Phosphoinositide 3-kinase δ regulates membrane fission of Golgi carriers for selective cytokine secretion

The Golgi Apparatus: A Key Player in Innate Immunity

The Golgi apparatus, long recognized for its roles in protein processing and vesicular trafficking, has recently been identified as a crucial contributor to innate immune signaling pathways. This review discusses our expanding understanding of the Golgi apparatus's involvement in initiating and activating these pathways. It highlights the significance of membrane connections between the Golgi and other organelles, such as the endoplasmic reticulum, mitochondria, endosomes, and autophagosomes. These connections are vital for the efficient transmission of innate immune signals and the activation of effector responses. Furthermore, the article delves into the Golgi apparatus's roles in key immune pathways, including the inflammasome-mediated activation of caspase-1, the cGAS-STING pathway, and TLR/RLR signaling. Overall, this review aims to provide insights into the multifunctional nature of the Golgi apparatus and its impact on innate immunity.

Phosphoinositide 3-kinase as a therapeutic target in angiogenic disease

Phosphoinositide 3-kinases (PI3Ks) generate lipids that control multitudinous intracellular cell signaling events which participate in cell survival and proliferation. In addition, PI3K signaling also contributes to metabolism, immunity, angiogenesis and cardiovascular homeostasis, and many diseases. The diverse actions of PI3K stem from the existence of their various isoforms and a variety of protein effectors. Hence, PI3K isoform-specific inhibitors have already achieved a wonderful effect on treating cancer. Herein, we summarize the molecular mechanism of PI3K inhibitors in preventing the permeability of vessels and neovascularization. Additionally, we briefly illustrate how PI3K signaling modulates blood vessel growth and discuss the different roles that PI3K isoforms play in angiogenesis.

Lipids and Secretory Vesicle Exocytosis

In recent years, the number of studies implicating lipids in the regulation of synaptic vesicle exocytosis has risen considerably. It has become increasingly clear that lipids such as phosphoinositides, lysophospholipids, cholesterol, arachidonic acid and myristic acid play critical regulatory roles in the processes leading up to exocytosis. Lipids may affect membrane fusion reactions by altering the physical properties of the membrane, recruiting key regulatory proteins, concentrating proteins into exocytic "hotspots" or by modulating protein functions allosterically. Discrete changes in phosphoinositides concentration are involved in multiple trafficking events including exocytosis and endocytosis. Lipid-modifying enzymes such as the DDHD2 isoform of phospholipase A1 were recently shown to contribute to memory acquisition via dynamic modifications of the brain lipid landscape. Considering the increasing reports on neurodegenerative disorders associated with aberrant intracellular trafficking, an improved understanding of the control of lipid pathways is physiologically and clinically significant and will afford unique insights into mechanisms and therapeutic methods for neurodegenerative diseases. Consequently, this chapter will discuss the different classes of lipids, phospholipase enzymes, the evidence linking them to synaptic neurotransmitter release and how they act to regulate key steps in the multi-step process leading to neuronal communication and memory acquisition.

Lack of Functional P110δ Affects Expression of Activation Marker CD80 but Does Not Influence Functions of Neutrophils

Neutrophils are specialized immune cells that are essential constituents of the innate immune response. They defend the organism against pathogens through various mechanisms. It was reported that phosphatidylinositols are key players in neutrophil functions, especially in the activity of class-I phosphoinositide 3-kinases (PI3Ks). P110δ, one of the PI3K subunits, is mostly expressed in immune cells, and its activity plays an important role in inflammatory responses. The aim of this study was to investigate the role of p110δ in neutrophil antimicrobial functions, activation status and cytokine production. To this end, we used bone marrow and splenic neutrophils isolated from a murine model expressing catalytically inactive p110δ^D910A/D910A. The level of phagocytosis and degranulation, the expressions of activation markers and cytokine production were determined by flow cytometry. ROS generation and NET release were assessed by fluorometry and fluorescent microscopy. We observed a significantly higher percentage of CD80-positive cells among the splenic granulocytes and found granulocytes subpopulations of differing phenotypes between WT and p110δ^D910A/D910A mice by multiparametric tSNE analysis. Moreover, we detected some differences in the expressions of activation markers, intracellular production of cytokines and bacterial killing. However, we did not observe any alterations in the selected neutrophil functions in p110δ mutant mice. Altogether, our data suggest that the catalytic p110 subunit(s), other than p110δ, is a key player in most neutrophil functions in mice. A follow-up study to correlate these in vitro results with in vivo observations is highly recommended.

Lipidomic Profiling in Synovial Tissue

The analysis of synovial tissue offers the potential for the comprehensive characterization of cell types involved in arthritis pathogenesis. The studies performed to date in synovial tissue have made it possible to define synovial pathotypes, which relate to disease severity and response to treatment. Lipidomics is the branch of metabolomics that allows the quantification and identification of lipids in different biological samples. Studies in animal models of arthritis and in serum/plasma from patients with arthritis suggest the involvement of different types of lipids (glycerophospholipids, glycerolipids, sphingolipids, oxylipins, fatty acids) in the pathogenesis of arthritis. We reviewed studies that quantified lipids in different types of tissues and their relationship with inflammation. We propose that combining lipidomics with currently used “omics” techniques can improve the information obtained from the analysis of synovial tissue, for a better understanding of pathogenesis and the development of new therapeutic strategies.

MiR-92a/KLF4/p110δ regulates titanium particles-induced macrophages inflammation and osteolysis

As total joint replacement is widely applied for severe arthropathy, peri-prosthetic aseptic loosening as one of the main causes of implant failure has drawn wide attention. Wear particles such as titanium particles (TiPs) derived from prosthesis can initiate macrophages inflammation and sequentially activate osteoclasts, which results in bone resorption and osteolysis for long-term. Therefore, inhibiting wear particles induced macrophages inflammation is considered as a promising therapy for AL. In this research, we found that the inhibition of p110δ, a member of class IA PI3Ks family, could significantly dampen the TiPs-induced secretion of TNFα and IL-6. By the transfection of siRNA targeting p110δ, we confirmed that p110δ was responsible for TNFα and IL-6 trafficking out of Golgi complex without affecting their expression in TiPs-treated macrophages. As the upstream transcription-repressor of p110δ, Krüppel-like factor 4 (KLF4), targeted by miR-92a, could also attenuate TiPs-induced inflammation by mediating NF-κB pathway and M1/M2 polarization. To further ascertain the roles of KLF4/p110δ, TiPs-induced mice cranial osteolysis model was established and vivo experiments validated that KLF4-knockdown could exacerbate TiPs-induced osteolysis, which was strikingly ameliorated by knockdown of p110δ. In summary, our study suggests the key role of miR-92a/KLF4/p110δ signal in TiPs-induced macrophages inflammation and osteolysis.

Rab6b localizes to the Golgi complex in murine macrophages and promotes tumor necrosis factor release in response to mycobacterial infection

The proinflammatory cytokine tumor necrosis factor (TNF) plays a central role in the host control of mycobacterial infections. Expression and release of TNF are tightly regulated, yet the molecular mechanisms that control the release of TNF by mycobacteria-infected host cells, in particular macrophages, are incompletely understood. Rab GTPases direct the transport of intracellular membrane-enclosed vesicles and are important regulators of macrophage cytokine secretion. Rab6b is known to be predominantly expressed in the brain where it functions in retrograde transport and anterograde vesicle transport for exocytosis. Whether it executes similar functions in the context of immune responses is unknown. Here we show that Rab6b is expressed by primary mouse macrophages, where it localized to the Golgi complex. Infection with Mycobacterium bovis bacille Calmette-Guérin (BCG) resulted in dynamic changes in Rab6b expression in primary mouse macrophages in vitro as well as in organs from infected mice in vivo. We further show that Rab6b facilitated TNF release by M. bovis BCG-infected macrophages, in the absence of discernible impact on Tnf messenger RNA and intracellular TNF protein expression. Our observations identify Rab6b as a positive regulator of M. bovis BCG-induced TNF trafficking and secretion by macrophages and positions Rab6b among the molecular machinery that orchestrates inflammatory cytokine responses by macrophages.

The Potential Role of RP105 in Regulation of Inflammation and Osteoclastogenesis During Inflammatory Diseases

Inflammatory diseases have a negative impact on bone homeostasis via exacerbated local and systemic inflammation. Bone resorbing osteoclasts are mainly derived from hematopoietic precursors and bone marrow monocytes. Induced osteoclastogenesis during inflammation, autoimmunity, metabolic diseases, and cancers is associated with bone loss and osteoporosis. Proinflammatory cytokines, pathogen-associated molecular patterns, or endogenous pathogenic factors induce osteoclastogenic differentiation by binding to the Toll-like receptor (TLR) family expressed on surface of osteoclast precursors. As a non-canonical member of the TLRs, radioprotective 105 kDa (RP105 or CD180) and its ligand, myeloid differentiation protein 1 (MD1), are involved in several bone metabolic disorders. Reports from literature had demonstrated RP105 as an important activator of B cells, bone marrow monocytes, and macrophages, which regulates inflammatory cytokines release from immune cells. Reports from literature had shown the association between RP105 and other TLRs, and the downstream signaling mechanisms of RP105 with different “signaling-competent” partners in immune cells during different disease conditions. This review is focused to summarize: (1) the role of RP105 on immune cells’ function and inflammation regulation (2) the potential regulatory roles of RP105 in different disease-mediated osteoclast activation and the underlying mechanisms, and (3) the different “signaling-competent” partners of RP105 that regulates osteoclastogenesis.

Broader Insights into Understanding Tumor Necrosis Factor and Neurodegenerative Disease Pathogenesis Infer New Therapeutic Approaches

Proinflammatory cytokines such as tumor necrosis factor (TNF), with its now appreciated key roles in neurophysiology as well as neuropathophysiology, are sufficiently well-documented to be useful tools for enquiry into the natural history of neurodegenerative diseases. We review the broader literature on TNF to rationalize why abruptly-acquired neurodegenerative states do not exhibit the remorseless clinical progression seen in those states with gradual onsets. We propose that the three typically non-worsening neurodegenerative syndromes, post-stroke, post-traumatic brain injury (TBI), and post cardiac arrest, usually become and remain static because of excess cerebral TNF induced by the initial dramatic peak keeping microglia chronically activated through an autocrine loop of microglial activation through excess cerebral TNF. The existence of this autocrine loop rationalizes post-damage repair with perispinal etanercept and proposes a treatment for cerebral aspects of COVID-19 chronicity. Another insufficiently considered aspect of cerebral proinflammatory cytokines is the fitness of the endogenous cerebral anti-TNF system provided by norepinephrine (NE), generated and distributed throughout the brain from the locus coeruleus (LC). We propose that an intact LC, and therefore an intact NE-mediated endogenous anti-cerebral TNF system, plus the DAMP (damage or danger-associated molecular pattern) input having diminished, is what allows post-stroke, post-TBI, and post cardiac arrest patients a strong long-term survival advantage over Alzheimer's disease and Parkinson's disease sufferers. In contrast, Alzheimer's disease and Parkinson's disease patients remorselessly worsen, being handicapped by sustained, accumulating, DAMP and PAMP (pathogen-associated molecular patterns) input, as well as loss of the LC-origin, NE-mediated, endogenous anti-cerebral TNF system. Adrenergic receptor agonists may counter this.

PI 3-kinase delta enhances axonal PIP3 to support axon regeneration in the adult CNS

Peripheral nervous system (PNS) neurons support axon regeneration into adulthood, whereas central nervous system (CNS) neurons lose regenerative ability after development. To better understand this decline whilst aiming to improve regeneration, we focused on phosphoinositide 3-kinase (PI3K) and its product phosphatidylinositol (3,4,5)-trisphosphate (PIP3 ). We demonstrate that adult PNS neurons utilise two catalytic subunits of PI3K for axon regeneration: p110α and p110δ. However, in the CNS, axonal PIP3 decreases with development at the time when axon transport declines and regenerative competence is lost. Overexpressing p110α in CNS neurons had no effect; however, expression of p110δ restored axonal PIP3 and increased regenerative axon transport. p110δ expression enhanced CNS regeneration in both rat and human neurons and in transgenic mice, functioning in the same way as the hyperactivating H1047R mutation of p110α. Furthermore, viral delivery of p110δ promoted robust regeneration after optic nerve injury. These findings establish a deficit of axonal PIP3 as a key reason for intrinsic regeneration failure and demonstrate that native p110δ facilitates axon regeneration by functioning in a hyperactive fashion.

Protein tyrosine phosphatase 1B is involved in efficient type I interferon secretion upon viral infection

Protein tyrosine phosphatase 1B (PTP1B, also known as PTPN1) is a negative regulator of the leptin and insulin signalling pathways. This phosphatase is of great interest as PTP1B-knockout mice are protected against the development of obesity and diabetes. Here, we provide evidence for a novel function of PTP1B that is independent of its phosphatase activity, but requires its localisation to the membrane of the endoplasmic reticulum. Upon activation of pattern recognition receptors, macrophages and plasmacytoid dendritic cells from PTP1B-knockout mice secrete lower amounts of type I interferon (IFN) than cells from wild-type mice. In contrast, secretion of the proinflammatory cytokines TNFα and IL6 was unaltered. While PTP1B deficiency did not affect Ifnb1 transcription, type I IFN accumulated in macrophages, suggesting a role for PTP1B in mediating secretion of type I IFN. In summary, we have uncovered that PTP1B positively regulates the type I IFN response by promoting secretion of key antiviral cytokines.

p110δ PI3-Kinase Inhibition Perturbs APP and TNFα Trafficking, Reduces Plaque Burden, Dampens Neuroinflammation, and Prevents Cognitive Decline in an Alzheimer's Disease Mouse Model

Alzheimer's disease (AD) is associated with the cleavage of the amyloid precursor protein (APP) to produce the toxic amyloid-β (Aβ) peptide. Accumulation of Aβ, together with the concomitant inflammatory response, ultimately leads to neuronal death and cognitive decline. Despite AD progression being underpinned by both neuronal and immunological components, therapeutic strategies based on dual targeting of these systems remains unexplored. Here, we report that inactivation of the p110δ isoform of phosphoinositide 3-kinase (PI3K) reduces anterograde axonal trafficking of APP in hippocampal neurons and dampens secretion of the inflammatory cytokine tumor necrosis factor-alpha by microglial cells in the familial AD APPswe/PS1ΔE9 (APP/PS1) mouse model. Moreover, APP/PS1 mice with kinase-inactive PI3Kδ (δD910A) had reduced Aβ peptides levels and plaques in the brain and an abrogated inflammatory response compared with APP/PS1 littermates. Mechanistic investigations reveal that PI3Kδ inhibition decreases the axonal transport of APP by eliciting the formation of highly elongated tubular-shaped APP-containing carriers, reducing the levels of secreted Aβ peptide. Importantly, APP/PS1/δD910A mice exhibited no spatial learning or memory deficits. Our data highlight inhibition of PI3Kδ as a new approach to protect against AD pathology due to its dual action of dampening microglial-dependent neuroinflammation and reducing plaque burden by inhibition of neuronal APP trafficking and processing.SIGNIFICANCE STATEMENT During Alzheimer's disease (AD), the accumulation of the toxic amyloid-β (Aβ) peptide in plaques is associated with a chronic excessive inflammatory response. Uncovering new drug targets that simultaneously reduce both Aβ plaque load and neuroinflammation holds therapeutic promise. Using a combination of genetic and pharmacological approaches, we found that the p110δ isoform of phosphoinositide 3-kinase (PI3K) is involved in anterograde trafficking of the amyloid precursor protein in neurons and in the secretion of tumor necrosis factor-alpha from microglial cells. Genetic inactivation of PI3Kδ reduces Aβ plaque deposition and abrogates the inflammatory response, resulting in a complete rescue of the life span and spatial memory performance. We conclude that inhibiting PI3Kδ represents a novel therapeutic approach to ameliorate AD pathology by dampening plaque accumulation and microglial-dependent neuroinflammation.

PI3K-p110δ contributes to antibody responses by macrophages in chronic lymphocytic leukemia

Fcγ receptor (FcγR) signalling in monocyte derived macrophages from chronic lymphocytic leukaemia (CLL) patients is poorly understood. This signalling pathway is the key determinant of the ability of the macrophages to respond to therapeutic antibodies in current clinical use for CLL. Muted FcγR signalling activity accompanies disease progression and results in resistance to therapeutic antibodies. The molecular mechanisms controlling FcγR signalling and resistance are unknown. Here, we demonstrate that the class I phosphoinositide 3-kinase (PI3K) catalytic subunit p110δ is essential for CLL-derived macrophages to respond to therapeutic antibodies. Inhibition of p110δ in the macrophages reduces FcγR-mediated antibody immune responses. Surprisingly, our studies indicated that FcγR downstream signalling is independent of SYK and BTK activity. Thus, we show that FcγR antibody responses occur via a previously unidentified p110δ-dependent pathway, which is independent of the previously described SYK/BTK activation pathway. These data provide novel insights into the effectors of antibody responses. Our data also provide mechanistic insights into therapy resistance in CLL.

Defining Bronchial Asthma with Phosphoinositide 3-Kinase Delta Activation: Towards Endotype-Driven Management

Phosphoinositide 3-kinase (PI3K) pathways play a critical role in orchestrating the chronic inflammation and the structural changes of the airways in patients with asthma. Recently, a great deal of progress has been made in developing selective and effective PI3K-targeted therapies on the basis of a vast amount of studies on the roles of specific PI3K isoforms and fine-tuned modulators of PI3Ks in a particular disease context. In particular, the pivotal roles of delta isoform of class I PI3Ks (PI3K-δ) in CD4-positive type 2 helper T cells-dominant disorders such as asthma have been consistently reported since the early investigations. Furthermore, there has been great advancement in our knowledge of the implications of PI3K-δ in various facets of allergic inflammation. This has involved the airway epithelial interface, adaptive T and B cells, potent effector cells (eosinophils and neutrophils), and, more recently, subcellular organelles (endoplasmic reticulum and mitochondria) and cytoplasmic innate immune receptors such as NLRP3 inflammasome, all of which make this PI3K isoform an important druggable target for treating asthma. Defining subpopulations of asthma patients with PI3K-δ activation, namely PI3K-δ-driven asthma endotype, may therefore provide us with a novel framework for the treatment of the disease, particularly for corticosteroid-resistant severe form, an important unresolved aspect of the current asthma management. In this review, we specifically summarize the recent advancement of our knowledge on the critical roles of PI3K-δ in the pathogenesis of bronchial asthma.

The Toxoplasma gondii dense granule protein TgGRA3 interacts with host Golgi and dysregulates anterograde transport

After entry into the host cell, the intracellular parasite Toxoplasma gondii resides within a membrane-bound compartment, the parasitophorous vacuole (PV). The PV defines an intracellular, parasite-specific niche surrounded by host organelles, including the Golgi apparatus. The mechanism by which T. gondii hijacks the host Golgi and subverts its functions remains unknown. Here, we present evidence that the dense granule protein TgGRA3 interacts with host Golgi, leading to the formation of tubules and the entry of host Golgi material into the PV. Targeted disruption of the TgGRA3 gene delays this engulfment of host Golgi. We also demonstrate that TgGRA3 oligomerizes and binds directly to host Golgi membranes. In addition, we show that TgGRA3 dysregulates anterograde transport in the host cell, thereby revealing one of the mechanisms employed by T. gondii to recruit host organelles and divert their functions.

This article has an associated First Person interview with the first author of the paper.

Summary : Toxoplasma gondii recruits various host organelles to enable parasite intracellular development. We describe a new role for TgGRA3 in modulating the host anterograde transport by binding to the Golgi apparatus.

Naringenin as a potential immunomodulator in therapeutics

Naringenin, a citrus flavonoid that possesses various biological activities, has emerged as a potential therapeutic agent for the management of a variety of diseases. Studies using cell culture system have shown that naringenin can inhibit inflammatory response in diverse cell types. Moreover, research using various animal models has further demonstrated therapeutic potentials of naringenin in the treatment of several inflammation-related disorders, such as sepsis, fulminant hepatitis, fibrosis and cancer. The mechanism of action of naringenin is not completely understood but recent mechanistic studies revealed that naringenin suppresses inflammatory cytokine production through both transcriptional and post-transcriptional mechanisms. Surprisingly, naringenin not only inhibits cytokine mRNA expression but also promotes lysosome-dependent cytokine protein degradation. This unique property of naringenin stands in sharp contrast with some widely-studied natural products such as apigenin and curcumin, which regulate cytokine production essentially at the transcriptional level. Therefore, naringenin may provide modality for the development of novel anti-inflammatory agent. This review article summarizes our recent studies in understanding how naringenin acts in cells and animal models. Particularly, we will discuss the anti-inflammatory activities of naringenin in various disease context and its potential use, as an immunomodulator, in the treatment of inflammatory related disease.

PI3K class II α regulates δ-opioid receptor export from the trans-Golgi network

The interplay between signaling and trafficking by G protein-coupled receptors (GPCRs) has focused mainly on endocytic trafficking. Whether and how surface delivery of newly synthesized GPCRs is regulated by extracellular signals is less understood. Here we define a signaling-regulated checkpoint at the trans-Golgi network (TGN) that controls the surface delivery of the delta opioid receptor (δR). In PC12 cells, inhibition of phosphoinositide-3 kinase (PI3K) activity blocked export of newly synthesized δR from the Golgi and delivery to the cell surface, similar to treatment with nerve growth factor (NGF). Depletion of class II phosphoinositide-3 kinase α (PI3K C2A), but not inhibition of class I PI3K, blocked δR export to comparable levels and attenuated δR-mediated cAMP inhibition. NGF treatment displaced PI3K C2A from the Golgi and optogenetic recruitment of the PI3K C2A kinase domain to the TGN-induced δR export downstream of NGF. Of importance, PI3K C2A expression promotes export of endogenous δR in primary trigeminal ganglion neurons. Taken together, our results identify PI3K C2A as being required and sufficient for δR export and surface delivery in neuronal cells and suggest that it could be a key modulator of a novel Golgi export checkpoint that coordinates GPCR delivery to the surface.

Functional crosstalk between membrane lipids and TLR biology

Toll-like receptors (TLRs) are important transmembrane proteins of the innate immune system that detect invading pathogens and subsequently orchestrate an immune response. The ensuing inflammatory processes are connected to lipid metabolism at multiple levels. Here, we describe different aspects of how membrane lipids can shape the response of TLRs. Recent reports have uncovered the role of individual lipid species on membrane protein function and mouse models have contributed to the understanding of how changes in lipid metabolism alter TLR signaling, endocytosis, and cytokine secretion. Finally, we discuss the importance of systematic approaches to identify the function of individual lipid species or the composition of membrane lipids in TLR-related processes.

Phosphatidylinositol 3-Kinase p110δ Isoform Regulates CD8+ T Cell Responses during Acute Viral and Intracellular Bacterial Infections

The p110δ isoform of PI3K is known to play an important role in immunity, yet its contribution to CTL responses has not been fully elucidated. Using murine p110δ-deficient CD8(+) T cells, we demonstrated a critical role for the p110δ subunit in the generation of optimal primary and memory CD8(+) T cell responses. This was demonstrated in both acute viral and intracellular bacterial infections in mice. We show that p110δ signaling is required for CD8(+) T cell activation, proliferation and effector cytokine production. We provide evidence that the effects of p110δ signaling are mediated via Akt activation and through the regulation of TCR-activated oxidative phosphorylation and aerobic glycolysis. In light of recent clinical trials that employ drugs targeting p110δ in certain cancers and other diseases, our study suggests caution in using these drugs in patients, as they could potentially increase susceptibility to infectious diseases. These studies therefore reveal a novel and direct role for p110δ signaling in in vivo CD8(+) T cell immunity to microbial pathogens.

The PI3Kδ inhibitor idelalisib suppresses liver and lung cellular respiration

Idelalisib (an inhibitor of phosphatidylinositol-3-kinase-delta) is approved for treatment of B-cell malignancies, with a Boxed Warning concerning potentially fatal hepatic, lung, and intestinal toxicities. The mechanisms of these tissue-specific adverse events have yet to be elucidated. This in vitro study investigated whether these effects could be attributed, at least in part, to altered cellular bioenergetics. A phosphorescence analyzer was used to measure cellular mitochondrial O2 consumption (kc , µM O2 min(-1) mg(-1)) in C57BL/6 mouse organs in the presence of 10 µM idelalisib or dimethyl-sulfoxide. Idelalisib significantly reduced the rate of cellular respiration in liver and lung fragments by 20% and 27%, respectively. Respiration in intestinal, thymic, and kidney fragments was unaffected. Idelalisib did not alter respiratory chain activities in mitochondria isolated from the liver and did not induce hepatocyte death. Thus, the drug mildly lowers liver and lung cellular respiration, an effect that may contribute to toxicities observed in these organs.

RP105 Engages Phosphatidylinositol 3-Kinase p110δ To Facilitate the Trafficking and Secretion of Cytokines in Macrophages during Mycobacterial Infection

Cytokines are key regulators of adequate immune responses to infection with Mycobacterium tuberculosis. We demonstrate that the p110δ catalytic subunit of PI3K acts as a downstream effector of the TLR family member RP105 (CD180) in promoting mycobacteria-induced cytokine production by macrophages. Our data show that the significantly reduced release of TNF and IL-6 by RP105(-/-) macrophages during mycobacterial infection was not accompanied by diminished mRNA or protein expression. Mycobacteria induced comparable activation of NF-κB and p38 MAPK signaling in wild-type (WT) and RP105(-/-) macrophages. In contrast, mycobacteria-induced phosphorylation of Akt was abrogated in RP105(-/-) macrophages. The p110δ-specific inhibitor, Cal-101, and small interfering RNA-mediated knockdown of p110δ diminished mycobacteria-induced TNF secretion by WT but not RP105(-/-) macrophages. Such interference with p110δ activity led to reduced surface-expressed TNF in WT but not RP105(-/-) macrophages, while leaving TNF mRNA and protein expression unaffected. Activity of Bruton's tyrosine kinase was required for RP105-mediated activation of Akt phosphorylation and TNF release by mycobacteria-infected macrophages. These data unveil a novel innate immune signaling axis that orchestrates key cytokine responses of macrophages and provide molecular insight into the functions of RP105 as an innate immune receptor for mycobacteria.

Role of SNARE proteins in tumourigenesis and their potential as targets for novel anti-cancer therapeutics

The function of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in cellular trafficking, membrane fusion and vesicle release in synaptic nerve terminals is well characterised. Recent studies suggest that SNAREs are also important in the control of tumourigenesis through the regulation of multiple signalling and transportation pathways. The majority of published studies investigated the effects of knockdown/knockout or overexpression of particular SNAREs on the normal function of cells as well as their dysfunction in tumourigenesis promotion. SNAREs are involved in the regulation of cancer cell invasion, chemo-resistance, the transportation of autocrine and paracrine factors, autophagy, apoptosis and the phosphorylation of kinases essential for cancer cell biogenesis. This evidence highlights SNAREs as potential targets for novel cancer therapy. This is the first review to summarise the expression and role of SNAREs in cancer biology at the cellular level, their interaction with non-SNARE proteins and modulation of cellular signalling cascades. Finally, a strategy is proposed for developing novel anti-cancer therapeutics using targeted delivery of a SNARE-inactivating protease into malignant cells.

Phosphatidylinositol 3-kinase and 4-kinase have distinct roles in intracellular trafficking of cellulose synthase complexes in Arabidopsis thaliana

The oriented deposition of cellulose microfibrils in the plant cell wall plays a crucial role in various plant functions such as cell growth, organ formation and defense responses. Cellulose is synthesized by cellulose synthase complexes (CSCs) embedded in the plasma membrane (PM), which comprise the cellulose synthases (CESAs). The abundance and localization of CSCs at the PM should be strictly controlled for precise regulation of cellulose deposition, which strongly depends on the membrane trafficking system. However, the mechanism of the intracellular transport of CSCs is still poorly understood. In this study, we explored requirements for phosphoinositides (PIs) in CESA trafficking by analyzing the effects of inhibitors of PI synthesis in Arabidopsis thaliana expressing green fluorescent protein-tagged CESA3 (GFP-CESA3). We found that a shift to a sucrose-free condition accelerated re-localization of PM-localized GFP-CESA3 into the periphery of the Golgi apparatus via the clathrin-enriched trans-Golgi network (TGN). Treatment with wortmannin (Wm), an inhibitor of phosphatidylinositol 3- (PI3K) and 4- (PI4K) kinases, and phenylarsine oxide (PAO), a more specific inhibitor for PI4K, inhibited internalization of GFP-CESA3 from the PM. In contrast, treatment with LY294002, which impairs the PI3K activity, did not exert such an inhibitory effect on the sequestration of GFP-CESA3, but caused a predominant accumulation of GFP-CESA3 at the ring-shaped periphery of the Golgi apparatus, resulting in the removal of GFP-CESA3 from the PM. These results indicate that PIs are essential elements for localization and intracellular transport of CESA3 and that PI4K and PI3K are required for distinct steps in secretory and/or endocytic trafficking of CESA3.

Cytokine Secretion in Macrophages: SNAREs, Rabs, and Membrane Trafficking

Macrophages have the capacity to rapidly secrete a wide range of inflammatory mediators that influence the development and extent of an inflammatory response. Newly synthesized and/or preformed stored cytokines and other inflammatory mediators are released upon stimulation, the timing, and volume of which is highly regulated. To finely tune this process, secretion is regulated at many levels; at the level of transcription and translation and post-translationally at the endoplasmic reticulum (ER), Golgi, and at or near the cell surface. Here, we discuss recent advances in deciphering these cytokine pathways in macrophages, focusing on recent discoveries regarding the cellular machinery and mechanisms implicated in the synthesis, trafficking, and secretion of cytokines. The specific roles of trafficking machinery including chaperones, GTPases, cytoskeletal proteins, and SNARE membrane fusion proteins will be discussed.

Vesicular trafficking and signaling for cytokine and chemokine secretion in mast cells

Upon activation mast cells (MCs) secrete numerous inflammatory compounds stored in their cytoplasmic secretory granules by a process called anaphylactic degranulation, which is responsible for type I hypersensitivity responses. Prestored mediators include histamine and MC proteases but also some cytokines and growth factors making them available within minutes for a maximal biological effect. Degranulation is followed by the de novo synthesis of lipid mediators such as prostaglandins and leukotrienes as well as a vast array of cytokines, chemokines, and growth factors, which are responsible for late phase inflammatory responses. While lipid mediators diffuse freely out of the cell through lipid bilayers, both anaphylactic degranulation and secretion of cytokines, chemokines, and growth factors depends on highly regulated vesicular trafficking steps that occur along the secretory pathway starting with the translocation of proteins to the endoplasmic reticulum. Vesicular trafficking in MCs also intersects with endocytic routes, notably to form specialized cytoplasmic granules called secretory lysosomes. Some of the mediators like histamine reach granules via specific vesicular monoamine transporters directly from the cytoplasm. In this review, we try to summarize the available data on granule biogenesis and signaling events that coordinate the complex steps that lead to the release of the inflammatory mediators from the various vesicular carriers in MCs.

PI3Kδ inhibition reduces TNF secretion and neuroinflammation in a mouse cerebral stroke model

Stroke is a major cause of death worldwide and the leading cause of permanent disability. Although reperfusion is currently used as treatment, the restoration of blood flow following ischaemia elicits a profound inflammatory response mediated by proinflammatory cytokines such as tumour necrosis factor (TNF), exacerbating tissue damage and worsening the outcomes for stroke patients. Phosphoinositide 3-kinase delta (PI3Kδ) controls intracellular TNF trafficking in macrophages and therefore represents a prospective target to limit neuroinflammation. Here we show that PI3Kδ inhibition confers protection in ischaemia/reperfusion models of stroke. In vitro, restoration of glucose supply following an episode of glucose deprivation potentiates TNF secretion from primary microglia-an effect that is sensitive to PI3Kδ inhibition. In vivo, transient middle cerebral artery occlusion and reperfusion in kinase-dead PI3Kδ (p110δ(D910A/D910A)) or wild-type mice pre- or post-treated with the PI3Kδ inhibitor CAL-101, leads to reduced TNF levels, decreased leukocyte infiltration, reduced infarct size and improved functional outcome. These data identify PI3Kδ as a potential therapeutic target in ischaemic stroke.

Innate PI3K p110δ regulates Th1/Th17 development and microbiota-dependent colitis

The p110δ subunit of class IA PI3K modulates signaling in innate immune cells. We previously demonstrated that mice harboring a kinase-dead p110δ subunit (p110δ(KD)) develop spontaneous colitis. Macrophages contributed to the Th1/Th17 cytokine bias in p110δ(KD) mice through increased IL-12 and IL-23 expression. In this study, we show that the enteric microbiota is required for colitis development in germfree p110δ(KD) mice. Colonic tissue and macrophages from p110δ(KD) mice produce significantly less IL-10 compared with wild-type mice. p110δ(KD) APCs cocultured with naive CD4+ Ag-specific T cells also produce significantly less IL-10 and induce more IFN-γ- and IL-17A-producing CD4+ T cells compared with wild-type APCs. Illustrating the importance of APC-T cell interactions in colitis pathogenesis in vivo, Rag1(-/-)/p110δ(KD) mice develop mild colonic inflammation and produced more colonic IL-12p40 compared with Rag1(-/-) mice. However, CD4+ CD45RB(high/low) T cell Rag1(-/-)/p110δ(KD) recipient mice develop severe colitis with increased percentages of IFN-γ- and IL-17A-producing lamina propria CD3+D4+ T cells compared with Rag1(-/-) recipient mice. Intestinal tissue samples from patients with Crohn's disease reveal significantly lower expression of PIK3CD compared with intestinal samples from non-inflammatory bowel disease control subjects (p < 0.05). PIK3CD expression inversely correlates with the ratio of IL12B:IL10 expression. In conclusion, the PI3K subunit p110δ controls homeostatic APC-T cell interactions by altering the balance between IL-10 and IL-12/23. Defects in p110δ expression and/or function may underlie the pathogenesis of human inflammatory bowel disease and lead to new therapeutic strategies.

Cinderella story: PI4P goes from precursor to key signaling molecule

Phosphatidylinositol lipids are signaling molecules involved in nearly all aspects of cellular regulation. Production of phosphatidylinositol 4-phosphate (PI4P) has long been recognized as one of the first steps in generating poly-phosphatidylinositol phosphates involved in actin organization, cell migration, and signal transduction. In addition, progress over the last decade has brought to light independent roles for PI4P in membrane trafficking and lipid homeostasis. Here, we describe recent advances that reveal the breadth of processes regulated by PI4P, the spectrum of PI4P effectors, and the mechanisms of spatiotemporal control that coordinate crosstalk between PI4P and cellular signaling pathways.

Effects of isoform-selective phosphatidylinositol 3-kinase inhibitors on osteoclasts: actions on cytoskeletal organization, survival, and resorption

Phosphatidylinositol 3-kinases (PI3K) participate in numerous signaling pathways, and control distinct biological functions. Studies using pan-PI3K inhibitors suggest roles for PI3K in osteoclasts, but little is known about specific PI3K isoforms in these cells. Our objective was to determine effects of isoform-selective PI3K inhibitors on osteoclasts. The following inhibitors were investigated (targets in parentheses): wortmannin and LY294002 (pan-p110), PIK75 (α), GDC0941 (α, δ), TGX221 (β), AS252424 (γ), and IC87114 (δ). In addition, we characterized a new potent and selective PI3Kδ inhibitor, GS-9820, and explored roles of PI3K isoforms in regulating osteoclast function. Osteoclasts were isolated from long bones of neonatal rats and rabbits. Wortmannin, LY294002, GDC0941, IC87114, and GS-9820 induced a dramatic retraction of osteoclasts within 15-20 min to 65-75% of the initial area. In contrast, there was no significant retraction in response to vehicle, PIK75, TGX221, or AS252424. Moreover, wortmannin and GS-9820, but not PIK75 or TGX221, disrupted actin belts. We examined effects of PI3K inhibitors on osteoclast survival. Whereas PIK75, TGX221, and GS-9820 had no significant effect on basal survival, all blocked RANKL-stimulated survival. When studied on resorbable substrates, osteoclastic resorption was suppressed by wortmannin and inhibitors of PI3Kβ and PI3Kδ, but not other isoforms. These data are consistent with a critical role for PI3Kδ in regulating osteoclast cytoskeleton and resorptive activity. In contrast, multiple PI3K isoforms contribute to the control of osteoclast survival. Thus, the PI3Kδ isoform, which is predominantly expressed in cells of hematopoietic origin, is an attractive target for anti-resorptive therapeutics.

RNAi screening reveals a large signaling network controlling the Golgi apparatus in human cells

RNAi screening and automated image analysis reveal 180 kinases and phosphatases regulating the organization of the Golgi apparatus. Most of these genes also control the expression of specific glycans, pointing to a web of interactions between signaling cascades and glycosylation at the Golgi.

Golgi organization was probed with three markers of different Golgi compartments and quantitative morphological analysis.

Knockdowns of ∼20% of all known kinases and phosphatases affected the Golgi globally or in a compartment-specific manner, and were comparable in degree to the depletion of known membrane traffic regulators such as SNAREs.

Several cell surface receptors, their cognate ligands and downstream effectors regulate Golgi organization, suggesting a large regulatory network.

Most signaling genes affected both Golgi morphology and the expression of specific glycans.

The Golgi apparatus has many important physiological functions, including sorting of secretory cargo and biosynthesis of complex glycans. These functions depend on the intricate and compartmentalized organization of the Golgi apparatus. To investigate the mechanisms that regulate Golgi architecture, we developed a quantitative morphological assay using three different Golgi compartment markers and quantitative image analysis, and performed a kinome- and phosphatome-wide RNAi screen in HeLa cells. Depletion of 159 signaling genes, nearly 20% of genes assayed, induced strong and varied perturbations in Golgi morphology. Using bioinformatics data, a large regulatory network could be constructed. Specific subnetworks are involved in phosphoinositides regulation, acto-myosin dynamics and mitogen activated protein kinase signaling. Most gene depletion also affected Golgi functions, in particular glycan biosynthesis, suggesting that signaling cascades can control glycosylation directly at the Golgi level. Our results provide a genetic overview of the signaling pathways that control the Golgi apparatus in human cells.

Intracellular trafficking and secretion of inflammatory cytokines

The secretion of cytokines by immune cells plays a significant role in determining the course of an inflammatory response. The levels and timing of each cytokine released are critical for mounting an effective but confined response, whereas excessive or dysregulated inflammation contributes to many diseases. Cytokines are both culprits and targets for effective treatments in some diseases. The multiple points and mechanisms that have evolved for cellular control of cytokine secretion highlight the potency of these mediators and the fine tuning required to manage inflammation. Cytokine production in cells is regulated by cell signaling, and at mRNA and protein synthesis levels. Thereafter, the intracellular transport pathways and molecular trafficking machinery have intricate and essential roles in dictating the release and activity of cytokines. The trafficking machinery and secretory (exocytic) pathways are complex and highly regulated in many cells, involving specialized membranes, molecules and organelles that enable these cells to deliver cytokines to often-distinct areas of the cell surface, in a timely manner. This review provides an overview of secretory pathways - both conventional and unconventional - and key families of trafficking machinery. The prevailing knowledge about the trafficking and secretion of a number of individual cytokines is also summarized. In conclusion, we present emerging concepts about the functional plasticity of secretory pathways and their modulation for controlling cytokines and inflammation.

Spleen tyrosine kinase (Syk)-dependent calcium signals mediate efficient CpG-induced exocytosis of tumor necrosis factor α (TNFα) in innate immune cells

Pattern recognition receptors expressed by cells of the innate immune system initiate the immune response upon recognition of microbial products. Activation of pattern recognition receptors result in the production and release of proinflammatory cytokines, including TNFα and IL-6. Because these cytokines promote disparate effector cell responses, understanding the signaling pathways involved in their regulation is critical for directing the immune response. Using macrophages and dendritic cells deficient in spleen tyrosine kinase (Syk), we identified a novel pathway by which TNFα trafficking and secretion are regulated by Syk following stimulation with CpG DNA. In the absence of PLCγ2, a Syk substrate, or the calcium-responsive kinase calcium calmodulin kinase II, CpG-induced TNFα secretion was impaired. Forced calcium mobilization rescued the TNFα secretion defect in Syk-deficient cells. In contrast to its effect on TNFα, Syk deficiency did not affect IL-6 secretion, suggesting that Syk-dependent signals participate in differential sorting of cytokines, thus tailoring the cytokine response. Our data report a novel pathway for TNFα regulation and provide insight into non-transcriptional mechanisms for shaping cytokine responses.

p110δ PI3 kinase pathway: emerging roles in cancer

Class IA PI3Ks consists of three isoforms of the p110 catalytic subunit designated p110α, p110β, and p110δ which are encoded by three separate genes. Gain-of-function mutations on PIK3CA gene encoding for p110α isoform have been detected in a wide variety of human cancers whereas no somatic mutations of genes encoding for p110β or p110δ have been reported. Unlike p110α and p110β which are ubiquitously expressed, p110δ is highly enriched in leukocytes and thus the p110δ PI3K pathway has attracted more attention for its involvement in immune disorders. However, findings have been accumulated showing that the p110δ PI3K plays a seminal role in the development and progression of some hematologic malignancies. A wealth of knowledge has come from studies showing the central role of p110δ PI3K in B-cell functions and B-cell malignancies. Further data have documented that wild-type p110δ becomes oncogenic when overexpressed in cell culture models and that p110δ is the predominant isoform expressed in some human solid tumor cells playing a prominent role in these cells. Genetic inactivation of p110δ in mice models and highly-selective inhibitors of p110δ have demonstrated an important role of this isoform in differentiation, growth, survival, motility, and morphology with the inositol phosphatase PTEN to play a critical role in p110δ signaling. In this review, we summarize our understanding of the p110δ PI3K signaling pathway in hematopoietic cells and malignancies, we highlight the evidence showing the oncogenic potential of p110δ in cells of non-hematopoietic origin and we discuss perspectives for potential novel roles of p110δ PI3K in cancer.

Rab6a/a' are important Golgi regulators of pro-inflammatory TNF secretion in macrophages

Lipopolysaccharide (LPS)-activated macrophages secrete pro-inflammatory cytokines, including tumor necrosis factor (TNF) to elicit innate immune responses. Secretion of these cytokines is also a major contributing factor in chronic inflammatory disease. In previous studies we have begun to elucidate the pathways and molecules that mediate the intracellular trafficking and secretion of TNF. Rab6a and Rab6a' (collectively Rab6) are trans-Golgi-localized GTPases known for roles in maintaining Golgi structure and Golgi-associated trafficking. We found that induction of TNF secretion by LPS promoted the selective increase of Rab6 expression. Depletion of Rab6 (via siRNA and shRNA) resulted in reorganization of the Golgi ribbon into more compact structures that at the resolution of electron microcopy consisted of elongated Golgi stacks that likely arose from fusion of smaller Golgi elements. Concomitantly, the delivery of TNF to the cell surface and subsequent release into the media was reduced. Dominant negative mutants of Rab6 had similar effects in disrupting TNF secretion. In live cells, Rab6-GFP were localized on trans-Golgi network (TGN)-derived tubular carriers demarked by the golgin p230. Rab6 depletion and inactive mutants altered carrier egress and partially reduced p230 membrane association. Our results show that Rab6 acts on TNF trafficking at the level of TGN exit in tubular carriers and our findings suggest Rab6 may stabilize p230 on the tubules to facilitate TNF transport. Both Rab6 isoforms are needed in macrophages for Golgi stack organization and for the efficient post-Golgi transport of TNF. This work provides new insights into Rab6 function and into the role of the Golgi complex in cytokine secretion in inflammatory macrophages.

PAQR3 modulates insulin signaling by shunting phosphoinositide 3-kinase p110α to the Golgi apparatus

Phosphoinositide 3-kinase (PI3K) mediates insulin actions by relaying signals from insulin receptors (IRs) to downstream targets. The p110α catalytic subunit of class IA PI3K is the primary insulin-responsive PI3K implicated in insulin signaling. We demonstrate here a new mode of spatial regulation for the p110α subunit of PI3K by PAQR3 that is exclusively localized in the Golgi apparatus. PAQR3 interacts with p110α, and the intracellular targeting of p110α to the Golgi apparatus is reduced by PAQR3 downregulation and increased by PAQR3 overexpression. Insulin-stimulated PI3K activity and phosphoinositide (3,4,5)-triphosphate production are enhanced by Paqr3 deletion and reduced by PAQR3 overexpression in hepatocytes. Deletion of Paqr3 enhances insulin-stimulated phosphorylation of AKT and glycogen synthase kinase 3β, but not phosphorylation of IR and IR substrate-1 (IRS-1), in hepatocytes, mouse liver, and skeletal muscle. Insulin-stimulated GLUT4 translocation to the plasma membrane and glucose uptake are enhanced by Paqr3 ablation. Furthermore, PAQR3 interacts with the domain of p110α involved in its binding with p85, the regulatory subunit of PI3K. Overexpression of PAQR3 dose-dependently reduces the interaction of p85α with p110α. Thus, PAQR3 negatively regulates insulin signaling by shunting cytosolic p110α to the Golgi apparatus while competing with p85 subunit in forming a PI3K complex with p110α.

Lipidomic profiling in Crohn's disease: abnormalities in phosphatidylinositols, with preservation of ceramide, phosphatidylcholine and phosphatidylserine composition

Crohn's disease is a chronic inflammatory condition largely affecting the terminal ileum and large bowel. A contributing cause is the failure of an adequate acute inflammatory response as a result of impaired secretion of pro-inflammatory cytokines by macrophages. This defective secretion arises from aberrant vesicle trafficking, misdirecting the cytokines to lysosomal degradation. Aberrant intestinal permeability is also well-established in Crohn's disease. Both the disordered vesicle trafficking and increased bowel permeability could result from abnormal lipid composition. We thus measured the sphingo- and phospholipid composition of macrophages, using mass spectrometry and stable isotope labelling approaches. Stimulation of macrophages with heat-killed Escherichia coli resulted in three main changes; a significant reduction in the amount of individual ceramide species, an altered composition of phosphatidylcholine, and an increased rate of phosphatidylcholine synthesis in macrophages. These changes were observed in macrophages from both healthy control individuals and patients with Crohn's disease. The only difference detected between control and Crohn's disease macrophages was a reduced proportion of newly-synthesised phosphatidylinositol 16:0/18:1 over a defined time period. Shotgun lipidomics analysis of macroscopically non-inflamed ileal biopsies showed a significant decrease in this same lipid species with overall preservation of sphingolipid, phospholipid and cholesterol composition.

The p110δ isoform of the kinase PI(3)K controls the subcellular compartmentalization of TLR4 signaling and protects from endotoxic shock

Lipopolysaccharide activates plasma-membrane signaling and endosomal signaling by Toll-like receptor 4 (TLR4) through the TIRAP-MyD88 and TRAM-TRIF adaptor complexes, respectively, but it is unclear how the signaling switch between these cell compartments is coordinated. In dendritic cells, we found that the p110δ isoform of phosphatidylinositol-3-OH kinase (PI(3)K) induced internalization of TLR4 and dissociation of TIRAP from the plasma membrane, followed by calpain-mediated degradation of TIRAP. Accordingly, inactivation of p110δ prolonged TIRAP-mediated signaling from the plasma membrane, which augmented proinflammatory cytokine production while decreasing TRAM-dependent endosomal signaling that generated anti-inflammatory cytokines (interleukin 10 and interferon-β). In line with that altered signaling output, p110δ-deficient mice showed enhanced endotoxin-induced death. Thus, by controlling the 'topology' of TLR4 signaling complexes, p110δ balances overall homeostasis in the TLR4 pathway.

Recycling endosome-dependent and -independent mechanisms for IL-10 secretion in LPS-activated macrophages

IL-10 is a key anti-inflammatory cytokine secreted by activated macrophages as a feedback control mechanism to prevent excessive inflammatory responses. Here, we define multiple intracellular trafficking pathways involved in the secretion of newly synthesized IL-10 from macrophages following TLR4 activation with LPS, and show how this relates to the previously defined trafficking pathways for IL-6 and TNF in macrophages simultaneously producing these proinflammatory cytokines. IL-10 exits the Golgi in multiple tubular carriers, including those dependent on p230GRIP. Some of the IL-10 is then delivered to recycling endosomes, where cytokine sorting may occur prior to its release. Another portion of the IL-10 is delivered to the cell surface in distinct vesicles colabeled for apoE. Thus, we show at least two post-Golgi pathways via which IL-10 is trafficked, ensuring its secretion from activated macrophages under different physiological conditions.

PI3Kδ is essential for tumor clearance mediated by cytotoxic T lymphocytes

Background

PI3Kδ is a lipid kinase of the phosphoinositide 3-kinase class 1A family and involved in early signaling events of leukocytes regulating proliferation, differentiation and survival. Currently, several inhibitors of PI3Kδ are under investigation for the treatment of hematopoietic malignancies. In contrast to the beneficial effect of inhibiting PI3Kδ in tumor cells, several studies reported the requirement of PI3Kδ for the function of immune cells, such as natural killer and T helper cells. Cytotoxic T lymphocytes (CTLs) are essential for tumor surveillance. The scope of this study is to clarify the potential impact of PI3Kδ inhibition on the function of CTLs with emphasis on tumor surveillance.

Principal Findings

PI3Kδ-deficient mice develop significantly bigger tumors when challenged with MC38 colon adenocarcinoma cells. This defect is accounted for by the fact that PI3Kδ controls the secretory perforin-granzyme pathway as well as the death-receptor pathway of CTL-mediated cytotoxicity, leading to severely diminished cytotoxicity against target cells in vitro and in vivo in the absence of PI3Kδ expression. PI3Kδ-deficient CTLs express low mRNA levels of important components of the cytotoxic machinery, e.g. prf1, grzmA, grzmB, fasl and trail. Accordingly, PI3Kδ-deficient tumor-infiltrating CTLs display a phenotype reminiscent of naïve T cells (CD69^lowCD62L^high). In addition, electrophysiological capacitance measurements confirmed a fundamental degranulation defect of PI3Kδ−/− CTLs.

Conclusion

Our results demonstrate that CTL-mediated tumor surveillance is severely impaired in the absence of PI3Kδ and predict that impaired immunosurveillance may limit the effectiveness of PI3Kδ inhibitors in long-term treatment.

Isoform-selective induction of human p110δ PI3K expression by TNFα: identification of a new and inducible PIK3CD promoter

PI3Ks (phosphoinositide 3-kinases) are signalling molecules and drug targets with important biological functions, yet the regulation of PI3K gene expression is poorly understood. Key PI3Ks are the class IA PI3Ks that consist of a catalytic subunit (p110α, p110β and p110δ) in complex with a p85 regulatory subunit. Whereas p110α and p110β are ubiquitously expressed, high levels of p110δ are mainly found in white blood cells, with most non-leucocytes expressing low levels of p110δ. In the present paper we report that TNFα (tumour necrosis factor α) stimulation induces p110δ expression in human ECs (endothelial cells) and synovial fibroblasts, but not in leucocytes, through transcription start sites located in a novel promoter region in the p110δ gene (PIK3CD). This promoter is used in all cell types, including solid tumour cell lines that express p110δ, and is activated by TNFα in ECs and synovial fibroblasts. We further present a detailed biochemical and bioinformatic characterization of p110δ gene regulation, demonstrating that PIK3CD has distinct promoters, some of which can be dynamically activated by pro-inflammatory mediators. This is the first molecular identification of a PI3K promoter under the control of acute extracellular stimulation.

MT1-MMP regulates the PI3Kδ·Mi-2/NuRD-dependent control of macrophage immune function

Macrophages play critical roles in events ranging from host defense to obesity and cancer, where they infiltrate affected tissues and orchestrate immune responses in tandem with the remodeling of the extracellular matrix (ECM). Despite the dual roles played by macrophages in inflammation, the functions of macrophage-derived proteinases are typically relegated to tissue-invasive or -degradative events. Here we report that the membrane-tethered matrix metalloenzyme MT1-MMP not only serves as an ECM-directed proteinase, but unexpectedly controls inflammatory gene responses wherein MT1-MMP(-/-) macrophages mount exaggerated chemokine and cytokine responses to immune stimuli both in vitro and in vivo. MT1-MMP modulates inflammatory responses in a protease-independent fashion in tandem with its trafficking to the nuclear compartment, where it triggers the expression and activation of a phosphoinositide 3-kinase δ (PI3Kδ)/Akt/GSK3β signaling cascade. In turn, MT1-MMP-dependent PI3Kδ activation regulates the immunoregulatory Mi-2/NuRD nucleosome remodeling complex that is responsible for controlling macrophage immune response. These findings identify a novel role for nuclear MT1-MMP as a previously unsuspected transactivator of signaling networks central to macrophage immune responses.

A novel pathway combining calreticulin exposure and ATP secretion in immunogenic cancer cell death

Surface-exposed calreticulin (ecto-CRT) and secreted ATP are crucial damage-associated molecular patterns (DAMPs) for immunogenic apoptosis. Inducers of immunogenic apoptosis rely on an endoplasmic reticulum (ER)-based (reactive oxygen species (ROS)-regulated) pathway for ecto-CRT induction, but the ATP secretion pathway is unknown. We found that after photodynamic therapy (PDT), which generates ROS-mediated ER stress, dying cancer cells undergo immunogenic apoptosis characterized by phenotypic maturation (CD80(high), CD83(high), CD86(high), MHC-II(high)) and functional stimulation (NO(high), IL-10(absent), IL-1β(high)) of dendritic cells as well as induction of a protective antitumour immune response. Intriguingly, early after PDT the cancer cells displayed ecto-CRT and secreted ATP before exhibiting biochemical signatures of apoptosis, through overlapping PERK-orchestrated pathways that require a functional secretory pathway and phosphoinositide 3-kinase (PI3K)-mediated plasma membrane/extracellular trafficking. Interestingly, eIF2α phosphorylation and caspase-8 signalling are dispensable for this ecto-CRT exposure. We also identified LRP1/CD91 as the surface docking site for ecto-CRT and found that depletion of PERK, PI3K p110α and LRP1 but not caspase-8 reduced the immunogenicity of the cancer cells. These results unravel a novel PERK-dependent subroutine for the early and simultaneous emission of two critical DAMPs following ROS-mediated ER stress.

The macrophage response towards LPS and its control through the p38(MAPK)-STAT3 axis

In macrophages detection of gram-negative bacteria particularly involves binding of the outer-wall component lipopolysaccharide (LPS) to its cognate receptor complex, comprising Toll like receptor 4 (TLR4), CD14 and MD2. LPS-induced formation of the LPS receptor complex elicits a signaling network, including intra-cellular signal-transduction directly activated by the TLR4 receptor complex as well as successional induction of indirect autocrine and paracrine signaling events. All these different pathways are integrated into the macrophage response towards an inflammatory stimulus by a highly complex cross-talk of the pathways engaged. This also includes a tight control by several intra- and inter-cellular feedback loops warranting an inflammatory response sufficient to battle invading pathogens and to avoid non-essential tissue damage caused by an overwhelming inflammatory response. Several evidences indicate that the reciprocal cross-talk between the p38(MAPK)-pathway and signal transducer and activator of transcription (STAT)3-mediated signal-transduction forms a critical axis successively activated by LPS. The balanced activation of this axis is essential for both induction and propagation of the inflammatory macrophage response as well as for the control of the resolution phase, which is largely driven by IL-10 and sustained STAT3 activation. In this context regulation of suppressor of cytokine signaling (SOCS)3 expression and the recently described divergent regulatory roles of the two p38(MAPK)-activated protein kinases MK2 and MK3 for the regulation of LPS-induced NF-κB- and IRF3-mediated signal-transduction and gene expression, which includes the regulation of IFNβ, IL-10 and DUSP1, appears to play an important role.

Phosphoinositides in Golgi complex function

The Golgi complex is a ribbon-like organelle composed of stacks of flat cisternae interconnected by tubular junctions. It occupies a central position in the endomembrane system as proteins and lipids that are synthesized in the endoplasmic reticulum (ER) pass through the Golgi complex to undergo biosynthetic modification (mainly glycosylation) and to be sorted to their final destinations. In addition the Golgi complex possesses a number of activities, apparently not directly connected with its main role in trafficking and sorting, which have been recently reviewed in Wilson et al. 2011. In spite of the constant massive flux of material the Golgi complex maintains its identity and phosphoinositides (PIs), among other factors, play a central role in this process. The active metabolism of PIs at the Golgi is necessary for the proper functioning of the organelle both in terms of membrane trafficking/sorting and its manifold metabolic and signalling activities. Phosphatidylinositol 4-phosphate (PtdIns4P), in particular, is responsible for the recruitment of numerous cytosolic proteins that recognise and bind PtdIns4P via specific lipid-binding domains. In this chapter we will summarize the findings that have contributed to our current understanding of the role of PIs in the biology of the Golgi complex in terms of the regulation of PI metabolism and the functional roles and regulation of PtdIns4P effectors.