A phosphorylation-controlled switch confers cell cycle-dependent protein relocalization

Tools for acute manipulation of protein localization enable elucidation of spatiotemporally defined functions, but their reliance on exogenous triggers can interfere with cell physiology. This limitation is particularly apparent for studying mitosis, whose highly choreographed events are sensitive to perturbations. Here we exploit the serendipitous discovery of a phosphorylation-controlled, cell cycle-dependent localization change of the adaptor protein PLEKHA5 to develop a system for mitosis-specific protein recruitment to the plasma membrane that requires no exogenous stimulus. Mitosis-enabled anchor-away/recruiter system comprises an engineered, 15 kDa module derived from PLEKHA5 capable of recruiting functional protein cargoes to the plasma membrane during mitosis, either through direct fusion or via GFP-GFP nanobody interaction. Applications of the mitosis-enabled anchor-away/recruiter system include both knock sideways to rapidly extract proteins from their native localizations during mitosis and conditional recruitment of lipid-metabolizing enzymes for mitosis-selective editing of plasma membrane lipid content, without the need for exogenous triggers or perturbative synchronization methods.

A phosphorylation-controlled switch confers cell cycle-dependent protein relocalization

Tools for acute manipulation of protein localization enable elucidation of spatiotemporally defined functions, but their reliance on exogenous triggers can interfere with cell physiology. This limitation is particularly apparent for studying mitosis, whose highly choreographed events are sensitive to perturbations. Here we exploit the serendipitous discovery of a phosphorylation-controlled, cell cycle-dependent localization change of the adaptor protein PLEKHA5 to develop a system for mitosis-specific protein recruitment to the plasma membrane that requires no exogenous stimulus. Mitosis-enabled Anchor-away/Recruiter System (MARS) comprises an engineered, 15-kDa module derived from PLEKHA5 capable of recruiting functional protein cargoes to the plasma membrane during mitosis, either through direct fusion or via GFP-GFP nanobody interaction. Applications of MARS include both knock sideways to rapidly extract proteins from their native localizations during mitosis and conditional recruitment of lipid-metabolizing enzymes for mitosis-selective editing of plasma membrane lipid content, without the need for exogenous triggers or perturbative synchronization methods.

Acute Adenoviral Infection Elicits an Arrhythmogenic Substrate Prior to Myocarditis

BACKGROUND

Viral cardiac infection represents a significant clinical challenge encompassing several etiological agents, disease stages, complex presentation, and a resulting lack of mechanistic understanding. Myocarditis is a major cause of sudden cardiac death in young adults, where current knowledge in the field is dominated by later disease phases and pathological immune responses. However, little is known regarding how infection can acutely induce an arrhythmogenic substrate before significant immune responses. Adenovirus is a leading cause of myocarditis, but due to species specificity, models of infection are lacking, and it is not understood how adenoviral infection may underlie sudden cardiac arrest. Mouse adenovirus type-3 was previously reported as cardiotropic, yet it has not been utilized to understand the mechanisms of cardiac infection and pathology.

METHODS

We have developed mouse adenovirus type-3 infection as a model to investigate acute cardiac infection and molecular alterations to the infected heart before an appreciable immune response or gross cardiomyopathy.

RESULTS

Optical mapping of infected hearts exposes decreases in conduction velocity concomitant with increased Cx43Ser368 phosphorylation, a residue known to regulate gap junction function. Hearts from animals harboring a phospho-null mutation at Cx43Ser368 are protected against mouse adenovirus type-3-induced conduction velocity slowing. Additional to gap junction alterations, patch clamping of mouse adenovirus type-3-infected adult mouse ventricular cardiomyocytes reveals prolonged action potential duration as a result of decreased IK1 and IKs current density. Turning to human systems, we find human adenovirus type-5 increases phosphorylation of Cx43Ser368 and disrupts synchrony in human induced pluripotent stem cell-derived cardiomyocytes, indicating common mechanisms with our mouse whole heart and adult cardiomyocyte data.

CONCLUSIONS

Together, these findings demonstrate that adenoviral infection creates an arrhythmogenic substrate through direct targeting of gap junction and ion channel function in the heart. Such alterations are known to precipitate arrhythmias and likely contribute to sudden cardiac death in acutely infected patients.

Response to Bruton's tyrosine kinase inhibitors in aggressive lymphomas linked to chronic selective autophagy

Diffuse large B cell lymphoma (DLBCL) is an aggressive, profoundly heterogeneous cancer, presenting a challenge for precision medicine. Bruton's tyrosine kinase (BTK) inhibitors block B cell receptor (BCR) signaling and are particularly effective in certain molecular subtypes of DLBCL that rely on chronic active BCR signaling to promote oncogenic NF-κB. The MCD genetic subtype, which often acquires mutations in the BCR subunit, CD79B, and in the innate immune adapter, MYD88L265P, typically resists chemotherapy but responds exceptionally to BTK inhibitors. However, the underlying mechanisms of response to BTK inhibitors are poorly understood. Herein, we find a non-canonical form of chronic selective autophagy in MCD DLBCL that targets ubiquitinated MYD88L265P for degradation in a TBK1-dependent manner. MCD tumors acquire genetic and epigenetic alterations that attenuate this autophagic tumor suppressive pathway. In contrast, BTK inhibitors promote autophagic degradation of MYD88L265P, thus explaining their exceptional clinical benefit in MCD DLBCL.

An Update on Protein Kinases as Therapeutic Targets-Part I: Protein Kinase C Activation and Its Role in Cancer and Cardiovascular Diseases

Protein kinases are one of the most significant drug targets in the human proteome, historically harnessed for the treatment of cancer, cardiovascular disease, and a growing number of other conditions, including autoimmune and inflammatory processes. Since the approval of the first kinase inhibitors in the late 1990s and early 2000s, the field has grown exponentially, comprising 98 approved therapeutics to date, 37 of which were approved between 2016 and 2021. While many of these small-molecule protein kinase inhibitors that interact orthosterically with the protein kinase ATP binding pocket have been massively successful for oncological indications, their poor selectively for protein kinase isozymes have limited them due to toxicities in their application to other disease spaces. Thus, recent attention has turned to the use of alternative allosteric binding mechanisms and improved drug platforms such as modified peptides to design protein kinase modulators with enhanced selectivity and other pharmacological properties. Herein we review the role of different protein kinase C (PKC) isoforms in cancer and cardiovascular disease, with particular attention to PKC-family inhibitors. We discuss translational examples and carefully consider the advantages and limitations of each compound (Part I). We also discuss the recent advances in the field of protein kinase modulators, leverage molecular docking to model inhibitor-kinase interactions, and propose mechanisms of action that will aid in the design of next-generation protein kinase modulators (Part II).

Pharmacological study on the enhancing effects of U46619 on guinea pig urinary bladder smooth muscle contraction induced by acetylcholine and α,β-methylene ATP and the possible involvement of protein kinase C

We examined whether U46619 (a prostanoid TP receptor agonist) could enhance the contractions of guinea pig urinary bladder smooth muscle (UBSM) in response to acetylcholine (ACh) and an ATP analog (α,β-methylene ATP (αβ-MeATP)) through stimulation of the UBSM TP receptor and whether protein kinase C (PKC) is involved. U46619 (10-7 M) markedly enhanced UBSM contractions induced by electrical field stimulation and ACh/αβ-MeATP (3 × 10-6 M each), the potentiation of which was completely suppressed by SQ 29,548 (a TP receptor antagonist, 6 × 10-7 M). PKC inhibitors did not attenuate the ACh-induced contractions enhanced by U46619 although they partly suppressed the U46619-enhanced, αβ-MeATP-induced contractions. While phorbol 12-myristate 13-acetate (PMA, a PKC activator, 10-6 M) did not enhance ACh-induced contractions, it enhanced αβ-MeATP-induced contractions, an effect that was completely suppressed by PKC inhibitors. αβ-MeATP-induced contractions, both with and without U46619 enhancement, were strongly inhibited by diltiazem. U46619/PMA enhanced 50 mM KCl-induced contractions, the potentiation of which was partly/completely attenuated by PKC inhibitors. These findings suggest that U46619 potentiates parasympathetic nerve-associated UBSM contractions by stimulating UBSM TP receptors. PKC-increased Ca2+ influx through voltage-dependent Ca2+ channels may partially play a role in purinergic receptor-mediated UBSM contractions enhanced by TP receptor stimulation.

HIV-1-induced nuclear invaginations mediated by VAP-A, ORP3, and Rab7 complex explain infection of activated T cells

The mechanism of human immunodeficiency virus 1 (HIV-1) nuclear entry, required for productive infection, is not fully understood. Here, we report that in HeLa cells and activated CD4+ T cells infected with HIV-1 pseudotyped with VSV-G and native Env protein, respectively, Rab7+ late endosomes containing endocytosed HIV-1 promote the formation of nuclear envelope invaginations (NEIs) by a molecular mechanism involving the VOR complex, composed of the outer nuclear membrane protein VAP-A, hyperphosphorylated ORP3 and Rab7. Silencing VAP-A or ORP3 and drug-mediated impairment of Rab7 binding to ORP3-VAP-A inhibited the nuclear transfer of the HIV-1 components and productive infection. In HIV-1-resistant quiescent CD4+ T cells, ORP3 was not hyperphosphorylated and neither VOR complex nor NEIs were formed. This new cellular pathway and its molecular players are potential therapeutic targets, perhaps shared by other viruses that require nuclear entry to complete their life cycle.

A phase Ib trial of combined PKC and MEK inhibition with sotrastaurin and binimetinib in patients with metastatic uveal melanoma

Background

Uveal melanoma is a disease characterized by constitutive activation of the G alpha pathway and downstream signaling of protein kinase C (PKC) and the mitogen-activated protein kinase (MAPK) pathway. While limited clinical activity has been observed in patients with metastatic disease with inhibition of PKC or MEK alone, preclinical data has demonstrated synergistic antitumor effects with concurrent inhibition of PKC and MEK.

Method

We conducted a phase Ib study of the PKC inhibitor sotrastaurin in combination with the MEK inhibitor binimetinib in patients with metastatic uveal melanoma using a Bayesian logistic regression model guided by the escalation with overdose control principle (NCT01801358). Serial blood samples and paired tumor samples were collected for pharmacokinetic (PK) and pharmacodynamic analysis.

Results

Thirty-eight patients were treated across six dose levels. Eleven patients experienced DLTs across the five highest dose levels tested, most commonly including vomiting (n=3), diarrhea (n=3), nausea (n=2), fatigue (n=2) and rash (n=2). Common treatment related adverse events included diarrhea (94.7%), nausea (78.9%), vomiting (71.1%), fatigue (52.6%), rash (39.5%), and elevated blood creating phosphokinase (36.8%). Two dose combinations satisfying criteria for the maximum tolerated dose (MTD) were identified: (1) sotrastaurin 300 mg and binimetinib 30 mg; and, (2) sotrastaurin 200 mg and binimetinib 45 mg. Exposure to both drugs in combination was consistent with single-agent data for either drug, indicating no PK interaction between sotrastaurin and binimetinib. Stable disease was observed in 60.5% of patients treated. No patient achieved a radiographic response per RECIST v1.1.

Conclusions

Concurrent administration of sotrastaurin and binimetinib is feasible but associated with substantial gastrointestinal toxicity. Given the limited clinical activity achieved with this regimen, accrual to the phase II portion of the trial was not initiated.

Effects of free fatty acid receptor-2 (FFAR2)-mediated signaling on the regulation of cellular functions in osteosarcoma cells

G protein coupled free fatty acid receptors (FFARs) are involved in the pathogenesis of several human diseases. FFAR2 and FFAR3 are activated by the binding of short-chain fatty acids (SCFAs). This study aimed to evaluate the roles of FFAR2 in the regulation of cellular functions in osteosarcoma HOS cells, using acetic acid and propanoic acid as FFAR2 and FFAR3 agonists. FFAR2 and FFAR3 genes were expressed in HOS cells. The cell motile activity of HOS cells was significantly stimulated by acetic acid and propanoic acid. In contrast, acetic acid and propanoic acid had no impact on the activation of matrix metalloproteinase-2 (MMP-2) and MMP-9. In cell survival assay, the cell survival rate to cisplatin (CDDP) of HOS cells was elevated by acetic acid and propanoic acid. To assess the effects of FFAR2 on cellular functions, FFAR2 knockdown (HOS-FFAR2) cells were generated from HOS cells. The cell motile activity of HOS-FFAR2 cells was enhanced by acetic acid and propanoic acid. In the presence of acetic acid and propanoic acid, MMP-2 and MMP-9 activities were reduced in HOS-FFAR2 cells, compared with control cells. When cells were treated with acetic acid and propanoic acid, the cell survival rate to CDDP of HOS-FFAR2 cells was significantly lower than that of control cells. These results suggest that activation of FFAR2-mediated signaling is involved in the modulation of cellular functions in HOS cells.

Autoreactive T-Cells in Psoriasis: Are They Spoiled Tregs and Can Therapies Restore Their Functions?

Psoriasis is a chronic inflammatory skin disease, which affects 2-4% of the population worldwide. T-cell derived factors such as Th17 and Th1 cytokines or cytokines such as IL-23, which favors Th17-expansion/differentiation, dominate in the disease. Therapies targeting these factors have been developed over the years. An autoimmune component is present, as autoreactive T-cells specific for keratins, the antimicrobial peptide LL37 and ADAMTSL5 have been described. Both autoreactive CD4 and CD8 T-cells exist, produce pathogenic cytokines, and correlate with disease activity. Along with the assumption that psoriasis is a T-cell-driven disease, Tregs have been studied extensively over the years, both in the skin and in circulation. This narrative review resumes the main findings about Tregs in psoriasis. We discuss how Tregs increase in psoriasis but are impaired in their regulatory/suppressive function. We debate the possibility that Tregs convert into T-effector cells under inflammatory conditions; for instance, they may turn into Th17-cells. We put particular emphasis on therapies that seem to counteract this conversion. We have enriched this review with an experimental section analyzing T-cells specific for the autoantigen LL37 in a healthy subject, suggesting that a shared specificity may exist between Tregs and autoreactive responder T-cells. This suggests that successful psoriasis treatments may, among other effects, restore Tregs numbers and functions.

Protein kinase C isoforms mediate the formation of neutrophil extracellular traps

Neutrophils release extracellular traps (NETs) in response to numerous pathogenic microbes as the last suicidal resource (NETosis) in the fight against infection. Apart from the host defense function, NETs play an essential role in the pathogenesis of various autoimmune, inflammatory and malignant diseases. Therefore, understanding the molecular mechanisms of NETosis is important for regulating the aberrant or excessive NET release. Protein kinase C (PKC) is a serine/threonine kinase which is involved in various neutrophil functions, however, little is known about its implication in NETosis activated by various physiological and pharmacological stimuli. Since there are conventional, novel and atypical PKC isoforms (α, βI, βII, δ, and ζ) found in human neutrophils, we investigated their impact in NETosis, oxidative burst and spreading applying pharmacological approach. Using specific inhibitors of PKC isoforms, we showed that PKCβ, PKCδ, and PKCζ are involved in the oxidative burst, spreading and NETosis activated by calcium ionophore A23187, while only PKCβ is implicated in these functions activated by phorbol 12-myristate 13-acetate (PMA). The data obtained in our study might help in the development of new drugs useful for the treatment of autoimmune and inflammatory diseases associated with NETs.

The thiophene α-terthienylmethanol isolated from Tagetes minuta inhibits angiogenesis by targeting protein kinase C isozymes α and β2

Background: Tumor angiogenesis is considered as a crucial pathologic feature of cancer with a key role in multidrug resistance (MDR). Adverse effects of the currently available drugs and the development of resistance to these remain as the hardest obstacles to defeat.

Objetive: This work explores flora from Argentina as a source of new chemical entities with antiangiogenic activity.

Methods: Tube formation assay using bovine aortic endothelial cells (BAECs) was the experiment of choice to assess antiangiogenic activity. The effect of the pure compound in cell invasiveness was investigated through the trans-well migration assay. The inhibitory effect of the pure compound on VEGFR-2 and PKC isozymes α and β2 activation was studied by molecular and massive dynamic simulations. Cytotoxicity on peripheral blood mononuclear cells and erythrocyte cells was evaluated by means of MTT and hemolysis assay, respectively. In silico prediction of pharmacological properties (ADME) and evaluation of drug-likeness features were performed using the SwissADME online tool.

Results: Among the plants screened, T. minuta, showed an outstanding effect with an IC₅₀ of 33.6 ± 3.4 μg/ml. Bio-guided isolation yielded the terthiophene α-terthienylmethanol as its active metabolite. This compound inhibited VEGF-induced tube formation with an IC₅₀ of 2.7 ± 0.4 μM and significantly impaired the invasiveness of bovine aortic endothelial cells (BAECs) as well as of the highly aggressive breast cancer cells, MDA-MB-231, when tested at 10 μM. Direct VEGFR-2 and PKC inhibition were both explored by means of massive molecular dynamics simulations. The results obtained validated the inhibitory effect on protein kinase C (PKC) isozymes α and β2 as the main mechanism underlying its antiangiogenic activity. α-terthienylmethanol showed no evidence of toxicity against peripheral blood mononuclear and erythrocyte cells.

Conclusion: These findings support this thiophene as a promising antiangiogenic phytochemical to fight against several types of cancer mainly those with MDR phenotype.

Protein kinase C targeting of luminal (T-47D), luminal/HER2-positive (BT474), and triple negative (HCC1806) breast cancer cells in-vitro with AEB071 (Sotrastaurin) is efficient but mediated by subtype specific molecular effects

Purpose

Protein kinase C (PKC) plays a pivotal role in malignant cell proliferation, apoptosis, invasiveness and migration. However, its exploitation as therapeutic target in breast cancer has been merely explored. Here were evaluated the AEB071 (Sotrastaurin™) treatment efficiency of breast cancer cell lines derived from estrogen receptor positive (T-47D), estrogen/HER2 receptor positive (BT474), and triple negative (HCC1806) breast cancer cells under 2D (monolayer) and 3D (multicellular tumor spheroids) culture conditions. Additionally, spheroid cocultures of BC and N1 fibroblasts were analyzed.

Methods

We quantitatively assessed the proliferation capacity of breast cancer cells and fibroblasts as a function of AEB071 treatment using flow cytometry. The activities of PKC isoforms, substrates, and key molecules of the PKC signaling known to be involved in the regulation of tumor cell proliferation and cellular survival were additionally evaluated. Moreover, a multigene expression analysis (PanCancer Pathways assay) using the nanoString™ technology was applied.

Results

All breast cancer cell lines subjected to this study were sensitive to AEB071 treatment, whereby cell proliferation in 2D culture was considerably (BT474) or moderately (HCC1806) retarded in G0/G1 or in G2/M phase (T-47D) of the cell cycle. Regardless of the breast cancer subtype the efficiency of AEB071 treatment was significantly lower in the presence of N1 fibroblast cells. Subtype specific driver molecules, namely IL19, c-myb, and NGFR were mostly affected by the AEB071 treatment.

Conclusion

A combined targeting of PKC and a subtype specific driver molecule might complement specified breast cancer treatment.

Phosphorylation of serine-893 in CARD11 suppresses the formation and activity of the CARD11-BCL10-MALT1 complex in T and B cells

CARD11 acts as a gatekeeper for adaptive immune responses after T cell or B cell antigen receptor (TCR/BCR) ligation on lymphocytes. PKCθ/β-catalyzed phosphorylation of CARD11 promotes the assembly of the CARD11-BCL10-MALT1 (CBM) complex and lymphocyte activation. Here, we demonstrated that PKCθ/β-dependent CARD11 phosphorylation also suppressed CARD11 functions in T or B cells. Through mass spectrometry-based proteomics analysis, we identified multiple constitutive and inducible CARD11 phosphorylation sites in T cells. We demonstrated that a single TCR- or BCR-inducible phosphorylation on Ser⁸⁹³ in the carboxyl terminus of CARD11 prevented the activation of the transcription factor NF-κB, the kinase JNK, and the protease MALT1. Moreover, CARD11 Ser⁸⁹³ phosphorylation sensitized BCR-addicted lymphoma cells to toxicity induced by Bruton's tyrosine kinase (BTK) inhibitors. Phosphorylation of Ser⁸⁹³ in CARD11 by PKCθ controlled the strength of CARD11 scaffolding by impairing the formation of the CBM complex. Thus, PKCθ simultaneously catalyzes both stimulatory and inhibitory CARD11 phosphorylation events, which shape the strength of CARD11 signaling in lymphocytes.

Insights into the potential of withanolides as Phosphodiesterase-4 (PDE4D) inhibitors

Medicinal herbs have been used as traditional medicines for centuries. The molecular mechanism of action of their bioactive molecules against various diseases or therapeutic targets is still being explored. Here, the active compounds (withanolides) of a well-known Indian medicinal herb, Ashwagandha (Withania somnifera), have been studied for their most potential therapeutic targets and their mechanism of action using ligand-based screening and receptor-based approaches. Ligand-based screening predicted the six top therapeutic targets, namely, Protein kinase C alpha (PRKCA), Protein kinase C delta (PRKCD), Protein kinase C epsilon (PRKCE), Androgenic Receptor (AR), Cycloxygenase-2 (PTGS-2) and Phosphodiesterase-4D (PDE4D). Further, when these predictions were validated using receptor-based studies, i.e. molecular docking, molecular dynamics simulation and free energy calculations, it was found that PDE4D was the most potent target for four withanolides, namely, Withaferin-A, 17-Hydroxywithaferin-A, 27-Hydroxywithanone and Withanolide-R. These compounds had a better binding affinity and similar interactions as that of an already known inhibitor (Zardaverine) of PDE4D. These results warrant further in-vitro and in-vivo investigations to examine their therapeutic potential as an inhibitor of PDE4D.Communicated by Ramaswamy H. Sarma.

Coordinated regulation of endothelial calcium signaling and shear stress-induced nitric oxide production by PKCβ and PKCη

BACKGROUND

Protein Kinase C (PKC) is a promiscuous serine/threonine kinase regulating vasodilatory responses in vascular endothelial cells. Calcium-dependent PKCbeta (PKCβ) and calcium-independent PKCeta (PKCη) have both been implicated in the regulation and dysfunction of endothelial responses to shear stress and agonists.

OBJECTIVE

We hypothesized that PKCβ and PKCη differentially modulate shear stress-induced nitric oxide (NO) production by regulating the transduced calcium signals and the resultant eNOS activation. As such, this study sought to characterize the contribution of PKCη and PKCβ in regulating calcium signaling and endothelial nitric oxide synthase (eNOS) activation after exposure of endothelial cells to ATP or shear stress.

METHODS

Bovine aortic endothelial cells were stimulated in vitro under pharmacological inhibition of PKCβ with LY333531 or PKCη targeting with a pseudosubstrate inhibitor. The participation of PKC isozymes in calcium flux, eNOS phosphorylation and NO production was assessed following stimulation with ATP or shear stress.

RESULTS

PKCη proved to be a robust regulator of agonist- and shear stress-induced eNOS activation, modulating calcium fluxes and tuning eNOS activity by multi-site phosphorylation. PKCβ showed modest influence in this pathway, promoting eNOS activation basally and in response to shear stress. Both PKC isozymes contributed to the constitutive and induced phosphorylation of eNOS. The observed PKC signaling architecture is intricate, recruiting Src to mediate a portion of PKCη's control on calcium entry and eNOS phosphorylation. Elucidation of the importance of PKCη in this pathway was tempered by evidence of a single stimulus producing concurrent phosphorylation at ser1179 and thr497 which are antagonistic to eNOS activity.

CONCLUSIONS

We have, for the first time, shown in a single species in vitro that shear stress- and ATP-stimulated NO production are differentially regulated by classical and novel PKCs. This study furthers our understanding of the PKC isozyme interplay that optimizes NO production. These considerations will inform the ongoing design of drugs for the treatment of PKC-sensitive cardiovascular pathologies.

Activators and Inhibitors of Protein Kinase C (PKC): Their Applications in Clinical Trials

Protein kinase C (PKC), a family of phospholipid-dependent serine/threonine kinase, is classed into three subfamilies based on their structural and activation characteristics: conventional or classic PKC isozymes (cPKCs; α, βI, βII, and γ), novel or non-classic PKC isozymes (nPKCs; δ, ε, η, and θ), and atypical PKC isozymes (aPKCs; ζ, ι, and λ). PKC inhibitors and activators are used to understand PKC-mediated intracellular signaling pathways and for the diagnosis and treatment of various PKC-associated diseases, such as cancers, neurological diseases, cardiovascular diseases, and infections. Many clinical trials of PKC inhibitors in cancers showed no significant clinical benefits, meaning that there is a limitation to design a cancer therapeutic strategy targeting PKC alone. This review will focus on the activators and inhibitors of PKC and their applications in clinical trials.

Protein kinase C theta (Prkcq) affects nerve degeneration and regeneration through the c-fos and c-jun pathways in injured rat sciatic nerves

BACKGROUND

Previous finding using DNA microarray and bioinformatics analysis, we have reported some key factors which regulated gene expression and signaling pathways in injured sciatic nerve during Wallerian Degeneration (WD). This research is focused on protein kinase C theta (Prkcq) participates in the regulation of the WD process.

METHODS

In this study, we explored the molecular mechanism by which Prkcq in Schwann cells (SCs) affects nerve degeneration and regeneration in vivo and in vitro after rat sciatic nerve injury.

RESULTS

Study of the cross-sectional model showed that Prkcq expression decreased significantly during sciatic nerve repair. Functional analysis showed that upregulation and downregulation of Prkcq could affect the proliferation, migration and apoptosis of Schwann cells and lead to the expression of related factors through the activation of the β-catenin, c-fos, and p-c-jun/c-jun pathways.

CONCLUSION

The study provides insights into the role of Prkcq in early WD during peripheral nerve degeneration and/or regeneration.

Long-Chain Acylcarnitines Decrease the Phosphorylation of the Insulin Receptor at Tyr1151 Through a PTP1B-Dependent Mechanism

The accumulation of lipid intermediates may interfere with energy metabolism pathways and regulate cellular energy supplies. As increased levels of long-chain acylcarnitines have been linked to insulin resistance, we investigated the effects of long-chain acylcarnitines on key components of the insulin signalling pathway. We discovered that palmitoylcarnitine induces dephosphorylation of the insulin receptor (InsR) through increased activity of protein tyrosine phosphatase 1B (PTP1B). Palmitoylcarnitine suppresses protein kinase B (Akt) phosphorylation at Ser473, and this effect is not alleviated by the inhibition of PTP1B by the insulin sensitizer bis-(maltolato)-oxovanadium (IV). This result indicates that palmitoylcarnitine affects Akt activity independently of the InsR phosphorylation level. Inhibition of protein kinase C and protein phosphatase 2A does not affect the palmitoylcarnitine-mediated inhibition of Akt Ser473 phosphorylation. Additionally, palmitoylcarnitine markedly stimulates insulin release by suppressing Akt Ser473 phosphorylation in insulin-secreting RIN5F cells. In conclusion, long-chain acylcarnitines activate PTP1B and decrease InsR Tyr1151 phosphorylation and Akt Ser473 phosphorylation, thus limiting the cellular response to insulin stimulation.

Ciliogenesis and autophagy are coordinately regulated by EphA2 in the cornea to maintain proper epithelial architecture

PURPOSE

To understand the relationship between ciliogenesis and autophagy in the corneal epithelium.

METHODS

siRNAs for EphA2 or PLD1 were used to inhibit protein expression in vitro. Morpholino-anti-EphA2 was used to knockdown EphA2 in Xenopus skin. An EphA2 knockout mouse was used to conduct loss of function studies. Autophagic vacuoles were visualized by contrast light microscopy. Autophagy flux, was measured by LC3 turnover and p62 protein levels. Immunostaining and confocal microscopy were conducted to visualize cilia in cultured cells and in vivo.

RESULTS

Loss of EphA2 (i) increased corneal epithelial thickness by elevating proliferative potential in wing cells, (ii) reduced the number of ciliated cells, (iii) increased large hollow vacuoles, that could be rescued by BafA1; (iv) inhibited autophagy flux and (v) increased GFP-LC3 puncta in the mouse corneal epithelium. This indicated a role for EphA2 in stratified epithelial assembly via regulation of proliferation as well as a positive role in both ciliogenesis and end-stage autophagy. Inhibition of PLD1, an EphA2 interacting protein that is a critical regulator of end-stage autophagy, reversed the accumulation of vacuoles, and the reduction in the number of ciliated cells due to EphA2 depletion, suggesting EphA2 regulation of both end-stage autophagy and ciliogenesis via PLD1. PLD1 mediated rescue of ciliogenesis by EphA2 depletion was blocked by BafA1, placing autophagy between EphA2 signaling and regulation of ciliogenesis.

CONCLUSION

Our findings demonstrate a novel role for EphA2 in regulating both autophagy and ciliogenesis, processes that are essential for proper corneal epithelial homeostasis.

The Emerging Function of PKCtheta in Cancer

Protein Kinase C theta (PKCθ) is a serine/threonine kinase that belongs to the novel PKC subfamily. In normal tissue, its expression is restricted to skeletal muscle cells, platelets and T lymphocytes in which PKCθ controls several essential cellular processes such as survival, proliferation and differentiation. Particularly, PKCθ has been extensively studied for its role in the immune system where its translocation to the immunological synapse plays a critical role in T cell activation. Beyond its physiological role in immune responses, increasing evidence implicates PKCθ in the pathology of various diseases, especially autoimmune disorders and cancers. In this review, we discuss the implication of PKCθ in various types of cancers and the PKCθ-mediated signaling events controlling cancer initiation and progression. In these types of cancers, the high PKCθ expression leads to aberrant cell proliferation, migration and invasion resulting in malignant phenotype. The recent development and application of PKCθ inhibitors in the context of autoimmune diseases could benefit the emergence of treatment for cancers in which PKCθ has been implicated.

Structurally different lysophosphatidylethanolamine species stimulate neurite outgrowth in cultured cortical neurons via distinct G-protein-coupled receptors and signaling cascades

Neurite outgrowth is important in neuronal circuit formation and functions, and for regeneration of neuronal networks following trauma and disease in the brain. Thus, identification and characterization of the molecules that regulate neurite outgrowth are essential for understanding how brain circuits form and function and for the development of treatment of neurological disorders. In this study, we found that structurally different lysophosphatidylethanolamine (LPE) species, palmitoyl-LPE (16:0 LPE) and stearoyl-LPE (18:0 LPE), stimulate neurite growth in cultured cortical neurons. Interestingly, YM-254890, an inhibitor of Gq/11 protein, inhibited 16:0 LPE-stimulated neurite outgrowth but not 18:0 LPE-stimulated neurite outgrowth. In contrast, pertussis toxin, an inhibitor of Gi/Go proteins, inhibited 18:0 LPE-stimulated neurite outgrowth but not 16:0 LPE-stimulated neurite outgrowth. The effects of protein kinase C inhibitors on neurite outgrowth were also different. In addition, both 16:0 LPE and 18:0 LPE activate mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1/2, but the effect of the MAPK inhibitor differed between the 16:0 LPE- and 18:0 LPE-treated cultures. Collectively, the results suggest that the structurally different LPE species, 16:0 LPE and 18:0 LPE stimulate neurite outgrowth through distinct signaling cascades in cultured cortical neurons and that distinct G protein-coupled receptors are involved in these processes.

Coxiella burnetii-Infected NK Cells Release Infectious Bacteria by Degranulation

Natural killer (NK) cells are critically involved in the early immune response against various intracellular pathogens, including Coxiella burnetii and Chlamydia psittaci Chlamydia-infected NK cells functionally mature, induce cellular immunity, and protect themselves by killing the bacteria in secreted granules. Here, we report that infected NK cells do not allow intracellular multiday growth of Coxiella, as is usually observed in other host cell types. C. burnetii-infected NK cells display maturation and gamma interferon (IFN-γ) secretion, as well as the release of Coxiella-containing lytic granules. Thus, NK cells possess a potent program to restrain and expel different types of invading bacteria via degranulation. Strikingly, though, in contrast to Chlamydia, expulsed Coxiella organisms largely retain their infectivity and, hence, escape the cell-autonomous self-defense mechanism in NK cells.

Reactivating latent HIV with PKC agonists induces resistance to apoptosis and is associated with phosphorylation and activation of BCL2

Eradication of HIV-1 by the "kick and kill" strategy requires reactivation of latent virus to cause death of infected cells by either HIV-induced or immune-mediated apoptosis. To date this strategy has been unsuccessful, possibly due to insufficient cell death in reactivated cells to effectively reduce HIV-1 reservoir size. As a possible cause for this cell death resistance, we examined whether leading latency reversal agents (LRAs) affected apoptosis sensitivity of CD4 T cells. Multiple LRAs of different classes inhibited apoptosis in CD4 T cells. Protein kinase C (PKC) agonists bryostatin-1 and prostratin induced phosphorylation and enhanced neutralizing capability of the anti-apoptotic protein BCL2 in a PKC-dependent manner, leading to resistance to apoptosis induced by both intrinsic and extrinsic death stimuli. Furthermore, HIV-1 producing CD4 T cells expressed more BCL2 than uninfected cells, both in vivo and after ex vivo reactivation. Therefore, activation of BCL2 likely contributes to HIV-1 persistence after latency reversal with PKC agonists. The effects of LRAs on apoptosis sensitivity should be considered in designing HIV cure strategies predicated upon the "kick and kill" paradigm.

AEB-071 Ameliorates Muscle Weakness by Altering Helper T Lymphocytes in an Experimental Autoimmune Myasthenia Gravis Rat Model

Background

Myasthenia gravis (MG) is an autoimmune neurological disorder of neuromuscular junctions. In this study we established experimental autoimmune myasthenia gravis (EAMG) rat models to investigate the effects of AEB-071 (AEB), which is a specific inhibitor of protein kinase C that prevents T lymphocyte activation.

Material/Methods

We utilized animals divided into 4 groups: (1) control rats, (2) EAMG, (3) AEB-071+EAMG, and (4) AZP+EAMG. Drug treatment was continued for 10 days. Ten weeks after immunization we measured body weights, assessed mortality rates, and used Lennon scores to evaluate EAMG grades. We also assessed the proportions of T_reg, T_h1, T_h2, T_h17, and lymphocytes using flow cytometry.

Results

In the absence of drug treatment, we found a significant decline in body weights in the EAMG group in comparison to control rats, and EAMG group rats also had higher Lennon scores (P<0.05). Interestingly, we found that AEB-071 restored the body weight of EAMG rats and the decreased mortality rate compared to AZP treatment. Although a decrease in the number of T_reg cells was observed, the proportion of T_h lymphocytes was significantly increased in the EAMG group, and AEB-071 treatment decreased the proportion of T_h lymphocytes.

Conclusions

We concluded that AEB-071 treatment imparts beneficial effects in EAMG rat models by reducing mortality rate and restoring T_h lymphocyte balance, and thus may be an attractive candidate for use in MG treatment.

Recent advances in the management of non-infectious posterior uveitis

PURPOSE

To review the current regimens and novel therapeutic modalities in various stages of research and development for the management of non-infectious posterior uveitis (NIPU).

METHODS

We performed a thorough review of current literature using PubMed, Google Scholar and Clinicaltrials.gov to identify the published literature about the available therapeutics and novel drugs/therapies in different stages of clinical trials.

RESULTS

The current management regimen for non-infectious posterior uveitis includes corticosteroids, immunomodulatory therapies and anti-metabolites. However, NIPU requires long-term management for efficacious remission of the disease and to prevent disease relapse. Long-term safety issues associated with steroids have led to efforts to develop novel therapeutic agents including biological response modulators and immunosuppressants. The current therapeutic agents in various stages of development include calcineurin inhibitors, biologic response modifiers and a more a comprehensive modalities like ocular gene therapy as well as novel drug delivery mechanisms for higher bioavailability to the target tissues, with minimal systemic effects.

CONCLUSION

Novel efficacious therapeutic modalities under development will help overcome the challenges associated with the traditional therapeutic agents.

Exogenous carbon monoxide suppresses LPS-Induced platelet SNAREs complex assembly and α-granule exocytosis via integrin αIIbβ3-Mediated PKCθ/Munc18a pathway

Activation of coagulation occurs in sepsis and contributes to the development of thrombosis. Platelet α-granule exocytosis plays an important role in septic coagulation abnormalities. The present study aimed to investigate the effects and the underlying mechanisms of exogenous carbon monoxide, carbon monoxide-releasing molecules II (CORM-2)-liberated CO, on suppressing platelet α-granule exocytosis in sepsis. It was shown that CORM-2 weakened α-granule membrane fusion with platelet plasma membrane and attenuated α-granule contents exocytosis in LPS-Induced platelet. Further studies revealed that CORM-2 suppressed the expression of integrin α_IIbβ₃ in platelets stimulated by LPS. This was accompanied by a decrease in production and phosphorylation of PKCθ and Munc18a, SNARE complex assembly and subsequently platelet α-granule exocytosis. Taken together, we suggested that the potential mechanism of suppressive effect of CORM-2 on LPS-induced platelet SNAREs complex assembly and α-Granule Exocytosis might involve integrin α_IIbβ₃-mediated PKCθ/Munc18a pathway activation.

The Dual Roles of the Atypical Protein Kinase Cs in Cancer

Atypical protein kinase C (aPKC) isozymes, PKCλ/ι and PKCζ, are now considered fundamental regulators of tumorigenesis. However, the specific separation of functions that determine their different roles in cancer is still being unraveled. Both aPKCs have pleiotropic context-dependent functions that can translate into tumor-promoter or -suppressive functions. Here, we review early and more recent literature to discuss how the different tumor types, and their microenvironments, might account for the selective signaling of each aPKC isotype. This is of clinical relevance because a better understanding of the roles of these kinases is essential for the design of new anti-cancer treatments.

Discovery of Selective, Orally Bioavailable Pyrazolopyridine Inhibitors of Protein Kinase Cθ (PKCθ) That Ameliorate Symptoms of Experimental Autoimmune Encephalomyelitis

PKCθ plays an important role in T cell biology and is a validated target for a number of disease states. A series of potent and selective PKCθ inhibitors were designed and synthesized starting from a HTS hit compound. Cell activity, while initially a challenge to achieve, was built into the series by transforming the nitrile unit of the scaffold into a primary amine, the latter predicted to form a new hydrogen bond to Asp508 near the entrance of the ATP binding site of PKCθ. Significant improvements in physiochemical parameters were observed on introduction of an oxetane group proximal to a primary amine leading to compound 22, which demonstrated a reduction of symptoms in a mouse model of multiple sclerosis.

NK Cell-Mediated Processing Of Chlamydia psittaci Drives Potent Anti-Bacterial Th1 Immunity

Natural killer (NK) cells are innate immune cells critically involved in the early immune response against various pathogens including chlamydia. Here, we demonstrate that chlamydia-infected NK cells prevent the intracellular establishment and growth of the bacteria. Upon infection, they display functional maturation characterized by enhanced IFN-γ secretion, CD146 induction, PKCϴ activation, and granule secretion. Eventually, chlamydia are released in a non-infectious, highly immunogenic form driving a potent Th1 immune response. Further, anti-chlamydial antibodies generated during immunization neutralize the infection of epithelial cells. The release of chlamydia from NK cells requires PKCϴ function and active degranulation, while granule-associated granzyme B drives the loss of chlamydial infectivity. Cellular infection and bacterial release can be undergone repeatedly and do not affect NK cell function. Strikingly, NK cells passing through such an infection cycle significantly improve their cytotoxicity. Thus, NK cells not only protect themselves against productive chlamydial infections but also actively trigger potent anti-bacterial responses.

Novel Targets of Immunosuppression in Transplantation

It is increasingly recognized that calcineurin inhibitors (CNI) such as cyclosporine and tacrolimus are not ideal immunosuppressive agents. Side effects, including increased rates of infection, hypertension, and malignancy, can be severe. Thus, in the past decade, there has been much focus on the development of novel therapeutic agents and strategies designed to replace or minimize CNI exposure in transplant patients. This article reviews potential novel targets in T cells, alloantibody-producing B cells, plasma cells, and complement in transplantation.

An allosteric MALT1 inhibitor is a molecular corrector rescuing function in an immunodeficient patient

MALT1 paracaspase is central for lymphocyte antigen-dependent responses including NF-κB activation. We discovered nanomolar, selective allosteric inhibitors of MALT1 that bind by displacing the side chain of Trp580, locking the protease in an inactive conformation. Interestingly, we had previously identified a patient homozygous for a MALT1 Trp580-to-serine mutation who suffered from combined immunodeficiency. We show that the loss of tryptophan weakened interactions between the paracaspase and C-terminal immunoglobulin MALT1 domains resulting in protein instability, reduced protein levels and functions. Upon binding of allosteric inhibitors of increasing potency, we found proportionate increased stabilization of MALT1-W580S to reach that of wild-type MALT1. With restored levels of stable MALT1 protein, the most potent of the allosteric inhibitors rescued NF-κB and JNK signaling in patient lymphocytes. Following compound washout, MALT1 substrate cleavage was partly recovered. Thus, a molecular corrector rescues an enzyme deficiency by substituting for the mutated residue, inspiring new potential precision therapies to increase mutant enzyme activity in other deficiencies.

Selective PKCδ Inhibitor B106 Elicits Uveal Melanoma Growth Inhibitory Effects Independent of Activated PKC Isoforms

In uveal melanoma (UM) cells, the protein kinase C (pathway) is almost generally constitutively activated as a result of an activating mutation in either the GNAQ or the GNA11 G-protein. A pan-PKC inhibitor, sotrastaurin (also named AEB071), is in clinical trials for treatment of UM patients with limited success and eliciting adverse effects. Interestingly, genetic interference with expression of just one PKC isoform, e.g., PKCδ, is sufficient to reduce UM cell proliferation. Therefore, we tested the effect of a recently described specific PKCδ inhibitor, B106, on growth and survival of UM cell lines. Surprisingly, we found that B106 efficiently induced apoptosis in several cell lines, but apparently independent of activated PKCδ.

Enhanced interaction between SEC2 mutant and TCR Vβ induces MHC II-independent activation of T cells via PKCθ/NF-κB and IL-2R/STAT5 signaling pathways

SEC2, a major histocompatibility complex class II (MHC II)-dependent T-cell mitogen, binds MHC II and T-cell receptor (TCR) Vβs to induce effective co-stimulating signals for clonal T-cell expansion. We previously characterized a SEC2 mutant with increased recognition of TCR Vβs, ST-4, which could intensify NF-κB signaling transduction, leading to IL-2 production and T-cell activation. In this study, we found that in contrast to SEC2, ST-4 could induce murine CD4⁺ T-cell proliferation in a Vβ8.2- and Vβ8.3-specific manner in the absence of MHC II⁺ antigen-presenting cells (APCs). Furthermore, although IL-2 secretion in response to either SEC2 or ST-4 stimulation was accompanied by up-regulation of protein kinase Cθ (PKCθ), inhibitor of κB (IκB), α and β IκB kinase (IKKα/β), IκBα, and NF-κB in mouse splenocytes, only ST-4 could activate CD4⁺ T cells in the absence of MHC II⁺ APCs through the PKCθ/NF-κB signaling pathway. The PKCθ inhibitor AEB071 significantly suppressed SEC2/ST-4-induced T-cell proliferation, CD69 and CD25 expression, and IL-2 secretion with or without MHC II⁺ APCs. Further, SEC2/ST-4-induced changes in PKCθ/NF-κB signaling were significantly relieved by AEB071 in a dose-dependent manner. Using Lck siRNA, we found that Lck controlled SEC2/ST-4-induced phosphorylation of PKCθ. We also demonstrated that the IL-2R/STAT5 pathway is essential for SEC2/ST-4-induced T-cell activation. Collectively, our data demonstrate that an enhanced ST-4-TCR interaction can compensate for lack of MHC II and stimulate MHC II-free CD4⁺ T-cell proliferation via PKCθ/NF-κB and IL-2R/STAT5 signaling pathways. Compared with SEC2, intensified PKCθ/NF-κB and IL-2R/STAT5 signals induced by ST-4 lead to enhanced T-cell activation. The results of this study will facilitate better understanding of TCR-based immunotherapies for cancer.

Increased Hepatic PDGF-AA Signaling Mediates Liver Insulin Resistance in Obesity-Associated Type 2 Diabetes

In type 2 diabetes (T2D), hepatic insulin resistance is strongly associated with nonalcoholic fatty liver disease (NAFLD). In this study, we hypothesized that the DNA methylome of livers from patients with T2D compared with livers of individuals with normal plasma glucose levels can unveil some mechanism of hepatic insulin resistance that could link to NAFLD. Using DNA methylome and transcriptome analyses of livers from obese individuals, we found that hypomethylation at a CpG site in PDGFA (encoding platelet-derived growth factor α) and PDGFA overexpression are both associated with increased T2D risk, hyperinsulinemia, increased insulin resistance, and increased steatohepatitis risk. Genetic risk score studies and human cell modeling pointed to a causative effect of high insulin levels on PDGFA CpG site hypomethylation, PDGFA overexpression, and increased PDGF-AA secretion from the liver. We found that PDGF-AA secretion further stimulates its own expression through protein kinase C activity and contributes to insulin resistance through decreased expression of insulin receptor substrate 1 and of insulin receptor. Importantly, hepatocyte insulin sensitivity can be restored by PDGF-AA-blocking antibodies, PDGF receptor inhibitors, and by metformin, opening therapeutic avenues. Therefore, in the liver of obese patients with T2D, the increased PDGF-AA signaling contributes to insulin resistance, opening new therapeutic avenues against T2D and possibly NAFLD.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

The immunological synapse as a pharmacological target

The development of T cell mediated immunity relies on the assembly of a highly specialized interface between T cell and antigen presenting cell (APC), known as the immunological synapse (IS). IS assembly is triggered when the T cell receptor (TCR) binds to specific peptide antigen presented in association to the major histocompatibility complex (MHC) by the APC, and is followed by the spatiotemporal dynamic redistribution of TCR, integrins, co-stimulatory receptors and signaling molecules, allowing for the fine-tuning and integration of the signals that lead to T cell activation. The knowledge acquired to date about the mechanisms of IS assembly underscores this structure as a robust pharmacological target. The activity of molecules involved in IS assembly and function can be targeted by specific compounds to modulate the immune response in a number of disorders, including cancers and autoimmune diseases, or in transplanted patients. Here, we will review the state-of-the art of the current therapies which exploit the IS to modulate the immune response.

Resistance to Ibrutinib in B Cell Malignancies: One Size Does Not Fit All

Ibrutinib resistance, as a result of coordinated rewiring of signaling networks and enforced tumor microenvironment (TME)-lymphoma interactions, drives unrestrained proliferation and disease progression. To combat resistance mechanisms, we must identify the compensatory resistance pathways and the central modulators of reprogramming events. Targeting the transcriptome and kinome reprogramming of lymphoma cells represents a rational approach to mitigate ibrutinib resistance in B cell malignancies. However, with the apparent heterogeneity and plasticity of tumors shown in therapy response, a one size fits all approach may be unattainable. To this end, a reliable and real-time drug screening platform to tailor effective individualized therapies in patients with B cell malignancies is warranted. Here, we describe the complexity of ibrutinib resistance in B cell lymphomas and the current approaches, including a drug screening assay, which has the potential to further explore the mechanisms of ibrutinib resistance and to design effective individualized combination therapies to overcome resistance and disable aggressive lymphomas (see Outstanding Questions).

Novel TCR-Mediated Mechanisms of Notch Activation and Signaling

The Notch receptor is an evolutionarily highly conserved transmembrane protein that is essential to a wide spectrum of cellular systems. Notch signaling is especially important to T cell development, and its deregulation leads to leukemia. Although not well characterized, it continues to play an integral role in peripheral T cells, in which a unique mode of Notch activation can occur. In contrast to canonical Notch activation initiated by adjacent ligand-expressing cells, TCR stimulation is sufficient to induce Notch signaling. However, the interactions between these two pathways have not been defined. In this article, we show that Notch activation occurs in peripheral T cells within a few hours post-TCR stimulation and is required for optimal T cell activation. Using a panel of inhibitors against components of the TCR signaling cascade, we demonstrate that Notch activation is facilitated through initiation of protein kinase C-induced ADAM activity. Moreover, our data suggest that internalization of Notch via endocytosis plays a role in this process. Although ligand-mediated Notch stimulation relies on mechanical pulling forces that disrupt the autoinhibitory domain of Notch, we hypothesized that, in T cells in the absence of ligands, these conformational changes are induced through chemical adjustments in the endosome, causing alleviation of autoinhibition and receptor activation. Thus, T cells may have evolved a unique method of Notch receptor activation, which is described for the first time, to our knowledge, in this article.

Targeting of B-cell receptor signalling in B-cell malignancies

Pharmacological agents that inhibit enzymes of the B-cell receptor (BCR) pathway are of increasing importance in the treatment of B-cell malignancies. These include inhibitors of Bruton tyrosine kinase (BTK), phosphatidylinositol 3-kinase (PI3K), splenic tyrosine kinase and protein kinase Cβ. Two agents are already approved in the USA and Europe: ibrutinib, a BTK inhibitor, for the treatment of chronic lymphatic leukaemia (CLL), mantle cell lymphoma (MCL) and Waldenström's macroglobulinemia; and idelalisib, a PI3Kδ inhibitor, for the treatment of CLL and follicular lymphoma. In addition, the role of these drugs in diffuse large B-cell lymphoma and marginal zone lymphoma is under investigation, as single agents and in combination with chemotherapy. In CLL, both ibrutinib and idelalisib have an established role as first-line therapy in patients with del(17p), and in MCL, ibrutinib is a standard option for patients relapsing after chemoimmunotherapy. Unexpected toxicities have been encountered when combining these potent new agents with other drugs, including chemotherapy and lenalidomide, and based on this experience the risks and benefits of novel combinations must be evaluated carefully. In this review, we summarize the efficacy and safety results with these inhibitors and discuss novel combinations that are under study and the future role of BCR inhibitors in these disorders.

Protein kinase C theta is dispensable for suppression mediated by CD25+CD4+ regulatory T cells

The activation of conventional T cells upon T cell receptor stimulation critically depends on protein kinase C theta (PKCθ). However, its role in regulatory T (Treg) cell function has yet to be fully elucidated. Using siRNA or the potent and PKC family-selective pharmacological inhibitor AEB071, we could show that murine Treg-mediated suppression in vitro is independent of PKCθ function. Likewise, Treg cells of PKCθ-deficient mice were fully functional, showing a similar suppressive activity as wild-type CD25⁺CD4⁺ T cells in an in vitro suppression assay. Furthermore, in vitro-differentiated wild-type and PKCθ-deficient iTreg cells showed comparable Foxp3 expression as well as suppressive activity. However, we observed a reduced percentage of Foxp3⁺CD25⁺ CD4⁺ T cells in the lymphatic organs of PKCθ-deficient mice. Taken together, our results suggest that while PKCθ is involved in Treg cell differentiation in vivo, it is dispensable for Treg-mediated suppression.

Emerging drugs for prevention of T-cell mediated rejection in liver and kidney transplantation

INTRODUCTION

Acute and chronic graft rejection continues to be an important problem after solid organ transplantation. With the introduction of potent immunosuppressive agents such as calcineurin inhibitors, the risk of rejection has been significantly reduced. However, the adverse effects of life-long immunosuppression remain a concern, and there exist a fine balance between over-immunosuppression and risk of rejection. Areas covered: In this review, the current standard of care in immunosuppressive therapy, including the use of steroids, calcineurin inhibitors, mycophenolate prodrugs and mammalian target of rapamycin inhibitors, will be discussed. Newer immunosuppressive agents showing promising early data after liver and kidney transplantation will also be explored. Expert Opinion: Currently, calcineurin inhibitors continue to be a vital component of immunosuppressive therapy after solid organ transplantation. Although minimization and avoidance strategies have been developed, the ultimate goal of inducing tolerance remains elusive. Newer emerging agents should have potent and specific immunosuppressive activity, with minimal associated side effects. An individualized approach should be adopted to tailor immunosuppression according to the different needs of recipients.

Inhibition of Akt and other AGC kinases: A target for clinical cancer therapy?

AGC kinases have been identified to contribute to cancer development and progression. Currently, most AGC inhibitors in clinical development are Akt inhibitors such as MK-2206 or GDC-0068, which are known to promote cell growth arrest and to sensitize cancer cells to radiotherapy. Response rates in clinical trials with single agent Akt inhibitors are typically low. The observed adverse events are within the expected limits for compounds inhibiting the PI3K-mTOR axis. Preclinical and early clinical data for combination therapies are accumulating. Based on these data, several Akt inhibitors are about to enter phase 3 trials. Besides drugs that target Akt, p70S6K inhibitors have entered clinical development. Again, the response rates were rather low. In addition, relevant toxicities were identified, including a risk for coagulopathies with these compounds. Multi-AGC kinase inhibitors are also in early clinical development but the data is not sufficient yet to draw conclusions regarding their efficacy and side-effect profile. PKC inhibitors have been tested in the phase 3 setting but were found to lack efficacy. More trials with isoform-specific PKC inhibitors are expected. Taken together, therapies with AGC kinase inhibitors as single agents are unlikely to meet success. However, combination therapies and a precise stratification of patients according to the activation of signaling axes may increase the probability to see relevant efficacy with these compounds. The emergence of onco-immunotherapies holds some new challenges for these agents.

Priming of transcriptional memory responses via the chromatin accessibility landscape in T cells

Memory T cells exhibit transcriptional memory and “remember” their previous pathogenic encounter to increase transcription on re-infection. However, how this transcriptional priming response is regulated is unknown. Here we performed global FAIRE-seq profiling of chromatin accessibility in a human T cell transcriptional memory model. Primary activation induced persistent accessibility changes, and secondary activation induced secondary-specific opening of previously less accessible regions associated with enhanced expression of memory-responsive genes. Increased accessibility occurred largely in distal regulatory regions and was associated with increased histone acetylation and relative H3.3 deposition. The enhanced re-stimulation response was linked to the strength of initial PKC-induced signalling, and PKC-sensitive increases in accessibility upon initial stimulation showed higher accessibility on re-stimulation. While accessibility maintenance was associated with ETS-1, accessibility at re-stimulation-specific regions was linked to NFAT, especially in combination with ETS-1, EGR, GATA, NFκB, and NR4A. Furthermore, NFATC1 was directly regulated by ETS-1 at an enhancer region. In contrast to the factors that increased accessibility, signalling from bHLH and ZEB family members enhanced decreased accessibility upon re-stimulation. Interplay between distal regulatory elements, accessibility, and the combined action of sequence-specific transcription factors allows transcriptional memory-responsive genes to “remember” their initial environmental encounter.