The PI3K p110delta controls T-cell development, differentiation and regulation

Phosphatidylinositol 3 kinase inhibitor-related pneumonitis: a systematic review and meta-analysis

INTRODUCTION

Serious phosphatidylinositol 3 kinase (PI3K) inhibitor-related pneumonitis has raised clinical concerns, and integrated data for this condition are lacking.

METHODS

Randomized controlled trials (RCTs) comparing PI3K inhibitor therapy with control treatments from electronic databases and registrations were searched from inception to 1 April 20231 April 2023seven1 April 2023. The outcomes of our study were the incidence and risk of all-grade and grade ≥ 3 PI3K inhibitor-associated pneumonitis compared with controls.

RESULTS

The meta-analysis included 13 studies comprising 3916 patients. The incidence of all-grade and grade ≥ 3 pneumonitis was 3.7% (82/2210) and 3.0% (35/1162) in patients treated with PI3K inhibitors. PI3K inhibitors significantly increased the risk of all-grade and grade ≥ 3 pneumonitis compared with controls (RR 5.63, 95% CI [2.97, 10.65], P < 0.00001; RR 6.85, 95% CI [2.45, 19.11], P = 0.0002, respectively) with no significant heterogeneity across studies. In terms of different PI3K inhibitors, copanlisib and idelalisib significantly increased the risk of pneumonitis compared to controls (RR 4.99, 95% CI [1.19, 21.01], P = 0.03; RR 5.53, 95% CI [2.35, 13.01], P < 0.0001, respectively).

CONCLUSION

PI3K inhibitors significantly increased the risk of pneumonitis compared with controls, and most cases are severe or even life-threatening.

PROSPERO REGISTRATION NUMBER

CRD42022318878.

Quantitative systems pharmacology model-based investigation of adverse gastrointestinal events associated with prolonged treatment with PI3-kinase inhibitors

Several PI3K inhibitors are in clinical development for the treatment of various forms of cancers, including pan-PI3K inhibitors targeting all four PI3K isoforms (α, β, γ, and δ), and isoform-selective inhibitors. Diarrhea and immune-mediated colitis are among the adverse events observed with PI3K inhibition which limits the maximal tolerated dose. A quantitative systems pharmacology model was developed to investigate PI3K-inhibitor-induced colitis. The effects of individual PI3K isoforms on relevant cellular pathways were incorporated into a mechanistic representation of mucosal inflammation. A virtual clinical population captures the observed clinical variability in the onset timing and rates of diarrhea and colitis for seven clinically tested PI3K inhibitors. Model-based analysis suggests that colitis development is governed by both the inhibition of PI3Kδ, which drives T cell differentiation and proliferation, and PI3Kα, which regulates epithelial barrier integrity. Specifically, when PI3Kα is inhibited below a given threshold, epithelial barrier dysfunction precipitates an exaggerated T effector response due to PI3Kδ-inhibition, leading to risk of diarrhea and colitis. This synergy explains why the lowest diarrhea and colitis rates are seen with the weakest PI3Kδ inhibition (alpelisib), and higher rates are seen with strong PI3Kδ inhibition if PI3Kα is even mildly inhibited (e.g., idelalisib), whereas strong PI3Kδ inhibition in the absence of PI3Kα inhibition does not result in high colitis rates (umbralisib). Thus, the model-based analysis suggests that PI3Kα and δ inhibition play unique but synergistic roles in driving colitis. Finally, we explore if and how dose-regimen might influence colitis rates for molecules that inhibit both PI3Kα and PI3Kδ.

A Case for Phosphoinositide 3-Kinase-Targeted Therapy for Infectious Disease

PI3Ks activate critical signaling cascades and have multifaceted regulatory functions in the immune system. Loss-of-function and gain-of-function mutations in the PI3Kδ isoform have revealed that this enzyme can substantially impact immune responses to infectious agents and their products. Moreover, reports garnered from decades of infectious disease studies indicate that pharmacologic inhibition of the PI3K pathway could potentially be effective in limiting the growth of certain microbes via modulation of the immune system. In this review, we briefly highlight the development and applications of PI3K inhibitors and summarize data supporting the concept that PI3Kδ inhibitors initially developed for oncology have immune regulatory potential that could be exploited to improve the control of some infectious diseases. This repurposing of existing kinase inhibitors could lay the foundation for alternative infectious disease therapy using available therapeutic agents.

Idelalisib induces apoptosis in the lymphoid tissues and impairs lung function in mice

Idelalisib, an inhibitor of the phosphatidylinositol-3-kinase p110δ subunit (PI3Kδ), is approved for treating lymphoid malignancy. The drug is associated with hematopoietic and pulmonary toxicities, which limit its clinical use. However, the toxicity mechanisms are not completely elucidated. In this study, mice were intraperitoneally injected with idelalisib (40 or 80 µg/g) or dimethyl sulfoxide for five days every week for up to four weeks to evaluate the changes in the thymus, spleen, and pulmonary functions. Idelalisib treatment induced thymic involution, decreased CD4⁺/CD8⁺ T-cell population, and increased CD4^-/CD8^- T-cell population. In the spleen, idelalisib dose dependently decreased the lymphocyte viability and cell count. Idelalisib-treated mice exhibited enhanced cleaved caspase-3 expression in the thymus, spleen, and lung tissues. Idelalisib augmented thoracic and airway resistance and decreased thoracic compliance. Thus, PI3Kδ has physiological roles in T-cell development and airway function. Monitoring drug toxicity is important for developing follow-up compounds that target PI3Kδ signalling.

Duvelisib: a new phosphoinositide-3-kinase inhibitor in chronic lymphocytic leukemia

P110-γ and -δ act in lymphocytes chemotaxis, presenting distinct, nonredundant roles in B- and T-cell migration and adhesion to stromal cells. Moreover, phosphoinositide-3-kinase-γ inhibition contributes to regulate macrophage polarization inhibiting cancer growth. Duvelisib (IPI-145) is an oral first-in-class, dual phosphoinositide-3-kinase inhibitor targeting p110-δ/γ exerting its activity in preclinical studies across different prognostic groups. In a large Phase III study, duvelisib showed superior progression-free survival and overall response rate compared with ofatumumab, thus leading to its approval for relapsed/refractory chronic lymphocytic leukemia/small lymphocytic lymphoma. Immune-related effects are the main reason for treatment suspension, thus affecting survival benefit. Nevertheless, the correct management of adverse events, eventually including dose modification, allows patients to remain on treatment. In conclusion, duvelisib represents a promising treatment in chronic lymphocytic leukemia and a salvage therapy after ibrutinib.

Identification of a novel de novo gain-of-function mutation of PIK3CD in a patient with activated phosphoinositide 3-kinase δ syndrome

Activated phosphoinositide 3-kinase δ (PI3Kδ) syndrome is a newly defined and relatively common primary immunodeficiency, which is caused by heterozygous gain-of-function (GOF) mutations in PIK3CD or PIK3R1. Here, we report a novel de novo GOF mutation (c.1570 T > A, p.Y524N) in PIK3CD in a 6-year-old Chinese girl. The patient suffered recurrent sinopulmonary infection, bronchiectasis, lymphoproliferation, herpesvirus infection, and distinctive nodular lymphoid hyperplasia of mucosal surfaces. Immunological analysis revealed increased CD4+ T cell senescence and B cell immaturity. Further analysis revealed an increase in almost all CD4+ T cell subsets to varying degrees, including effector T cells and Treg cells. Increased levels of plasma T cell-related cytokines corroborated these results. Hyperactivation of the PI3Kδ-Akt-mTOR signaling pathway was also confirmed. Treatment with rapamycin ameliorated the lymphoproliferative immunodeficiency caused by hyperactivation of mTOR. These results expand genetic spectrum of APDS and will facilitate further study of the genotype-phenotype correlation in those with PIK3CD mutations.

The p110δ isoforme of phosphatidylinositol 3-kinase plays an important role in host defense against chlamydial lung infection through influencing CD4+ T-cell function

PI3Ks display integrant significance in T-cell development and differentiation, which is related to host defense against infections. Here, we investigated the role of p110δ isoform of PI3Ks in host defense against chlamydial lung infection in a mouse model. Our data showed that lung infection with Chlamydia muridarum (Cm) activated PI3K/AKT signaling pathway. Compared to WT mice, p110δD910A mice, mice with an inactivating knockin mutation in the p110δ Isoform of PI3Ks, showed more sever disease phenotype and slower recovery, which was associated with reduced Chlamydia-specific Th1 and Th17 immune responses following infection. Further adoptive transfer experiment showed that mice which received CD4+ T cells from infected p110δD910A mice exhibited greater body weight loss and higher bacterial loads in the lung than those which received CD4+ T cells from WT mice following challenge infection. These results provide in vivo evidence that p110δ isoform of PI3Ks plays an important role in host defense against chlamydial infection by promoting CD4+ T-cell immunity.

GRK2 mediates TCR-induced transactivation of CXCR4 and TCR-CXCR4 complex formation that drives PI3Kγ/PREX1 signaling and T cell cytokine secretion

The immune system includes abundant examples of biologically-relevant cross-regulation of signaling pathways by the T cell antigen receptor (TCR) and the G protein-coupled chemokine receptor, CXCR4. TCR ligation induces transactivation of CXCR4 and TCR-CXCR4 complex formation, permitting the TCR to signal via CXCR4 to activate a phosphatidylinositol 3,4,5-trisphosphate-dependent Rac exchanger 1 protein (PREX1)-dependent signaling pathway that drives robust cytokine secretion by T cells. To understand this receptor heterodimer and its regulation, we characterized the molecular mechanisms required for TCR-mediated TCR-CXCR4 complex formation. We found that the cytoplasmic C-terminal domain of CXCR4 and specifically phosphorylation of Ser-339 within this region were required for TCR-CXCR4 complex formation. Interestingly, siRNA-mediated depletion of G protein-coupled receptor kinase-2 (GRK2) or inhibition by the GRK2-specific inhibitor, paroxetine, inhibited TCR-induced phosphorylation of CXCR4-Ser-339 and TCR-CXCR4 complex formation. Either GRK2 siRNA or paroxetine treatment of human T cells significantly reduced T cell cytokine production. Upstream, TCR-activated tyrosine kinases caused inducible tyrosine phosphorylation of GRK2 and were required for the GRK2-dependent events of CXCR4-Ser-339 phosphorylation and TCR-CXCR4 complex formation. Downstream of TCR-CXCR4 complex formation, we found that GRK2 and phosphatidylinositol 3-kinase γ (PI3Kγ) were required for TCR-stimulated membrane recruitment of PREX1 and for stabilization of cytokine mRNAs and robust cytokine secretion. Together, our results identify a novel role for GRK2 as a target of TCR signaling that is responsible for TCR-induced transactivation of CXCR4 and TCR-CXCR4 complex formation that signals via PI3Kγ/PREX1 to mediate cytokine production. Therapeutic regulation of GRK2 or PI3Kγ may therefore be useful for limiting cytokines produced by T cell malignancies or autoimmune diseases.

The Antitumor Effect of Xihuang Pill on Treg Cells Decreased in Tumor Microenvironment of 4T1 Breast Tumor-Bearing Mice by PI3K/AKT~AP-1 Signaling Pathway

To study the antitumor effect of Xihuang pill (XHP) on the number of Treg cells in the tumor microenvironment of 4T1 breast tumor-bearing mice by PI3K/AKT/AP-1 pathway, a mouse model was established. Flow cytometry (FCM) and immunohistochemistry (IHC) were used to detect the number of Treg cells in the tumor microenvironment; terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was used to detect the apoptosis of Treg cells in tumor microenvironment. Quantitative real-time PCR (RT-qPCR) was used to detect the mRNA expression of PI3K, AKT, and AP-1 in Treg cells in tumor microenvironment; immunofluorescence (IF) and Western Blot (WB) were used to detect the protein expression of PI3K, AKT, and AP-1 in Treg cells in tumor microenvironment. Compared with the naive control group, the tumor weight in XHP groups decreased significantly (P < 0.05); FCM and IHC results showed that the number of Treg cells in the tumor microenvironment decreased with the dose of XHP groups (P < 0.05); TUNEL staining showed that the number of Treg cells in tumor microenvironment increased with the dose of XHP groups (P < 0.05); RT-qPCR results showed that the mRNA expression of PI3K and AKT in Treg cells decreased with the dose of XHP groups, while RNA expression of AP-1 increased with the dose of XHP groups (P < 0.05); IF and WB results showed that the protein expression of PI3K and AKT in Treg cells decreased with the dose of XHP groups and the protein expression of AP-1 increased with the dose of XHP groups (P < 0.05). The results suggested that XHP decreased the number of Treg cells via inhibiting PI3K and AKT expression and upregulating AP-1 expression in Treg cells and then promoting the apoptosis of Treg cells. Thus, XHP could improve the immunosuppressive state of tumor microenvironment and reverse the immune escape to inhibit tumor growth.

Hepatic deletion of p110α and p85α results in insulin resistance despite sustained IRS1-associated phosphatidylinositol kinase activity

BACKGROUND

Class IA phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) is an integral mediator of insulin signaling. The p110 catalytic and p85 regulatory subunits of PI3K are the products of separate genes, and while they come together to make the active heterodimer, they have opposing roles in insulin signaling and action. Deletion of hepatic p110α results in an impaired insulin signal and severe insulin resistance, whereas deletion of hepatic p85α results in improved insulin sensitivity due to sustained levels of phosphatidylinositol (3,4,5)-trisphosphate. Here, we created mice with combined hepatic deletion of p110α and p85α (L-DKO) to study the impact on insulin signaling and whole body glucose homeostasis.

METHODS

Six-week old male flox control and L-DKO mice were studied over a period of 18 weeks, during which weight and glucose levels were monitored, and glucose tolerance tests, insulin tolerance test and pyruvate tolerance test were performed. Fasting insulin, insulin signaling mediators, PI3K activity and insulin receptor substrate (IRS)1-associated phosphatidylinositol kinase activity were examined at 10 weeks. Liver, muscle and white adipose tissue weight was recorded at 10 weeks and 25 weeks.

RESULTS

The L-DKO mice showed a blunted insulin signal downstream of PI3K, developed markedly impaired glucose tolerance, hyperinsulinemia and had decreased liver and adipose tissue weights. Surprisingly, however, these mice displayed normal hepatic glucose production, normal insulin tolerance, and intact IRS1-associated phosphatidylinositol kinase activity without compensatory upregulated signaling of other classes of PI3K.

CONCLUSIONS

The data demonstrate an unexpectedly overall mild metabolic phenotype of the L-DKO mice, suggesting that lipid kinases other than PI3Ks might partially compensate for the loss of p110α/p85α by signaling through other nodes than Akt/Protein Kinase B.

Hepatic deletion of p110α and p85α results in insulin resistance despite sustained IRS1-associated phosphatidylinositol kinase activity

Background: Class IA phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) is an integral mediator of insulin signaling. The p110 catalytic and p85 regulatory subunits of PI3K are the products of separate genes, and while they come together to make the active heterodimer, they have opposing roles in insulin signaling and action. Deletion of hepatic p110α results in an impaired insulin signal and severe insulin resistance, whereas deletion of hepatic p85α results in improved insulin sensitivity due to sustained levels of phosphatidylinositol (3,4,5)-trisphosphate. Here, we created mice with combined hepatic deletion of p110α and p85α (L-DKO) to study the impact on insulin signaling and whole body glucose homeostasis. Methods: Six-week old male flox control and L-DKO mice were studied over a period of 18 weeks, during which weight and glucose levels were monitored, and glucose tolerance tests, insulin tolerance test and pyruvate tolerance test were performed. Fasting insulin, insulin signaling mediators, PI3K activity and insulin receptor substrate (IRS)1-associated phosphatidylinositol kinase activity were examined at 10 weeks. Liver, muscle and white adipose tissue weight was recorded at 10 weeks and 25 weeks. Results: The L-DKO mice showed a blunted insulin signal downstream of PI3K, developed markedly impaired glucose tolerance, hyperinsulinemia and had decreased liver and adipose tissue weights. Surprisingly, however, these mice displayed normal hepatic glucose production, normal insulin tolerance, and intact IRS1-associated phosphatidylinositol kinase activity without compensatory upregulated signaling of other classes of PI3K. Conclusions: The data demonstrate an unexpectedly overall mild metabolic phenotype of the L-DKO mice, suggesting that lipid kinases other than PI3Ks might partially compensate for the loss of p110α/p85α by signaling through other nodes than Akt/Protein Kinase B.

Clinical use of PI3K inhibitors in B-cell lymphoid malignancies: today and tomorrow

INTRODUCTION

PI3K inhibitors are an important new therapeutic option for the treatment of relapsed and refractory B-cell lymphoid malignancies. Idelalisib is a PI3Kδ inhibitor that has been approved for the treatment of lymphoma and chronic lymphocytic leukemia in the relapsed/refractory setting, and several other PI3K inhibitors are being developed targeting other isoforms of the PI3K enzyme, which results in distinct toxicities and variable efficacy in the clinical setting. Areas covered: We provide a general overview of PI3K inhibitors, recommended applications, and the mechanism and management of toxicities. We further review trials, ongoing and completed, leading to the approval of idelalisib as well other PI3K inhibitors currently in development. Articles were obtained from PubMed, and abstracts were searched for the past 5 years from the websites for ASCO, ASH, EHA, and ICML/Lugano. Expert commentary: PI3K inhibitors provide an important and powerful pharmacologic tool in the armamentarium against hematologic malignancies, especially for relapsed/refractory B-cell lymphoid malignancies. Unique toxicities are associated with inhibition of different isoforms of the PI3K enzyme, as demonstrated with the infectious and autoimmune toxicities associated with the PI3Kδ inhibitor, idelalisib. Due to these unique toxicities, PI3K inhibitors should only be used in formally approved combinations and settings.

p110α Hot Spot Mutations E545K and H1047R Exert Metabolic Reprogramming Independently of p110α Kinase Activity

The phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) catalytic subunit p110α is the most frequently mutated kinase in human cancer, and the hot spot mutations E542K, E545K, and H1047R are the most common mutations in p110α. Very little is known about the metabolic consequences of the hot spot mutations of p110α in vivo. In this study, we used adenoviral gene transfer in mice to investigate the effects of the E545K and H1047R mutations on hepatic and whole-body glucose metabolism. We show that hepatic expression of these hot spot mutations results in rapid hepatic steatosis, paradoxically accompanied by increased glucose tolerance, and marked glycogen accumulation. In contrast, wild-type p110α expression does not lead to hepatic accumulation of lipids or glycogen despite similar degrees of upregulated glycolysis and expression of lipogenic genes. The reprogrammed metabolism of the E545K and H1047R p110α mutants was surprisingly not dependent on altered p110α lipid kinase activity.

Immunomodulation of Selective Naive T Cell Functions by p110δ Inactivation Improves the Outcome of Mismatched Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) can treat certain hematologic malignancies due to the graft versus leukemia (GvL) effect but is complicated by graft versus host disease (GvHD). Expression of the p110δ catalytic subunit of the phosphoinositide 3-kinase pathway is restricted to leukocytes, where it regulates proliferation, migration, and cytokine production. Here, in a mouse model of fully mismatched hematopoietic cell transplantation (HCT), we show that genetic inactivation of p110δ in T cells leads to milder GvHD, whereas GvL is preserved. Inactivation of p110δ in human lymphocytes reduced T cell allorecognition. We demonstrate that both allostimulation and granzyme B expression were dependent on p110δ in naive T cells, which are the main mediators of GvHD, whereas memory T cells were unaffected. Strikingly, p110δ is not mandatory for either naive or memory T cells to mediate GvL. Therefore, immunomodulation of selective naive T cell functions by p110δ inactivation improves the outcome of allogeneic HSCT.

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Genetic p110δ inactivation in donor naive T cells mitigates GvHD in mice

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Pharmacological p110δ inactivation in human T cells reduces alloreactivity

Phosphatidylinositol-3,4,5-trisphosphate: tool of choice for class I PI 3-kinases

Class I PI 3-kinases signal by producing the signaling lipid phosphatidylinositol(3,4,5) trisphosphate, which in turn acts by recruiting downstream effectors that contain specific lipid-binding domains. The class I PI 3-kinases comprise four distinct catalytic subunits linked to one of seven different regulatory subunits. All the class I PI 3-kinases produce the same signaling lipid, PIP3, and the different isoforms have overlapping expression patterns and are coupled to overlapping sets of upstream activators. Nonetheless, studies in cultured cells and in animals have demonstrated that the different isoforms are coupled to distinct ranges of downstream responses. This review focuses on the mechanisms by which the production of a common product, PIP3, can produce isoform-specific signaling by PI 3-kinases.

TNFR-associated factor 6 regulates TCR signaling via interaction with and modification of LAT adapter

TNFR-associated factor (TRAF)6 is an essential ubiquitin E3 ligase in immune responses, but its function in adaptive immunity is not well understood. In this study, we show that TRAF6 is recruited to the peripheral ring of the T cell immunological synapse in Jurkat T cells or human primary CD4(+) T cells conjugated with staphylococcal enterotoxin E-pulsed B cells. This recruitment depends on TRAF6 interacting with linker for activation of T cells (LAT) via its TRAF domain. Although LAT was indispensable for TCR/CD28-induced TRAF6 ubiquitination and its ligase activity, RNA interference-induced TRAF6 knockdown in T cells decreased TCR/CD28-induced LAT ubiquitination, tyrosine phosphorylation, and association with tyrosine kinase ZAP70. Overexpression of TRAF6 or its catalytically inactive form C70A promoted and decreased, respectively, LAT tyrosine phosphorylation upon stimulation. Moreover, LAT was ubiquitinated at Lys(88) by TRAF6 via K63-linked chain. In addition, TRAF6 was required for and synergized with LAT to promote the TCR/CD28-induced activation of NFAT. These results reveal a novel function and mechanism of TRAF6 action in the TCR-LAT signaling pathway distinct from its role in TCR-induced NF-κB activation, indicating that LAT also plays an adapter role in TCR/CD28-induced activation of TRAF6.

Pten loss in CD4 T cells enhances their helper function but does not lead to autoimmunity or lymphoma

PTEN, one of the most commonly mutated or lost tumor suppressors in human cancers, antagonizes signaling by the PI3K pathway. Mice with thymocyte-specific deletion of Pten rapidly develop peripheral lymphomas and autoimmunity, which may be caused by failed negative selection of thymocytes or from dysregulation of postthymic T cells. We induced conditional deletion of Pten from CD4 Th cells using a Cre knocked into the Tnfrsf4 (OX40) locus to generate OX40(Cre)Pten(f) mice. Pten-deficient Th cells proliferated more and produced greater concentrations of cytokines. The OX40(Cre)Pten(f) mice had a general increase in the number of lymphocytes in the lymph nodes, but not in the spleen. When transferred into wild-type (WT) mice, Pten-deficient Th cells enhanced anti-Listeria responses and the clearance of tumors under conditions in which WT T cells had no effect. Moreover, inflammatory responses were exaggerated and resolved later in OX40(Cre)Pten(f) mice than in WT mice. However, in contrast with models of thymocyte-specific Pten deletion, lymphomas and autoimmunity were not observed, even in older OX40(Cre)Pten(f) mice. Hence loss of Pten enhances Th cell function without obvious deleterious effects.

Electroacupuncture inhibits phosphorylation of spinal phosphatidylinositol 3-kinase/Akt in a carrageenan-induced inflammatory rat model

We investigated the changes of pain-related spinal signaling pathway after electroacupuncture (EA) stimulation in a carrageenan-induced rat model. EA stimulation (2Hz, 1mA) was needle-delivered for 30 min at acupoints corresponding to Zusanli and Sanyinjiao 3 h after carrageenan injection. Thermal and mechanical sensitivity of the hindpaw induced by carrageenan was strongly inhibited by EA stimulation. Phosphorylation of extracellular signal-regulated kinase, phosphatidylinositol 3-kinase (PI3K), Akt, and cAMP response element-binding protein (CREB) were examined in the L4-5 segments of the spinal cord by Western blot analysis 4h and 5h after carrageenan injection. Phosphorylation of Akt and especially PI3K were significantly induced by carrageenan-induction, but these expressions were markedly inhibited by EA stimulation. CREB phosphorylation showed a similar, but insignificant, pattern as like PI3k/Akt. Immunohistochemical analyses confirmed that phosphorylation of PI3K and Akt showed a similar pattern as Western blotting and were observed in most neurons and a few astrocytes. EA and PI3K inhibitor synergistically inhibited carrageenan-induced hyperalgesia. These results reveal that both neuronal PI3K and Akt may play an important role in EA-induced antinociception via inactivation in an inflammatory pain model.

p37δ is a new isoform of PI3K p110δ that increases cell proliferation and is overexpressed in tumors

The phosphatidylinositol 3-kinases (PI3Ks) regulate cell growth, proliferation and survival, and are frequently affected in human cancer. PI3K is composed of a catalytic subunit, p110, and a regulatory subunit, p85. The PI3K catalytic subunit p110δ is encoded by PIK3CD and contains p85- and RAS-binding domains, and a kinase domain. Here we present an alternatively spliced PIK3CD transcript encoding a previously unknown protein, p37δ, and demonstrate that this protein is expressed in human ovarian and colorectal tumors. p37δ retains the p85-binding domain and a fraction of the RAS-binding domain, lacks the catalytic domain, and has a unique carboxyl-terminal region. In contrast to p110δ, which stabilizes p85, p37δ promoted p85 sequestering. Despite the truncated RAS-binding domain, p37δ bound to RAS and we found a strong positive correlation between the protein levels of p37δ and RAS. Overexpressing p37δ, but not p110δ, increased the proliferation and invasive properties of HEK-293 cells and mouse embryonic fibroblasts. Cells overexpressing p37δ showed a quicker phosphorylation response of AKT and ERK1/2 following serum stimulation. Ubiquitous expression of human p37δ in the fruit fly increased body size, DNA content and phosphorylated ERK1/2 levels. Thus, p37δ appears to be a new tumor-specific isoform of p110δ with growth-promoting properties.

Phosphatidylinositol 3-kinase: the oncoprotein

The catalytic and regulatory subunits of class I phosphoinositide 3-kinase (PI3K) have oncogenic potential. The catalytic subunit p110α and the regulatory subunit p85 undergo cancer-specific gain-of-function mutations that lead to enhanced enzymatic activity, ability to signal constitutively, and oncogenicity. The β, γ, and δ isoforms of p110 are cell-transforming as overexpressed wild-type proteins. Class I PI3Ks have the unique ability to generate phosphoinositide 3,4,5 trisphosphate (PIP(3)). Class II and class III PI3Ks lack this ability. Genetic and cell biological evidence suggests that PIP(3) is essential for PI3K-mediated oncogenicity, explaining why class II and class III enzymes have not been linked to cancer. Mutational analysis reveals the existence of at least two distinct molecular mechanisms for the gain of function seen with cancer-specific mutations in p110α; one causing independence from upstream receptor tyrosine kinases, the other inducing independence from Ras. An essential component of the oncogenic signal that is initiated by PI3K is the TOR (target of rapamycin) kinase. TOR is an integrator of growth and of metabolic inputs. In complex with the raptor protein (TORC1), it controls cap-dependent translation, and this function is essential for PI3K-initiated oncogenesis.

Phosphatidylinositol 3-kinase: the oncoprotein

The catalytic and regulatory subunits of class I phosphoinositide 3-kinase (PI3K) have oncogenic potential. The catalytic subunit p110α and the regulatory subunit p85 undergo cancer-specific gain-of-function mutations that lead to enhanced enzymatic activity, ability to signal constitutively, and oncogenicity. The β, γ, and δ isoforms of p110 are cell-transforming as overexpressed wild-type proteins. Class I PI3Ks have the unique ability to generate phosphoinositide 3,4,5 trisphosphate (PIP(3)). Class II and class III PI3Ks lack this ability. Genetic and cell biological evidence suggests that PIP(3) is essential for PI3K-mediated oncogenicity, explaining why class II and class III enzymes have not been linked to cancer. Mutational analysis reveals the existence of at least two distinct molecular mechanisms for the gain of function seen with cancer-specific mutations in p110α; one causing independence from upstream receptor tyrosine kinases, the other inducing independence from Ras. An essential component of the oncogenic signal that is initiated by PI3K is the TOR (target of rapamycin) kinase. TOR is an integrator of growth and of metabolic inputs. In complex with the raptor protein (TORC1), it controls cap-dependent translation, and this function is essential for PI3K-initiated oncogenesis.

The class II phosphatidylinositol 3 kinase C2beta is required for the activation of the K+ channel KCa3.1 and CD4 T-cells

The Ca(2+)-activated K(+) channel KCa3.1 is required for Ca(2+) influx and the subsequent activation of T-cells. We previously showed that nucleoside diphosphate kinase beta (NDPK-B), a mammalian histidine kinase, directly phosphorylates and activates KCa3.1 and is required for the activation of human CD4 T lymphocytes. We now show that the class II phosphatidylinositol 3 kinase C2beta (PI3K-C2beta) is activated by the T-cell receptor (TCR) and functions upstream of NDPK-B to activate KCa3.1 channel activity. Decreased expression of PI3K-C2beta by siRNA in human CD4 T-cells resulted in inhibition of KCa3.1 channel activity. The inhibition was due to decreased phosphatidylinositol 3-phosphate [PI(3)P] because dialyzing PI3K-C2beta siRNA-treated T-cells with PI(3)P rescued KCa3.1 channel activity. Moreover, overexpression of PI3K-C2beta in KCa3.1-transfected Jurkat T-cells led to increased TCR-stimulated activation of KCa3.1 and Ca(2+) influx, whereas silencing of PI3K-C2beta inhibited both responses. Using total internal reflection fluorescence microscopy and planar lipid bilayers, we found that PI3K-C2beta colocalized with Zap70 and the TCR in peripheral microclusters in the immunological synapse. This is the first demonstration that a class II PI3K plays a critical role in T-cell activation.

Phosphatidylinositol 3-kinase is a key mediator of central sensitization in painful inflammatory conditions

Here, we show that phosphatidylinositol 3-kinase (PI3K) is a key player in the establishment of central sensitization, the spinal cord phenomenon associated with persistent afferent inputs and contributing to chronic pain states. We demonstrated electrophysiologically that PI3K is required for the full expression of spinal neuronal wind-up. In an inflammatory pain model, intrathecal administration of LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one], a potent PI3K inhibitor, dose-dependently inhibited pain-related behavior. This effect was correlated with a reduction of the phosphorylation of ERK (extracellular signal-regulated kinase) and CaMKII (calcium/calmodulin-dependent protein kinase II). In addition, we observed a significant decrease in the phosphorylation of the NMDA receptor subunit NR2B, decreased translocation to the plasma membrane of the GluR1 (glutamate receptor 1) AMPA receptor subunit in the spinal cord, and a reduction of evoked neuronal activity as measured using c-Fos immunohistochemistry. Our study suggests that PI3K is a major factor in the expression of central sensitization after noxious inflammatory stimuli.

CD28 provides T-cell costimulation and enhances PI3K activity at the immune synapse independently of its capacity to interact with the p85/p110 heterodimer

Activation of PI3K is among the earliest signaling events observed in T cells after conjugate formation with antigen-presenting cells (APCs). The relevant PI3K catalytic isoform and relative contribution of the TcR and CD28 to PI3K activity at the immune synapse have not been determined unequivocally. Using a quantitative imaging-based assay, we show that the PI3K activity at the T cell–APC contact area is dependent on the p110δ, but not the p110γ, isoform of PI3K. CD28 enhanced PIP3 production at the T-cell synapse independently of its YMNM PI3K-recruitment motif that instead was required for efficient PKCθ recruitment. CD28 could partially compensate for the lack of p110δ activity during T-cell activation, which indicates that CD28 and p110δ act in parallel and complementary pathways to activate T cells. Consistent with this, CD28 and p110δ double-deficient mice were severely immune compromised. We therefore suggest that combined pharmaceutic targeting of p110δ activity and CD28 costimulation has potent therapeutic potential.