PDGF-dependent tyrosine phosphorylation stimulates production of novel polyphosphoinositides in intact cells

Improved production of class I phosphatidylinositol 4,5-bisphosphate 3-kinase

Phosphatidylinositol 4,5-bisphosphate 3-kinases (PI3K) are a family of kinases whose activity affects pathways needed for basic cell functions. As a result, PI3K is one of the most mutated genes in all human cancers and serves as an ideal therapeutic target for cancer treatment. Expanding on work done by other groups we improved protein yield to produce stable and pure protein using a variety of modifications including improved solubility tag, novel expression modalities, and optimized purification protocol and buffer. By these means, we achieved a 40-fold increase in yield for p110α/p85α and a 3-fold increase in p110α. We also used these protocols to produce comparable constructs of the β and δ isoforms of PI3K. Increased yield enhanced the efficiency of our downstream high throughput drug discovery efforts on the PIK3 family of kinases.

Diet induced insulin resistance is due to induction of PTEN expression

Type 2 Diabetes (T2D) is a condition that is often associated with obesity and defined by reduced sensitivity of PI3K signaling to insulin (insulin resistance), hyperinsulinemia and hyperglycemia. Molecular causes and early signaling events underlying insulin resistance are not well understood. Insulin activation of PI3K signaling causes mTOR dependent induction of PTEN translation, a negative regulator of PI3K signaling. We speculated that insulin resistance is due to insulin dependent induction of PTEN protein that prevent further increases in PI3K signaling. Here we show that in a diet induced model of obesity and insulin resistance, PTEN levels are increased in fat, muscle and liver tissues. Onset of hyperinsulinemia and PTEN induction in tissue is followed by hyperglycemia, hepatic steatosis and severe glucose intolerance. Treatment with a PTEN phosphatase inhibitor prevents and reverses these phenotypes, whereas an mTORC1 kinase inhibitor reverses all but the hepatic steatosis. These data suggest that induction of PTEN by increasing levels of insulin elevates feedback inhibition of the pathway to a point where downstream PI3K signaling is reduced and hyperglycemia ensues. PTEN induction is thus necessary for insulin resistance and the type 2 diabetes phenotype and a potential therapeutic target.

Pten, PI3K, and PtdIns(3,4,5)P3 dynamics control pulsatile actin branching in Drosophila retina morphogenesis

Epithelial remodeling of the Drosophila retina depends on the pulsatile contraction and expansion of apical contacts between the cells that form its hexagonal lattice. Phosphoinositide PI(3,4,5)P3 (PIP3) accumulates around tricellular adherens junctions (tAJs) during contact expansion and dissipates during contraction, but with unknown function. Here, we found that manipulations of Pten or PI3-kinase (PI3K) that either decreased or increased PIP3 resulted in shortened contacts and a disordered lattice, indicating a requirement for PIP3 dynamics and turnover. These phenotypes are caused by a loss of branched actin, resulting from impaired activity of the Rac1 Rho GTPase and the WAVE regulatory complex (WRC). We additionally found that during contact expansion, PI3K moves into tAJs to promote the cyclical increase of PIP3 in a spatially and temporally precise manner. Thus, dynamic control of PIP3 by Pten and PI3K governs the protrusive phase of junctional remodeling, which is essential for planar epithelial morphogenesis.

Molecular dissection of PI3Kβ synergistic activation by receptor tyrosine kinases, GβGγ, and Rho-family GTPases

Phosphoinositide 3-kinase (PI3K) beta (PI3Kβ) is functionally unique in the ability to integrate signals derived from receptor tyrosine kinases (RTKs), G-protein coupled receptors, and Rho-family GTPases. The mechanism by which PI3Kβ prioritizes interactions with various membrane-tethered signaling inputs, however, remains unclear. Previous experiments did not determine whether interactions with membrane-tethered proteins primarily control PI3Kβ localization versus directly modulate lipid kinase activity. To address this gap in our knowledge, we established an assay to directly visualize how three distinct protein interactions regulate PI3Kβ when presented to the kinase in a biologically relevant configuration on supported lipid bilayers. Using single molecule Total Internal Reflection Fluorescence (TIRF) Microscopy, we determined the mechanism controlling PI3Kβ membrane localization, prioritization of signaling inputs, and lipid kinase activation. We find that auto-inhibited PI3Kβ prioritizes interactions with RTK-derived tyrosine phosphorylated (pY) peptides before engaging either GβGγ or Rac1(GTP). Although pY peptides strongly localize PI3Kβ to membranes, stimulation of lipid kinase activity is modest. In the presence of either pY/GβGγ or pY/Rac1(GTP), PI3Kβ activity is dramatically enhanced beyond what can be explained by simply increasing membrane localization. Instead, PI3Kβ is synergistically activated by pY/GβGγ and pY/Rac1 (GTP) through a mechanism consistent with allosteric regulation.

Give and Take: The Reciprocal Control of Metabolism and Cell Cycle

Cell cycle is an ordered sequence of events that occur in a cell preparing for cell division . The cell cycle is a four-stage process in which the cell increases in size, copies its DNA , prepares to divide, and divides. All these stages require a coordination of signaling pathways as well as adequate levels of energy and building blocks. These specific signaling and metabolic switches are tightly orchestrated in order for the cell cycle to occur properly. In this book chapter, we will provide information on the basis of metabolism and cell cycle interplay, and we will finish by an unexhaustive list of metabolomics approaches available to study the reciprocal control of metabolism and cell cycle.

Molecular dissection of PI3Kβ synergistic activation by receptor tyrosine kinases, GβGγ, and Rho-family GTPases

The class 1A phosphoinositide 3-kinase (PI3K) beta (PI3Kβ) is functionally unique in the ability to integrate signals derived from receptor tyrosine kinases (RTKs), heterotrimeric guanine nucleotide-binding protein (G-protein)-coupled receptors (GPCRs), and Rho-family GTPases. The mechanism by which PI3Kβ prioritizes interactions with various membrane tethered signaling inputs, however, remains unclear. Previous experiments have not been able to elucidate whether interactions with membrane-tethered proteins primarily control PI3Kβ localization versus directly modulate lipid kinase activity. To address this gap in our understanding of PI3Kβ regulation, we established an assay to directly visualize and decipher how three distinct protein interactions regulate PI3Kβ when presented to the kinase in a biologically relevant configuration on supported lipid bilayers. Using single molecule Total Internal Reflection Fluorescence (TIRF) Microscopy, we determined the mechanism controlling membrane localization of PI3Kβ, prioritization of signaling inputs, and lipid kinase activation. We find that auto-inhibited PI3Kβ prioritizes interactions with RTK-derived tyrosine phosphorylated (pY) peptides before engaging either GβGγ or Rac1(GTP). Although pY peptides strongly localize PI3Kβ to membranes, stimulation of lipid kinase activity is modest. In the presence of either pY/GβGγ or pY/Rac1(GTP), PI3Kβ activity is dramatically enhanced beyond what can be explained by simply increasing the strength of membrane localization. Instead, PI3Kβ is synergistically activated by pY/GβGγ and pY/Rac1(GTP) through a mechanism consistent with allosteric regulation.

Phosphoinositide Signaling in Immune Cell Migration

In response to different immune challenges, immune cells migrate to specific sites in the body, where they perform their functions such as defense against infection, inflammation regulation, antigen recognition, and immune surveillance. Therefore, the migration ability is a fundamental aspect of immune cell function. Phosphoinositide signaling plays critical roles in modulating immune cell migration by controlling cell polarization, cytoskeletal rearrangement, protrusion formation, and uropod contraction. Upon chemoattractant stimulation, specific phosphoinositide kinases and phosphatases control the local phosphoinositide levels to establish polarized phosphoinositide distribution, which recruits phosphoinositide effectors to distinct subcellular locations to facilitate cell migration. In this Special Issue of "Molecular Mechanisms Underlying Cell Adhesion and Migration", we discuss the significance of phosphoinositide production and conversion by phosphoinositide kinases and phosphatases in the migration of different types of immune cells.

Role of gut commensal bacteria in juvenile developmental growth of the host: insights from Drosophila studies

The gut microbiome plays a crucial role in maintaining health in a variety of organisms, from insects to humans. Further, beneficial symbiotic microbes are believed to contribute to improving the quality of life of the host. Drosophila is an optimal model for studying host-commensal microbe interactions because it allows for convenient manipulation of intestinal microbial composition. Fly microbiota has a simple taxonomic composition and can be cultivated and genetically tracked. This permits functional studies and analyses of the molecular mechanisms underlying their effects on host physiological processes. In this context, we briefly introduce the principle of juvenile developmental growth in Drosophila. Then, we discuss the current understanding of the molecular mechanisms underlying the effects of gut commensal bacteria, such as Lactiplantibacillus plantarum and Acetobacter pomorum, in the fly gut microbiome on Drosophila juvenile growth, including specific actions of gut hormones and metabolites in conserved cellular signaling systems, such as the insulin/insulin-like (IIS) and the target of rapamycin (TOR) pathways. Given the similarities in tissue function/structure, as well as the high conservation of physiological systems between Drosophila and mammals, findings from the Drosophila model system will have significant implications for understanding the mechanisms underlying the interaction between the host and the gut microbiome in metazoans.

Phosphoinositide 3-kinase as a therapeutic target in angiogenic disease

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

Apelin receptor inhibition in ischemia-reperfused mouse hearts protected by endogenous n-3 polyunsaturated fatty acids

Background: While the protective effects of n-3 polyunsaturated fatty acids (PUFAs) on cardiac ischemia-reperfusion (IR) injury have been previously reported, limited data are available regarding how these fatty acids affect membrane receptors and their downstream signaling following IR injury. We aimed to identify potential receptors activated by n-3 PUFAs in IR hearts to understand the regulatory mechanisms of these receptors. Methods: We used fat-1 mice, which naturally have elevated levels of n-3 PUFAs, and C57BL/6J mice as a control group to create a myocardial IR injury model through Langendorff perfusion. We assessed the impact of endogenous n-3 PUFAs on left ventricular function, myocardial infarct size, myocardial apoptosis, and ATP production. RNA sequencing (RNA-seq) and bioinformatics analysis were conducted to identify molecular targets affected by n-3 PUFAs. Based on these analyses we then treated IR hearts of WT and fat-1 mice with an antagonist (ML221) or an agonist (apelin-13) for the predicted receptor to assess cardiac contractile function and intracellular signaling pathways. An in vitro hypoxia-reoxygenation (HR) model was also used to confirm the effects of n-3 PUFAs on the examined intracellular signaling pathways. Results: Endogenous n-3 PUFAs protected cardiac structure and function in post-IR hearts, and modulated phosphorylation patterns in the PI3K-AKT-mTOR signaling pathways. RNA-seq analysis revealed that n-3 PUFAs affected multiple biological processes as well as levels of the apelin receptor (APLNR). Consistent with a role for the PLNNR, ML221 synchronized the activation of the PI3K-AKT-mTOR signaling axis, suppressed the expression of PKCδ and phosphorylated p38α, upregulated PKCε expression, upregulated or restored the phosphorylation of myofilaments, and prevented myocardial injury and contractile dysfunction in WT IR hearts. By contrast, apelin-13 disrupted the PI3K-AKT-mTOR signaling axis in post-IR fat-1 hearts. The phosphorylation signaling targeted by APLNR inhibition in post-IR fat-1 hearts was also observed after treating HR cells with eicosatetraenoic acid (EPA). Conclusion: Endogenous n-3 PUFAs protect against post-IR injury and preserve cardiac contractile function possibly through APLNR inhibition. This inhibition synchronizes the PI3K-AKT-mTOR axis, suppresses detrimental phosphorylation signaling, and restores or increases myofilament phosphorylation in post-IR hearts. The beneficial effects observed in fat-1 transgenic mouse hearts can be attributed, at least in part, to elevated EPA levels. This study is the first to demonstrate that n-3 PUFAs protect hearts against IR injury through APLNR inhibition.

Phosphoinositide 3-kinase (PI3K) classes: From cell signaling to endocytic recycling and autophagy

Lipid signaling is defined as any biological signaling action in which a lipid messenger binds to a protein target, converting its effects to specific cellular responses. In this complex biological pathway, the family of phosphoinositide 3-kinase (PI3K) represents a pivotal role and affects many aspects of cellular biology from cell survival, proliferation, and migration to endocytosis, intracellular trafficking, metabolism, and autophagy. While yeasts have a single isoform of phosphoinositide 3-kinase (PI3K), mammals possess eight PI3K types divided into three classes. The class I PI3Ks have set the stage to widen research interest in the field of cancer biology. The aberrant activation of class I PI3Ks has been identified in 30-50% of human tumors, and activating mutations in PIK3CA is one of the most frequent oncogenes in human cancer. In addition to indirect participation in cell signaling, class II and III PI3Ks primarily regulate vesicle trafficking. Class III PI3Ks are also responsible for autophagosome formation and autophagy flux. The current review aims to discuss the original data obtained from international research laboratories on the latest discoveries regarding PI3Ks-mediated cell biological processes. Also, we unravel the mechanisms by which pools of the same phosphoinositides (PIs) derived from different PI3K types act differently.

Pten, Pi3K and PtdIns(3,4,5)P 3 dynamics modulate pulsatile actin branching in Drosophila retina morphogenesis

Epithelial remodeling of the Drosophila retina depends on the pulsatile contraction and expansion of apical contacts between the cells that form its hexagonal lattice. Phosphoinositide PI(3,4,5)P 3 (PIP 3 ) accumulates around tricellular adherens junctions (tAJs) during contact expansion and dissipates during contraction, but with unknown function. Here we found that manipulations of Pten or Pi3K that either decreased or increased PIP 3 resulted in shortened contacts and a disordered lattice, indicating a requirement for PIP 3 dynamics and turnover. These phenotypes are caused by a loss of protrusive branched actin, resulting from impaired activity of the Rac1 Rho GTPase and the WAVE regulatory complex (WRC). We additionally found that during contact expansion, Pi3K moves into tAJs to promote the cyclical increase of PIP 3 in a spatially and temporally precise manner. Thus, dynamic regulation of PIP 3 by Pten and Pi3K controls the protrusive phase of junctional remodeling, which is essential for planar epithelial morphogenesis.

Repurposing Inhibitors of Phosphoinositide 3-kinase as Adjuvant Therapeutics for Bacterial Infections

The rise in antimicrobial resistance and the decline in new antibiotics has created a great need for novel approaches to treat drug resistant bacterial infections. Increasing the burden of antimicrobial resistance, bacterial virulence factors allow for survival within the host, where they can evade host killing and antimicrobial therapy within their intracellular niches. Repurposing host directed therapeutics has great potential for adjuvants to allow for more effective bacterial killing by the host and antimicrobials. To this end, phosphoinositide 3-kinase inhibitors are FDA approved for cancer therapy, but also have potential to eliminate intracellular survival of pathogens. This review describes the PI3K pathway and its potential as an adjuvant target to treat bacterial infections more effectively.

Apolipoprotein A1 Protects Against Necrotic Core Development in Atherosclerotic Plaques: PDZK1-Dependent High-Density Lipoprotein Suppression of Necroptosis in Macrophages

BACKGROUND

Atherosclerosis is a chronic disease affecting artery wall and a major contributor to cardiovascular diseases. Large necrotic cores increase risk of plaque rupture leading to thrombus formation. Necrotic cores are rich in debris from dead macrophages. Programmed necrosis (necroptosis) contributes to necrotic core formation. HDL (high-density lipoprotein) exerts direct atheroprotective effects on different cells within atherosclerotic plaques. Some of these depend on the SR-B1 (scavenger receptor class B type I) and the adapter protein PDZK1 (postsynaptic density protein/Drosophila disc-large protein/Zonula occludens protein containing 1). However, a role for HDL in protecting against necroptosis and necrotic core formation in atherosclerosis is not completely understood.

METHODS

Low-density lipoprotein receptor-deficient mice engineered to express different amounts of ApoA1 (apolipoprotein A1), or to lack PDZK1 were fed a high fat diet for 10 weeks. Atherosclerotic plaque areas, necrotic cores, and key necroptosis mediators, RIPK3 (receptor interacting protein kinase 3), and MLKL (mixed lineage kinase domain-like protein) were characterized. Cultured macrophages were treated with HDL to determine its effects, as well as the roles of SR-B1, PDZK1, and the PI3K (phosphoinositide 3-kinase) signaling pathway on necroptotic cell death.

RESULTS

Genetic overexpression reduced, and ApoA1 knockout increased necrotic core formation and RIPK3 and MLKL within atherosclerotic plaques. Macrophages were protected against necroptosis by HDL and this protection required SR-B1, PDZK1, and PI3K/Akt pathway. PDZK1 knockout increased atherosclerosis in LDLR^KO mice, increasing necrotic cores and phospho-MLKL; both of which were reversed by restoring PDZK1 in BM-derived cells.

CONCLUSIONS

Our findings demonstrate that HDL in vitro and ApoA1, in vivo, protect against necroptosis in macrophages and necrotic core formation in atherosclerosis, suggesting a pathway that could be a target for the treatment of atherosclerosis.

PIK3R2 predicts poor outcomes for patients with melanoma and contributes to the malignant progression via PI3K/AKT/NF-κB axis

BACKGROUND

Melanoma is an aggressive form of skin cancer worldwide. Phosphoinositide-3-kinase regulatory subunit 2 (PIK3R2) exerts carcinogenic roles in various tumors. So far, the function and mechanism of PIK3R2 in melanoma are not been fully clarified.

OBJECTIVE

We aimed to clarify the role of PIK3R2 in melanoma.

METHODS

PIK3R2 expressions in melanoma clinical tissues and melanoma cells were measured using quantitative real-time PCR and Western blot. In addition, PIK3R2 expressions in different tumor stages of melanoma were determined by immunohistochemistry assay. Meanwhile, PIK3R2 function was evaluated using loss or gain-of-function assays, Cell Counting Kit-8 assay, flow cytometry, and Transwell analysis. Furthermore, PIK3R2 mechanism in melanoma was assessed by a series of rescue experiments.

RESULTS

PIK3R2 was highly expressed in melanoma tissues and cells, and PIK3R2 expressions were the highest in Stage IV. Functionally, PIK3R2 knockdown repressed melanoma cell proliferation, invasion, epithelial-mesenchymal transition, and facilitated cell apoptosis. Also, PIK3R2 overexpression produced an opposite trend. Mechanistically, PIK3R2 facilitated melanoma progression by activating PI3K/AKT/NF-κB pathway. Furthermore, PIK3R2 knockdown restrained the melanoma tumor growth in vivo.

CONCLUSIONS

PIK3R2 aggravated melanoma by activating PI3K/AKT/NF-κB pathway, prompting that PIK3R2 might be a therapeutic target for melanoma.

PI3K signalling at the intersection of cardio-oncology networks: cardiac safety in the era of AI

Class I phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases. They are super elevated in many human cancer types and exert their main cellular functions by activating Akt to trigger an array of distinct responses, affecting metabolism and cell polarity. The signal equally plays important roles in cardiovascular pathophysiology. PI3K is required for cardiogenesis and regulation of cardiac structure and function. Overexpression of PI3K governs the development of cardiac pressure overload adaptation and compensatory hypertrophy. Therefore, inhibition of PI3K shortens life span, enhances cardiac dysfunction and pathological hypertrophy. The inverse inhibition effect, however, desirably destroys many cancer cells by blocking several aspects of the tumorigenesis phenotype. Given the contrasting effects in cardio-oncology; the best therapeutic strategy to target PI3K in cancer, while maintaining or rather increasing cardiac safety is under intense investigational scrutiny. To improve our molecular understanding towards identifying cardiac safety signalling of PI3K and/or better therapeutic strategy for cancer treatment, this article reviews PI3K signalling in cardio-oncology. PI3K signalling at the interface of metabolism, inflammation and immunity, and autonomic innervation networks were examined. Examples were then given of cardiovascular drugs that target the networks, being repurposed for cancer treatment. This was followed by an intersection scheme of the networks that can be functionalised with machine learning for safety and risk prediction, diagnoses, and defining new novel encouraging leads and targets for clinical translation. This will hopefully overcome the challenges of the one-signalling-one-health-outcome alliance, and expand our knowledge of the totality of PI3K signalling in cardio-oncology.

Drosophila melanogaster diabetes models and its usage in the research of anti-diabetes management with traditional Chinese medicines

The prevalence of diabetes mellitus (DM) is increasing rapidly worldwide, but the underlying molecular mechanisms of disease development have not been elucidated, and the current popular anti-diabetic approaches still have non-negligible limitations. In the last decades, several different DM models were established on the classic model animal, the fruit fly (Drosophila melanogaster), which provided a convenient way to study the mechanisms underlying diabetes and to discover and evaluate new anti-diabetic compounds. In this article, we introduce the Drosophila Diabetes model from three aspects, including signal pathways, established methods, and pharmacodynamic evaluations. As a highlight, the progress in the treatments and experimental studies of diabetes with Traditional Chinese Medicine (TCM) based on the Drosophila Diabetes model is reviewed. We believe that the values of TCMs are underrated in DM management, and the Drosophila Diabetes models can provide a much more efficient tool to explore its values of it.

Externalized phosphatidylinositides on apoptotic cells are eat-me signals recognized by CD14

Apoptotic cells are rapidly engulfed and removed by phagocytes after displaying cell surface eat-me signals. Among many phospholipids, only phosphatidylserine (PS) is known to act as an eat-me signal on apoptotic cells. Using unbiased proteomics, we identified externalized phosphatidylinositides (PIPs) as apoptotic eat-me signals recognized by CD14⁺ phagocytes. Exofacial PIPs on the surfaces of early and late-apoptotic cells were observed in patches and blebs using anti-PI(3,4,5)P₃ antibody, AKT- and PLCδ PH-domains, and CD14 protein. Phagocytosis of apoptotic cells was blocked either by masking exofacial PIPs or by CD14 knockout in phagocytes. We further confirmed that exofacial PIP⁺ thymocytes increased dramatically after in vivo irradiation and that exofacial PIP⁺ cells represented more significant populations in tissues of Cd14^−/− than WT mice, especially after induction of apoptosis. Our findings reveal exofacial PIPs to be previously unknown cell death signals recognized by CD14⁺ phagocytes.

At a crossroads: how to translate the roles of PI3K in oncogenic and metabolic signalling into improvements in cancer therapy

Numerous agents targeting various phosphatidylinositol 3-kinase (PI3K) pathway components, including PI3K, AKT and mTOR, have been tested in oncology clinical trials, resulting in regulatory approvals for the treatment of selected patients with breast cancer, certain other solid tumours or particular haematological malignancies. However, given the prominence of PI3K signalling in cancer and the crucial role of this pathway in linking cancer growth with metabolism, these clinical results could arguably be improved upon. In this Review, we discuss past and present efforts to overcome the somewhat limited clinical efficacy of PI3Kα pathway inhibitors, including optimization of inhibitor specificity, patient selection and biomarkers across cancer types, with a focus on breast cancer, as well as identification and abrogation of signalling-related and metabolic mechanisms of resistance, and interventions to improve management of prohibitive adverse events. We highlight the advantages and limitations of laboratory-based model systems used to study the PI3K pathway, and propose technologies and experimental inquiries to guide the future clinical deployment of PI3K pathway inhibitors in the treatment of cancer.

Alpelisib monotherapy for PI3K-altered, pre-treated advanced breast cancer: a phase 2 study

There is limited knowledge on the benefit of the α-subunit specific PI3K inhibitor alpelisib in later lines of therapy for advanced ER+HER2- and triple negative breast cancer (TNBC). We conducted a phase 2 multi-cohort study of alpelisib monotherapy in patients with advanced PI3K pathway mutant ER+HER2- and TNBC. In the intention to treat ER+ cohort, the overall response rate was 30% and the clinical benefit rate was 36%. Decline in PI3K pathway mutant ctDNA levels from baseline to week 8 while on therapy was significantly associated with a partial response, clinical benefit and improved progression free-survival (HR 0.24 95% CI 0.083 - 0.67, P = 0.0065). Detection of ESR1 mutations at baseline in plasma was also associated with clinical benefit and improved progression free survival (HR 0.22 95% CI 0.078 - 0.60, P = 0.003).

The non-canonical nuclear functions of key players of the PI3K-AKT-MTOR pathway

The PI3K-AKT-MTOR signal transduction pathway is one of the essential signalling cascades within the cell due to its involvement in many vital functions. The pathway initiates with the recruitment of phosphatidylinositol-3 kinases (PI3Ks) onto the plasma membrane, generating phosphatidylinositol-3,4,5-triphosphate [PtdIns(3,4,5)P₃ ] and subsequently activating AKT. Being the central node of the PI3K network, AKT activates the mechanistic target of rapamycin kinase complex 1 (MTORC1) via Tuberous sclerosis complex 2 inhibition in the cytoplasm. Although the cytoplasmic role of the pathway has been widely explored for decades, we now know that most of the effector molecules of the PI3K axis diverge from the canonical route and translocate to other cell organelles including the nucleus. The presence of phosphoinositides (PtdIns) inside the nucleus itself indicates the existence of a nuclear PI3K signalling. The nuclear localization of these signaling components is evident in regulating many nuclear processes like DNA replication, transcription, DNA repair, maintenance of genomic integrity, chromatin architecture, and cell cycle control. Here, our review intends to present a comprehensive overview of the nuclear functions of the PI3K-AKT-MTOR signaling biomolecules.

Interplay between PI3K/AKT pathway and heart disorders

The PI3K/AKT signaling has crucial role in the regulation of numerous physiological functions through activation of downstream effectors and modulation of cell cycle transition, growth and proliferation. This pathway participates in the pathogenesis of several human disorders such as heart diseases through regulation of size and survival of cardiomyocytes, angiogenic processes as well as inflammatory responses. Moreover, PI3K/AKT pathway participates in the process of myocardial injury induced by a number of substances such as H₂O₂, Mercury, lipopolysaccharides, adriamycin, doxorubicin and epirubicin. In this review, we describe the contribution of this pathway in the pathoetiology of myocardial ischemia/reperfusion injury and myocardial infarction, heart failure, cardiac hypertrophy, cardiomyopathy and toxins-induced cardiac injury.

Aloperine: A Potent Modulator of Crucial Biological Mechanisms in Multiple Diseases

Aloperine is an alkaloid found in the seeds and leaves of the medicinal plant Sophora alopecuroides L. It has been used as herbal medicine in China for centuries due to its potent anti-inflammatory, antioxidant, antibacterial, and antiviral properties. Recently, aloperine has been widely investigated for its therapeutic activities. Aloperine is proven to be an effective therapeutic agent against many human pathological conditions, including cancer, viral diseases, and cardiovascular and inflammatory disorders. Aloperine is reported to exert therapeutic effects through triggering various biological processes, including cell cycle arrest, apoptosis, autophagy, suppressing cell migration, and invasion. It has also been found to be associated with the modulation of various signaling pathways in different diseases. In this review, we summarize the most recent knowledge on the modulatory effects of aloperine on various critical biological processes and signaling mechanisms, including the PI3K, Akt, NF-κB, Ras, and Nrf2 pathways. These data demonstrate that aloperine is a promising therapeutic candidate. Being a potent modulator of signaling mechanisms, aloperine can be employed in clinical settings to treat various human disorders in the future.

Crucial Players for Inter-Organelle Communication: PI5P4Ks and Their Lipid Product PI-4,5-P2 Come to the Surface

While organelles are individual compartments with specialized functions, it is becoming clear that organellar communication is essential for maintaining cellular homeostasis. This cooperation is carried out by various interactions taking place on the membranes of organelles. The membranes themselves contain a multitude of proteins and lipids that mediate these connections and one such class of molecules facilitating these relations are the phospholipids. There are several phospholipids, but the focus of this perspective is on a minor group called the phosphoinositides and specifically, phosphatidylinositol 4,5-bisphosphate (PI-4,5-P₂). This phosphoinositide, on intracellular membranes, is largely generated by the non-canonical Type II PIPKs, namely, Phosphotidylinositol-5-phosphate-4-kinases (PI5P4Ks). These evolutionarily conserved enzymes are emerging as key stress response players in cells. Further, PI5P4Ks have been shown to modulate pathways by regulating organelle crosstalk, revealing roles in preserving metabolic homeostasis. Here we will attempt to summarize the functions of the PI5P4Ks and their product PI-4,5-P₂ in facilitating inter-organelle communication and how they impact cellular health as well as their relevance to human diseases.

MAPK4 promotes triple negative breast cancer growth and reduces tumor sensitivity to PI3K blockade

About 15–20% of breast cancer (BCa) is triple-negative BCa (TNBC), a devastating disease with limited therapeutic options. Aberrations in the PI3K/PTEN signaling pathway are common in TNBC. However, the therapeutic impact of PI3K inhibitors in TNBC has been limited and the mechanism(s) underlying this lack of efficacy remain elusive. Here, we demonstrate that a large subset of TNBC expresses significant levels of MAPK4, and this expression is critical for driving AKT activation independent of PI3K and promoting TNBC cell and xenograft growth. The ability of MAPK4 to bypass PI3K for AKT activation potentially provides a direct mechanism regulating tumor sensitivity to PI3K inhibition. Accordingly, repressing MAPK4 greatly sensitizes TNBC cells and xenografts to PI3K blockade. Altogether, we conclude that high MAPK4 expression defines a large subset or subtype of TNBC responsive to MAPK4 blockage. Targeting MAPK4 in this subset/subtype of TNBC both represses growth and sensitizes tumors to PI3K blockade.

PI3K inhibitors have limited efficacy in triple negative breast cancer (TNBC). Here, the authors show that MAPK4 activates AKT independent of PI3K and thus promotes tumour growth in a subset of TNBC and that MAPK4 inhibition sensitizes to PI3K blockade in these tumours.’

How a first research experience had an impact on my scientific journey

As I look back to my scientific trajectory on the occasion of being the recipient of the E. B. Wilson Medal of the American Society for Cell Biology, I realize how much an early scientific experience had an impact on my research many years later. The major influence that the first scientific encounters can have in defining a scientist’s path makes the choice of the training environment so important for a future career.

Class I PI3K Provide Lipid Substrate in T Cell Autophagy Through Linked Activity of Inositol Phosphatases

Autophagy, a highly conserved intracellular process, has been identified as a novel mechanism regulating T lymphocyte homeostasis. Herein, we demonstrate that both starvation- and T cell receptor-mediated autophagy induction requires class I phosphatidylinositol-3 kinases to produce PI(3)P. In contrast, common gamma chain cytokines are suppressors of autophagy despite their ability to activate the PI3K pathway. T cells lacking the PI3KI regulatory subunits, p85 and p55, were almost completely unable to activate TCR-mediated autophagy and had concurrent defects in PI(3)P production. Additionally, T lymphocytes upregulate polyinositol phosphatases in response to autophagic stimuli, and the activity of the inositol phosphatases Inpp4 and SHIP are required for TCR-mediated autophagy induction. Addition of exogenous PI(3,4)P₂ can supplement cellular PI(3)P and accelerate the outcome of activation-induced autophagy. TCR-mediated autophagy also requires internalization of the TCR complex, suggesting that this kinase/phosphatase activity is localized in internalized vesicles. Finally, HIV-induced bystander CD4⁺ T cell autophagy is dependent upon PI3KI. Overall, our data elucidate an important pathway linking TCR activation to autophagy, via induction of PI3KI activity and inositol phosphatase upregulation to produce PI(3)P.

The Importance of Being PI3K in the RAS Signaling Network

Ras proteins are essential mediators of a multitude of cellular processes, and its deregulation is frequently associated with cancer appearance, progression, and metastasis. Ras-driven cancers are usually aggressive and difficult to treat. Although the recent Food and Drug Administration (FDA) approval of the first Ras G12C inhibitor is an important milestone, only a small percentage of patients will benefit from it. A better understanding of the context in which Ras operates in different tumor types and the outcomes mediated by each effector pathway may help to identify additional strategies and targets to treat Ras-driven tumors. Evidence emerging in recent years suggests that both oncogenic Ras signaling in tumor cells and non-oncogenic Ras signaling in stromal cells play an essential role in cancer. PI3K is one of the main Ras effectors, regulating important cellular processes such as cell viability or resistance to therapy or angiogenesis upon oncogenic Ras activation. In this review, we will summarize recent advances in the understanding of Ras-dependent activation of PI3K both in physiological conditions and cancer, with a focus on how this signaling pathway contributes to the formation of a tumor stroma that promotes tumor cell proliferation, migration, and spread.

Combined Treatment with JFKD and Gefitinib Overcomes Drug Resistance in Non-Small Cell Lung Cancer

BACKGROUND

Gefitinib is an important drug used to treat Non-Small Cell Lung Cancer (NSCLC) with EGFR activating mutations, but drug resistance restricts its clinical application. In this present study, combined Jin Fu Kang Decoction (JFKD) and gefitinib showed specific cytotoxicity to gefitinib-resistant cancer cells (PC-9/gef).

OBJECTIVE

This study aimed to decipher the molecular mechanism of the JFKD on drug resistance when used together with Gefitinib and to find the contributing bio-active substance(s) in JFKD based on the putative mechanism.

METHODS

To investigate the combined effect of gefitinib and JFKD, in vitro experiments were conducted on the established gefitinib-resistant PC-9 subclone, while in vivo experiments were conducted on the BALB/c nude mice with PC-9/gef xenografts. Western blot was used to evaluate the protein expression, and Ultra-Performance Liquid Chromatography (UPLC) coupled with quadrupole time-offlight Mass Spectrometry (MS) was used to detect the bio-active compounds of JFKD.

RESULTS

The expression of the PTEN-relevant protein p-EGFR, p-Akt in vitro was inhibited more when combined JKFD and gefitinib were used, whereas the activities of PDCD4 and PTEN were increased; remarkably, in vivo experiments showed enhanced tumor growth inhibition when treated with this combination. Due to this combination, the effect on the gefitinib-resistant cell line, one of the JFKD-induced anti-cancer mechanisms, was found. To link the putative mechanism and the anticancer compounds in JFKD, 14 saponins and flavonoids were detected.

CONCLUSION

The results suggested that a promising TCM-participated therapy can be established by the putative mechanism of the combined treatment in resistant NSCLC and screening the contributing bio-active substance(s) in JFKD is meaningful on new TCM formula discovery.

Mechanisms of Resistance to PI3K Inhibitors in Cancer: Adaptive Responses, Drug Tolerance and Cellular Plasticity

The phosphatidylinositol-3-kinase (PI3K) pathway plays a central role in the regulation of several signalling cascades which regulate biological processes such as cellular growth, survival, proliferation, motility and angiogenesis. The hyperactivation of this pathway is linked to tumour progression and is one of the most common events in human cancers. Additionally, aberrant activation of the PI3K pathway has been demonstrated to limit the effectiveness of a number of anti-tumour agents paving the way for the development and implementation of PI3K inhibitors in the clinic. However, the overall effectiveness of these compounds has been greatly limited by inadequate target engagement due to reactivation of the pathway by compensatory mechanisms. Herein, we review the common adaptive responses that lead to reactivation of the PI3K pathway, therapy resistance and potential strategies to overcome these mechanisms of resistance. Furthermore, we highlight the potential role in changes in cellular plasticity and PI3K inhibitor resistance.

Regulation of PTEN translation by PI3K signaling maintains pathway homeostasis

The PI3K pathway regulates cell metabolism, proliferation, and migration, and its dysregulation is common in cancer. We now show that both physiologic and oncogenic activation of PI3K signaling increase the expression of its negative regulator PTEN. This limits the duration of the signal and output of the pathway. Physiologic and pharmacologic inhibition of the pathway reduces PTEN and contributes to the rebound in pathway activity in tumors treated with PI3K inhibitors and limits their efficacy. Regulation of PTEN is due to mTOR/4E-BP1-dependent control of its translation and is lost when 4E-BP1 is deleted. Translational regulation of PTEN is therefore a major homeostatic regulator of physiologic PI3K signaling and plays a role in reducing the pathway activation by oncogenic PIK3CA mutants and the antitumor activity of PI3K pathway inhibitors. However, pathway output is hyperactivated in tumor cells with coexistent PI3K mutation and loss of PTEN function.

MAPK4 promotes prostate cancer by concerted activation of androgen receptor and AKT

Prostate cancer (PCa) is the second leading cause of cancer death in American men. Androgen receptor (AR) signaling is essential for PCa cell growth/survival and remains a key therapeutic target for lethal castration-resistant PCa (CRPC). GATA2 is a pioneer transcription factor crucial for inducing AR expression/activation. We recently reported that MAPK4, an atypical MAPK, promotes tumor progression via noncanonical activation of AKT. Here, we demonstrated that MAPK4 activated AR by enhancing GATA2 transcriptional expression and stabilizing GATA2 protein through repression of GATA2 ubiquitination/degradation. MAPK4 expression correlated with AR activation in human CRPC. Concerted activation of both GATA2/AR and AKT by MAPK4 promoted PCa cell proliferation, anchorage-independent growth, xenograft growth, and castration resistance. Conversely, knockdown of MAPK4 decreased activation of both AR and AKT and inhibited PCa cell and xenograft growth, including castration-resistant growth. Both GATA2/AR and AKT activation were necessary for MAPK4 tumor-promoting activity. Interestingly, combined overexpression of GATA2 plus a constitutively activated AKT was sufficient to drive PCa growth and castration resistance, shedding light on an alternative, MAPK4-independent tumor-promoting pathway in human PCa. We concluded that MAPK4 promotes PCa growth and castration resistance by cooperating parallel pathways of activating GATA2/AR and AKT and that MAPK4 is a novel therapeutic target in PCa, especially CRPC.

The molecular mechanisms mediating class II PI 3-kinase function in cell physiology

The phosphoinositide 3-kinase (PI3K) family of lipid-modifying enzymes plays vital roles in cell signaling and membrane trafficking through the production of 3-phosphorylated phosphoinositides. Numerous studies have analyzed the structure and function of class I and class III PI3Ks. In contrast, we know comparably little about the structure and physiological functions of the class II enzymes. Only recent studies have begun to unravel their roles in development, endocytic and endolysosomal membrane dynamics, signal transduction, and cell migration, while the mechanisms that control their localization and enzymatic activity remain largely unknown. Here, we summarize our current knowledge of the class II PI3Ks and outline open questions related to their structure, enzymatic activity, and their physiological and pathophysiological functions.

Lipid transfer proteins and instructive regulation of lipid kinase activities: Implications for inositol lipid signaling and disease

Cellular membranes are critical platforms for intracellular signaling that involve complex interfaces between lipids and proteins, and a web of interactions between a multitude of lipid metabolic pathways. Membrane lipids impart structural and functional information in this regulatory circuit that encompass biophysical parameters such as membrane thickness and fluidity, as well as chaperoning the interactions of protein binding partners. Phosphatidylinositol and its phosphorylated derivatives, the phosphoinositides, play key roles in intracellular membrane signaling, and these involvements are translated into an impressively diverse set of biological outcomes. The phosphatidylinositol transfer proteins (PITPs) are key regulators of phosphoinositide signaling. Found in a diverse array of organisms from plants, yeast and apicomplexan parasites to mammals, PITPs were initially proposed to be simple transporters of lipids between intracellular membranes. It now appears increasingly unlikely that the soluble versions of these proteins perform such functions within the cell. Rather, these serve to facilitate the activity of intrinsically biologically insufficient inositol lipid kinases and, in so doing, promote diversification of the biological outcomes of phosphoinositide signaling. The central engine for execution of such functions is the lipid exchange cycle that is a fundamental property of PITPs. How PITPs execute lipid exchange remains very poorly understood. Molecular dynamics simulation approaches are now providing the first atomistic insights into how PITPs, and potentially other lipid-exchange/transfer proteins, operate.

PIK3R2/Pik3r2 Activating Mutations Result in Brain Overgrowth and EEG Changes

OBJECTIVE

Mutations in phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) complex have been associated with a broad spectrum of brain and organ overgrowth syndromes. For example, mutations in phosphatidylinositol-3-kinase regulatory subunit 2 (PIK3R2) have been identified in human patients with megalencephaly polymicrogyria polydactyly hydrocephalus (MPPH) syndrome, which includes brain overgrowth. To better understand the pathogenesis of PIK3R2-related mutations, we have developed and characterized a murine model.

METHODS

We generated a knock-in mouse model for the most common human PIK3R2 mutation, p.G373R (p.G367R in mice) using CRISPR/Cas9. The mouse phenotypes, including brain size, seizure activity, cortical lamination, cell proliferation/size/density, interneuron migration, and PI3K pathway activation, were analyzed using standard methodologies. For human patients with PIK3R2 mutations, clinical data (occipitofrontal circumference [OFC] and epilepsy) were retrospectively obtained from our clinical records (published / unpublished).

RESULTS

The PI3K-AKT pathway was hyperactivated in these mice, confirming the p.G367R mutation is an activating mutation in vivo. Similar to human patients with PIK3R2 mutations, these mice have enlarged brains. We found cell size to be increased but not cell numbers. The embryonic brain showed mild defects in cortical lamination, although not observed in the mature brain. Furthermore, electroencephalogram (EEG) recordings from mutant mice showed background slowing and rare seizures, again similar to our observations in human patients.

INTERPRETATION

We have generated a PIK3R2 mouse model that exhibits megalencephaly and EEG changes, both of which overlap with human patients. Our data provide novel insight into the pathogenesis of the human disease caused by PIK3R2 p.G373R mutation. We anticipate this model will be valuable in testing therapeutic options for human patients with MPPH. ANN NEUROL 2020;88:1077-1094.

Imatinib improves insulin resistance and inhibits injury-induced neointimal hyperplasia in high fat diet-fed mice

Imatinib, a PDGF receptor tyrosine kinase inhibitor, has been shown to suppress intimal hyperplasia in different animal models under normal metabolic milieu, diabetic, and/or hypercholesterolemic conditions. However, the impact of imatinib treatment on injury-induced neointimal hyperplasia has not yet been investigated in the setting of insulin resistance without frank diabetes. Using a mouse model of high fat diet (HFD)-induced insulin resistance and guidewire-induced arterial injury, the present study demonstrates that intraperitoneal administration of imatinib (25 mg/kg/day) for ~3 weeks resulted in a marked attenuation of neointimal hyperplasia (intima/media ratio) by ~78% (n = 6-9 per group; P < 0.05). Imatinib treatment also led to significant improvements in key metabolic parameters. In particular, imatinib improved insulin resistance and glucose tolerance, as revealed by complete inhibition of HFD-induced increase in HOMA-IR index and AUC_IPGTT, respectively. In addition, imatinib treatment led to diminutions in HFD-induced increases in plasma total cholesterol and triglycerides by ~73% and ~59%, respectively. Furthermore, imatinib decreased HFD-induced increase in visceral fat accumulation by ~51% (as determined by epididymal white adipose tissue weight). Importantly, imatinib treatment in HFD-fed mice enhanced plasma levels of high-molecular-weight adiponectin by ~2-fold without affecting total adiponectin. However, there were no significant changes in mean arterial pressure in insulin-resistant state or after imatinib exposure, as measured by tail-cuff method. Together, the present findings suggest that targeting PDGF receptor tyrosine kinase using imatinib may provide a realistic treatment option to prevent injury-induced neointimal hyperplasia and diet-induced insulin resistance in obesity.

Role of Protein Kinase CK2 in Aberrant Lipid Metabolism in Cancer

Uncontrolled proliferation is a feature defining cancer and it is linked to the ability of cancer cells to effectively adapt their metabolic needs in response to a harsh tumor environment. Metabolic reprogramming is considered a hallmark of cancer and includes increased glucose uptake and processing, and increased glutamine utilization, but also the deregulation of lipid and cholesterol-associated signal transduction, as highlighted in recent years. In the first part of the review, we will (i) provide an overview of the major types of lipids found in eukaryotic cells and their importance as mediators of intracellular signaling pathways (ii) analyze the main metabolic changes occurring in cancer development and the role of oncogenic signaling in supporting aberrant lipid metabolism and (iii) discuss combination strategies as powerful new approaches to cancer treatment. The second part of the review will address the emerging role of CK2, a conserved serine/threonine protein kinase, in lipid homeostasis with an emphasis regarding its function in lipogenesis and adipogenesis. Evidence will be provided that CK2 regulates these processes at multiple levels. This suggests that its pharmacological inhibition combined with dietary restrictions and/or inhibitors of metabolic targets could represent an effective way to undermine the dependency of cancer cells on lipids to interfere with tumor progression.

Power to see-Drivers of aerobic glycolysis in the mammalian retina: A review

The mammalian retina converts most glucose to lactate rather than catabolizing it completely to carbon dioxide via oxidative phosphorylation, despite the availability of oxygen. This unusual metabolism is known as aerobic glycolysis or the Warburg effect. Molecules and pathways that drive aerobic glycolysis have been identified and thoroughly studied in the context of cancer but remain relatively poorly understood in the retina. Here, we review recent research on the molecular mechanisms that underly aerobic glycolysis in the retina, focusing on key glycolytic enzymes including hexokinase 2 (HK2), pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA). We also discuss the potential involvement of cell signalling and transcriptional pathways including phosphoinositide 3-kinase (PI3K) signalling, fibroblast growth factor receptor (FGFR) signalling, and hypoxia-inducible factor 1 (HIF-1), which have been implicated in driving aerobic glycolysis in the context of cancer.

Phosphatidylinositol 5 Phosphate 4-Kinase Regulates Plasma-Membrane PIP3 Turnover and Insulin Signaling

Phosphatidylinositol 3,4,5-trisphosphate (PIP₃) generation at the plasma membrane is a key event during activation of receptor tyrosine kinases such as the insulin receptor required for normal growth and metabolism. We report that in Drosophila, phosphatidylinositol 5 phosphate 4-kinase (PIP4K) is required to limit PIP₃ levels during insulin receptor activation. Depletion of PIP4K increases the levels of PIP₃ produced in response to insulin stimulation. We find that PIP4K function at the plasma membrane enhances class I phosphoinositide 3-kinase (PI3K) activity, although the catalytic ability of PIP4K to produce phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂] at the plasma membrane is dispensable for this regulation. Animals lacking PIP4K show enhanced insulin signaling-dependent phenotypes and are resistant to the metabolic consequences of a high-sugar diet, highlighting the importance of PIP4K in normal metabolism and development. Thus, PIP4Ks are key regulators of receptor tyrosine kinase signaling with implications for growth factor-dependent processes including tumor growth, T cell activation, and metabolism.

p110δ PI3K as a therapeutic target of solid tumours

From the time of first characterization of PI3K as a heterodimer made up of a p110 catalytic subunit and a regulatory subunit, a wealth of evidence have placed the class IA PI3Ks at the forefront of drug development for the treatment of various diseases including cancer. The p110α isoform was quickly brought at the centre of attention in the field of cancer research by the discovery of cancer-specific gain-of-function mutations in PIK3CA gene in a range of human solid tumours. In contrast, p110δ PI3K was placed into the spotlight of immunity, inflammation and haematologic malignancies because of the preferential expression of this isoform in leucocytes and the rare mutations in PIK3CD gene. The last decade, however, several studies have provided evidence showing that the correlation between the PIK3CA mutations and the response to PI3K inhibition is less clear than originally considered, whereas concurrently an unexpected role of p110δ PI3K in solid tumours has being emerging. While PIK3CD is mostly non-mutated in cancer, the expression levels of p110δ protein seem to act as an intrinsic cancer-causing driver in various solid tumours including breast, prostate, colorectal and liver cancer, Merkel-Cell carcinoma, glioblastoma and neurobalstoma. Furthermore, p110δ selective inhibitors are being studied as potential single agent treatments or as combination partners in attempt to improve cancer immunotherapy, with both strategies to shown great promise for the treatment of several solid tumours. In this review, we discuss the evidence implicating the p110δ PI3K in human solid tumours, their impact on the current state of the field and the potential of using p110δ-selective inhibitors as monotherapy or combined therapy in different cancer contexts.

Significance of PI3K signalling pathway in clear cell renal cell carcinoma in relation to VHL and HIF status

Renal cell carcinoma (RCC) includes diverse tumour types characterised by various genetic abnormalities. The genetic changes, like mutations, deletions and epigenetic alterations, play a crucial role in the modification of signalling networks, tumour pathogenesis and prognosis. The most prevalent RCC type, clear cell RCC (ccRCC), is asymptomatic in the early stages and has a poorer prognosis compared with the papillary and the chromophobe types RCCs. Generally, ccRCC is refractory to chemotherapy and radiation therapy. Loss of von Hippel-Lindau (VHL) gene and upregulation of hypoxia-inducible factors (HIF), the signature of most sporadic ccRCC, promote multiple growth factors. Hence, VHL/HIF and a variety of pathways, including phosphatase and TEnsin homolog on chromosome 10/phosphatidylinositol-3-kinase (PI3K)/AKT, are closely connected and contribute to the ontogeny of ccRCC. In the recent decade, multiple targeting agents have been developed based on blocking major signalling pathways directly or indirectly involved in ccRCC tumour progression, metastasis, angiogenesis and survival. However, most of these drugs have limitations; either metastatic ccRCC develops resistance to these agents, or despite blocking receptors, tumour cells use alternate signalling pathways. This review compiles the state of knowledge about the PI3K/AKT signalling pathway confined to ccRCC and its cross-talks with VHL/HIF pathway.

Rac1 Activity Is Modulated by Huntingtin and Dysregulated in Models of Huntington's Disease

Background:

Previous studies suggest that Huntingtin, the protein mutated in Huntington’s disease (HD), is required for actin based changes in cell morphology, and undergoes stimulus induced targeting to plasma membranes where it interacts with phospholipids involved in cell signaling. The small GTPase Rac1 is a downstream target of growth factor stimulation and PI 3-kinase activity and is critical for actin dependent membrane remodeling.

Objective:

To determine if Rac1 activity is impaired in HD or regulated by normal Huntingtin.

Methods:

Analyses were performed in differentiated control and HD human stem cells and HD Q140/Q140 knock-in mice. Biochemical methods included SDS-PAGE, western blot, immunoprecipitation, affinity chromatography, and ELISA based Rac activity assays.

Results:

Basal Rac1 activity increased following depletion of Huntingtin with Huntingtin specific siRNA in human primary fibroblasts and in human control neuron cultures. Human cells (fibroblasts, neural stem cells, and neurons) with the HD mutation failed to increase Rac1 activity in response to growth factors. Rac1 activity levels were elevated in striatum of 1.5-month-old HD Q140/Q140 mice and in primary embryonic cortical neurons from HD mice. Affinity chromatography analysis of striatal lysates showed that Huntingtin is in a complex with Rac1, p85α subunit of PI 3-kinase, and the actin bundling protein α-actinin and interacts preferentially with the GTP bound form of Rac1. The HD mutation reduced Huntingtin interaction with p85α.

Conclusions:

These findings suggest that Huntingtin regulates Rac1 activity as part of a coordinated response to growth factor signaling and this function is impaired early in HD.

The Effects of Inositol Metabolism in Pregnant Women on Offspring in the North and South of China

Background

Inositol is an essential nutrient for cell growth, survival and embryonic development. Myo-inositol is the predominant form in natural. To investigate the correlation between inositol metabolism and embryonic development, we assessed the metabolic characteristics of myo-inositol, phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) and phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P₃) of pregnant women in the North China (Yangquan and Weihai) and South China (Nanchang and Haikou) China.

Material/Methods

All data were collected by face-to-face interview during pregnant women health visits using a questionnaire. Plasma levels of myo-inositol, PI(4,5)P₂ and PI(3,4,5)P₃ from 89 randomly collected pregnant women were detected by gas chromatography-mass spectrometry and enzyme linked immunosorbent assay.

Results

A total of 400 pregnant women were included in this survey. The plasma levels of myo-inositol and PI(4,5)P₂ in the North China group of pregnant women were significantly higher than that in the South China group (P<0.01). The birth weight of fetuses in the North China group was heavier than that in the South China group (P<0.01). The birth length of fetuses in Yangquan was the longest among the 4 cities (P<0.01). The incidence rate of birth defects was 3.05% in the North China group, and 0.0% in the South China group. In bivariate linear correlation analysis, the body weight correlated with myo-inositol (r=0.5044, P<0.0001), PI(4,5)P₂ (r=0.5950, P<0.0001) and PI(3,4,5)P₃ (r=0.4710, P<0.0001), the body length was correlated with PI(4,5)P₂ (r=0.3114, P=0.0035) and PI(3,4,5)P₃ (r=0.2638, P<0.0130).

Conclusions

The plasma levels of myo-inositol and PI(4,5)P₂ in pregnant women had significant difference between the North and the South of China, which might be correlated with fetal development and birth defects.

Investigating the duality of Inpp4b function in the cellular transformation of mouse fibroblasts

Inositol Polyphosphate 4-Phosphatase, Type II (INPP4B) is a tumour suppressor in breast, ovarian, prostate, thyroid and other cancers, attributed to its ability to reduce oncogenic Akt-signaling. However, emerging studies show that INPP4B also has tumour-promoting properties in cancers including acute myeloid leukemia, colon cancer, melanoma and breast cancer. Together these findings suggest that INPP4B may be a context dependent cancer gene. Whether INPP4B functions solely in a tumour suppressing or tumour promoting manner, or both in non-transformed cells is currently not clear. In this study, consequences of deficiency and overexpression of INPP4B on cellular transformation was investigated using a mouse embryonic fibroblast (MEF) model of cellular transformation. We observed that neither deficiency nor overexpression of INPP4B was sufficient to induce neoplastic transformation, alone or in combination with H-Ras ^V12 or E1A overexpression. However, Inpp4b-deficiency did cooperate with SV40 T-Large-mediated cellular transformation, a finding which was associated with increased phosphorylated-Akt levels. Transformation and phosphorylated-Akt levels were dampened upon overexpression of INPP4B in SV40 T-Large-MEF. Together, our findings support a model where INPP4B function suppresses transformation mediated by SV40 T-Large, but is inconsequential for Ras and E1A mediated transformation.

The role of PI3K-mediated AMPA receptor changes in post-conditioning of propofol in brain protection

BACKGROUND

We aimed to study the role of amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) glutamate receptor 2 (GluR2) subunit trafficking, and activity changes in short-term neuroprotection provided by propofol post-conditioning. We also aimed to determine the role of phosphoinositide-3-kinase (PI3K) in the regulation of these processes.

METHODS

Rats underwent 1 h of focal cerebral ischemia followed by 23 h of reperfusion were randomly divided into 6 groups (n = 36 per group): sham- operation (S), ischemia-reperfusion (IR), propofol (P group, propofol 20 mg/kg/h at the onset of reperfusion for 2 h after 60 min of occlusion), and LY294002 (PI3K non-selective antagonist) + sham (L + S, LY294002 of 1.5 mg/kg was infused 30 min before sham operation), LY294002+ ischemia-reperfusion (L + IR, LY294002 of 1.5 mg/kg was infused 30 min before middle cerebral artery occlusion), LY294002 + IR + propofol (L + P, LY294002 of 1.5 mg/kg was infused 30 min before middle cerebral artery occlusion and propofol 20 mg/kg/h at the onset of reperfusion for 2 h after 60 min of occlusion).

RESULTS

Compared with group IR, rats in group P had significant lower neurologic defect scores and infarct volume. Additionally, consistent with enhanced expression of PI3K-AMPAR GluR2 subunit complex substances in ipsilateral hippocampus, GluR2 subunits showed increased levels in both the plasma and postsynaptic membranes of neurons, while pGluR2 expression was reduced in group P. Furthermore, LY294002, the PI3K non-selective antagonist, blocked those effects.

CONCLUSION

These observations demonstrated that propofol post-conditioning revealed acute neuroprotective role against transient MCAO in rats. The short-term neuroprotective effect was contributed by enhanced GluR2 subunits trafficking to membrane and postsynaptic membranes of neurons, as well as down-regulated the expression of pGluR2 in damaged hippocampus. Finally, the above-mentioned protective mechanism might be contributed by increased combination of PI3K to AMPAR GluR2 subunit, thus maintained the expression and activation of AMPAR GluR2 in the ipsilateral hippocampus.