PLEKHS1 drives PI3Ks and remodels pathway homeostasis in PTEN-null prostate.

The PIP3/PI3K network is a central regulator of metabolism and is frequently activated in cancer, commonly by loss of the PIP3/PI(3,4)P2 phosphatase, PTEN. Despite huge research investment, the drivers of the PI3K network in normal tissues and how they adapt to overactivation are unclear. We find that in healthy mouse prostate PI3K activity is driven by RTK/IRS signaling and constrained by pathway feedback. In the absence of PTEN, the network is dramatically remodeled. A poorly understood YXXM- and PIP3/PI(3,4)P2-binding PH domain-containing adaptor, PLEKHS1, became the dominant activator and was required to sustain PIP3, AKT phosphorylation, and growth in PTEN-null prostate. This was because PLEKHS1 evaded pathway-feedback and experienced enhanced PI3K- and Src-family kinase-dependent phosphorylation of Y258XXM, eliciting PI3K activation. hPLEKHS1 mRNA and activating Y419 phosphorylation of hSrc correlated with PI3K pathway activity in human prostate cancers. We propose that in PTEN-null cells receptor-independent, Src-dependent tyrosine phosphorylation of PLEKHS1 creates positive feedback that escapes homeostasis, drives PIP3 signaling, and supports tumor progression.

Attenuated cerebellar phenotypes in Inpp4a truncation mutants with preserved phosphatase activity.

Phosphoinositides (PIPs) act as intracellular signaling molecules that regulate various cellular processes. Abnormalities in PIP metabolism cause various pathological conditions, including neurodegenerative diseases, cancer and immune disorders. Several neurological diseases with diverse phenotypes, such as ataxia with cerebellar atrophy or intellectual disability without brain malformation, are caused by mutations in INPP4A, which encodes a phosphoinositide phosphatase. We examined two strains of Inpp4a mutant mice with distinct cerebellar phenotypes: the Inpp4aΔEx1,2 mutant exhibited striatal degeneration without cerebellar atrophy, and the Inpp4aΔEx23 mutant exhibited a severe striatal phenotype with cerebellar atrophy. Both strains exhibited reduced expression of Inpp4a mutant proteins in the cerebellum. N-terminal-truncated Inpp4a proteins were expressed from the Inpp4aΔEx1,2 allele by alternative translation initiation and had phosphatase activity for PI(3,4)P2, whereas the Inpp4a mutant protein encoded by Inpp4aΔEx23 completely lacked phosphatase activity. Our results indicate that the diverse phenotypes observed in Inpp4a-related neurological diseases could be due to the varying protein expression levels and retained phosphatase activity in different Inpp4a variants. These findings provide insights into the role of INPP4A mutations in disease pathogenesis and may help to develop personalized therapy.

INPP5D modulates TREM2 loss-of-function phenotypes in a ß-amyloidosis mouse model.

The genetic associations of TREM2 loss-of-function variants with Alzheimer disease (AD) indicate the protective roles of microglia in AD pathogenesis. Functional deficiencies of TREM2 disrupt microglial clustering around amyloid ß (Aß) plaques, impair their transcriptional response to Aß, and worsen neuritic dystrophy. However, the molecular mechanism underlying these phenotypes remains unclear. In this study, we investigated the pathological role of another AD risk gene, INPP5D, encoding a phosphoinositide PI(3,4,5)P3 phosphatase expressed in microglia. In a Tyrobp-deficient TREM2 loss-of-function mouse model, Inpp5d haplodeficiency restored the association of microglia with Aß plaques, partially restored plaque compaction, and astrogliosis, and reduced phosphorylated tau+ dystrophic neurites. Mechanistic analyses suggest that TREM2/TYROBP and INPP5D exert opposing effects on PI(3,4,5)P3 signaling pathways as well as on phosphoproteins involved in the actin assembly. Our results suggest that INPP5D acts downstream of TREM2/TYROBP to regulate the microglial barrier against Aß toxicity, thereby modulates Aß-dependent pathological conversion of tau.

Plasma membrane phosphatidylinositol (4,5)-bisphosphate is critical for determination of epithelial characteristics.

Epithelial cells provide cell-cell adhesion that is essential to maintain the integrity of multicellular organisms. Epithelial cell-characterizing proteins, such as epithelial junctional proteins and transcription factors are well defined. However, the role of lipids in epithelial characterization remains poorly understood. Here we show that the phospholipid phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P2] is enriched in the plasma membrane (PM) of epithelial cells. Epithelial cells lose their characteristics upon depletion of PM PI(4,5)P2, and synthesis of PI(4,5)P2 in the PM results in the development of epithelial-like morphology in osteosarcoma cells. PM localization of PARD3 is impaired by depletion of PM PI(4,5)P2 in epithelial cells, whereas expression of the PM-targeting exocyst-docking region of PARD3 induces osteosarcoma cells to show epithelial-like morphological changes, suggesting that PI(4,5)P2 regulates epithelial characteristics by recruiting PARD3 to the PM. These results indicate that a high level of PM PI(4,5)P2 plays a crucial role in the maintenance of epithelial characteristics.

A cross-sectional study of the correlation between diabetic therapy and serum zinc concentrations.

AIM: Zinc, an essential trace element, has various functions in humans. Zinc deficiency is associated with the elderly, patients with diabetes, and patients with frailty, a common geriatric syndrome. As few studies have reported the effects of anti-diabetic medication on zinc levels, we examined serum zinc concentrations in patients with diabetes and their correlation with anti-diabetic medications, especially in the elderly and patients with frailty, in Japan. METHODS: This cross-sectional study was conducted in 2014 and included 1033 patients with diabetes. Blood samples were taken, and a survey for the 8-item Short Form Health Survey of the Medical Outcomes Study was conducted. RESULTS: Because of renal dysfunction (with an estimated glomerular filtration rate of < 60 mL/min/1.73 m2), 337 patients out of 1033 were excluded. Hypozincemia was observed in 43.8% of the patients with diabetes. In 177 elderly patients with a low physical component summary score, multivariable logistic regression analysis revealed two anti-diabetic medications associated with hypozincemia: GLP-1RA (multivariable-adjusted odds ratio [OR] 0.08, 95% confidence interval [CI] 0.010-0.657, p = 0.019) and metformin (OR 0.415, 95% CI 0.222-0.774, p = 0.006). In addition, metformin had a dose-dependent correlation with zinc levels (R = 0.3067, p < 0.0001). CONCLUSIONS: Oral administration of metformin in the elderly with diabetes and non-progressive renal dysfunction was not associated with hypozincemia, even at high doses. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13340-021-00521-6.

A mass spectrometric method for in-depth profiling of phosphoinositide regioisomers and their disease-associated regulation.

Phosphoinositides are a family of membrane lipids essential for many biological and pathological processes. Due to the existence of multiple phosphoinositide regioisomers and their low intracellular concentrations, profiling these lipids and linking a specific acyl variant to a change in biological state have been difficult. To enable the comprehensive analysis of phosphoinositide phosphorylation status and acyl chain identity, we develop PRMC-MS (Phosphoinositide Regioisomer Measurement by Chiral column chromatography and Mass Spectrometry). Using this method, we reveal a severe skewing in acyl chains in phosphoinositides in Pten-deficient prostate cancer tissues, extracellular mobilization of phosphoinositides upon expression of oncogenic PIK3CA, and a unique profile for exosomal phosphoinositides. Thus, our approach allows characterizing the dynamics of phosphoinositide acyl variants in intracellular and extracellular milieus.

PI4P/PS countertransport by ORP10 at ER-endosome membrane contact sites regulates endosome fission.

Membrane contact sites (MCSs) serve as a zone for nonvesicular lipid transport by oxysterol-binding protein (OSBP)-related proteins (ORPs). ORPs mediate lipid countertransport, in which two distinct lipids are transported counterdirectionally. How such lipid countertransport controls specific biological functions, however, remains elusive. We report that lipid countertransport by ORP10 at ER-endosome MCSs regulates retrograde membrane trafficking. ORP10, together with ORP9 and VAP, formed ER-endosome MCSs in a phosphatidylinositol 4-phosphate (PI4P)-dependent manner. ORP10 exhibited a lipid exchange activity toward its ligands, PI4P and phosphatidylserine (PS), between liposomes in vitro, and between the ER and endosomes in situ. Cell biological analysis demonstrated that ORP10 supplies a pool of PS from the ER, in exchange for PI4P, to endosomes where the PS-binding protein EHD1 is recruited to facilitate endosome fission. Our study highlights a novel lipid exchange at ER-endosome MCSs as a nonenzymatic PI4P-to-PS conversion mechanism that organizes membrane remodeling during retrograde membrane trafficking.

Increased fatty acyl saturation of phosphatidylinositol phosphates in prostate cancer progression.

Phosphoinositides (PIPs) participate in many cellular processes, including cancer progression; however, the metabolic features of PIPs associated with prostate cancer (PCa) are unknown. We investigated PIPs profiles in PTEN-deficient prostate cancer cell lines, human prostate tissues obtained from patients with PCa and benign prostate hyperplasia (BPH) specimens using mass spectrometry. In immortalized normal human prostate PNT1B cells, PTEN deficiency increased phosphatidylinositol tris-phosphate (PIP3) and decreased phosphatidylinositol mono- and bis-phosphate (PIP1 and PIP2), consistent with PTEN's functional role as a PI(3,4,5)P3 3-phosphatase. In human prostate tissues, levels of total (sum of all acyl variants) phosphatidylinositol (PI) and PIP1 in PCa were significantly higher than in BPH, whereas PIP2 and PIP3 contents were significantly lower than in BPH. PCa patients had significantly higher proportion of PI, PIP1, and PIP2 with 0-2 double bonds in acyl chains than BPH patients. In subgroup analyses based on PCa aggressiveness, mean total levels of PI with 0-2 double bonds in acyl chains were significantly higher in patients with pathological stage T3 than in those with pathological stage T2. These data indicate that alteration of PIPs level and the saturation of acyl chains may be associated with the development and aggressiveness of prostate cancer, although it is unknown whether this alteration is causative.

PTEN Regulates PI(3,4)P2 Signaling Downstream of Class I PI3K.

The PI3K signaling pathway regulates cell growth and movement and is heavily mutated in cancer. Class I PI3Ks synthesize the lipid messenger PI(3,4,5)P3. PI(3,4,5)P3 can be dephosphorylated by 3- or 5-phosphatases, the latter producing PI(3,4)P2. The PTEN tumor suppressor is thought to function primarily as a PI(3,4,5)P3 3-phosphatase, limiting activation of this pathway. Here we show that PTEN also functions as a PI(3,4)P2 3-phosphatase, both in vitro and in vivo. PTEN is a major PI(3,4)P2 phosphatase in Mcf10a cytosol, and loss of PTEN and INPP4B, a known PI(3,4)P2 4-phosphatase, leads to synergistic accumulation of PI(3,4)P2, which correlated with increased invadopodia in epidermal growth factor (EGF)-stimulated cells. PTEN deletion increased PI(3,4)P2 levels in a mouse model of prostate cancer, and it inversely correlated with PI(3,4)P2 levels across several EGF-stimulated prostate and breast cancer lines. These results point to a role for PI(3,4)P2 in the phenotype caused by loss-of-function mutations or deletions in PTEN.

Myeloid cell-specific inositol polyphosphate-4-phosphatase type I knockout mice impair bacteria clearance in a murine peritonitis model.

Phosphatidylinositol 3-kinase (PI3K)/Akt signaling has been implicated in the anti-inflammatory response in a mouse model of endotoxemia and sepsis. The present study focused on the role of inositol polyphosphate-4-phosphatase type I (Inpp4a), which dephosphorylates PtdIns(3,4)P2 to PtdIns(3)P, in bacterial infections. We prepared myeloid cell-specific Inpp4a-conditional knockout mice. Macrophages from these mice showed increased Akt phosphorylation and reduced production of inflammatory cytokines in response to LPS or Escherichia coli in vitro The Inpp4a knockout mice survived for a shorter time than wild type mice after i.p. infection with E. coli, with less production of inflammatory cytokines. Additionally, E. coli clearance from blood and lung was significantly impaired in the knockout mice. A likely mechanism is that the Inpp4a-catalyzed dephosphorylation of PtdIns(3,4)P2 down-regulates Akt pathways, which, in turn, increases the production of inflammatory mediators. This mechanism at least fits the decreased E. coli clearance and short survival in the Inpp4a knockout mice.

Inositol Polyphosphate-4-Phosphatase Type I Negatively Regulates Phagocytosis via Dephosphorylation of Phagosomal PtdIns(3,4)P2.

Phagocytosis is a highly conserved process whereby phagocytic cells engulf pathogens and apoptotic bodies. The present study focused on the role of inositol polyphosphate-4-phosphatase type I (Inpp4a) in phagocytosis. Raw264.7 cells that express shRNA against Inpp4a (shInpp4a cells) showed significantly increased phagocytic activity. The introduction of shRNA-resistant human Inpp4a abolished this increase. Macrophages from Inpp4a knockout mice showed similar increases in the phagocytic activity. Inpp4a was recruited to the phagosome membrane by a mechanism other than the direct interaction with Rab5. PtdIns(3,4)P2 increased on the phagosome of shInpp4a cells, while PtdIns(3)P significantly decreased. The results indicate that Inpp4a negatively regulates the phagocytic activity of macrophages as a member of the sequential dephosphorylation system that metabolizes phagosomal PtdIns(3,4,5)P3 to PtdIns(3)P.

In Vivo Role of INPP4B in Tumor and Metastasis Suppression through Regulation of PI3K-AKT Signaling at Endosomes.

UNLABELLED: The phosphatases PTEN and INPP4B have been proposed to act as tumor suppressors by antagonizing PI3K-AKT signaling and are frequently dysregulated in human cancer. Although PTEN has been extensively studied, little is known about the underlying mechanisms by which INPP4B exerts its tumor-suppressive function and its role in tumorigenesis in vivo. Here, we show that a partial or complete loss of Inpp4b morphs benign thyroid adenoma lesions in Pten heterozygous mice into lethal and metastatic follicular-like thyroid cancer (FTC). Importantly, analyses of human thyroid cancer cell lines and specimens reveal INPP4B downregulation in FTC. Mechanistically, we find that INPP4B, but not PTEN, is enriched in the early endosomes of thyroid cancer cells, where it selectively inhibits AKT2 activation and in turn tumor proliferation and anchorage-independent growth. We therefore identify INPP4B as a novel tumor suppressor in FTC oncogenesis and metastasis through localized regulation of the PI3K-AKT pathway at the endosomes. SIGNIFICANCE: Although both PTEN and INPP4B can inhibit PI3K-AKT signaling through their lipid phosphatase activities, here we demonstrate lack of an epistatic relationship between the two tumor suppressors. Instead, the qualitative regulation of PI3K-AKT2 signaling by INPP4B provides a mechanism for their cooperation in suppressing thyroid tumorigenesis and metastasis.

INPP4B Is a PtdIns(3,4,5)P3 Phosphatase That Can Act as a Tumor Suppressor.

UNLABELLED: Inositol polyphosphate 4-phosphatase B (INPP4B) has been identified as a tumor suppressor mutated in human breast, ovary, and prostate cancers. The molecular mechanism underlying INPP4B's tumor-suppressive role is currently unknown. Here, we demonstrate that INPP4B restrains tumor development by dephosphorylating the PtdIns(3,4,5)P3 that accumulates in situations of PTEN deficiency. In vitro, INPP4B directly dephosphorylates PtdIns(3,4,5)P3. In vivo, neither inactivation of Inpp4b (Inpp4b(Δ/Δ)) nor heterozygous deletion of Pten (Pten(+/-)) in mice causes thyroid abnormalities, but a combination of these mutations induces malignant thyroid cancers with lung metastases. At the molecular level, simultaneous deletion of Inpp4b and Pten synergistically increases PtdIns(3,4,5)P3 levels and activates AKT downstream signaling proteins in thyroid cells. We propose that the PtdIns(3,4,5)P3 phosphatase activity of INPP4B can function as a "back-up" mechanism when PTEN is deficient, making INPP4B a potential novel therapeutic target for PTEN-deficient or PIK3CA-activated cancers. SIGNIFICANCE: Although INPP4B expression is reduced in several types of human cancers, our work on Inpp4B-deficient mice provides the first evidence that INPP4B is a bona fide tumor suppressor whose function is particularly important in situations of PTEN deficiency. Our biochemical data demonstrate that INPP4B directly dephosphorylates PtdIns(3,4,5)P3.

Loss of INPP4B causes a DNA repair defect through loss of BRCA1, ATM and ATR and can be targeted with PARP inhibitor treatment.

Treatment options for ovarian cancer patients remain limited and overall survival is less than 50% despite recent clinical advances. The lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) has been described as a tumor suppressor in the PI3K/Akt pathway with loss of expression found most pronounced in breast, ovarian cancer and melanoma. Using microarray technology we identified a DNA repair defect in INPP4B-deficient cells, which we further characterized by comet assays and quantification of γH2AX, RAD51 and 53BP1 foci formation. INPP4B loss resulted in significantly increased sensitivity towards PARP inhibition, comparable to loss of BRCA1 in two- and three-dimensional in vitro models, as well as in in vivo xenograft models. Mechanistically, we discovered that INPP4B forms a protein complex with the key players of DNA repair, ATR and BRCA1, in GST pulldown and 293T overexpression assays, and INPP4B loss affects BRCA1, ATM and ATR protein stability resulting in the observed DNA repair defect. Given that INPP4B loss has been found in 40% of ovarian cancer patients, this study provides the rationale for establishing INPP4B as a biomarker of PARP inhibitor response, and consequently offers novel therapeutic options for a significant subset of patients. Loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

Critical roles of type III phosphatidylinositol phosphate kinase in murine embryonic visceral endoderm and adult intestine.

The metabolism of membrane phosphoinositides is critical for a variety of cellular processes. Phosphatidylinositol-3,5-bisphosphate [PtdIns(3,5)P(2)] controls multiple steps of the intracellular membrane trafficking system in both yeast and mammalian cells. However, other than in neuronal tissues, little is known about the physiological functions of PtdIns(3,5)P(2) in mammals. Here, we provide genetic evidence that type III phosphatidylinositol phosphate kinase (PIPKIII), which produces PtdIns(3,5)P(2), is essential for the functions of polarized epithelial cells. PIPKIII-null mouse embryos die by embryonic day 8.5 because of a failure of the visceral endoderm to supply the epiblast with maternal nutrients. Similarly, although intestine-specific PIPKIII-deficient mice are born, they fail to thrive and eventually die of malnutrition. At the mechanistic level, we show that PIPKIII regulates the trafficking of proteins to a cell's apical membrane domain. Importantly, mice with intestine-specific deletion of PIPKIII exhibit diarrhea and bloody stool, and their gut epithelial layers show inflammation and fibrosis, making our mutants an improved model for inflammatory bowel diseases. In summary, our data demonstrate that PIPKIII is required for the structural and functional integrity of two different types of polarized epithelial cells and suggest that PtdIns(3,5)P(2) metabolism is an unexpected and critical link between membrane trafficking in intestinal epithelial cells and the pathogenesis of inflammatory bowel disease.

A Ca(2+)-dependent signalling circuit regulates influenza A virus internalization and infection.

Various viruses enter host cells via endocytosis, but the molecular mechanisms underlying the specific internalization pathways remain unclear. Here we show that influenza A viruses (IAVs) enter cells via redundant pathways of clathrin-mediated and clathrin-independent endocytosis, with intracellular Ca(2+) having a central role in regulation of both pathways by activating a signalling axis comprising RhoA, Rho-kinase, phosphatidylinositol 4-phosphate 5-kinase (PIP5K) and phospholipase C (PLC). IAV infection induces oscillations in the cytosolic Ca(2+) concentration of host cells, the prevention of which markedly attenuates virus internalization and infection. The small GTPase RhoA is found both to function downstream of the virus-induced Ca(2+) response and itself to induce Ca(2+) oscillations in a manner dependent on Rho-kinase and subsequent PIP5K-PLC signalling. This signalling circuit regulates both clathrin-mediated and clathrin-independent endocytosis during virus infection and seems to constitute a key mechanism for regulation of IAV internalization and infection.

Construction of a global pain systems network highlights phospholipid signaling as a regulator of heat nociception.

The ability to perceive noxious stimuli is critical for an animal's survival in the face of environmental danger, and thus pain perception is likely to be under stringent evolutionary pressure. Using a neuronal-specific RNAi knock-down strategy in adult Drosophila, we recently completed a genome-wide functional annotation of heat nociception that allowed us to identify α2δ3 as a novel pain gene. Here we report construction of an evolutionary-conserved, system-level, global molecular pain network map. Our systems map is markedly enriched for multiple genes associated with human pain and predicts a plethora of novel candidate pain pathways. One central node of this pain network is phospholipid signaling, which has been implicated before in pain processing. To further investigate the role of phospholipid signaling in mammalian heat pain perception, we analysed the phenotype of PIP5Kα and PI3Kγ mutant mice. Intriguingly, both of these mice exhibit pronounced hypersensitivity to noxious heat and capsaicin-induced pain, which directly mapped through PI3Kγ kinase-dead knock-in mice to PI3Kγ lipid kinase activity. Using single primary sensory neuron recording, PI3Kγ function was mechanistically linked to a negative regulation of TRPV1 channel transduction. Our data provide a systems map for heat nociception and reinforces the extraordinary conservation of molecular mechanisms of nociception across different species.

Blockade of class IB phosphoinositide-3 kinase ameliorates obesity-induced inflammation and insulin resistance.

Obesity and insulin resistance, the key features of metabolic syndrome, are closely associated with a state of chronic, low-grade inflammation characterized by abnormal macrophage infiltration into adipose tissues. Although it has been reported that chemokines promote leukocyte migration by activating class IB phosphoinositide-3 kinase (PI3Kγ) in inflammatory states, little is known about the role of PI3Kγ in obesity-induced macrophage infiltration into tissues, systemic inflammation, and the development of insulin resistance. In the present study, we used murine models of both diet-induced and genetically induced obesity to examine the role of PI3Kγ in the accumulation of tissue macrophages and the development of obesity-induced insulin resistance. Mice lacking p110γ (Pik3cg(-/-)), the catalytic subunit of PI3Kγ, exhibited improved systemic insulin sensitivity with enhanced insulin signaling in the tissues of obese animals. In adipose tissues and livers of obese Pik3cg(-/-) mice, the numbers of infiltrated proinflammatory macrophages were markedly reduced, leading to suppression of inflammatory reactions in these tissues. Furthermore, bone marrow-specific deletion and pharmacological blockade of PI3Kγ also ameliorated obesity-induced macrophage infiltration and insulin resistance. These data suggest that PI3Kγ plays a crucial role in the development of both obesity-induced inflammation and systemic insulin resistance and that PI3Kγ can be a therapeutic target for type 2 diabetes.

The PtdIns(3,4)P(2) phosphatase INPP4A is a suppressor of excitotoxic neuronal death.

Phosphorylated derivatives of phosphatidylinositol, collectively referred to as phosphoinositides, occur in the cytoplasmic leaflet of cellular membranes and regulate activities such as vesicle transport, cytoskeletal reorganization and signal transduction. Recent studies have indicated an important role for phosphoinositide metabolism in the aetiology of diseases such as cancer, diabetes, myopathy and inflammation. Although the biological functions of the phosphatases that regulate phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) have been well characterized, little is known about the functions of the phosphatases regulating the closely related molecule phosphatidylinositol-3,4-bisphosphate (PtdIns(3,4)P(2)). Here we show that inositol polyphosphate phosphatase 4A (INPP4A), a PtdIns(3,4)P(2) phosphatase, is a suppressor of glutamate excitotoxicity in the central nervous system. Targeted disruption of the Inpp4a gene in mice leads to neurodegeneration in the striatum, the input nucleus of the basal ganglia that has a central role in motor and cognitive behaviours. Notably, Inpp4a(-/-) mice show severe involuntary movement disorders. In vitro, Inpp4a gene silencing via short hairpin RNA renders cultured primary striatal neurons vulnerable to cell death mediated by N-methyl-d-aspartate-type glutamate receptors (NMDARs). Mechanistically, INPP4A is found at the postsynaptic density and regulates synaptic NMDAR localization and NMDAR-mediated excitatory postsynaptic current. Thus, INPP4A protects neurons from excitotoxic cell death and thereby maintains the functional integrity of the brain. Our study demonstrates that PtdIns(3,4)P(2), PtdIns(3,4,5)P(3) and the phosphatases acting on them can have distinct regulatory roles, and provides insight into the unique aspects and physiological significance of PtdIns(3,4)P(2) metabolism. INPP4A represents, to our knowledge, the first signalling protein with a function in neurons to suppress excitotoxic cell death. The discovery of a direct link between PtdIns(3,4)P(2) metabolism and the regulation of neurodegeneration and involuntary movements may aid the development of new approaches for the treatment of neurodegenerative disorders.