Role of phosphoinositide 3-kinase regulatory isoforms in development and actin rearrangement

Non-catalytic role of phosphoinositide 3-kinase in mesenchymal cell migration through non-canonical induction of p85β/AP2-mediated endocytosis

Class IA phosphoinositide 3-kinase (PI3K) galvanizes fundamental cellular processes such as migration, proliferation, and differentiation. To enable these multifaceted roles, the catalytic subunit p110 utilizes the multi-domain, regulatory subunit p85 through its inter SH2 domain (iSH2). In cell migration, its product PI(3,4,5)P3 generates locomotive activity. While non-catalytic roles are also implicated, underlying mechanisms and their relationship to PI(3,4,5)P3 signaling remain elusive. Here, we report that a disordered region of iSH2 contains AP2 binding motifs which can trigger clathrin and dynamin-mediated endocytosis independent of PI3K catalytic activity. The AP2 binding motif mutants of p85 aberrantly accumulate at focal adhesions and increase both velocity and persistency in fibroblast migration. We thus propose the dual functionality of PI3K in the control of cell motility, catalytic and non-catalytic, arising distinctly from juxtaposed regions within iSH2.

Therapeutic Role of Synthetic Lethality in ARID1A-Deficient Malignancies

AT-rich interaction domain 1A (ARID1A), a mammalian switch/sucrose nonfermenting complex subunit, modulates several cellular processes by regulating chromatin accessibility. It is encoded by ARID1A, an immunosuppressive gene frequently disrupted in a many tumors, affecting the proliferation, migration, and invasion of cancer cells. Targeting molecular pathways and epigenetic regulation associated with ARID1A loss, such as inhibiting the PI3K/AKT pathway or modulating Wnt/β-catenin signaling, may help suppress tumor growth and progression. Developing epigenetic drugs like histone deacetylase or DNA methyltransferase inhibitors could restore normal chromatin structure and function in cells with ARID1A loss. As ARID1A deficiency correlates with enhanced tumor mutability, microsatellite instability, high tumor mutation burden, increased programmed death-ligand 1 expression, and T-lymphocyte infiltration, ARID1A-deficient cells can be a potential therapeutic target for immune checkpoint inhibitors that warrants further exploration. In this review, we discuss the role of ARID1A in carcinogenesis, its crosstalk with other signaling pathways, and strategies to make ARID1A-deficient cells a potential therapeutic target for patients with cancer.

Non-catalytic role of phosphoinositide 3-kinase in mesenchymal cell migration through non-canonical induction of p85β/AP-2-mediated endocytosis

Class IA phosphoinositide 3-kinase (PI3K) galvanizes fundamental cellular processes such as migration, proliferation, and differentiation. To enable multifaceted roles, the catalytic subunit p110 utilizes a multi-domain, regulatory subunit p85 through its inter SH2 domain (iSH2). In cell migration, their product PI(3,4,5)P3 generates locomotive activity. While non-catalytic roles are also implicated, underlying mechanisms and its relationship to PI(3,4,5)P3 signaling remain elusive. Here, we report that a disordered region of iSH2 contains previously uncharacterized AP-2 binding motifs which can trigger clathrin and dynamin-mediated endocytosis independent of PI3K catalytic activity. The AP-2 binding motif mutants of p85 aberrantly accumulate at focal adhesions and upregulate both velocity and persistency in fibroblast migration. We thus propose the dual functionality of PI3K in the control of cell motility, catalytic and non-catalytic, arising distinctly from juxtaposed regions within iSH2.

Non-catalytic role of phosphoinositide 3-kinase in mesenchymal cell migration through non-canonical induction of p85β/AP-2-mediated endocytosis

Class IA phosphoinositide 3-kinase (PI3K) galvanizes fundamental cellular processes such as migration, proliferation, and differentiation. To enable multifaceted roles, the catalytic subunit p110 utilizes a multidomain, regulatory subunit p85 through its inter SH2 domain (iSH2). In cell migration, their product PI(3,4,5)P3 generates locomotive activity. While non-catalytic roles are also implicated, underlying mechanisms and its relationship to PI(3,4,5)P3 signaling remain elusive. Here, we report that a disordered region of iSH2 contains previously uncharacterized AP-2 binding motifs which can trigger clathrin and dynamin-mediated endocytosis independent of PI3K catalytic activity. The AP-2 binding motif mutants of p85 aberrantly accumulate at focal adhesions and upregulate both velocity and persistency in fibroblast migration. We thus propose the dual functionality of PI3K in the control of cell motility, catalytic and non-catalytic, arising distinctly from juxtaposed regions within iSH2.

ARID1A-deficient bladder cancer is dependent on PI3K signaling and sensitive to EZH2 and PI3K inhibitors

Metastatic urothelial carcinoma is generally incurable with current systemic therapies. Chromatin modifiers are frequently mutated in bladder cancer, with ARID1A-inactivating mutations present in about 20% of tumors. EZH2, a histone methyltransferase, acts as an oncogene that functionally opposes ARID1A. In addition, PI3K signaling is activated in more than 20% of bladder cancers. Using a combination of in vitro and in vivo data, including patient-derived xenografts, we show that ARID1A-mutant tumors were more sensitive to EZH2 inhibition than ARID1A WT tumors. Mechanistic studies revealed that (a) ARID1A deficiency results in a dependency on PI3K/AKT/mTOR signaling via upregulation of a noncanonical PI3K regulatory subunit, PIK3R3, and downregulation of MAPK signaling and (b) EZH2 inhibitor sensitivity is due to upregulation of PIK3IP1, a protein inhibitor of PI3K signaling. We show that PIK3IP1 inhibited PI3K signaling by inducing proteasomal degradation of PIK3R3. Furthermore, ARID1A-deficient bladder cancer was sensitive to combination therapies with EZH2 and PI3K inhibitors in a synergistic manner. Thus, our studies suggest that bladder cancers with ARID1A mutations can be treated with inhibitors of EZH2 and/or PI3K and revealed mechanistic insights into the role of noncanonical PI3K constituents in bladder cancer biology.

Interrelation between α-Cardiac Actin Treadmilling and Myocardin-Related Transcription Factor-A Nuclear Shuttling in Cardiomyocytes

Myocardin-related transcription factors (MRTFs) play a central role in the regulation of actin expression and cytoskeletal dynamics that are controlled by Rho GTPases. SRF is a ubiquitous transcription factor strongly expressed in muscular tissues. The depletion of SRF in the adult mouse heart leads to severe dilated cardiomyopathy associated with the down-regulation of target genes encoding sarcomeric proteins including α-cardiac actin. The regulatory triad, composed of SRF, its cofactor MRTFA and actin, plays a major role in the coordination of the nuclear transcriptional response to adapt actin filament dynamics associated with changes in cell shape, and contractile and migratory activities. Most of the knowledge on the regulation of the SRF–MRTF–Actin axis has been obtained in non-muscle cells with α-actin and smooth muscle cells with α-smooth actin. Here, we visualized for the first time by a time-lapse video, the nucleocytoplasmic shuttling of MRTFA induced by serum or pro-hypertrophic agonists such as angiotensin II, phenylephrine and endothelin-1, using an MRTFA-GFP adenovirus in cultures of neonatal rat cardiomyocytes. We showed that an inhibitor of the RhoA/ROCK signaling pathway leads to an α-cardiac actin polymerization disruption and inhibition of MRTFA nucleocytoplasmic shuttling. Moreover, inhibition of the PI3K/Akt signaling pathway also prevents the entry of MRTFA into the nuclei. Our findings point out a central role of the SRF–MRTFA–actin axis in cardiac remodeling.

Differential regulation of cranial and cardiac neural crest by serum response factor and its cofactors

Serum response factor (SRF) is an essential transcription factor that influences many cellular processes including cell proliferation, migration, and differentiation. SRF directly regulates and is required for immediate early gene (IEG) and actin cytoskeleton-related gene expression. SRF coordinates these competing transcription programs through discrete sets of cofactors, the ternary complex factors (TCFs) and myocardin-related transcription factors (MRTFs). The relative contribution of these two programs to in vivo SRF activity and mutant phenotypes is not fully understood. To study how SRF utilizes its cofactors during development, we generated a knock-in SrfaI allele in mice harboring point mutations that disrupt SRF-MRTF-DNA complex formation but leave SRF-TCF activity unaffected. Homozygous SrfaI/aI mutants die at E10.5 with notable cardiovascular phenotypes, and neural crest conditional mutants succumb at birth to defects of the cardiac outflow tract but display none of the craniofacial phenotypes associated with complete loss of SRF in that lineage. Our studies further support an important role for MRTF mediating SRF function in cardiac neural crest and suggest new mechanisms by which SRF regulates transcription during development.

The Crossroads between RAS and RHO Signaling Pathways in Cellular Transformation, Motility and Contraction

Ras and Rho proteins are GTP-regulated molecular switches that control multiple signaling pathways in eukaryotic cells. Ras was among the first identified oncogenes, and it appears mutated in many forms of human cancer. It mainly promotes proliferation and survival through the MAPK pathway and the PI3K/AKT pathways, respectively. However, the myriad proteins close to the plasma membrane that activate or inhibit Ras make it a major regulator of many apparently unrelated pathways. On the other hand, Rho is weakly oncogenic by itself, but it critically regulates microfilament dynamics; that is, actin polymerization, disassembly and contraction. Polymerization is driven mainly by the Arp2/3 complex and formins, whereas contraction depends on myosin mini-filament assembly and activity. These two pathways intersect at numerous points: from Ras-dependent triggering of Rho activators, some of which act through PI3K, to mechanical feedback driven by actomyosin action. Here, we describe the main points of connection between the Ras and Rho pathways as they coordinately drive oncogenic transformation. We emphasize the biochemical crosstalk that drives actomyosin contraction driven by Ras in a Rho-dependent manner. We also describe possible routes of mechanical feedback through which myosin II activation may control Ras/Rho activation.

Insulin-PI3K signalling: an evolutionarily insulated metabolic driver of cancer

Cancer is driven by incremental changes that accumulate, eventually leading to oncogenic transformation. Although genetic alterations dominate the way cancer biologists think about oncogenesis, growing evidence suggests that systemic factors (for example, insulin, oestrogen and inflammatory cytokines) and their intracellular pathways activate oncogenic signals and contribute to targetable phenotypes. Systemic factors can have a critical role in both tumour initiation and therapeutic responses as increasingly targeted and personalized therapeutic regimens are used to treat patients with cancer. The endocrine system controls cell growth and metabolism by providing extracellular cues that integrate systemic nutrient status with cellular activities such as proliferation and survival via the production of metabolites and hormones such as insulin. When insulin binds to its receptor, it initiates a sequence of phosphorylation events that lead to activation of the catalytic activity of phosphoinositide 3-kinase (PI3K), a lipid kinase that coordinates the intake and utilization of glucose, and mTOR, a kinase downstream of PI3K that stimulates transcription and translation. When chronically activated, the PI3K pathway can drive malignant transformation. Here, we discuss the insulin-PI3K signalling cascade and emphasize its roles in normal cells (including coordinating cell metabolism and growth), highlighting the features of this network that make it ideal for co-option by cancer cells. Furthermore, we discuss how this signalling network can affect therapeutic responses and how novel metabolic-based strategies might enhance treatment efficacy for cancer.

Dysregulated actin dynamics in activated PI3Kδ syndrome

Activated PI3Kδ syndrome (APDS) Type I results from gain-of-function mutations in PIK3CD, which encodes the p110δ subunit of PI3Kδ. Abnormal actin dynamics have been hypothesized to contribute to the lymphopenia associated with this disease but have not been studied in patients with APDS. We report a patient with APDS who had widespread necrotic skin lesions that were responsive specifically to immunosuppressive therapy. EBV-transformed lymphoblastoid cells (EBV-LCLs) from patients with APDS exhibit increased polymerized actin and increased apoptosis, suggesting a contribution of impaired actin dynamics to this disease.

Synthesis and Evaluation of Novel 2H-Benzo[e]-[1,2,4]thiadiazine 1,1-Dioxide Derivatives as PI3Kδ Inhibitors

In previous work, we applied the rotation-limiting strategy and introduced a substituent at the 3-position of the pyrazolo [3,4-d]pyrimidin-4-amine as the affinity element to interact with the deeper hydrophobic pocket, discovered a series of novel quinazolinones as potent PI3Kδ inhibitors. Among them, the indole derivative 3 is one of the most selective PI3Kδ inhibitors and the 3,4-dimethoxyphenyl derivative 4 is a potent and selective dual PI3Kδ/γ inhibitor. In this study, we replaced the carbonyl group in the quinazolinone core with a sulfonyl group, designed a series of novel 2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide derivatives as PI3Kδ inhibitors. After the reduction of nitro group in N-(2,6-dimethylphenyl)-2-nitrobenzenesulfonamide 5 and N-(2,6-dimethylphenyl)-2-nitro-5-fluorobenzenesulfonamide 6, the resulting 2-aminobenzenesulfonamides were reacted with trimethyl orthoacetate to give the 3-methyl-2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide derivatives. After bromination of the 3-methyl group, the nucleophilic substitution with the 3-iodo-1H-pyrazolo[3,4-d]pyrimidin-4-amine provided the respective iodide derivatives, which were further reacted with a series of arylboronic acids via Suzuki coupling to furnish the 2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide derivatives 15a-J and 16a-d. In agreement with the quinazolinone derivatives, the introduction of a 5-indolyl or 3,4-dimethoxyphenyl at the affinity pocket generated the most potent analogues 15a and 15b with the IC₅₀ values of 217 to 266 nM, respectively. In comparison with the quinazolinone lead compounds 3 and 4, these 2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide derivatives exhibited much decreased PI3Kδ inhibitory potency, but maintained the high selectivity over other PI3K isoforms. Unlike the quinazolinone lead compound 4 that was a dual PI3Kδ/γ inhibitor, the benzthiadiazine 1,1-dioxide 15b with the same 3,4-dimethoxyphenyl moiety was more than 21-fold selective over PI3Kγ. Moreover, the introducing of a fluorine atom at the 7-position of the 2H-benzo[e][1,2,4]thiadiazine 1,1-dioxide core, in general, was not favored for the PI3Kδ inhibitory activity. In agreement with their high PI3Kδ selectivity, 15a and 15b significantly inhibited the SU-DHL-6 cell proliferation.

Design, synthesis and biological evaluation of novel chromeno[4,3-c]pyrazol-4(2H)-one derivates containing sulfonamido as potential PI3Kα inhibitors

A series of novel chromeno[4,3-c]pyrazol-4(2H)-one derivates contained sulfonamido were designed and synthesized, and their anticancer effects in vitro was evaluated to develop some new PI3Kα inhibitors. Most of desired compounds exhibited the better antiproliferative activities against four cancer cell lines than that of LY294002. Out of them, compound 4o displayed the potent antiproliferative activity and high selectivity against the PI3Kα protein and it can induce apoptosis of HCT116 in a dose-dependent manner. Western blot assay indicated that compound 4o obviously down-regulated expression of p-Akt (S473). Molecular docking was performed to clarify the possible binding mode between compound 4o and PI3Kα. All these results indicated that compound 4o could be a potential inhibitor of PI3Kα.

The Opposing Roles of PIK3R1/p85α and PIK3R2/p85β in Cancer

Dysregulation of the PI3K/PTEN pathway is a frequent event in cancer, and PIK3CA and PTEN are the most commonly mutated genes after TP53. PIK3R1 is the predominant regulatory isoform of PI3K. PIK3R2 is an ubiquitous isoform that has been so far overlooked, but data from The Cancer Genome Atlas shows that increased expression of PIK3R2 is also frequent in cancer. In contrast to PIK3R1, which is a tumor-suppressor gene, PIK3R2 is an oncogene. We review here the opposing roles of PIK3R1 and PIK3R2 in cancer, the regulatory mechanisms that control PIK3R2 expression, and emerging therapeutic approaches targeting PIK3R2.

MAP kinase and autophagy pathways cooperate to maintain RAS mutant cancer cell survival

Oncogenic mutations in the small GTPase KRAS are frequently found in human cancers, and, currently, there are no effective targeted therapies for these tumors. Using a combinatorial siRNA approach, we analyzed a panel of KRAS mutant colorectal and pancreatic cancer cell lines for their dependency on 28 gene nodes that represent canonical RAS effector pathways and selected stress response pathways. We found that RAF node knockdown best differentiated KRAS mutant and KRAS WT cancer cells, suggesting RAF kinases are key oncoeffectors for KRAS addiction. By analyzing all 376 pairwise combination of these gene nodes, we found that cotargeting the RAF, RAC, and autophagy pathways can improve the capture of KRAS dependency better than targeting RAF alone. In particular, codepletion of the oncoeffector kinases BRAF and CRAF, together with the autophagy E1 ligase ATG7, gives the best therapeutic window between KRAS mutant cells and normal, untransformed cells. Distinct patterns of RAS effector dependency were observed across KRAS mutant cell lines, indicative of heterogeneous utilization of effector and stress response pathways in supporting KRAS addiction. Our findings revealed previously unappreciated complexity in the signaling network downstream of the KRAS oncogene and suggest rational target combinations for more effective therapeutic intervention.

MAPK and PI3K signaling: At the crossroads of neural crest development

Receptor tyrosine kinase-mediated growth factor signaling is essential for proper formation and development of the neural crest. The many ligands and receptors implicated in these processes signal through relatively few downstream pathways, frequently converging on the MAPK and PI3K pathways. Despite decades of study, there is still considerable uncertainty about where and when these signaling pathways are required and how they elicit particular responses. This review summarizes our current understanding of growth factor-induced MAPK and PI3K signaling in the neural crest.

Endothelial cell rearrangements during vascular patterning require PI3-kinase-mediated inhibition of actomyosin contractility

Angiogenesis is a dynamic process relying on endothelial cell rearrangements within vascular tubes, yet the underlying mechanisms and functional relevance are poorly understood. Here we show that PI3Kα regulates endothelial cell rearrangements using a combination of a PI3Kα-selective inhibitor and endothelial-specific genetic deletion to abrogate PI3Kα activity during vessel development. Quantitative phosphoproteomics together with detailed cell biology analyses in vivo and in vitro reveal that PI3K signalling prevents NUAK1-dependent phosphorylation of the myosin phosphatase targeting-1 (MYPT1) protein, thereby allowing myosin light chain phosphatase (MLCP) activity and ultimately downregulating actomyosin contractility. Decreased PI3K activity enhances actomyosin contractility and impairs junctional remodelling and stabilization. This leads to overstretched endothelial cells that fail to anastomose properly and form aberrant superimposed layers within the vasculature. Our findings define the PI3K/NUAK1/MYPT1/MLCP axis as a critical pathway to regulate actomyosin contractility in endothelial cells, supporting vascular patterning and expansion through the control of cell rearrangement.

Angiogenesis requires dynamic endothelial rearrangements and relative position changes within the vascular tubes. Here the authors show that a PI3K/NUAK1/MYPT1/MLCP pathway regulates actomyosin contractility in endothelial cells and cellular rearrangement during vascular patterning.

Isoform-specific activities of the regulatory subunits of phosphatidylinositol 3-kinases - potentially novel therapeutic targets

INTRODUCTION

The main regulatory subunits of Class IA phosphatidylinositol 3-kinase (PI3K), p85α and p85β, initiate diverse cellular activities independent of binding to the catalytic subunit p110. Several of these signaling processes directly or indirectly contribute to a regulation of PI3K and could become targets for therapeutic efforts. Areas covered: This review will highlight two general areas of p85 activity: (1) direct interaction with regulatory proteins and with determinants of the cytoskeleton, and (2) a genetic analysis by deletion and domain switches identifying new functions for p85 domains. Expert Opinion: Isoform-specific activities of regulatory subunits have long been at the periphery of the PI3K field. Our understanding of these unique functions of the regulatory subunits is fragmentary and raises many important questions. At this time, there is insufficient information to translate this knowledge into the clinic, but some tempting targets have emerged that could move the field forward with the help of novel technologies in drug design and identification.

Phosphoinositide 3-Kinase Is Integral for the Acute Activity of Leptin and Insulin in Male Arcuate NPY/AgRP Neurons

Neuropeptide Y (NPY)/Agouti-related protein (AgRP) neurons in the arcuate nucleus of the hypothalamus are part of a neuroendocrine feedback loop that regulates feeding behavior and glucose homeostasis. NPY/AgRP neurons sense peripheral signals (including the hormones leptin, insulin, and ghrelin) and integrate those signals with inputs from other brain regions. These inputs modify both long-term changes in gene transcription and acute changes in the electrical activity of these neurons, leading to a coordinated response to maintain energy and glucose homeostasis. However, the mechanisms by which the hormones insulin and leptin acutely modify the electrical activity of these neurons remain unclear. In this study, we show that loss of the phosphoinositide 3-kinase catalytic subunits p110α and p110β in AgRP neurons abrogates the leptin- and insulin-induced inhibition of AgRP neurons. Moreover, continual disruption of p110α and p110β in AgRP neurons results in increased weight gain. The increased adiposity was concomitant with a hypometabolic phenotype: decreased energy expenditure independent of changes in food intake. Deficiency of p110α and p110β in AgRP neurons also impaired glucose homeostasis and insulin sensitivity. In summary, these data highlight the requirement of both p110α and p110β in AgRP neurons for the proper regulation of energy balance and glucose homeostasis.

A RAB35-p85/PI3K axis controls oscillatory apical protrusions required for efficient chemotactic migration

How cells move chemotactically remains a major unmet challenge in cell biology. Emerging evidence indicates that for interpreting noisy, shallow gradients of soluble cues a system must behave as an excitable process. Here, through an RNAi-based, high-content screening approach, we identify RAB35 as necessary for the formation of growth factors (GFs)-induced waves of circular dorsal ruffles (CDRs), apically restricted actin-rich migratory protrusions. RAB35 is sufficient to induce recurrent and polarized CDRs that travel as propagating waves, thus behaving as an excitable system that can be biased to control cell steering. Consistently, RAB35 is essential for promoting directed chemotactic migration and chemoinvasion of various cells in response to gradients of motogenic GFs. Molecularly, RAB35 does so by directly regulating the activity of p85/PI3K polarity axis. We propose that RAB35 is a molecular determinant for the control of an excitable, oscillatory system that acts as a steering wheel for GF-mediated chemotaxis and chemoinvasion.

Circular dorsal ruffles (CDRs) are apical actin enriched structures involved in the interpretation of growth factor gradients during cell migration. Here, the authors find that a RAB35/PI3K axis is necessary and sufficient for the formation and stabilization of polarized CDRs and persistent directional migration.

Identification of a Potent, Selective, and Efficacious Phosphatidylinositol 3-Kinase δ (PI3Kδ) Inhibitor for the Treatment of Immunological Disorders

PI3Kδ plays an important role controlling immune cell function and has therefore been identified as a potential target for the treatment of immunological disorders. This article highlights our work toward the identification of a potent, selective, and efficacious PI3Kδ inhibitor. Through careful SAR, the successful replacement of a polar pyrazole group by a simple chloro or trifluoromethyl group led to improved Caco-2 permeability, reduced Caco-2 efflux, reduced hERG PC activity, and increased selectivity profile while maintaining potency in the CD69 hWB assay. The optimization of the aryl substitution then identified a 4'-CN group that improved the human/rodent correlation in microsomal metabolic stability. Our lead molecule is very potent in PK/PD assays and highly efficacious in a mouse collagen-induced arthritis model.

The regulation of tumor-suppressive microRNA, miR-126, in chronic lymphocytic leukemia

The introduction of miR profiling of chronic lymphocytic leukemia (CLL) patients with different cytogenetic profiles and responses to therapy has allowed incorporation of important miR‐mRNA interactions into the understanding of disease biology. In this study, we performed miR expression analysis using NanoString nCounter to discover differentially regulated miRs after therapy with the Bruton tyrosine kinase inhibitor ibrutinib. Of the differentially regulated miRs in the discovery set, miR‐29c and miR‐126 were confirmed using real‐time PCR to be upregulated in CLL patient cells with ibrutinib therapy. In the validation set, an inverse correlation was observed between miR‐126 levels and expression of its putative target p85β, an isoform of the phosphoinositide 3‐kinase p85 regulatory subunit. We found that mRNA for the host gene EGFL7, primary unprocessed miR‐126, and mature miR‐126 are all downregulated in CLL cells compared to normal B cells. Patients in later stages of disease have a greater decrease in miR‐126 expression compared to treatment‐naive patients, indicating that lower miR‐126 levels may associate with disease progression. Overexpression of miR‐126 in leukemia cell lines significantly downregulates p85β expression and decreases activation of prosurvival mitogen‐activated protein kinase (MAPK) signaling. These results implicate miR‐126 in the pathology of CLL.

PDGFRβ regulates craniofacial development through homodimers and functional heterodimers with PDGFRα

Craniofacial development is a complex morphogenetic process, disruptions in which result in highly prevalent human birth defects. While platelet-derived growth factor (PDGF) receptor α (PDGFRα) has well-documented functions in this process, the role of PDGFRβ in murine craniofacial development is not well established. We demonstrate that PDGFRα and PDGFRβ are coexpressed in the craniofacial mesenchyme of mid-gestation mouse embryos and that ablation of Pdgfrb in the neural crest lineage results in increased nasal septum width, delayed palatal shelf development, and subepidermal blebbing. Furthermore, we show that the two receptors genetically interact in this lineage, as double-homozygous mutant embryos exhibit an overt facial clefting phenotype more severe than that observed in either single-mutant embryo. We reveal a physical interaction between PDGFRα and PDGFRβ in the craniofacial mesenchyme and demonstrate that the receptors form functional heterodimers with distinct signaling properties. Our studies thus uncover a novel mode of signaling for the PDGF family during vertebrate development.

Genetic insights into the mechanisms of Fgf signaling

The fibroblast growth factor (Fgf) family of ligands and receptor tyrosine kinases is required throughout embryonic and postnatal development and also regulates multiple homeostatic functions in the adult. Here, Brewer et al. review the mechanisms of Fgf signaling by focusing on genetic strategies that enable in vivo analysis.

The fibroblast growth factor (Fgf) family of ligands and receptor tyrosine kinases is required throughout embryonic and postnatal development and also regulates multiple homeostatic functions in the adult. Aberrant Fgf signaling causes many congenital disorders and underlies multiple forms of cancer. Understanding the mechanisms that govern Fgf signaling is therefore important to appreciate many aspects of Fgf biology and disease. Here we review the mechanisms of Fgf signaling by focusing on genetic strategies that enable in vivo analysis. These studies support an important role for Erk1/2 as a mediator of Fgf signaling in many biological processes but have also provided strong evidence for additional signaling pathways in transmitting Fgf signaling in vivo.

Phosphoinositide 3-Kinase Regulates Glycolysis through Mobilization of Aldolase from the Actin Cytoskeleton

The phosphoinositide 3-kinase (PI3K) pathway regulates multiple steps in glucose metabolism and also cytoskeletal functions, such as cell movement and attachment. Here, we show that PI3K directly coordinates glycolysis with cytoskeletal dynamics in an AKT-independent manner. Growth factors or insulin stimulate the PI3K-dependent activation of Rac, leading to disruption of the actin cytoskeleton, release of filamentous actin-bound aldolase A, and an increase in aldolase activity. Consistently, PI3K inhibitors, but not AKT, SGK, or mTOR inhibitors, cause a significant decrease in glycolysis at the step catalyzed by aldolase, while activating PIK3CA mutations have the opposite effect. These results point toward a master regulatory function of PI3K that integrates an epithelial cell's metabolism and its form, shape, and function, coordinating glycolysis with the energy-intensive dynamics of actin remodeling.

Snail Is a Critical Mediator of Invadosome Formation and Joint Degradation in Arthritis

Progressive cartilage destruction, mediated by invasive fibroblast-like synoviocytes, is a central feature in the pathogenesis of rheumatoid arthritis (RA). Members of the Snail family of transcription factors are required for cell migration and invasion, but their role in joint destruction remains unknown. Herein, we demonstrate that Snail is essential for the formation of extracellular matrix-degrading invadosomal structures by synovial cells from collagen-induced arthritis (CIA) rats and RA patients. Mechanistically, Snail induces extracellular matrix degradation in synovial cells by repressing PTEN, resulting in increased phosphorylation of platelet-derived growth factor receptor and activation of the phosphatidylinositol 3-kinase/AKT pathway. Of significance, Snail is overexpressed in synovial cells and tissues of CIA rats and RA patients, whereas knockdown of Snail in CIA joints prevents cartilage invasion and joint damage. Furthermore, Snail expression is associated with an epithelial-mesenchymal transition gene signature characteristic of transglutaminase 2/transforming growth factor-β activation. Transforming growth factor-β and transglutaminase 2 stimulate Snail-dependent invadosome formation in rat and human synoviocytes. Our results identify the Snail-PTEN platelet-derived growth factor receptor/phosphatidylinositol 3-kinase axis as a novel regulator of the prodestructive invadosome-forming phenotype of synovial cells. New therapies for RA target inflammation, and are only partly effective in preventing joint damage. Blocking Snail and/or its associated gene expression program may provide an additional tool to improve the efficacy of treatments to prevent joint destruction.

Myristoylated p110α Causes Embryonic Death Due to Developmental and Vascular Defects

The phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates many important cellular functions. The functional impact of deregulating the PIK3CA gene, encoding the p110α catalytic subunit of PI3K, is validated by frequent gain of function mutations in a range of human cancers. We generated a mouse model with an inducible constitutively active form of PI3K. In this model Cre recombinase activates expression of a myristoylated form of p110α (myr-p110α). The myristoylated version of p110α brings the protein to the cytoplasmic side of the cell membrane, which mimics the normal activation mechanism for the p110α catalytic subunit and activates the PI3K enzyme. Constitutively activated PI3K signaling induced by myr-p110α in all cells of the developing mouse caused lethality during embryonic development. Transgenic Cre;myr-p110α heterozygous embryos displayed morphological malformation and poor vascular development with extremely dilated blood vessels and hemorrhage in the embryo and the extraembryonic yolk sac. Previous studies demonstrated that loss of p110α during embryonic development causes angiogenic disruption and here we show that constitutive activation of p110α by gain of function mutation during development also disrupts vasculogenesis/angiogenesis in what appears to be a similar manner. These finding demonstrate the importance of tight regulation of PI3K signaling during embryonic vasculogenesis/angiogenesis..

Oncogenic activity of the regulatory subunit p85β of phosphatidylinositol 3-kinase (PI3K)

Expression of the regulatory subunit p85β of PI3K induces oncogenic transformation of primary avian fibroblasts. The transformed cells proliferate at an increased rate compared with nontransformed controls and show elevated levels of PI3K signaling. The oncogenic activity of p85β requires an active PI3K-TOR signaling cascade and is mediated by the p110α and p110β isoforms of the PI3K catalytic subunit. The data suggest that p85β is a less effective inhibitor of the PI3K catalytic subunit than p85α and that this reduced level of p110 inhibition accounts for the oncogenic activity of p85β.

Downregulation of PI3Kcb utilizing adenovirus-mediated transfer of siRNA attenuates bone cancer pain

Phosphatidylinositol 3-kinase (PI3K) signaling plays a pivotal role in intracellular signal transduction pathways involved in chronic pain states. PI3K is implicated in pathomechanisms of enhanced synaptic strength, such as wind-up and central sensitization in the spinal dorsal horn. The PI3Kcb gene encoding the class 1A PI3K catalytic subunit p110beta is one of the most important molecular of the P13K signaling pathway. Here, we used small interfering RNA (siRNA) targeted to PI3Kcb by adenovirus-mediated transfer, to determine whether inhibition of PI3Kcb was a potential therapeutic target for bone cancer pain (BCP). In this study, treatment of BCP model in rats with PI3Kcb-specific siRNA resulted in inhibited pain-related behavior. Depletion of PI3Kcb decreased the protein levels of spinal PI3Kcb and phospho-Akt (P-Akt)-downstream targets of PI3K. Knockdown of PI3Kcb by siRNA also induced decreased expression of GFAP and OX42, suggesting that the upregulation of spinal PI3Kcb may increase glia excitability, at least in part by regulating glia message. Our findings suggest that siRNA-mediated gene silencing of PI3Kcb may be a useful therapeutic strategy for BCP.

Phosphoinositide 3-kinase p85beta regulates invadopodium formation

The acquisition of invasiveness is characteristic of tumor progression. Numerous genetic changes are associated with metastasis, but the mechanism by which a cell becomes invasive remains unclear. Expression of p85β, a regulatory subunit of phosphoinositide-3-kinase, markedly increases in advanced carcinoma, but its mode of action is unknown. We postulated that p85β might facilitate cell invasion. We show that p85β localized at cell adhesions in complex with focal adhesion kinase and enhanced stability and maturation of cell adhesions. In addition, p85β induced development at cell adhesions of an F-actin core that extended several microns into the cell z-axis resembling the skeleton of invadopodia. p85β lead to F-actin polymerization at cell adhesions by recruiting active Cdc42/Rac at these structures. In accordance with p85β function in invadopodium-like formation, p85β levels increased in metastatic melanoma and p85β depletion reduced invadopodium formation and invasion. These results show that p85β enhances invasion by inducing cell adhesion development into invadopodia-like structures explaining the metastatic potential of tumors with increased p85β levels.

Expression pattern of class I phosphoinositide 3-kinase and distribution of its product, phosphatidylinositol-3,4,5-trisphosphate, during Drosophila embryogenesis

The class I phosphoinositide 3-kinase (PI3K) can be activated by a large variety of extracellular stimuli and is responsible for generating phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P(3)) from phosphatidylinositol-4,5-bisphosphate at the plasma membrane. The expression pattern of the class I PI3K and distribution of PI(3,4,5)P(3), visualized by its specific binding protein, GRP1-PH, were examined during Drosophila embryogenesis. We found that the RNA of Pi3K21B, encoding the Drosophila p60 regulatory subunit of the class I PI3Ks, was expressed maternally and expressed primarily in pole cells after cellularization until completion of germ band elongation. The RNA of Pi3K92E, encoding the Drosophila p110 catalytic subunit of the class I PI3Ks, was also expressed maternally. During gastrulation, its transcript level became lower and was slightly enriched in invaginating cells. Both Pi3K21B and Pi3K92E were expressed ubiquitously after germ band elongation and persisted during germ band shortening. PI(3,4,5)P(3) was distributed at the apical region of the invaginating cells during gastrulation. These findings suggest a possible involvement of class I PI3K and PI(3,4,5)P(3) in the regulation of invagination during gastrulation.

PI3K-mediated PDGFRα signaling regulates survival and proliferation in skeletal development through p53-dependent intracellular pathways

PI3K is the main downstream effector of PDGFRα signaling during murine skeletal development. Fantauzzo et al. discovered skeletal defects in embryos in which PDGFRα is unable to bind PI3K. They identified 56 proteins that are phosphorylated by Akt downstream from PI3K-mediated PDGFRα signaling. Several of these proteins, including Ybox1, mediate cell survival through regulation of p53. These findings identify p53 as a novel effector downstream from PI3K-engaged PDGFRα signaling that regulates survival and proliferation during skeletal development in vivo.

Previous studies have identified phosphatidylinositol 3-kinase (PI3K) as the main downstream effector of PDGFRα signaling during murine skeletal development. Autophosphorylation mutant knock-in embryos in which PDGFRα is unable to bind PI3K (Pdgfra^PI3K/PI3K) exhibit skeletal defects affecting the palatal shelves, shoulder girdle, vertebrae, and sternum. To identify proteins phosphorylated by Akt downstream from PI3K-mediated PDGFRα signaling, we immunoprecipitated Akt phosphorylation substrates from PDGF-AA-treated primary mouse embryonic palatal mesenchyme (MEPM) lysates and analyzed the peptides by nanoliquid chromatography coupled to tandem mass spectrometry (nano-LC-MS/MS). Our analysis generated a list of 56 proteins, including 10 that regulate cell survival and proliferation. We demonstrate that MEPM cell survival is impaired in the presence of a PI3K inhibitor and that Pdgfra^PI3K/PI3K-derived MEPMs do not proliferate in response to PDGF-AA treatment. Several of the identified Akt phosphorylation targets, including Ybox1, mediate cell survival through regulation of p53. We show that Ybox1 binds both the Trp53 promoter and the p53 protein and that expression of Trp53 is significantly decreased upon PDGF-AA treatment in MEPMs. Finally, we demonstrate that introduction of a Trp53-null allele attenuates the vertebral defects found in Pdgfra^PI3K/PI3K neonates. Our findings identify p53 as a novel effector downstream from PI3K-engaged PDGFRα signaling that regulates survival and proliferation during skeletal development in vivo.

How to understand and outwit adaptation

Adaptation is the ability of a system to respond and reset itself even in the continuing presence of a stimulus. On one hand, adaptation is a physiological necessity that enables proper neuronal signaling and cell movement. On the other hand, adaptation can be a source of annoyance, as it can make biological systems resistant to experimental perturbations. Here we speculate where adaptation might live in eukaryotic chemotaxis and how it can be encoded in the signaling network. We then discuss tools and strategies that can be used to both understand and outwit adaptation in a wide range of cellular contexts.

Beta interferon regulation of glucose metabolism is PI3K/Akt dependent and important for antiviral activity against coxsackievirus B3

An effective type I interferon (IFN)-mediated immune response requires the rapid expression of antiviral proteins that are necessary to inhibit viral replication and virus spread. We provide evidence that IFN-β regulates metabolic events important for the induction of a rapid antiviral response: IFN-β decreases the phosphorylation of AMP-activated protein kinase (AMPK), coincident with an increase in intracellular ATP. Our studies reveal a biphasic IFN-β-inducible uptake of glucose by cells, mediated by phosphatidylinositol 3-kinase (PI3K)/Akt, and IFN-β-inducible regulation of GLUT4 translocation to the cell surface. Additionally, we provide evidence that IFN-β-regulated glycolytic metabolism is important for the acute induction of an antiviral response during infection with coxsackievirus B3 (CVB3). Last, we demonstrate that the antidiabetic drug metformin enhances the antiviral potency of IFN-β against CVB3 both in vitro and in vivo. Taken together, these findings highlight an important role for IFN-β in modulating glucose metabolism during a virus infection and suggest that the use of metformin in combination with IFN-β during acute virus infection may result in enhanced antiviral responses.

IMPORTANCE

Type I interferons (IFN) are critical effectors of an antiviral response. These studies describe for the first time a role for IFN-β in regulating metabolism--glucose uptake and ATP production--to meet the energy requirements of a robust cellular antiviral response. Our data suggest that IFN-β regulates glucose metabolism mediated by signaling effectors similarly to activation by insulin. Interference with IFN-β-inducible glucose metabolism diminishes the antiviral response, whereas treatment with metformin, a drug that increases insulin sensitivity, enhances the antiviral potency of IFN-β.

Identification of mutations in distinct regions of p85 alpha in urothelial cancer

Bladder cancers commonly show genetic aberrations in the phosphatidylinositol 3-kinase signaling pathway. Here we have screened for mutations in PIK3R1, which encodes p85α, one of the regulatory subunits of PI3K. Two hundred and sixty-four bladder tumours and 41 bladder tumour cell lines were screened and 18 mutations were detected. Thirteen mutations were in C-terminal domains and are predicted to interfere with the interaction between p85α and p110α. Five mutations were in the BH domain of PIK3R1. This region has been implicated in p110α-independent roles of p85α, such as binding to and altering the activities of PTEN, Rab4 and Rab5. Expression of these mutant BH-p85α forms in mouse embryonic fibroblasts with p85α knockout indicated that all forms, except the truncation mutants, could bind and stabilize p110α but did not increase AKT phosphorylation, suggesting that BH mutations function independently of p110α. In a panel of 44 bladder tumour cell lines, 80% had reduced PIK3R1 mRNA expression relative to normal urothelial cells. This, along with mutation of PIK3R1, may alter BH domain functioning. Our findings suggest that mutant forms of p85α may play an oncogenic role in bladder cancer, not only via loss of ability to regulate p110α but also via altered function of the BH domain.

Chlamydia pneumoniae infection induces vascular smooth muscle cell migration via Rac1 activation

Chlamydia pneumoniae infection has been shown to be associated with the development of atherosclerosis by promoting the migration of vascular smooth muscle cells (VSMCs). However, how C. pneumoniae infection induces VSMC migration is not fully understood. A primary role of Ras-related C3 botulinum toxin substrate 1 (Rac1) is to generate a protrusive force at the leading edge that contributes to cell migration. Whether Rac1 activation plays a role in C. pneumoniae infection-induced VSMC migration is not well defined. In the present study, we therefore examined Rac1 activation in C. pneumoniae-infected rat primary VSMCs and the role of Rac1 activation in C. pneumoniae infection-induced VSMC migration. Glutathione S-transferase pull-down assay results showed that Rac1 was activated in C. pneumoniae-infected rat primary VSMCs. A Rac1 inhibitor, NSC23766 (50 µM,) suppressed Rac1 activation stimulated by C. pneumoniae infection, and thereby inhibited C. pneumoniae infection-induced VSMC migration. In addition, C. pneumoniae infection-induced Rac1 activation in the VSMCs was blocked by LY294002 (25 µM), an inhibitor of phosphatidylinositol 3-kinase (PI3K). Taken together, these data suggest that C. pneumoniae infection promotes VSMC migration, possibly through activating Rac1 via PI3K.

Phosphoinositides: tiny lipids with giant impact on cell regulation

Phosphoinositides (PIs) make up only a small fraction of cellular phospholipids, yet they control almost all aspects of a cell's life and death. These lipids gained tremendous research interest as plasma membrane signaling molecules when discovered in the 1970s and 1980s. Research in the last 15 years has added a wide range of biological processes regulated by PIs, turning these lipids into one of the most universal signaling entities in eukaryotic cells. PIs control organelle biology by regulating vesicular trafficking, but they also modulate lipid distribution and metabolism via their close relationship with lipid transfer proteins. PIs regulate ion channels, pumps, and transporters and control both endocytic and exocytic processes. The nuclear phosphoinositides have grown from being an epiphenomenon to a research area of its own. As expected from such pleiotropic regulators, derangements of phosphoinositide metabolism are responsible for a number of human diseases ranging from rare genetic disorders to the most common ones such as cancer, obesity, and diabetes. Moreover, it is increasingly evident that a number of infectious agents hijack the PI regulatory systems of host cells for their intracellular movements, replication, and assembly. As a result, PI converting enzymes began to be noticed by pharmaceutical companies as potential therapeutic targets. This review is an attempt to give an overview of this enormous research field focusing on major developments in diverse areas of basic science linked to cellular physiology and disease.

p85β phosphoinositide 3-kinase subunit regulates tumor progression

PIK3R2 encodes a ubiquitous regulatory subunit (p85β) of PI3K, an enzyme that generates 3-polyphosphoinositides at the plasma membrane. PI3K activation triggers cell survival and migration. We found that p85β expression is elevated in breast and colon carcinomas and that its increased expression correlates with PI3K pathway activation and tumor progression. p85β expression induced moderate PIP(3) generation at the cell membrane and enhanced cell invasion. In accordance, genetic alteration of pik3r2 expression levels modulated tumor progression in vivo. Increased p85β expression thus represents a cellular strategy in cancer progression.

Functional roles of the phosphatidylinositol 3-kinases (PI3Ks) signaling in the mammalian ovary

Phosphatidylinositol 3-kinase (PI3K) signaling is a fundamental pathway for the regulation of cell proliferation, survival, migration, and metabolism in a variety of physiological and pathological processes. In recent years information provided by genetically modified mouse models has revealed that PI3K signaling plays vital roles in oogenesis, folliculogenesis, ovulation, and carcinogenesis in mouse ovary. In this review, we summarize (1) the physiological function of intra-oocyte PI3K signaling in regulation of primordial follicle survival and activation; (2) intra-granulosa cell PI3K signaling in regulation of cyclic follicular recruitment and ovulation; (3) intra-oocyte PI3K signaling in regulation of meiosis resumption and early embryogenesis; and also (4) the pathological function of PI3K signaling in ovarian diseases such as premature ovarian failure, granulosa cell tumors, and ovarian surface epithelium carcinomas. This updated info hopefully will lead to a better understanding of the human ovary and provide potential therapies for treating human infertility.

PERK utilizes intrinsic lipid kinase activity to generate phosphatidic acid, mediate Akt activation, and promote adipocyte differentiation

The endoplasmic reticulum (ER) resident PKR-like kinase (PERK) is necessary for Akt activation in response to ER stress. We demonstrate that PERK harbors intrinsic lipid kinase, favoring diacylglycerol (DAG) as a substrate and generating phosphatidic acid (PA). This activity of PERK correlates with activation of mTOR and phosphorylation of Akt on Ser473. PERK lipid kinase activity is regulated in a phosphatidylinositol 3-kinase (PI3K) p85α-dependent manner. Moreover, PERK activity is essential during adipocyte differentiation. Because PA and Akt regulate many cellular functions, including cellular survival, proliferation, migratory responses, and metabolic adaptation, our findings suggest that PERK has a more extensive role in insulin signaling, insulin resistance, obesity, and tumorigenesis than previously thought.

The p101 subunit of PI3Kγ restores activation by Gβ mutants deficient in stimulating p110γ

G-protein-regulated PI3Kγ (phosphoinositide 3-kinase γ) plays a crucial role in inflammatory and allergic processes. PI3Kγ, a dimeric protein formed by the non-catalytic p101 and catalytic p110γ subunits, is stimulated by receptor-released Gβγ complexes. We have demonstrated previously that Gβγ stimulates both monomeric p110γ and dimeric p110γ/p101 lipid kinase activity in vitro. In order to identify the Gβ residues responsible for the Gβγ–PI3Kγ interaction, we examined Gβ1 mutants for their ability to stimulate lipid and protein kinase activities and to recruit PI3Kγ to lipid vesicles. Our findings revealed different interaction profiles of Gβ residues interacting with p110γ or p110γ/p101. Moreover, p101 was able to rescue the stimulatory activity of Gβ1 mutants incapable of modulating monomeric p110γ. In addition to the known adaptor function of p101, in the present paper we show a novel regulatory role of p101 in the activation of PI3Kγ.

Maternal control of mouse preimplantation development

Mammalian preimplantation development is a process of dedifferentiation from the terminally differentiated eggs to the totipotent blastomeres at the cleavage stage, and then to the pluripotent cells at the blastocyst stage. Maternal factors that accumulate during oogenesis dominate early preimplantation development until the embryonic factors gain control after the activation of the embryonic genome. Recently, a handful of maternal factors that are encoded by the maternal-effect genes have been characterized in genetically modified mouse models. These factors are shown to participate in many aspects of preimplantation development, such as the degradation of maternal macromolecues, epigenetic modification, protein translation, cellular signaling transduction, and cell compaction. Even so, little is known about the interactions between different maternal factors. In this chapter, we have summarized the functions of known maternal factors and hopefully this will lead to a better understanding of the regulation of preimplantation embryogenesis by the maternal regulatory network.

Overexpression of 14-3-3ζ in cancer cells activates PI3K via binding the p85 regulatory subunit

The ubiquitously expressed 14-3-3 proteins regulate many pathways involved in transformation. Previously, we found that 14-3-3ζ overexpression increased Akt phosphorylation in human mammary epithelial cells. Here, we investigated the clinical relevance and molecular mechanism of 14-3-3ζ overexpression-mediated Akt phosphorylation and the potential impact on breast cancer progression. We found that 14-3-3ζ overexpression was significantly (P = 0.005) associated with increased Akt phosphorylation in human breast tumors. Additionally, 14-3-3ζ overexpression combined with strong Akt phosphorylation was significantly (P=0.01) associated with increased cancer recurrence in patients. In contrast, knockdown of 14-3-3ζ expression by siRNA in cancer cell lines and tumor xenografts reduced Akt phosphorylation. Furthermore, 14-3-3ζ enhanced Akt phosphorylation through activation of PI3K. Mechanistically, 14-3-3ζ bound to the p85 regulatory subunit of PI3K and increased PI3K translocation to the cell membrane. A single 14-3-3 binding motif encompassing serine 83 on p85 is largely responsible for 14-3-3ζ-mediated p85 binding and PI3K/Akt activation. Mutation of serine 83 to alanine on p85 inhibited 14-3-3ζ binding to the p85 subunit of PI3K, reduced PI3K membrane localization and activation, impeded anchorage independent growth and enhanced stress induced apoptosis. These findings revealed a novel mechanism by which 14-3-3ζ overexpression activates PI3K, a key node in the mitogenic signaling network known to promote malignancies in many cell types.

Is prenatal myo-inositol deficiency a mechanism of CNS injury in galactosemia?

Classic Galactosemia due to galactose-1-phosphate uridyltransferase (GALT) deficiency is associated with apparent diet-independent complications including cognitive impairment, learning problems and speech defects. As both galactose-1-phosphate and galactitol may be elevated in cord blood erythrocytes and amniotic fluid despite a maternal lactose-free diet, endogenous production of galactose may be responsible for the elevated fetal galactose metabolites, as well as postnatal CNS complications. A prenatal deficiency of myo-inositol due to an accumulation of both galactose-1- phosphate and galactitol may play a role in the production of the postnatal CNS dysfunction. Two independent mechanisms may result in fetal myo-inositol deficiency: competitive inhibition of the inositol monophosphatase1 (IMPA1)-mediated hydrolysis of inositol monophosphate by high galactose-1- phosphate levels leading to a sequestration of cellular myo-inositol as inositol monophosphate and galactitol-induced reduction in SMIT1-mediated myo-inositol transport. The subsequent reduction of myo-inositol within fetal brain cells could lead to inositide deficiencies with resultant perturbations in calcium and protein kinase C signaling, the AKT/mTOR/ cell growth and development pathway, cell migration, insulin sensitivity, vescular trafficking, endocytosis and exocytosis, actin cytoskeletal remodeling, nuclear metabolism, mRNA export and nuclear pore complex regulation, phosphatidylinositol-anchored proteins, protein phosphorylation and/or endogenous iron "chelation". Using a knockout animal model we have shown that a marked deficiency of myo-inositol in utero is lethal but the phenotype can be rescued by supplementing the drinking water of the pregnant mouse. If myo-inositol deficiency is found to exist in the GALT-deficient fetal brain, then the use of myo-inositol to treat the fetus via oral supplementation of the pregnant female may warrant consideration.