Role of phosphoinositide 3-kinase signaling in autoimmunity

A Review of Phosphocreatine 3 Kinase δ Subtype (PI3Kδ) and Its Inhibitors in Malignancy

Most cancer deaths are caused by metastasis. The phosphocreatine 3-kinase (PI3K) family includes the I–III classes, with class I divided into 4 subtypes (α, β, γ, δ); and PI3K signaling participates in the regulatory processes of cell proliferation, differentiation, apoptosis, and glucose transport. Moreover, PI3Ks are modulators of cellular membrane lipids involved in signaling and trafficking events. The PI3Kdelta isoform (PI3Kδ), which is not only specifically expressed in hematopoietic cells, but also in different tumor cell lines, is expressed extensively. The increase in PI3Kδ activity is often associated with a variety of cancers. Currently, the strategy of tumor therapy based on PI3Kδ and its related signaling pathway is developing. Besides its established role in controlling functions in autoimmunity and inflammation, the role of PI3Kδ in tumor and metastasis is not clearly elucidated, with the effects of inhibiting PI3Kδ in several types of tumors also remaining unexplored. In addition, the specific inhibitor of PI3Kδ in tumor progression and metastasis and its underlying mechanism need to be further studied. The purpose of this review is to rationalize the existing functions and mechanisms of PI3Kδ in tumor metastasis and the relationship with hematopoietic cells in cancers as well cross-talking with miRNA, which provides a new theoretical basis and potential therapeutic target for the drug therapy of tumor metastasis.

PI3K inhibitors are finally coming of age

Overactive phosphoinositide 3-kinase (PI3K) in cancer and immune dysregulation has spurred extensive efforts to develop therapeutic PI3K inhibitors. Although progress has been hampered by issues such as poor drug tolerance and drug resistance, several PI3K inhibitors have now received regulatory approval - the PI3Kα isoform-selective inhibitor alpelisib for the treatment of breast cancer and inhibitors mainly aimed at the leukocyte-enriched PI3Kδ in B cell malignancies. In addition to targeting cancer cell-intrinsic PI3K activity, emerging evidence highlights the potential of PI3K inhibitors in cancer immunotherapy. This Review summarizes key discoveries that aid the clinical translation of PI3Kα and PI3Kδ inhibitors, highlighting lessons learnt and future opportunities.

Effect of Sishen Pill on Memory T Cells From Experimental Colitis Induced by Dextran Sulfate Sodium

Immune memory has a protective effect on the human body, but abnormal immune memory is closely related to the occurrence and development of autoimmune diseases including inflammatory bowel disease (IBD). Sishen Pill (SSP) is a classic prescription of traditional Chinese medicine, which is often used to treat chronic colitis, but it is not clear whether SSP can alleviate experimental colitis by remodeling immune memory. In the present study, the therapeutic effect of SSP on chronic colitis induced by dextran sulfate sodium (DSS) was evaluated by colonic length, colonic weight index, macroscopic and microscopic scores, and pathological observation. The cytokine levels were tested by enzyme-linked immunosorbent assay (ELISA); the percentages of central memory T (Tcm) and effector memory T (Tem) cells were analyze\d by flow cytometry; and activation of phosphoinositide 3-kinase (PI3K)/Akt signaling proteins was measured by western blotting. After 7-days' treatment, SSP alleviated DSS-induced colitis, which was demonstrated by decreased colonic weight index, colonic weight, histopathological injury scores, restored colonic length, gradual recovery of colonic mucosa, and lower levels of interleukin (IL)-2, IL-7, IL-12, and IL-15, while SSP increased IL-10 expression. SSP obviously regulated the quantity and subpopulation of Tcm and Tem cells. Furthermore, SSP markedly inhibited activation of PI3K, Akt, phospho-Akt, Id2, T-bet, forkhead box O3a, Noxa, and C-myc proteins in the PI3K/Akt signaling pathway and activated Rictor, Raptor, tuberous sclerosis complex (TSC)1, TSC2, phospho-AMP-activated kinase (AMPK)-α, AMPK-α, eukaryotic translation initiation factor 4E-binding protein 2, kinesin family member 2a, and 70-kDa ribosomal protein S6 kinase. These results indicate that SSP effectively controls Tem cells in the peripheral blood to relieve experimental colitis induced by DSS, which were potentially related with inhibiting the PI3K/Akt signaling pathway.

The flavonoid baicalin improves glucose metabolism by targeting the PH domain of AKT and activating AKT/GSK3β phosphorylation

Baicalin is one of the main flavonoids of the dried root of Scutellaria baicalensis Georgi and is reported to exert beneficial effects on the regulation of glucose/lipid metabolism. However, understanding its specific target and unique mechanism for improving glucose utilization is a challenge. In this paper, target fishing with a baicalin probe reveals that baicalin interacts with AKT. An immunofluorescence assay further demonstrates the colocalization of baicalin with AKT in the cytoplasm. A competitive test and virtual docking show that baicalin might bind to the pleckstrin homology domain of AKT. This specific binding hampers AKT membrane translocation, activates the phosphorylation of AKT on Ser473, induces the downstream glycogen synthase kinase 3β activation, and affects glycogen synthesis.

Activating PIK3CD mutations impair human cytotoxic lymphocyte differentiation and function and EBV immunity

BACKGROUND

Germline gain-of function (GOF) mutations in PIK3CD, encoding the catalytic p110δ subunit of phosphoinositide 3-kinase (PI3K), result in hyperactivation of the PI3K-AKT-mechanistic target of rapamycin pathway and underlie a novel inborn error of immunity. Affected subjects exhibit perturbed humoral and cellular immunity, manifesting as recurrent infections, autoimmunity, hepatosplenomegaly, uncontrolled EBV and/or cytomegalovirus infection, and increased incidence of B-cell lymphoproliferation, lymphoma, or both. Mechanisms underlying disease pathogenesis remain unknown.

OBJECTIVE

Understanding the cellular and molecular mechanisms underpinning inefficient surveillance of EBV-infected B cells is required to understand disease in patients with PIK3CD GOF mutations, identify key molecules required for cell-mediated immunity against EBV, and develop immunotherapeutic interventions for the treatment of this and other EBV-opathies.

METHODS

We studied the consequences of PIK3CD GOF mutations on the generation, differentiation, and function of CD8⁺ T cells and natural killer (NK) cells, which are implicated in host defense against infection with herpesviruses, including EBV.

RESULTS

PIK3CD GOF total and EBV-specific CD8⁺ T cells were skewed toward an effector phenotype, with exaggerated expression of markers associated with premature immunosenescence/exhaustion and increased susceptibility to reactivation-induced cell death. These findings were recapitulated in a novel mouse model of PI3K GOF mutations. NK cells in patients with PIK3CD GOF mutations also exhibited perturbed expression of differentiation-associated molecules. Both CD8⁺ T and NK cells had reduced capacity to kill EBV-infected B cells. PIK3CD GOF B cells had increased expression of CD48, programmed death ligand 1/2, and CD70.

CONCLUSIONS

PIK3CD GOF mutations aberrantly induce exhaustion, senescence, or both and impair cytotoxicity of CD8⁺ T and NK cells. These defects might contribute to clinical features of affected subjects, such as impaired immunity to herpesviruses and tumor surveillance.

IL-15-PI3K-AKT-mTOR: A Critical Pathway in the Life Journey of Natural Killer Cells

Among numerous cytokines modulating natural killer (NK) cell function, interleukin 15 (IL-15) exerts a broad range of effect from development and homeostasis, to activation of mature NK cells during infection. Its significance is further highlighted by clinical trials in which IL-15 is being used to boost the proliferation and anti-tumor response of NK cells. Among the signal transduction pathways triggered by the engagement of IL-15 receptor with its ligand, the PI3K–AKT–mTOR pathway seems to be critical for the IL-15-mediated activation of NK cells, therefore being responsible for efficient anti-viral and anti-tumor responses. This review provides an overview of the role of IL-15 at multiple stages of NK cell life journey. Understanding the pathway by which IL-15 conveys critical signals for the generation of NK cells with efficient effector functions, in combination with established protocols for NK cell expansion ex vivo, will undoubtedly open new avenues for therapeutic applications for immunomodulation against infections and cancers.

Failure to upregulate cell surface PD-1 is associated with dysregulated stimulation of T cells by TGN1412-like CD28 superagonist

The CD28 superagonist (CD28SA) TGN1412 was administered to humans as an agent that can selectively activate and expand regulatory T cells but resulted in uncontrolled T cell activation accompanied by cytokine storm. The molecular mechanisms that underlie this uncontrolled T cell activation are unclear. Physiological activation of T cells leads to upregulation of not only activation molecules but also inhibitory receptors such as PD-1. We hypothesized that the uncontrolled activation of CD28SA-stimulated T cells is due to both the enhanced expression of activation molecules and the lack of or reduced inhibitory signals. In this study, we show that anti-CD3 antibody-stimulated human T cells undergo time-limited controlled DNA synthesis, proliferation and interleukin-2 secretion, accompanied by PD-1 expression. In contrast, CD28SA-activated T cells demonstrate uncontrolled activation parameters including enhanced expression of LFA-1 and CCR5 but fail to express PD-1 on the cell surface. We demonstrate the functional relevance of the lack of PD-1 mediated regulatory mechanism in CD28SA-stimulated T cells. Our findings provide a molecular explanation for the dysregulated activation of CD28SA-stimulated T cells and also highlight the potential for the use of differential expression of PD-1 as a biomarker of safety for T cell immunostimulatory biologics.

Enhanced activity of Akt in Teff cells from children with lupus nephritis is associated with reduced induction of tumor necrosis factor receptor-associated factor 6 and increased OX40 expression

OBJECTIVE

The breakdown of peripheral tolerance mechanisms is central to the pathogenesis of systemic lupus erythematosus (SLE). Although true Treg cells in patients with SLE exhibit intact suppressive activity, Teff cells are resistant to suppression. The underlying mechanisms are incompletely understood. This study was undertaken to examine the Akt signaling pathway and molecules that may alter its activity in T cells in lupus patients.

METHODS

The Akt pathway and its regulators were analyzed in Teff and Treg cells from children with lupus nephritis and controls using flow cytometry and real-time quantitative polymerase chain reaction. T cell proliferation was assessed by analysis of 5,6-carboxyfluorescein succinimidyl ester dilution.

RESULTS

CD4+CD45RA-FoxP3(low) and FoxP3- Teff cells from children with lupus nephritis expressed high levels of activated Akt, resulting in the down-regulation of the proapoptotic protein Bim and an enhanced proliferative response. The induction of tumor necrosis factor receptor-associated factor 6 (TRAF6) was impaired, and TRAF6 levels inversely correlated with Akt activity. Although the expression of OX40 was enhanced on Teff cells from children with lupus nephritis compared to controls, OX40 stimulation failed to significantly increase TRAF6 expression in cells from patients, in contrast to those from healthy controls, but resulted in further increased Akt activation that was reversed by blockade of OX40 signaling. Moreover, inhibition of Akt signaling markedly decreased the proliferation of Teff cells from lupus patients.

CONCLUSION

Our findings indicate that hyperactivation of the Akt pathway in Teff cells from children with lupus nephritis is associated with reduced induction of TRAF6 and up-regulation of OX40, which may cause Teff cell resistance to Treg cell-mediated suppression.

Identifying novel spatiotemporal regulators of innate immunity

The innate immune response plays a critical role in pathogen clearance. However, dysregulation of innate immunity contributes to acute inflammatory diseases such as sepsis and many chronic inflammatory diseases including asthma, arthritis, and Crohn's disease. Pathogen recognition receptors including the Toll-like family of receptors play a pivotal role in the initiation of inflammation and in the pathogenesis of many diseases with an inflammatory component. Studies over the last 15 years have identified complex innate immune signal transduction pathways involved in inflammation that have provided many new potential therapeutic targets to treat disease. We are investigating several novel genes that exert spatial and in some cases temporal regulation on innate immunity signaling pathways. These novel genes include Tbc1d23, a RAB-GAP that inhibits innate immunity. In this review, we will discuss inflammation, the role of inflammation in disease, innate immune signal transduction pathways, and the use of spatiotemporal regulators of innate immunity as potential targets for discovery and therapeutics.

Role of PI3K/Akt signaling in memory CD8 T cell differentiation

The clonal expansion, differentiation into effectors and establishing an immunological memory are crucial components of the adaptive immune response. Following the initial encounter with a pathogen, clonal CD8 T cell expansion yields at least two distinct populations of effector cells, short-lived effector cells (SLECs) and memory precursor effector cells (MPECs). SLECs are the terminally differentiated cells, which play an active role in pathogen clearance and undergo apoptosis once the pathogen is eliminated. In contrast, MPECs persist and give rise to self-renewing memory cells. These memory CD8 T cells maintain a state of heightened alertness and are poised to rapidly respond and swiftly clear the pathogen upon antigen re-encounter. As one of the goals of vaccination is to induce the development of these memory CD8 T cells, understanding the cellular and molecular basis of memory cell differentiation is critical to rational vaccine design. It is clear that memory differentiation is complex and involves multiple interrelated signaling pathways. It is influenced by factors such as the strength and duration of antigen receptor signaling and concurrent exposure to cytokines. Several signaling pathways that influence T cell fate have been recently described, and many culminate in the differential expression of specific transcription factors. Unfortunately, the mechanisms underlying the coordination and confluence of these signaling pathways remain largely unknown. In this review, we will discuss the role of the phosphatidylinositol 3-kinase signaling pathway as a central signaling node, and the function of Akt as a rheostat in orchestrating the differentiation of memory CD8 T cells.

IL-6 increases B-cell IgG production in a feed-forward proinflammatory mechanism to skew hematopoiesis and elevate myeloid production

Src homology 2 domain-containing inositol 5-phosphatase (SHIP(-/-)) animals display an age-related increase in interleukin-6 (IL-6), a decrease in B lymphopoiesis, and an elevation in myelopoiesis. We investigated the origin of the IL-6 production and show that it is largely produced by peritoneal and splenic macrophages. IL-6 production by these macrophages is not a direct result of the loss of SHIP: IL-6 production is not spontaneous, is absent from bone marrow-derived macrophages, declines with prolonged culture of macrophages, and requires a stimulus present in vivo. The IL-6-rich peritoneal cavity of SHIP(-/-) mice shows more than 700-fold more immunoglobulin G (IgG) than wild-type, approximately 20% of which is aggregated or in an immune complex and contains B220(+) cells that secrete IgG. The SHIP-deficient peritoneal macrophages show evidence of IgG receptor stimulation. Animals lacking both the signal-transducing gamma-chain of IgG receptors and SHIP or Ig and SHIP produce less IL-6. The data indicate a feed-forward process in which peripheral macrophages, responding through IgG receptors to secreted IgG, produce IL-6, to support further B-cell production of IgG. Because of the proinflammatory phenotype of SHIP(-/-) animals, these findings emphasize the importance of IL-6-neutralizing strategies in autoimmune and proinflammatory diseases.

Fine tuning the immune response with PI3K

The phosphoinositide 3-kinase (PI3K) family of lipid kinases regulates diverse aspects of lymphocyte behavior. This review discusses how genetic and pharmacological tools have yielded an increasingly detailed understanding of how PI3K enzymes function at different stages of lymphocyte development and activation. Following antigen receptor engagement, activated PI3K generates 3-phosphorylated inositol lipid products that serve as membrane targeting signals for numerous proteins involved in the assembly of multiprotein complexes, termed signalosomes, and immune synapse formation. In B cells, class IA PI3K is the dominant subgroup whose loss causes profound defects in development and antigen responsiveness. In T cells, both class IA and IB PI3K contribute to development and immune function. PI3K also regulates both chemokine responsiveness and antigen-driven changes in lymphocyte trafficking. PI3K modulates the function not only of effector T cells, but also regulatory T cells; these disparate functions culminate in unexpected autoimmune phenotypes in mice with PI3K-deficient T cells. Thus, PI3K signaling is not a simple switch to promote cellular activation, but rather an intricate web of interactions that must be properly balanced to ensure appropriate cellular responses and maintain immune homeostasis. Defining these complexities remains a challenge for pharmaceutical development of PI3K inhibitors to combat inflammation and autoimmunity.