistently, in spite of the current dogma that PKCθ inhibition might be sufficient to achieve complete immunosuppressive effects, more recent results have indicated that the pharmacological inhibition of PKCθ, and additionally, at least PKCα, appears to be needed to provide a successful approach for the prevention of allograft rejection and treatment of autoimmune diseases.

Protein kinase D isoforms are dispensable for integrin-mediated lymphocyte adhesion and homing to lymphoid tissues

Leukocyte function-associated antigen-1 (LFA-1) and very late antigen-4 (VLA-4) integrins are essential for lymphocyte adhesion, trafficking and effector functions. Protein kinase D (PKD) has previously been implicated in lymphocyte integrin regulation through regulation of Rap1 activity. However, the true role of PKD in integrin regulation in primary lymphocytes has not previously been investigated. The major PKD isoform in lymphocytes is PKD2. Here we employed PKD2-deficient mice, a specific PKD kinase inhibitor, as well as PKD-null DT40 B cells to investigate the role of PKD in integrin regulation in lymphocytes. We report that PKD2-deficient lymphocytes bound normally to integrin ligands in static and shear flow adhesion assays. They also homed normally to lymphoid organs after adoptive transfer into wild-type mice. DT40 B cells devoid of any PKD isoforms and primary lymphocytes pretreated with a specific PKD inhibitor bound normally to integrin ligands, indicating that multiple PKD isoforms do not redundantly regulate lymphocyte integrins. In addition, PKD2-deficient lymphocytes, as well as DT40 cells devoid of any PKD isoforms, could activate Rap1 in response to B-cell receptor ligation or phorbol ester treatment. Together, these results show that the PKD family does not play a critical role in lymphocyte integrin-mediated cell adhesion or lymphocyte trafficking in vivo.

The role of protein kinase cη in T cell biology

Protein kinase Cη (PKCη) is a member of the novel PKC subfamily, which also includes δ, ε, and θ isoforms. Compared to the other novel PKCs, the function of PKCη in the immune system is largely unknown. Several studies have started to reveal the role of PKCη, particularly in T cells. PKCη is highly expressed in T cells, and is upregulated during thymocyte positive selection. Interestingly, like the θ isoform, PKCη is also recruited to the immunological synapse that is formed between a T cell and an antigen-presenting cell. However, unlike PKCθ, which becomes concentrated to the central region of the synapse, PKCη remains in a diffuse pattern over the whole area of the synapse, suggesting distinctive roles of these two isoforms in signal transduction. Although PKCη is dispensable for thymocyte development, further analysis of PKCη- or PKCθ-deficient and double-knockout mice revealed the redundancy of these two isoforms in thymocyte development. In contrast, PKCη rather than PKCθ, plays an important role for T cell homeostatic proliferation, which requires recognition of self-antigen. Another piece of evidence demonstrating that PKCη and PKCθ have isoform-specific as well as redundant roles come from the analysis of CD4 to CD8 T cell ratios in the periphery of these knockout mice. Deficiency in PKCη or PKCθ had opposing effects as PKCη knockout mice had a higher ratio of CD4 to CD8 T cells compared to that of wild-type mice, whereas PKCθ-deficient mice had a lower ratio. Biochemical studies showed that calcium flux and NFκB translocation is impaired in PKCη-deficient T cells upon TCR crosslinking stimulation, a character shared with PKCθ-deficient T cells. However, unlike the case with PKCθ, the mechanistic study of PKCη is at early stage and the signaling pathways involving PKCη, at least in T cells, are essentially unknown. In this review, we will cover the topics mentioned above as well as provide some perspectives for further investigations regarding PKCη.

Leukocyte function-associated antigen-1/intercellular adhesion molecule-1 interaction induces a novel genetic signature resulting in T-cells refractory to transforming growth factor-β signaling

The immunesuppressive cytokine TGF-β plays crucial regulatory roles in the induction and maintenance of immunologic tolerance and prevention of immunopathologies. However, it remains unclear how circulating T-cells can escape from the quiescent state maintained by TGF-β. Here, we report that the T-cell integrin leukocyte function-associated antigen-1 (LFA-1) interaction with its ligand intercellular adhesion molecule-1 (ICAM-1) induces a genetic signature associated with reduced TGF-β responsiveness via up-regulation of SKI, E3 ubiquitin-protein ligase SMURF2, and SMAD7 (mothers against decapentaplegic homolog 7) genes and proteins. We confirmed that the expression of these TGF-β inhibitory molecules was dependent on STAT3 and/or JNK activation. Increased expression of SMAD7 and SMURF2 in LFA-1/ICAM-1 cross-linked T-cells resulted in impaired TGF-β-mediated phosphorylation of SMAD2 and suppression of IL-2 secretion. Expression of SKI caused resistance to TGF-β-mediated suppression of IL-2, but SMAD2 phosphorylation was unaffected. Blocking LFA-1 by neutralizing antibody or specific knockdown of TGF-β inhibitory molecules by siRNA substantially restored LFA-1/ICAM-1-mediated alteration in TGF-β signaling. LFA-1/ICAM-1-stimulated human and mouse T-cells were refractory to TGF-β-mediated induction of FOXP3(+) (forkhead box P3) and RORγt(+) (retinoic acid-related orphan nuclear receptor γt) Th17 differentiation. These mechanistic data suggest an important role for LFA-1/ICAM-1 interactions in immunoregulation concurrent with lymphocyte migration that may have implications at the level of local inflammatory response and for anti-LFA-1-based therapies.

Ezrin, radixin, and moesin are phosphorylated in response to 2-methoxyestradiol and modulate endothelial hyperpermeability

We showed previously that microtubule disruptor 2-methoxyestradiol (2ME) induces hyperpermeability of the endothelial monolayer via mechanisms that include the activation of p38 and Rho kinase (ROCK) and rearrangement of the actin cytoskeleton. Using the protein kinase C (PKC) inhibitors Ro-31-7549 and Ro-32-0432, we show in vitro and in vivo that 2ME-induced barrier dysfunction is also PKC-dependent. The known PKC substrates ezrin, radixin, and moesin (ERM) were recently implicated in the regulation of endothelial permeability. This study tested the hypotheses that ERM proteins are phosphorylated in response to 2ME, and that this phosphorylation is involved in 2ME-induced barrier dysfunction. We show that the application of 2ME leads to a dramatic increase in the level of ERM phosphorylation. This increase is attenuated in cells pretreated with the microtubule stabilizer taxol. In human pulmonary artery endothelial cells (HPAECs), the phosphorylation of ERM occurs in a p38-dependent and PKC-dependent manner. The activation of p38 appears to occur upstream from the activation of PKC, in response to 2ME. Phosphorylated ERM are localized at the cell periphery during the early phase of response to 2ME (15 minutes), and colocalize with F-actin branching points during the later phase of response (60 minutes). Using the short interfering RNA approach, we also showed that individual ERM depletion significantly attenuates 2ME-induced hyperpermeability. HPAEC monolayers, depleted of ERM proteins and monolayers, overexpressing phosphorylation-deficient ERM mutants, exhibit less attenuation of 2ME-induced barrier disruption in response to the PKC inhibitor Ro-31-7549. These results suggest a critical role of PKC activation in response to microtubule-disrupting agents, and implicate the phosphorylation of ERM in the barrier dysfunction induced by 2ME.

Rear polarization of the microtubule-organizing center in neointimal smooth muscle cells depends on PKCα, ARPC5, and RHAMM

Directed migration of smooth muscle cells (SMCs) from the media to the intima in arteries occurs during atherosclerotic plaque formation and during restenosis after angioplasty or stent application. The polarized orientation of the microtubule-organizing center (MTOC) is a key determinant of this process, and we therefore investigated factors that regulate MTOC polarity in vascular SMCs. SMCs migrating in vivo from the medial to the intimal layer of the rat carotid artery following balloon catheter injury were rear polarized, with the MTOC located posterior of the nucleus. In tissue culture, migrating neointimal cells maintained rear polarization, whereas medial cells were front polarized. Using phosphoproteomic screening and mass spectrometry, we identified ARPC5 and RHAMM as protein kinase C (PKC)-phosphorylated proteins associated with rear polarization of the MTOC in neointimal SMCs. RNA silencing of ARPC5 and RHAMM, PKC inhibition, and transfection with a mutated nonphosphorylatable ARPC5 showed that these proteins regulate rear polarization by organizing the actin and microtubule cytoskeletons in neointimal SMCs. Both ARPC5 and RHAMM, in addition to PKC, were required for migration of neointimal SMCs.

A cascade of protein kinase C isozymes promotes cytoskeletal polarization in T cells

Polarization of the T cell microtubule-organizing center (MTOC) toward the antigen-presenting cell (APC) is driven by the accumulation of diacylglycerol (DAG) at the immunological synapse (IS). The mechanisms that couple DAG to the MTOC are not known. By single-cell photoactivation of the T cell antigen receptor (TCR), we found that three distinct isoforms of protein kinase C (PKC) were recruited by DAG to the IS in two steps. PKC-ɛ and PKC-η accumulated first in a broad region of membrane, whereas PKC-θ arrived later in a smaller zone. Functional experiments indicated that PKC-θ was required for MTOC reorientation and that PKC-ɛ and PKC-η operated redundantly to promote the recruitment of PKC-θ and subsequent polarization responses. Our results establish a previously uncharacterized role for PKC proteins in T cell polarity.

Analysis of dynamic tyrosine phosphoproteome in LFA-1 triggered migrating T-cells

The ordered, directional migration of T-lymphocytes is a key process during immune surveillance and response. This requires cell adhesion to the high endothelial venules or to the extracellular matrix by a series of surface receptor/ligand interactions involving adhesion molecules of the integrin family including lymphocyte function associated molecule-1 (LFA-1) and intercellular adhesion molecules (ICAMs). Reversible protein phosphorylation is emerging as a key player in the regulation of biological functions with tyrosine phosphorylation playing a crucial role in signal transduction. Thus, the study of this type of post-translational modification at the proteomic level has great biological significance. In this work, phospho-enriched cell lysates from LFA-1-triggered migrating human T-cells were subjected to immunoaffinity purification of tyrosine phosphorylated proteins, mass spectrometric, and bioinformatic analysis. In addition to the identification of several well-documented proteins, the analysis suggested involvement of a number of new and novel proteins in LFA-1 induced T-cell migration. This dataset expands the list of the signaling components of the LFA-1 induced phosphotyrosine protein complexes in migrating T-cells that will be extremely useful in the study of their specific roles within LFA-1 associated signaling pathways. Identification of proteins previously not reported in the context of LFA-1 stimulated signal transduction might provide new insights into understanding the LFA-1 signaling networks and aid in the search for new potential therapeutic targets.

Adhesion shapes T cells for prompt and sustained T-cell receptor signalling

During T-cell migration, cell polarity is orchestrated by chemokine receptors and adhesion molecules and involves the functional redistribution of molecules and organelles towards specific cell compartments. In contrast, it is generally believed that the cell polarity established when T cells meet antigen-presenting cells (APCs) is controlled by the triggered T-cell receptor (TCR). Here, we show that, during activation of human T lymphocytes by APCs, chemokines and LFA-1 establish cell polarity independently of TCR triggering. Chemokine-induced LFA-1 activation results in fast recruitment of MTOC and mitochondria towards the potential APC, a process required to amplify TCR Ca(2+) signalling at the upcoming immunological synapse, to promote nuclear translocation of transcriptional factor NFATc2 and boost CD25 expression. Our data show that the initial adhesive signals delivered by chemokines and LFA-1 shape and prepare T cells for antigen recognition.

Cytoskeletal cross-talk in the control of T cell antigen receptor signaling

T cell antigen receptor signaling is triggered and controlled in specialized cellular interfaces formed between T cells and antigen-presenting cells named immunological synapses. Both microtubules and actin cytoskeleton rearrange at the immunological synapse in response to T cell receptor triggering, ensuring in turn the accuracy of intracellular signaling. Recent reports show that the cross-talk between the cortical actin cytoskeleton and microtubule networks is key for structuring the immunological synapse and for controlling T cell receptor signaling. Immunological synapse architecture and the interaction between the signaling machinery and various cytoskeletal elements are therefore crucial for the fine-tuning of T cell signaling.

A high-content analysis toolbox permits dissection of diverse signaling pathways for T lymphocyte polarization

RNA interfering (RNAi) screening strategies offer the potential to elucidate the signaling pathways that regulate integrin and adhesion receptor-mediated changes in T lymphocyte morphology. Of crucial importance, however, is the definition of key sets of parameters that will provide accurate, quantitative, and nonredundant information to flag relevant hits in such assays. In this study, the authors have used an image-based high-content analysis (HCA) technology platform and a panel of 24 pharmacological inhibitors, at a range of concentrations, to define key sets of parameters that enables sensitive and quantitative effects on integrin (LFA-1)-mediated lymphocyte morphology to be evaluated. In particular, multiparametric analysis of lymphocyte morphology that was based on intracellular staining of both the F-actin and alpha-tubulin cytoskeleton resulted in improved ability to discriminate morphological behavior compared to F-actin staining alone. Morphological and fluorescence intensity/distribution profiling of pharmacologically treated lymphocytes stimulated with integrin (LFA-1) and adhesion receptors (CD44) also revealed notable differences in their sensitivity to inhibitors. The assay described here may be used in HCA strategies such as RNAi screening assays to elucidate the signaling pathways and molecules that regulate integrin/adhesion receptor-mediated T lymphocyte polarization.

Cysteine protease-mediated cytoskeleton interactions with LFA-1 promote T-cell morphological changes

T cells migrate through restrictive barriers in a protease-independent, amoeboid fashion that is characterized by morphological cell polarization. The interaction of cysteine-dependent carboxypeptidase cathepsin X with beta(2) integrin LFA-1 (lymphocyte function associated antigen 1) induces T-cell morphological changes, displaying into a 3D extracellular matrix a cytoplasmic projection termed a uropod. In the present study we show that inhibition of cathepsin X and a cysteine-dependent endopeptidase, cathepsin L, markedly inhibits T-cell actin polymerization, shape polarization, and chemotaxis. We propose that cathepsin L promotes T-cell migration associated processes by activating procathepsin X in the endolysosomal vesicles near the cell membrane and at the peak of the uropod, where both proteases were colocalized. We show that active cathepsin X modifies the beta(2) cytoplasmic tail of LFA-1 in the uropod, promoting its high affinity conformation. We suggest that LFA-1 cleavage contributes to the conformational change in the cytoplasmic tail, promoting the binding of the cytoskeletal protein talin. This interaction is restricted to the uropod and results in the stabilization of this region, promoting LFA-1-mediated cell uropod elongation.

STAT3 knockdown by siRNA induces apoptosis in human cutaneous T-cell lymphoma line Hut78 via downregulation of Bcl-xL

Cutaneous T-cell lymphomas (CTCLs) are non-Hodgkin's lymphomas resulting from clonal expansion and localization of malignant T-lymphocytes to the skin. CTCL cells have defective apoptosis. Signal transducers and activators of transcription (STAT) are a family of transcription factors known to play important roles in the development and progression of several human cancers by promoting cell proliferation and protecting against apoptosis. In this study, we investigated the specific role of STAT3, a major component of the STAT family, in growth and survival of human CTCL cell line Hut78. Western immunoblot analysis showed elevated expression of STAT3 and phospho-STAT3(Y705) in human CTCL cells as compared to freshly isolated peripheral blood lymphocytes (PBLs). Specific knockdown of STAT3 expression in Hut78 cells by RNA interference induced morphological and biochemical changes indicating apoptotic cell death. Moreover, STAT3 inhibition downregulated the expression of Bcl2 family of anti-apoptotic gene Bcl-xL. These observations suggest that STAT3 is required for the survival of CTCL cells and strongly indicate that targeting STAT3 using siRNA techniques may serve a novel therapeutic strategy for the treatment of CTCL.

Microtubules regulate migratory polarity through Rho/ROCK signaling in T cells

Background

Migrating leukocytes normally have a polarized morphology with an actin-rich lamellipodium at the front and a uropod at the rear. Microtubules (MTs) are required for persistent migration and chemotaxis, but how they affect cell polarity is not known.

Methodology/Principal Findings

Here we report that T cells treated with nocodazole to disrupt MTs are unable to form a stable uropod or lamellipodium, and instead often move by membrane blebbing with reduced migratory persistence. However, uropod-localized receptors and ezrin/radixin/moesin proteins still cluster in nocodazole-treated cells, indicating that MTs are required specifically for uropod stability. Nocodazole stimulates RhoA activity, and inhibition of the RhoA target ROCK allows nocodazole-treated cells to re-establish lamellipodia and uropods and persistent migratory polarity. ROCK inhibition decreases nocodazole-induced membrane blebbing and stabilizes MTs. The myosin inhibitor blebbistatin also stabilizes MTs, indicating that RhoA/ROCK act through myosin II to destabilize MTs.

Conclusions/Significance

Our results indicate that RhoA/ROCK signaling normally contributes to migration by affecting both actomyosin contractility and MT stability. We propose that regulation of MT stability and RhoA/ROCK activity is a mechanism to alter T-cell migratory behavior from lamellipodium-based persistent migration to bleb-based migration with frequent turning.

Involvement of the PRKCB1 gene in autistic disorder: significant genetic association and reduced neocortical gene expression

Protein kinase C enzymes play an important role in signal transduction, regulation of gene expression and control of cell division and differentiation. The fsI and betaII isoenzymes result from the alternative splicing of the PKCbeta gene (PRKCB1), previously found to be associated with autism. We performed a family-based association study in 229 simplex and 5 multiplex families, and a postmortem study of PRKCB1 gene expression in temporocortical gray matter (BA41/42) of 11 autistic patients and controls. PRKCB1 gene haplotypes are significantly associated with autism (P<0.05) and have the autistic endophenotype of enhanced oligopeptiduria (P<0.05). Temporocortical PRKCB1 gene expression was reduced on average by 35 and 31% for the PRKCB1-1 and PRKCB1-2 isoforms (P<0.01 and <0.05, respectively) according to qPCR. Protein amounts measured for the PKCbetaII isoform were similarly decreased by 35% (P=0.05). Decreased gene expression characterized patients carrying the 'normal' PRKCB1 alleles, whereas patients homozygous for the autism-associated alleles displayed mRNA levels comparable to those of controls. Whole genome expression analysis unveiled a partial disruption in the coordinated expression of PKCbeta-driven genes, including several cytokines. These results confirm the association between autism and PRKCB1 gene variants, point toward PKCbeta roles in altered epithelial permeability, demonstrate a significant downregulation of brain PRKCB1 gene expression in autism and suggest that it could represent a compensatory adjustment aimed at limiting an ongoing dysreactive immune process. Altogether, these data underscore potential PKCbeta roles in autism pathogenesis and spur interest in the identification and functional characterization of PRKCB1 gene variants conferring autism vulnerability.

Dok-4 is a novel negative regulator of T cell activation

Dok-4 (downstream of tyrosine kinase-4) is a recently identified member of the Dok family of adaptor proteins, which are characterized by an amino-terminal pleckstrin homology domain, a phosphotyrosine-binding domain, and a carboxyl-terminal region containing several tyrosines and poly-proline-rich motifs. Two members of the Dok family, Dok-1 and Dok-2, have already been described as negative regulators in T cells. However, the function of Dok-4, which is also expressed in T cells, remains unknown. In this study, we report that Dok-4 is phosphorylated after TCR engagement and shuttled within the cytoplasm of T cells before being recruited to the polarized microtubule organizing center after the formation of the immunological synapse. Loss-of-function experiments using RNA interference constructs show that Dok-4 is a negative regulator of ERK phosphorylation, IL-2 promoter activity, and T cell proliferation. Exogenous expression of wild-type Dok-4 induces a significant activation of Rap1, which is involved in the regulation of ERK. The pleckstrin homology domain of Dok-4 is required both for its cytoplasmic shuttling and relocalization as well as for its inhibitory properties on T cell activation. Thus, Dok-4 represents a novel negative regulator of T cells.

Involvement of thyroid hormones in the alterations of T-cell immunity and tumor progression induced by chronic stress

BACKGROUND

Stress alters the neuroendocrine system, immunity, and cancer. Although the classic stress hormones are glucocorticoids and catecholamines, thyroid hormones have also been related to stress. We recently reported that chronic restraint stress impairs T-cell mediated immunity and enhances tumor growth in mice.

METHODS

To study the participation of these hormones on the stress-induced alterations of the immune function and lymphoma growth, mice were subjected to acute or chronic stress, with or without thyroxin supplementation. Hormone levels, immune status, and cancer progression were evaluated.

RESULTS

Differential endocrine alterations were observed in response to acute and chronic stress. Although corticosterone and noradrenaline levels were increased by acute stress, they were restored after prolonged exposure to the stressor. Instead, thyroid hormone levels were only reduced in chronically stressed animals in comparison with control subjects. Correlating, chronic but not acute stress impaired T-cell reactivity. Thyroxin replacement treatment of chronic restraint stress-exposed mice, which restored the euthyroid status, reversed the observed reduction of T-cell lymphoproliferative responses. Moreover, therapeutic thyroid replacement also reversed the alterations of lymphoma growth induced by chronic stress in syngeneic mice bearing tumors as well as Interleukin-2 production and specific cytotoxic response against tumor cells. Finally, we found that the isoforms theta and alpha of the protein kinase C are involved in these events.

CONCLUSIONS

These results show for the first time that thyroid hormones are important neuroendocrine regulators of tumor evolution, most probably acting through the modulation of T-cell mediated immunity affected by chronic stress.

Aberrant TGF-beta signaling reduces T regulatory cells in ICAM-1-deficient mice, increasing the inflammatory response to Mycobacterium tuberculosis

Foxp3+ T regulatory cells are required to prevent autoimmune disease, but also prevent clearance of some chronic infections. While natural T regulatory cells are produced in the thymus, TGF-beta1 signaling combined with T-cell receptor signaling induces the expression of Foxp3 in CD4+ T cells in the periphery. We found that ICAM-1-/- mice have fewer T regulatory cells in the periphery than WT controls, due to a role for ICAM-1 in induction of Foxp3 expression in response to TGF-beta1. Further investigation revealed a functional deficiency in the TGF-beta1-induced translocation of phosphorylated Smad3 from the cytoplasmic compartment to the nucleus in ICAM-1-deficient mice. This impairment in the TGF-beta1 signaling pathway is most likely responsible for the decrease in T regulatory cell induction in the absence of ICAM-1. We hypothesized that in the presence of an inflammatory response, reduced production of inducible T regulatory cells would be evident in ICAM-1-/- mice. Indeed, following Mycobacterium tuberculosis infection, ICAM-1-/- mice had a pronounced reduction in T regulatory cells in the lungs compared with control mice. Consequently, the effector T-cell response and inflammation were greater in the lungs of ICAM-1-/- mice, resulting in morbidity due to overwhelming pathology.

Lymphocyte crawling and transendothelial migration require chemokine triggering of high-affinity LFA-1 integrin

Endothelial chemokines are instrumental for integrin-mediated lymphocyte adhesion and transendothelial migration (TEM). By dissecting how chemokines trigger lymphocyte integrins to support shear-resistant motility on and across cytokine-stimulated endothelial barriers, we found a critical role for high-affinity (HA) LFA-1 integrin in lymphocyte crawling on activated endothelium. Endothelial-presented chemokines triggered HA-LFA-1 and adhesive filopodia at numerous submicron dots scattered underneath crawling lymphocytes. Shear forces applied to endothelial-bound lymphocytes dramatically enhanced filopodia density underneath crawling lymphocytes. A fraction of the adhesive filopodia invaded the endothelial cells prior to and during TEM and extended large subluminal leading edge containing dots of HA-LFA-1 occupied by subluminal ICAM-1. Memory T cells generated more frequent invasive filopodia and transmigrated more rapidly than their naive counterparts. We propose that shear forces exerted on HA-LFA-1 trigger adhesive and invasive filopodia at apical endothelial surfaces and thereby promote lymphocyte crawling and probing for TEM sites.