Regulation of p110delta PI 3-kinase gene expression

Non-Clinical Toxicology Evaluation of the Novel Non-ATP Competitive Oral PI3 Kinase Delta Inhibitor Roginolisib

Roginolisib (IOA-244) is a novel, non-ATP competitive phosphoinositide-3-kinase (PI3K) delta inhibitor that regulates Akt/mTOR signaling. Roginolisib was administered once daily to rats and dogs in dose-range finding (DRF) and 4-week GLP toxicology studies. Free plasma levels of roginolisib exceeded the cellular target engagement IC90 for PI3Kδ for ≥12 hours at doses of 5 mg/kg, the IC90 for PI3Kβ for ≥2 hours at doses ≥15 mg/kg, and the IC50 for PI3Kα for ≥2 hours at dose levels ≥45 mg/kg. Toxicity in rats occurred at doses ≥100 mg/kg. In dogs, we observed dose-dependent skin and gastrointestinal toxicity and doses ≥30 mg/kg had a greater incidence of mortality. Lymphoid tissue toxicity occurred in both species. Toxicities in dogs observed at the ≥15 mg/kg dose, affecting the digestive mucosa, liver, and skin, cleared after treatment cessation. Doses ≤75 mg/kg were tolerated in rats and the no-observed-adverse-effect-level (NOAEL) in rats was 15 mg/kg. Due to mainly epithelial lesions of the skin at 5 mg/kg and necrotizing damage of the intestinal epithelia at ≥15 mg/kg, no NOAEL was determined in dogs. However, the adverse effects observed in dogs at 5 mg/kg were considered monitorable and reversible in patients with advanced malignancies. Furthermore, the PK profile subsequently proved to be a decisive factor for achieving selective PI3Kδ inhibition without the toxicities observed in dogs. As the result of the unique PK profile of roginolisib, patients were able to take daily roginolisib without dose modification and showed pharmacodynamic PI3Kδ inhibition over several months without gastrointestinal or dermatologic toxicities.

PI3K/Akt/mTOR Signaling Pathway in Blood Malignancies-New Therapeutic Possibilities

Blood malignancies remain a therapeutic challenge despite the development of numerous treatment strategies. The phosphatidylinositol-3 kinase (PI3K)/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway plays a central role in regulating many cellular functions, including cell cycle, proliferation, quiescence, and longevity. Therefore, dysregulation of this pathway is a characteristic feature of carcinogenesis. Increased activation of PI3K/Akt/mTOR signaling enhances proliferation, growth, and resistance to chemo- and immunotherapy in cancer cells. Overactivation of the pathway has been found in various types of cancer, including acute and chronic leukemia. Inhibitors of the PI3K/Akt/mTOR pathway have been used in leukemia treatment since 2014, and some of them have improved treatment outcomes in clinical trials. Recently, new inhibitors of PI3K/Akt/mTOR signaling have been developed and tested both in preclinical and clinical models. In this review, we outline the role of the PI3K/Akt/mTOR signaling pathway in blood malignancies' cells and gather information on the inhibitors of this pathway that might provide a novel therapeutic opportunity against leukemia.

Comprehensive bioinformatics analyses reveal immune genes responsible for altered immune microenvironment in intervertebral disc degeneration

We sought to identify novel biomarkers and related mechanisms that might shape the immune infiltration in IDD, thereby providing novel perspective for IDD diagnosis and therapies. Gene expression data sets GSE124272 (for initial analysis) and GSE56081 (for validation analysis) involving samples from IDD patients and healthy controls were retrieved from the Gene Expression Omnibus (GEO) database. Immune genes associated with IDD were identified by GSEA; module genes that exhibited coordinated expression patterns and the strongest positive or negative correlation with IDD were identified by WGCNA. The intersection between immune genes and module genes was used for LASSO variable selection, whereby we obtained pivotal genes that were highly representative of IDD. We then correlated (Pearson correlation) the expression of pivotal genes with immune cell proportion inferred by CIBERSORT algorithm, and revealed the potential immune-regulatory roles of pivotal genes on the pathogenesis of IDD. We discovered several immune-associated pathways in which IDD-associated immune genes were highly clustered, and identified two gene modules that might promote or inhibit the pathogenesis of IDD. These candidate genes were further narrowed down to 8 pivotal genes, namely, MSH2, LY96, ADAM8, HEBP2, ANXA3, RAB24, ZBTB16 and PIK3CD, among which ANXA3, MSH2, ZBTB16, LY96, PIK3CD, ZBTB16, and ADAM8 were revealed to be correlated with the proportion of CD8 T cells and resting memory CD4 T cells. This work identified 8 pivotal genes that might be involved in the pathogenesis of IDD through triggering various immune-associated pathways and altering the composition of immune and myeloid cells in IDD patients, which provides novel perspectives on IDD diagnosis and treatment.

Phosphoinositide 3-Kinases as Potential Targets for Thrombosis Prevention

As integral parts of pathological arterial thrombi, platelets are the targets of pharmacological regimens designed to treat and prevent thrombosis. A detailed understanding of platelet biology and function is thus key to design treatments that prevent thrombotic cardiovascular disease without significant disruption of the haemostatic balance. Phosphoinositide 3-kinases (PI3Ks) are a group of lipid kinases critical to various aspects of platelet biology. There are eight PI3K isoforms, grouped into three classes. Our understanding of PI3K biology has recently progressed with the targeting of specific isoforms emerging as an attractive therapeutic strategy in various human diseases, including for thrombosis. This review will focus on the role of PI3K subtypes in platelet function and subsequent thrombus formation. Understanding the mechanisms by which platelet function is regulated by the various PI3Ks edges us closer toward targeting specific PI3K isoforms for anti-thrombotic therapy.

PI3K Targeting in Non-solid Cancer

Despite the therapeutic progress, relapse remains a major problem in the treatment of acute lymphoblastic leukemia (ALL). Most leukemia cells that survive chemotherapy are found in the bone marrow (BM), thus resistance to chemotherapy and other treatments may be partially attributed to pro-survival signaling to leukemic cells mediated by leukemia cell-microenvironment interactions. Adhesion of leukemia cells to BM stromal cells may lead to cell adhesion-mediated drug resistance (CAM-DR) mediating intracellular signaling changes that support survival of leukemia cells. In ALL and chronic lymphocytic leukemia (CLL), adhesion-mediated activation of the PI3K/AKT signaling pathway has been shown to be critical in CAM-DR. PI3K targeting inhibitors have been approved for CLL and have been evaluated preclinically in ALL. However, PI3K inhibition has yet to be approved for clinical use in ALL. Here, we review the role of PI3K signaling for normal hematopoietic and leukemia cells and summarize preclinical inhibitors of PI3K in ALL.

Targeting PI3K/AKT/mTOR Signaling Pathway in Breast Cancer

Breast cancer is the most frequently diagnosed cancer and the primary cause of cancer death in women worldwide. Although early diagnosis and cancer growth inhibition has significantly improved breast cancer survival rate over the years, there is a current need to develop more effective systemic treatments to prevent metastasis. One of the most commonly altered pathways driving breast cancer cell growth, survival, and motility is the PI3K/AKT/mTOR signaling cascade. In the past 30 years, a great surge of inhibitors targeting these key players has been developed at a rapid pace, leading to effective preclinical studies for cancer therapeutics. However, the central role of PI3K/AKT/mTOR signaling varies among diverse biological processes, suggesting the need for more specific and sophisticated strategies for their use in cancer therapy. In this review, we provide a perspective on the role of the PI3K signaling pathway and the most recently developed PI3K-targeting breast cancer therapies.

PI3Kδ Forms Distinct Multiprotein Complexes at the TCR Signalosome in Naïve and Differentiated CD4+ T Cells

Phosphoinositide 3-kinases (PI3Ks) play a central role in adaptive immunity by transducing signals from the T cell antigen receptor (TCR) via production of PIP₃. PI3Kδ is a heterodimer composed of a p110δ catalytic subunit associated with a p85α or p85β regulatory subunit and is preferentially engaged by the TCR upon T cell activation. The molecular mechanisms leading to PI3Kδ recruitment and activation at the TCR signalosome remain unclear. In this study, we have used quantitative mass spectrometry, biochemical approaches and CRISPR-Cas9 gene editing to uncover the p110δ interactome in primary CD4⁺ T cells. Moreover, we have determined how the PI3Kδ interactome changes upon the differentiation of small naïve T cells into T cell blasts expanded in the presence of IL-2. Our interactomic analyses identified multiple constitutive and inducible PI3Kδ-interacting proteins, some of which were common to naïve and previously-activated T cells. Our data reveals that PI3Kδ rapidly interacts with as many as seven adaptor proteins upon TCR engagement, including the Gab-family proteins, GAB2 and GAB3, a CD5-CBL signalosome and the transmembrane proteins ICOS and TRIM. Our results also suggest that PI3Kδ pre-forms complexes with the adaptors SH3KBP1 and CRKL in resting cells that could facilitate the localization and activation of p110δ at the plasma membrane by forming ternary complexes during early TCR signalling. Furthermore, we identify interactions that were not previously known to occur in CD4⁺ T cells, involving BCAP, GAB3, IQGAP3 and JAML. We used CRISPR-Cas9-mediated gene knockout in primary T cells to confirm that BCAP is a positive regulator of PI3K-AKT signalling in CD4⁺ T cell blasts. Overall, our results provide evidence for a large protein network that regulates the recruitment and activation of PI3Kδ in T cells. Finally, this work shows how the PI3Kδ interactome is remodeled as CD4⁺ T cells differentiate from naïve T cells to activated T cell blasts. These activated T cells upregulate additional PI3Kδ adaptor proteins, including BCAP, GAB2, IQGAP3 and ICOS. This rewiring of TCR-PI3K signalling that occurs upon T cell differentiation may serve to reduce the threshold of activation and diversify the inputs for the PI3K pathway in effector T cells.

The delta isoform of phosphatidylinositol-3-kinase predominates in chronic myelomonocytic leukemia and can be targeted effectively with umbralisib and ruxolitinib

Chronic myelomonocytic leukemia (CMML) is a myelodysplastic syndrome/myeloproliferative neoplasm overlap syndrome characterized by monocytic proliferation in the presence of dysplastic bone marrow changes, inflammatory symptoms, and propensity for transformation to acute myeloid leukemia (AML), with a poor prognosis and limited treatment options. Unlike the α and β isoforms, the phosphatidylinositol-3-kinase (PI3K)-δ signaling protein is predominantly expressed by hematopoietic cells and therefore has garnered interest as a potential target for the treatment of lymphomas and leukemias. We revealed a pattern of increased PIK3CD:PIK3CA ratio in monocytic M5 AML patients and cell lines, and this ratio correlated with responsiveness to pharmacological PI3K-δ inhibition in vitro. Because CMML is a disease defined by monocytic clonal proliferation, we tested the PI3K-δ inhibitor umbralisib as a single agent and in combination with the JAK1/2 inhibitor ruxolitinib, in CMML. Our ex vivo experiments with primary CMML patient samples revealed synergistic inhibition of viability and clonogenicity with this combination. Phospho-specific flow cytometry revealed that dual inhibition had the unique ability to decrease STAT5, ERK, AKT, and S6 phosphorylation simultaneously, which offers a mechanistic hypothesis for the enhanced efficacy of the combination treatment. These preclinical data indicate promising activity by co-inhibition of PI3K-δ and JAK1/2 and support the use of ruxolitinib + umbralisib combination therapy in CMML under active clinical investigation.

Targeting PI3K/Akt/mTOR in AML: Rationale and Clinical Evidence

Acute myeloid leukemia (AML) is a highly heterogeneous hematopoietic malignancy characterized by excessive proliferation and accumulation of immature myeloid blasts in the bone marrow. AML has a very poor 5-year survival rate of just 16% in the UK; hence, more efficacious, tolerable, and targeted therapy is required. Persistent leukemia stem cell (LSC) populations underlie patient relapse and development of resistance to therapy. Identification of critical oncogenic signaling pathways in AML LSC may provide new avenues for novel therapeutic strategies. The phosphatidylinositol-3-kinase (PI3K)/Akt and the mammalian target of rapamycin (mTOR) signaling pathway, is often hyperactivated in AML, required to sustain the oncogenic potential of LSCs. Growing evidence suggests that targeting key components of this pathway may represent an effective treatment to kill AML LSCs. Despite this, accruing significant body of scientific knowledge, PI3K/Akt/mTOR inhibitors have not translated into clinical practice. In this article, we review the laboratory-based evidence of the critical role of PI3K/Akt/mTOR pathway in AML, and outcomes from current clinical studies using PI3K/Akt/mTOR inhibitors. Based on these results, we discuss the putative mechanisms of resistance to PI3K/Akt/mTOR inhibition, offering rationale for potential candidate combination therapies incorporating PI3K/Akt/mTOR inhibitors for precision medicine in AML.

Deletion of P110δ promotes the development of myocarditis in ApoE‑deficient mice by increasing mononuclear cell peritoneal infiltration

Phosphoinositide 3-kinase catalytic subunit δ isoform (P110δ) is mainly expressed in white blood cells. It is involved in T and B lymphocyte differentiation, maturation and the neutrophil chemotaxis process. Apolipoprotein E (ApoE) is an arginine‑rich alkaline protein, which is present in plasma chylomicron, low‑density lipoprotein and very low‑density lipoprotein. The present study aimed to determine the effects of P110δ deletion on myocarditis in ApoE‑/‑ mice. A mouse model of ApoE and P110δ double deletion was initially constructed; hematoxylin and eosin (H&E) staining was performed to detect the histological alterations in the mouse myocardium. Systolic and diastolic alterations, and alterations in the left ventricular fractional shortening (LVFS) and left ventricular ejection fraction (LVEF) were examined by electrocardiogram. Blood cell of ApoE and P110δ double mice was used to detect changes in white blood cells and monocytes. Western blotting was used to detect the expression levels of apoptosis‑associated proteins, whereas flow cytometry was used to detect the percentage of apoptosis. Morphological alterations in myocardial cells were observed under a microscope. The results of polymerase chain reaction demonstrated that double deletion mice were successfully constructed. H&E staining revealed that cells in the ApoE‑/‑ mice were spindle‑shaped; however, the nuclei were smaller in the double deletion mice. There was no change in cardiac contraction in normal mice; however, in double deletion mice, the systolic and diastolic contractions were markedly reduced. LVFS and LVEF were decreased compared with in the control group. Blood cell analysis indicated that the content of white blood cells and monocytes in the experimental group was significantly higher than that in the control group. Western blotting demonstrated that the expression levels of apoptotic proteins in double deletion mice were significantly higher compared with in the control group. Flow cytometry revealed that the apoptotic ratio was increased in double deletion mice compared with in the control group (42 vs. 21%). These findings suggested that deletion of P110δ may induce monocyte peritoneal infiltration and increase apoptosis, thus promoting the development of myocarditis.

Transcription of PIK3CD in human brain and schizophrenia: regulation by proinflammatory cytokines

PIK3CD encodes the phosphoinositide 3-kinase (PI3K) catalytic subunit, p110δ, a lipid kinase linked to neurodevelopmental disorders, including schizophrenia (SZ). PIK3CD is regulated at the transcript level through alternate use of 5' untranslated exons (UTRs), promoters, and proinflammatory cytokines. Increases in global PIK3CD expression and downregulation by neuroleptics are observed in SZ, and preclinical efficacy of a p110δ-selective inhibitor is seen in rodent models of risk. Here, we cloned PIK3CD alternative transcripts in human brain and evaluated temporal- and tissue-specific expression. We quantified PIK3CD transcripts in B-lymphoblastoid cells from patients with SZ and examined 5' UTR transcriptional regulation by tumor necrosis factor α (TNFα) and interleukin-1β (IL1β) in patient-derived fibroblasts. We report that PIK3CD transcripts are differentially expressed in human brain in a developmental-specific manner. Transcripts encoding 5' UTRs -2A and alternative exon -1 (Alt1), P37 and AS1 and AS2 were increased in SZ. Alt1, P37, and AS2 were also preferentially expressed in fetal brain, and all transcripts were regulated by TNFα and IL1β. Our findings provide novel insight into the complexity of PIK3CD regulation in human brain, implicate PIK3CD in human neurodevelopment, and identify isoform-specific disruption in SZ.

The Msp Protein of Treponema denticola Interrupts Activity of Phosphoinositide Processing in Neutrophils

Periodontal disease is a significant health burden, causing tooth loss and poor oral and overall systemic health. Dysbiosis of the oral biofilm and a dysfunctional immune response drive chronic inflammation, causing destruction of soft tissue and alveolar bone supporting the teeth. Treponema denticola, a spirochete abundant in the plaque biofilm of patients with severe periodontal disease, perturbs neutrophil function by modulating appropriate phosphoinositide (PIP) signaling. Through a series of immunoblotting and quantitative PCR (qPCR) experiments, we show that Msp does not alter the gene transcription or protein content of key enzymes responsible for PIP3 signaling: 3' phosphatase and tensin homolog (PTEN), phosphatidylinositol 3-kinase (PI3K), or 5' Src homology 2 domain-containing inositol phosphatase 1 (SHIP1). Instead, using immunoblotting and enzyme-linked immunosorbent assays (ELISAs), we found that Msp activates PTEN through dephosphorylation specifically at the S380 site. Msp in intact organisms or outer membrane vesicles also restricts PIP signaling. SHIP1 phosphatase release was assessed using chemical inhibition and immunoprecipitation to show that Msp moderately decreases SHIP1 activity. Msp also prevents secondary activation of the PTEN/PI3K response. We speculate that this result is due to the redirection of the PIP3 substrate away from SHIP1 to PTEN. Immunofluorescence microscopy revealed a redistribution of PTEN from the cytoplasm to the plasma membrane following exposure to Msp, which may contribute to PTEN activation. Mechanisms of how T. denticola modulates and evades the host immune response are still poorly described, and here we provide further mechanistic evidence of how spirochetes modify PIP signaling to dampen neutrophil function. Understanding how oral bacteria evade the immune response to perpetuate the cycle of inflammation and infection is critical for combating periodontal disease to improve overall health outcomes.

Regulation of platelet-activating factor-mediated interleukin-6 promoter activation by the 48 kDa but not the 45 kDa isoform of protein tyrosine phosphatase non-receptor type 2

Background

An underlying state of inflammation is thought to be an important cause of cardiovascular disease. Among cells involved in the early steps of atherosclerosis, monocyte-derived dendritic cells (Mo-DCs) respond to inflammatory stimuli, including platelet-activating factor (PAF), by the induction of various cytokines, such as interleukin 6 (IL-6). PAF is a potent phospholipid mediator involved in both the onset and progression of atherosclerosis. It mediates its effects by binding to its cognate G-protein coupled receptor, PAFR. Activation of PAFR-induced signaling pathways is tightly coordinated to ensure specific cell responses.

Results

Here, we report that PAF stimulated the phosphatase activity of both the 45 and 48 kDa isoforms of the protein tyrosine phosphatase non-receptor type 2 (PTPN2). However, we found that only the 48 kDa PTPN2 isoform has a role in PAFR-induced signal transduction, leading to activation of the IL-6 promoter. In luciferase reporter assays, expression of the 48 kDa, but not the 45 kDa, PTPN2 isoform increased human IL-6 (hIL-6) promoter activity by 40% after PAF stimulation of HEK-293 cells, stably transfected with PAFR (HEK-PAFR). Our results suggest that the differential localization of the PTPN2 isoforms and the differences in PAF-induced phosphatase activation may contribute to the divergent modulation of PAF-induced IL-6 promoter activation. The involvement of PTPN2 in PAF-induced IL-6 expression was confirmed in immature Mo-DCs (iMo-DCs), using siRNAs targeting the two isoforms of PTPN2, where siRNAs against the 48 kDa PTPN2 significantly inhibited PAF-stimulated IL-6 mRNA expression. Pharmacological inhibition of several signaling pathways suggested a role for PTPN2 in early signaling events. Results obtained by Western blot confirmed that PTPN2 increased the activation of the PI3K/Akt pathway via the modulation of protein kinase D (PKD) activity. WT PKD expression counteracted the effect of PTPN2 on PAF-induced IL-6 promoter transactivation and phosphorylation of Akt. Using siRNAs targeting the individual isoforms of PTPN2, we confirmed that these pathways were also active in iMo-DCs.

Conclusion

Taken together, our data suggest that PTPN2, in an isoform-specific manner, could be involved in the positive regulation of PI3K/Akt activation, via the modulation of PKD activity, allowing for the maximal induction of PAF-stimulated IL-6 mRNA expression.

The Impact of Immunodeficiency on NK Cell Maturation and Function

PURPOSE OF REVIEW

Natural killer cells are innate lymphoid cells (ILCs) that play critical roles in human host defense and are especially useful in combating viral pathogens and malignancy.

RECENT FINDINGS

The NK cell deficiency (NKD) is particularly underscored in patients with a congenital immunodeficiency in which NK cell development or function is affected. The classical NK cell deficiency (cNKD) is a result of absent or a profound decrease in the number of circulating NK cells. In contrast, functional NKD (fNKD) is characterized by abnormal NK cell function but with normal number of NK cells. The combined immune deficiencies with significant impact on NK cells are not considered classical or functional NK cell deficiencies. In these disorders, the impairment of NK cells represents an important aspect of the overall immunodeficiency. In turn, this leads to improved insights on the NK cell development and function. Here, we detail the NK cell biology based upon recent natural killer cell defects described in combined immune deficiencies.

Targeting PI3K Signaling in Acute Lymphoblastic Leukemia

Adhesion of acute lymphoblastic leukemia (ALL) cells to bone marrow stroma cells triggers intracellular signals regulating cell-adhesion-mediated drug resistance (CAM-DR). Stromal cell protection of ALL cells has been shown to require active AKT. In chronic lymphocytic leukemia (CLL), adhesion-mediated activation of the PI3K/AKT pathway is reported. A novel FDA-approved PI3Kδ inhibitor, CAL-101/idelalisib, leads to downregulation of p-AKT and increased apoptosis of CLL cells. Recently, two additional PI3K inhibitors have received FDA approval. As the PI3K/AKT pathway is also implicated in adhesion-mediated survival of ALL cells, PI3K inhibitors have been evaluated preclinically in ALL. However, PI3K inhibition has yet to be approved for clinical use in ALL. Here, we review the role of PI3K in normal hematopoietic cells, and in ALL. We focus on summarizing targeting strategies of PI3K in ALL.

Immunological changes with kinase inhibitor therapy for chronic lymphocytic leukemia

Ibrutinib and idelalisib are kinase inhibitors that have revolutionized the treatment of chronic lymphocytic leukemia (CLL). Capable of inducing durable remissions, these agents also modulate the immune system. Both ibrutinib and idelalisib abrogate the tumor-supporting microenvironment by disrupting cell-cell interactions, modulating the T-cell compartment, and altering the cytokine milieu. Ibrutinib also partially restores T-cell and myeloid defects associated with CLL. In contrast, immune-related adverse effects, including pneumonitis, colitis, hepatotoxicity, and infections are of particular concern with idelalisib. While opportunistic infections and viral reactivations occur with both ibrutinib and idelalisib, these complications are less common and less severe with ibrutinib, especially when used as monotherapy without additional immunosuppressive agents. This review discusses the impact of ibrutinib and idelalisib on the immune system, including infectious and auto-immune complications as well as their specific effects on the B-cell, T-cell, and myeloid compartment.

Characterization of potential driver mutations involved in human breast cancer by computational approaches

Breast cancer is the second most frequently occurring form of cancer and is also the second most lethal cancer in women worldwide. A genetic mutation is one of the key factors that alter multiple cellular regulatory pathways and drive breast cancer initiation and progression yet nature of these cancer drivers remains elusive. In this article, we have reviewed various computational perspectives and algorithms for exploring breast cancer driver mutation genes. Using both frequency based and mutational exclusivity based approaches, we identified 195 driver genes and shortlisted 63 of them as candidate drivers for breast cancer using various computational approaches. Finally, we conducted network and pathway analysis to explore their functions in breast tumorigenesis including tumor initiation, progression, and metastasis.

Idelalisib sensitivity and mechanisms of disease progression in relapsed TCF3-PBX1 acute lymphoblastic leukemia

TCF3-PBX1 (E2A-PBX1) is a recurrent gene fusion in B-cell precursor acute lymphoblastic leukemia (BCP-ALL), which is caused by the translocation t(1;19)(q23;p13). TCF3-PBX1 BCP-ALL patients typically benefit from chemotherapy; however, many relapse and subsequently develop resistant disease with few effective treatment options. Mechanisms driving disease progression and therapy resistance have not been studied in TCF3-PBX1 BCP-ALL. Here, we aimed to identify novel treatment options for TCF3-PBX1 BCP-ALL by profiling leukemia cells from a relapsed patient, and determine molecular mechanisms underlying disease pathogenesis and progression. By drug-sensitivity testing of leukemic blasts from the index patient, control samples and TCF3-PBX1 positive and negative BCP-ALL cell lines, we identified the phosphatidylinositide 3-kinase delta (p110δ) inhibitor idelalisib as an effective treatment for TCF3-PBX1 BCP-ALL. This was further supported by evidence showing TCF3-PBX1 directly regulates expression of PIK3CD, the gene encoding p110δ. Other somatic mutations to TP53 and MTOR, as well as aberrant expression of CXCR4, may influence additional drug sensitivities specific to the index patient and accompanied progression of the disease. Our results suggest that idelalisib is a promising treatment option for patients with TCF3-PBX1 BCP-ALL, whereas other drugs could be useful depending on the genetic context of individual patients.

Increased expression of the PI3K catalytic subunit p110δ underlies elevated S6 phosphorylation and protein synthesis in an individual with autism from a multiplex family

Background

Dysfunctions in the PI3K/mTOR pathway have gained a lot of attention in autism research. This was initially based on the discovery of several monogenic autism spectrum disorders with mutations or defects in PI3K/mTOR signaling components. Recent genetic studies corroborate that defective PI3K/mTOR signaling might be a shared pathomechanism in autism disorders of so far unknown etiology, but functional molecular analyses in human cells are rare. The goals of this study were to perform a functional screen of cell lines from patients with idiopathic autism for defects in PI3K/mTOR signaling, to test if further functional analyses are suitable to detect underlying molecular mechanisms, and to evaluate this approach as a biomarker tool to identify therapeutic targets.

Methods

We performed phospho-S6- and S6-specific ELISA experiments on 21 lymphoblastoid cell lines from the AGRE collection and on 37 lymphoblastoid cell lines from the Simons Simplex Collection and their healthy siblings. Cell lines from one individual with increased S6 phosphorylation and his multiplex family were analyzed in further detail to identify upstream defects in PI3K signaling associated with autism diagnosis.

Results

We detected significantly increased S6 phosphorylation in 3 of the 21 lymphoblastoid cell lines from AGRE compared to a healthy control and in 1 of the 37 lymphoblastoid cell lines from the Simons Simplex Collection compared to the healthy sibling. Further analysis of cells from one individual with elevated S6 phosphorylation showed increased expression of the PI3K catalytic subunit p110δ, which was also observed in lymphoblastoid cells from other autistic siblings but not unaffected members in his multiplex family. The p110δ-selective inhibitor IC87114 reduced elevated S6 phosphorylation and protein synthesis in this cell line.

Conclusions

Our results suggest that functional analysis of PI3K/mTOR signaling is a biomarker tool to identify disease-associated molecular defects that could serve as therapeutic targets in autism. Using this approach, we discovered impaired signaling and protein synthesis through the PI3K catalytic subunit p110δ as an underlying molecular defect and potential treatment target in select autism spectrum disorders. Increased p110δ activity was recently associated with schizophrenia, and our results suggest that p110δ may also be implicated in autism.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-015-0066-4) contains supplementary material, which is available to authorized users.

Disrupted PI3K p110δ Signaling Dysregulates Maternal Immune Cells and Increases Fetal Mortality In Mice

Maternal immune cells are an integral part of reproduction, but how they might cause pregnancy complications remains elusive. Macrophages and their dual function in inflammation and tissue repair are thought to play key yet undefined roles. Altered perinatal growth underpins adult morbidity, and natural killer (NK) cells may sustain fetal growth by establishing the placental blood supply. Using a mouse model of genetic inactivation of PI3K p110δ, a key intracellular signaling molecule in leukocytes, we show that p110δ regulates macrophage dynamics and NK-cell-mediated arterial remodeling. The uterus of dams with inactive p110δ had decreased IFN-γ and MHC class II^low macrophages but enhanced IL-6. Poor vascular remodeling and a pro-inflammatory uterine milieu resulted in fetal death or growth retardation. Our results provide one mechanism that explains how imbalanced adaptations of maternal innate immune cells to gestation affect offspring well-being with consequence perinatally and possibly into adulthood.

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Genetic inactivation of p110δ in pregnant mice perturbs maternal immune cells

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Uterine NK cells produce less cytokines, resulting in fetal growth restriction

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Inflammatory macrophages are overrepresented, resulting in increased fetal loss

Phosphatidylinositolphosphate phosphatase activities and cancer

Signaling through the phosphoinositide 3-kinase pathways mediates the actions of a plethora of hormones, growth factors, cytokines, and neurotransmitters upon their target cells following receptor occupation. Overactivation of these pathways has been implicated in a number of pathologies, in particular a range of malignancies. The tight regulation of signaling pathways necessitates the involvement of both stimulatory and terminating enzymes; inappropriate activation of a pathway can thus result from activation or inhibition of the two signaling arms. The focus of this review is to discuss, in detail, the activities of the identified families of phosphoinositide phosphatase expressed in humans, and how they regulate the levels of phosphoinositides implicated in promoting malignancy.

Phosphoinositide 3-kinase p110δ promotes lumen formation through the enhancement of apico-basal polarity and basal membrane organization

Signalling triggered by adhesion to the extracellular matrix plays a key role in the spatial orientation of epithelial polarity and formation of lumens in glandular tissues. Phosphoinositide 3-kinase signalling in particular is known to influence the polarization process during epithelial cell morphogenesis. Here, using Madin-Darby canine kidney epithelial cells grown in 3D culture, we show that the p110δ isoform of phosphoinositide 3-kinase co-localizes with focal adhesion proteins at the basal surface of polarized cells. Pharmacological, siRNA- or kinase-dead-mediated inhibition of p110δ impair the early stages of lumen formation, resulting in inverted polarized cysts, with no laminin or type IV collagen assembly at cell/extracellular matrix contacts. p110δ also regulates the organization of focal adhesions and membrane localization of dystroglycan. Thus, we uncover a previously unrecognized role for p110δ in epithelial cells in the orientation of the apico-basal axis and lumen formation.

Aberrant methylation of ERBB pathway genes in sporadic colorectal cancer

The ErbB signalling network plays a crucial role in the growth and progression of several cancers, including colorectal cancer (CRC), and includes potentially drug-targetable genes. Oncogenic activation of the ErbB pathway by mutations and focal amplifications have emerged recently as an important predictive marker of the prognosis of CRC patients. However, in contrast to genetic events, little is known about epigenetic alternations of ErbB-associated genes and their impact on gene expression. Genome-wide methylation in sporadic CRCs (n = 12) paired with adjacent normal tissues have been previously analysed by Illumina Infinium HumanMethylation27 (HM27) at 27,578 CpG sites. For confirmation of our initial genome-wide analysis, we used a published HM27 dataset (GSE25062). Subsequently, CpG island methylation of selected ErbB pathway-associated genes was assessed on 233 CRC samples using methylation-sensitive polymerase chain reaction (MS-PCR) and analysed along with various genetic factors associated with CRC [epigenotype, BRAF and KRAS mutations, microsatellite instability (MSI)]. Methylation and expression integration was performed using published datasets including 25 pairs of CRC and normal colon tissues (GSE25062 and GSE25070), and confirmed with real-time PCR. Our previous microarray-based genome-wide DNA methylation analysis of 12 CRCs revealed that four ErbB-associated genes (PIK3CD, PKCΒ, ERBB4, ) were differentially methylated in CRCs. This was further confirmed by statistical re-analysis of an HM27 dataset (GSE25062). Frequent methylation at these loci in tumours was subsequently confirmed by MS-PCR (63 %, 43 %, 43 % and 92 %, respectively). Hypermethylation of PKCΒ associated with KRAS mutation (p = 0.04), whereas hypermethylation of ERBB4 associated with high-methylation epigenotypes (HME), BRAF mutation and MSI (p = 0.001, 0.002 and 0.0002, respectively). One of the four analysed genes (PKCΒ) was significantly downregulated in CRC tissue, as revealed by real-time PCR and re-analysis of the GSE25062 and GSE25070 datasets. After careful re-analysis of published methylation and expression data, we conclude that methylation of ERBB4, PAK7 and PIK3CD has no functional role in CRC carcinogenesis. In contrast, methylation seems to have a potential impact on the biology of colorectal tumours by negatively modulating the expression of PKCΒ. Importantly, the relationship between DNA methylation of PKCΒ and gene expression may warrant further attention in the context of colon cancer chemoprevention and anti-cancer therapy.

Molecular mechanisms and functional implications of polarized actin remodeling at the T cell immunological synapse

Transient,specialized cell-cell interactions play a central role in leukocyte function by enabling specific intercellular communication in the context of a highly dynamic systems level response. The dramatic structural changes required for the formation of these contacts are driven by rapid and precise cytoskeletal remodeling events. In recent years, the immunological synapse that forms between a T lymphocyte and its antigen-presenting target cell has emerged as an important model system for understanding immune cell interactions. In this review, we discuss how regulators of the cortical actin cytoskeleton control synaptic architecture and in this way specify T cell function.

A chemical biology approach identified PI3K as a potential therapeutic target for neurofibromatosis type 2

Mutations in the merlin tumor suppressor gene cause Neurofibromatosis type 2 (NF2), which is a disease characterized by development of multiple benign tumors in the nervous system. The current standard of care for NF2 calls for surgical resection of the characteristic tumors, often with devastating neurological consequences. There are currently no approved non-surgical therapies for NF2. In an attempt to identify much needed targets and therapeutically active compounds for NF2 treatment, we employed a chemical biology approach using ultra-high-throughput screening. To support this goal, we created a merlin-null mouse Schwann cell (MSC) line to screen for compounds that selectively decrease their viability and proliferation. We optimized conditions for 384-well plate assays and executed a proof-of-concept screen of the Library of Pharmacologically Active Compounds. Further confirmatory and selectivity assays identified phosphatidylinositol 3-kinase (PI3K) as a potential NF2 drug target. Notably, loss of merlin function is associated with activation of the PI3K/Akt pathway in human schwannomas. We report that AS605240, a PI3K inhibitor, decreased merlin-null MSC viability in a dose-dependent manner without significantly decreasing viability of control Schwann cells. AS605240 exerted its action on merlin-null MSCs by promoting caspase-dependent apoptosis and inducing autophagy. Additional PI3K inhibitors tested also decreased viability of merlin-null MSCs in a dose-dependent manner. In summary, our chemical genomic screen and subsequent hit validation studies have identified PI3K as potential target for NF2 therapy.

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.

PDK1 controls upstream PI3K expression and PIP3 generation

The PI3K/PDK1/Akt signaling axis is centrally involved in cellular homeostasis and controls cell growth and proliferation. Due to its key function as regulator of cell survival and metabolism, the dysregulation of this pathway is manifested in several human pathologies including cancers and immunological diseases. Thus, current therapeutic strategies target the components of this signaling cascade. In recent years, numerous feedback loops have been identified that attenuate PI3K/PDK1/Akt-dependent signaling. Here, we report the identification of an additional level of feedback regulation that depends on the negative transcriptional control of phosphatidylinositol 3-kinase (PI3K) class IA subunits. Genetic deletion of 3-phosphoinositide-dependent protein kinase 1 (PDK1) or the pharmacological inhibition of its downstream effectors, that is, Akt and mammalian target of rapamycin (mTOR), relieves this suppression and leads to the upregulation of PI3K subunits, resulting in enhanced generation of phosphatidylinositol-3,4,5-trisphosphate (PIP3). Apparently, this transcriptional induction is mediated by the concerted action of different transcription factor families, including the transcription factors cAMP-responsive element-binding protein and forkhead box O. Collectively, we propose that PDK1 functions as a cellular sensor that balances basal PIP3 generation at levels sufficient for survival but below a threshold being harmful to the cell. Our study suggests that the efficiency of therapies targeting the aberrantly activated PI3K/PDK1/Akt pathway might be increased by the parallel blockade of feedback circuits.

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.

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.

High levels of p110δ PI3K expression in solid tumor cells suppress PTEN activity, generating cellular sensitivity to p110δ inhibitors through PTEN activation

Class IA PI3K isoforms have divergent, nonredundant cell biological roles. In untransformed cells and tissues, p110α and p110β are ubiquitously expressed, whereas p110δ expression is highly enriched in leukocytes. High levels of p110δ expression have been documented in some solid tumor cell lines, but the functional role is unknown. This study aimed to elucidate the link between elevated expression of p110δ PI3K and cancer. We report that in breast and prostate cancer cells that contain leukocyte levels of p110δ, p110δ activity dampens the activity of the PTEN tumor suppressor. Indeed, inactivation of p110δ in these cells led to PTEN activation, suppression of Akt phosphorylation, and inhibition of cell proliferation, with inhibition of PTEN activity being able to counterbalance p110δ inactivation. Likewise, forced overexpression of p110δ in cells with low p110δ expression reduced PTEN activity, resulting in increased Akt phosphorylation. Our data indicate that the oncogenic potential of p110δ PI3K overexpression might at least partially act through PTEN inactivation, and that p110δ-selective PI3K inhibitors can have a dual antitumor mechanism, namely by directly inhibiting p110δ signaling and by a broader inhibition of class I PI3K activity through PTEN activation. These data may have important implications in the intervention of breast cancer.

Imidazo[1,2-a]pyrazines as novel PI3K inhibitors

Phosphoinositide-3-kinase (PI3K) is an important target for cancer therapeutics due to the deregulation of its signaling pathway in a wide variety of human cancers. We describe herein a novel series of imidazo[1,2-a]pyrazines as PI3K inhibitors.

LPS induced inflammatory responses in human peripheral blood mononuclear cells is mediated through NOX4 and Giα dependent PI-3kinase signalling

COPD is a disease of innate immunity and bacterial infections are a dominant cause of exacerbations in the later stages resulting in poor health and high mortality. The pathogen-associated molecular pattern (PAMP) lipopolysaccharide (LPS) is sensed by immune cells through activation of the toll-like receptor 4 (TLR4). This leads to the activation of NADPH oxidase (NOX) and NF-κB which together drive COPD inflammation. In this study we show in human PBMCs that LPS stimulated proinflammatory cytokine release (CXCL8 and IL6) was inhibited by approximately 50% by the broad specificity phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin. Our results also demonstrate that activation of PI3K following LPS stimulation is mediated by a NOX4 dependent mechanism releasing endogenous H2O2, as the NOX4 inhibitor apocynin blocked LPS induced AKT phosphorylation. Moreover, LPS-induced PI3K activation was inhibited by the anti-oxidant N-acetylcysteine in a concentration dependent manner (IC50 ~100 μM). In addition, our data demonstrated that inhibition of small G proteins, by pre-treatment with pertussis toxin, inhibited LPS-induced AKT phosphorylation. Furthermore, the G-protein inhibitors pertussis toxin and mastoparan both inhibited LPS-induced CXCL8 and IL-6 release by approximately 50%. Together, these data indicate there is a mechanism in human PBMCs where TLR4 activation by LPS leads to ROS generation through NOX4 and activation of the PI3K pathway. This effect is apparently mediated through small G proteins facilitating the release of pro-inflammatory cytokines.

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.

Kinome profiling reveals an interaction between jasmonate, salicylate and light control of hyponastic petiole growth in Arabidopsis thaliana

Plants defend themselves against infection by biotic attackers by producing distinct phytohormones. Especially jasmonic acid (JA) and salicylic acid (SA) are well known defense-inducing hormones. Here, the effects of MeJA and SA on the Arabidopsis thaliana kinome were monitored using PepChip arrays containing kinase substrate peptides to analyze posttranslational interactions in MeJA and SA signaling pathways and to test if kinome profiling can provide leads to predict posttranslational events in plant signaling. MeJA and SA mediate differential phosphorylation of substrates for many kinase families. Also some plant specific substrates were differentially phosphorylated, including peptides derived from Phytochrome A, and Photosystem II D protein. This indicates that MeJA and SA mediate cross-talk between defense signaling and light responses. We tested the predicted effects of MeJA and SA using light-mediated upward leaf movement (differential petiole growth also called hyponastic growth). We found that MeJA, infestation by the JA-inducing insect herbivore Pieris rapae, and SA suppressed low light-induced hyponastic growth. MeJA and SA acted in a synergistic fashion via two (partially) divergent signaling routes. This work demonstrates that kinome profiling using PepChip arrays can be a valuable complementary ∼omics tool to give directions towards predicting behavior of organisms after a given stimulus and can be used to obtain leads for physiological relevant phenomena in planta.

Distinct patterns of DNA damage response and apoptosis correlate with Jak/Stat and PI3kinase response profiles in human acute myelogenous leukemia

Background

Single cell network profiling (SCNP) utilizing flow cytometry measures alterations in intracellular signaling responses. Here SCNP was used to characterize Acute Myeloid Leukemia (AML) disease subtypes based on survival, DNA damage response and apoptosis pathways.

Methodology and Principal Findings

Thirty four diagnostic non-M3 AML samples from patients with known clinical outcome were treated with a panel of myeloid growth factors and cytokines, as well as with apoptosis-inducing agents. Analysis of induced Jak/Stat and PI3K pathway responses in blasts from individual patient samples identified subgroups with distinct signaling profiles that were not seen in the absence of a modulator. In vitro exposure of patient samples to etoposide, a DNA damaging agent, revealed three distinct “DNA damage response (DDR)/apoptosis” profiles: 1) AML blasts with a defective DDR and failure to undergo apoptosis; 2) AML blasts with proficient DDR and failure to undergo apoptosis; 3) AML blasts with proficiency in both DDR and apoptosis pathways. Notably, AML samples from clinical responders fell within the “DDR/apoptosis” proficient profile and, as well, had low PI3K and Jak/Stat signaling responses. In contrast, samples from clinical non responders had variable signaling profiles often with in vitro apoptotic failure and elevated PI3K pathway activity. Individual patient samples often harbored multiple, distinct, leukemia-associated cell populations identifiable by their surface marker expression, functional performance of signaling pathway in the face of cytokine or growth factor stimulation, as well as their response to apoptosis-inducing agents.

Conclusions and Significance

Characterizing and tracking changes in intracellular pathway profiles in cell subpopulations both at baseline and under therapeutic pressure will likely have important clinical applications, potentially informing the selection of beneficial targeted agents, used either alone or in combination with chemotherapy.

Role of the PI3K/AKT and mTOR signaling pathways in acute myeloid leukemia

The PI3K/AKT and mTOR signaling pathways are activated in acute myeloid leukemia, including in the more immature leukemic populations. Constitutive PI3K activation is detectable in 50% of acute myeloid leukemia samples whereas mTORC1 is activated in all cases of this disease. In leukemic cells, the PI3K activity relates to the expression of the p110delta isoform of class IA PI3K. Constitutive PI3K activation is the result of autocrine IGF-1/IGF-1R signaling in 70% of acute myeloid leukemia samples but specific inhibition of this pathway does not induce apoptosis. Specific inhibition of PI3K/AKT or mTORC1 alone in vitro has anti-leukemic effects which are essentially exerted via the suppression of proliferation. However, as mTORC1 activation is independent of PI3K/AKT in acute myeloid leukemia, dual PI3K and mTOR inhibitors may induce apoptosis in blast cells. Moreover, mTORC1 inhibition using sirolimus overactivates PI3K/AKT via the upregulation of IRS2 expression and by favoring IGF-1/IGF-1R autocrine signaling. Recent data also indicate that mTORC1 does not control protein translation in acute myeloid leukemia. These results open the way for the design of direct inhibitors of protein synthesis as novel acute myeloid leukemia therapies and also for the development of second generation mTOR inhibitors (the TORKinhibs).