Nuclear phosphoinositide signaling promotes YAP/TAZ-TEAD transcriptional activity in breast cancer.

The Hippo pathway effectors Yes-associated protein 1 (YAP) and its homolog TAZ are transcriptional coactivators that control gene expression by binding to TEA domain (TEAD) family transcription factors. The YAP/TAZ-TEAD complex is a key regulator of cancer-specific transcriptional programs, which promote tumor progression in diverse types of cancer, including breast cancer. Despite intensive efforts, the YAP/TAZ-TEAD complex in cancer has remained largely undruggable due to an incomplete mechanistic understanding. Here, we report that nuclear phosphoinositides function as cofactors that mediate the binding of YAP/TAZ to TEADs. The enzymatic products of phosphoinositide kinases PIPKIα and IPMK, including phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) and phosphatidylinositol 3,4,5-trisphosphate (P(I3,4,5)P3), bridge the binding of YAP/TAZ to TEAD. Inhibiting these kinases or the association of YAP/TAZ with PI(4,5)P2 and PI(3,4,5)P3 attenuates YAP/TAZ interaction with the TEADs, the expression of YAP/TAZ target genes, and breast cancer cell motility. Although we could not conclusively exclude the possibility that other enzymatic products of IPMK such as inositol phosphates play a role in the mechanism, our results point to a previously unrecognized role of nuclear phosphoinositide signaling in control of YAP/TAZ activity and implicate this pathway as a potential therapeutic target in YAP/TAZ-driven breast cancer.

Electromagnetic drag forces between HTS magnet and tube infrastructure for hyperloop.

Maglevs are typically accelerated using electromagnetic propulsion and levitation. High-temperature superconducting (HTS) magnets along with electrodynamic suspension (EDS) and linear synchronous motors are one of the best options for Hyperloop. However, the strong magnetic fields generated by HTS magnets on the pods inevitably interact with the magnetic and conductive structures in the vacuum tubes, along with the tube itself, while the pods move through the tubes. This interaction is observed as a drag force on the pods, significantly reducing the propulsion efficiency. This study comprehensively analyzes the electromagnetic drag force (EDF) generated by HTS magnets on pods, which accounts for most of the drag forces faced by Hyperloop. Theoretical analysis and 3D FEA simulations are performed to analyze the propulsion forces with HTS magnets and all the drag forces on the pods. The EDF generated by AISI 1010 steel rebars in concrete guideways is even greater than the designed propulsion forces of 40 kN. Consequently, high-manganese (Hi-Mn) steel and insulated steel rebars are adopted and analyzed using 3D FEA simulations. The EDFs generated by the AISI 1010 steel and Hi-Mn steel vacuum tubes are determined by varying the distance between the HTS magnets and tubes at 50 and 1200 km/h, respectively; a minimum distance of 0.75 m is determined by a drag force below 8 kN within their operating velocities. Lastly, the total EDFs of the AISI 1010 steel and Hi-Mn steel tubes with EDS rails are obtained through the optimal design of rebars and tubes. The simulation results show that the total EDFs can be significantly reduced to below 10 kN (approximately 25% of the designed propulsion force after the levitation of pods).

A p53-phosphoinositide signalosome regulates nuclear AKT activation.

The tumour suppressor p53 and PI3K-AKT pathways have fundamental roles in the regulation of cell growth and apoptosis, and are frequently mutated in cancer. Here, we show that genotoxic stress induces nuclear AKT activation through a p53-dependent mechanism that is distinct from the canonical membrane-localized PI3K-AKT pathway. Following genotoxic stress, a nuclear PI3K binds p53 in the non-membranous nucleoplasm to generate a complex of p53 and phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3), which recruits AKT, PDK1 and mTORC2 to activate AKT and phosphorylate FOXO proteins, thereby inhibiting DNA damage-induced apoptosis. Wild-type p53 activates nuclear AKT in an on/off fashion following stress, whereas mutant p53 dose-dependently stimulates high basal AKT activity. The p53-PtdIns(3,4,5)P3 complex is dephosphorylated to p53-phosphatidylinositol 4,5-bisphosphate by PTEN to inhibit AKT activation. The nuclear p53-phosphoinositide signalosome is distinct from the canonical membrane-localized pathway and insensitive to PI3K inhibitors currently in the clinic, which underscores its therapeutic relevance.

Equivalent inductance model for the design analysis of electrodynamic suspension coils for hyperloop.

Hyperloop is a new concept of ground transportation. In Hyperloop, travelling occurs in near-vacuum tubes under 0.001 atm at a subsonic speed of up to 1200 km/h. During acceleration to and driving at a subsonic speed, magnetic levitation is employed. Thus far, various levitation technologies in existing high-speed maglev trains have been considered. Among those technologies, superconducting (SC) electrodynamic suspension (EDS) is a highly effective levitation system for Hyperloop owing to its advantages of a large levitation gap, levitation stability, and control being unnecessary. However, analyzing an EDS system requires the electromagnetic transient analysis of complex three-dimensional (3D) features, and its computational load generally limits the use of numerical methods, such as the 3D finite element method (FEM) or dynamic circuit theory. In this study, a novel model that can rapidly and accurately calculate the frequency-dependent equivalent inductance was developed. The developed model was then applied to design an EDS system using the decoupled resistance-inductance equations of levitation coils. Next, levitation coils of SC-EDS were designed and analyzed for use in Hyperloop. The obtained results were compared with the FEM results to validate the developed model. In addition, the model was experimentally validated by measuring currents induced by moving pods.

Role of IQGAP1 in Papillomavirus-Associated Head and Neck Tumorigenesis.

Approximately 25% of head and neck squamous cell carcinomas (HNSCC) are associated with human papillomavirus (HPV) infection. In these cancers as well as in HPV-associated anogenital cancers, PI3K signaling is highly activated. We previously showed that IQ motif-containing GTPase activating protein 1 (IQGAP1), a PI3K pathway scaffolding protein, is overexpressed in and contributes to HNSCC and that blocking IQGAP1-mediated PI3K signaling reduces HPV-positive HNSCC cell survival and migration. In this study, we tested whether IQGAP1 promotes papillomavirus (PV)-associated HNSCCs. IQGAP1 was necessary for optimal PI3K signaling induced by HPV16 oncoproteins in transgenic mice and MmuPV1 infection, a mouse papillomavirus that causes HNSCC in mice. Furthermore, we found that, at 6 months post-infection, MmuPV1-infected Iqgap1-/- mice developed significantly less severe tumor phenotypes than MmuPV1-infected Iqgap1+/+ mice, indicating a role of IQGAP1 in MmuPV1-associated HNSCC. The tumors resulting from MmuPV1 infection showed features consistent with HPV infection and HPV-associated cancer. However, such IQGAP1-dependent effects on disease severity were not observed in an HPV16 transgenic mouse model for HNC. This may reflect that IQGAP1 plays a role in earlier stages of viral pathogenesis, or other activities of HPV16 oncogenes are more dominant in driving carcinogenesis than their influence on PI3K signaling.

Phosphatidylinositol-3-OH kinase signalling is spatially organized at endosomal compartments by microtubule-associated protein 4.

The canonical model of agonist-stimulated phosphatidylinositol-3-OH kinase (PI3K)-Akt signalling proposes that PI3K is activated at the plasma membrane, where receptors are activated and phosphatidylinositol-4,5-bisphosphate is concentrated. Here we show that phosphatidylinositol-3,4,5-trisphosphate generation and activated Akt are instead largely confined to intracellular membranes upon receptor tyrosine kinase activation. Microtubule-associated protein 4 (MAP4) interacts with and controls localization of membrane vesicle-associated PI3Kα to microtubules. The microtubule-binding domain of MAP4 binds directly to the C2 domain of the p110α catalytic subunit. MAP4 controls the interaction of PI3Kα with activated receptors at endosomal compartments along microtubules. Loss of MAP4 results in the loss of PI3Kα targeting and loss of PI3K-Akt signalling downstream of multiple agonists. The MAP4-PI3Kα assembly defines a mechanism for spatial control of agonist-stimulated PI3K-Akt signalling at internal membrane compartments linked to the microtubule network.

The nuclear phosphoinositide response to stress.

Accumulating evidence reveals that nuclear phosphoinositides (PIs) serve as central signaling hubs that control a multitude of nuclear processes by regulating the activity of nuclear proteins. In response to cellular stressors, PIs accumulate in the nucleus and multiple PI isomers are synthesized by the actions of PI-metabolizing enzymes, kinases, phosphatases and phospholipases. By directly interacting with effector proteins, phosphoinositide signals transduce changes in cellular functions. Here we describe nuclear phosphoinositide signaling in multiple sub-nuclear compartments and summarize the literature that demonstrates roles for specific kinases, phosphatases, and phospholipases in the orchestration of nuclear phosphoinositide signaling in response to cellular stress. Additionally, we discuss the specific PI-protein complexes through which these lipids execute their functions by regulating the configuration, stability, and transcription activity of their effector proteins. Overall, our review provides a detailed landscape of the current understanding of the nuclear PI-protein interactome and its role in shaping the coordinated response to cellular stress.

A PI3K/AKT Scaffolding Protein, IQ Motif-Containing GTPase Associating Protein 1 (IQGAP1), Promotes Head and Neck Carcinogenesis.

PURPOSE: Head and neck cancer (HNC) is the sixth most common cancer worldwide with a 5-year survival rate of less than 50%. The PI3K/AKT/mTOR signaling pathway is frequently implicated in HNC. Recently, IQ motif-containing GTPase-activating protein 1 (IQGAP1) was discovered to scaffold the PI3K/AKT signaling pathway. IQGAP1 gene expression is increased in HNC, raising the hypothesis that IQGAP1 contributes to HNC. EXPERIMENTAL DESIGN: We performed a combination of in vitro studies using human cancer cell lines treated with a cell-permeable peptide that interferes with IQGAP1's ability to bind to PI3K, and in vivo studies utilizing mice genetically knocked out for the Iqgap1 (Iqgap1 -/-). In vivo EGF stimulation assays were used to evaluate PI3K signaling. To study the role of IQGAP1 in HNC, we used a well-validated mouse model that drives HNC via a synthetic oral carcinogen, 4-nitroquinoline 1-oxide (4NQO). RESULTS: IQGAP1 is necessary for efficient PI3K signaling in vitro and in vivo. Disruption of IQGAP1-scaffolded PI3K/AKT signaling reduced HNC cell survival. Iqgap1 -/- mice had significantly lower cancer incidences, lesser disease severity, and fewer cancer foci. IQGAP1 protein levels were increased in HNC arising in Iqgap1+/+ mice. The level of PI3K signaling in 4NQO-induced HNC arising in Iqgap1 -/- mice was significantly reduced, consistent with the hypothesis that IQGAP1 contributes to HNC at least partly through PI3K signaling. High IQGAP1 expression correlated with reduced survival, and high pS6 levels correlated with high IQGAP1 levels in patients with HNC. CONCLUSIONS: These data demonstrate that IQGAP1 contributes to head and neck carcinogenesis.

The Specificity of EGF-Stimulated IQGAP1 Scaffold Towards the PI3K-Akt Pathway is Defined by the IQ3 motif.

Epidermal growth factor receptor (EGFR) and its downstream phosphoinositide 3-kinase (PI3K) pathway are commonly deregulated in cancer. Recently, we have shown that the IQ motif-containing GTPase-activating protein 1 (IQGAP1) provides a molecular platform to scaffold all the components of the PI3K-Akt pathway and results in the sequential generation of phosphatidylinositol-3,4,5-trisphosphate (PI3,4,5P3). In addition to the PI3K-Akt pathway, IQGAP1 also scaffolds the Ras-ERK pathway. To define the specificity of IQGAP1 for the control of PI3K signaling, we have focused on the IQ3 motif in IQGAP1 as PIPKIα and PI3K enzymes bind this region. An IQ3 deletion mutant loses interactions with the PI3K-Akt components but retains binding to ERK and EGFR. Consistently, blocking the IQ3 motif of IQGAP1 using an IQ3 motif-derived peptide mirrors the effect of IQ3 deletion mutant by reducing Akt activation but has no impact on ERK activation. Also, the peptide disrupts the binding of IQGAP1 with PI3K-Akt pathway components, while IQGAP1 interactions with ERK and EGFR are not affected. Functionally, deleting or blocking the IQ3 motif inhibits cell proliferation, invasion, and migration in a non-additive manner to a PIPKIα inhibitor, establishing the functional specificity of IQ3 motif towards the PI3K-Akt pathway. Taken together, the IQ3 motif is a specific target for suppressing activation of the PI3K-Akt but not the Ras-ERK pathway. Although EGFR stimulates the IQGAP1-PI3K and -ERK pathways, here we show that IQGAP1-PI3K controls migration, invasion, and proliferation independent of ERK. These data illustrate that the IQ3 region of IQGAP1 is a promising therapeutic target for PI3K-driven cancer.

A nuclear phosphoinositide kinase complex regulates p53.

The tumour suppressor p53 (encoded by TP53) protects the genome against cellular stress and is frequently mutated in cancer. Mutant p53 acquires gain-of-function oncogenic activities that are dependent on its enhanced stability. However, the mechanisms by which nuclear p53 is stabilized are poorly understood. Here, we demonstrate that the stability of stress-induced wild-type and mutant p53 is regulated by the type I phosphatidylinositol phosphate kinase (PIPKI-α (also known as PIP5K1A)) and its product phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). Nuclear PIPKI-α binds to p53 upon stress, resulting in the production and association of PtdIns(4,5)P2 with p53. PtdIns(4,5)P2 binding promotes the interaction between p53 and the small heat shock proteins HSP27 (also known as HSPB1) and αB-crystallin (also known as HSPB5), which stabilize nuclear p53. Moreover, inhibition of PIPKI-α or PtdIns(4,5)P2 association results in p53 destabilization. Our results point to a previously unrecognized role of nuclear phosphoinositide signalling in regulating p53 stability and implicate this pathway as a promising therapeutic target in cancer.

Phosphoinositide 3-kinase pathways and autophagy require phosphatidylinositol phosphate kinases.

Phosphatidylinositol phosphate kinases (PIPKs) generate a lipid messenger phosphatidylinositol 4,5-bisphosphate (PI4,5P2) that controls essentially all aspects of cellular functions. PI4,5P2 rapidly diffuses in the membrane of the lipid bilayer and does not greatly change in membrane or cellular content, and thus PI4,5P2 generation by PIPKs is tightly linked to its usage in subcellular compartments. Based on this verity, recent study of PI4,5P2 signal transduction has been focused on investigations of individual PIPKs and their underlying molecular regulation of cellular processes. Here, we will discuss recent advances in the study of how PIPKs control specific cellular events through assembly and regulation of PI4,5P2 effectors that mediate specific cellular processes. A focus will be on the roles of PIPKs in control of the phosphoinositide 3-kinase pathway and autophagy.

The Hidden Conundrum of Phosphoinositide Signaling in Cancer.

Phosphoinositide 3-kinase (PI3K) generation of PI(3,4,5)P3 from PI(4,5)P2 and the subsequent activation of Akt and its downstream signaling cascades (e.g. mTORC1) dominates the landscape of phosphoinositide signaling axis in cancer research. However, PI(4,5)P2 is breaking its boundary as merely a substrate for PI3K and phospholipase C (PLC), and is now an established lipid messenger pivotal for different cellular events in cancer. Here, we review the phosphoinositide signaling axis in cancer, giving due weight to PI(4,5)P2 and its generating enzymes, the phosphatidylinositol phosphate (PIP) kinases (PIPKs). We highlighted how PI(4,5)P2 and PIP kinases serve as a proximal node in phosphoinositide signaling axis and how its interaction with cytoskeletal proteins regulates migratory and invasive nexus of metastasizing tumor cells.

Agonist-stimulated phosphatidylinositol-3,4,5-trisphosphate generation by scaffolded phosphoinositide kinases.

Generation of the lipid messenger phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) is crucial for development, cell growth and survival, and motility, and it becomes dysfunctional in many diseases including cancers. Here we reveal a mechanism for PtdIns(3,4,5)P3 generation by scaffolded phosphoinositide kinases. In this pathway, class I phosphatidylinositol-3-OH kinase (PI(3)K) is assembled by IQGAP1 with PI(4)KIIIα and PIPKIα, which sequentially generate PtdIns(3,4,5)P3 from phosphatidylinositol. By scaffolding these kinases into functional proximity, the PtdIns(4,5)P2 generated is selectively used by PI(3)K for PtdIns(3,4,5)P3 generation, which then signals to PDK1 and Akt that are also in the complex. Moreover, multiple receptor types stimulate the assembly of this IQGAP1-PI(3)K signalling complex. Blockade of IQGAP1 interaction with PIPKIα or PI(3)K inhibited PtdIns(3,4,5)P3 generation and signalling, and selectively diminished cancer cell survival, revealing a target for cancer chemotherapy.

PtdIns(4,5)P2 signaling regulates ATG14 and autophagy.

Autophagy is a regulated self-digestion pathway with fundamental roles in cell homeostasis and diseases. Autophagy is regulated by coordinated actions of a series of autophagy-related (ATG) proteins. The Barkor/ATG14(L)-VPS34 (a class III phosphatidylinositol 3-kinase) complex and its product phosphatidylinositol 3-phosphate [PtdIns(3)P] play key roles in autophagy initiation. ATG14 contains a C-terminal Barkor/ATG14(L) autophagosome-targeting sequence (BATS) domain that senses the curvature of PtdIns(3)P-containing membrane. The BATS domain also strongly binds PtdIns(4,5)P2, but the functional significance has been unclear. Here we show that ATG14 specifically interacts with type Iγ PIP kinase isoform 5 (PIPKIγi5), an enzyme that generates PtdIns(4,5)P2 in mammalian cells. Autophagosomes have associated PIPKIγi5 and PtdIns(4,5)P2 that are colocalized with late endosomes and the endoplasmic reticulum. PtdIns(4,5)P2 generation at these sites requires PIPKIγi5. Loss of PIPKIγi5 results in a loss of ATG14, UV irradiation resistance-associated gene, and Beclin 1 and a block of autophagy. PtdIns(4,5)P2 binding to the ATG14-BATS domain regulates ATG14 interaction with VPS34 and Beclin 1, and thus plays a key role in ATG14 complex assembly and autophagy initiation. This study identifies an unexpected role for PtdIns(4,5)P2 signaling in the regulation of ATG14 complex and autophagy.

IQGAP1 is a phosphoinositide effector and kinase scaffold.

Phosphatidylinositol 4,5-bisphosphate (PI4,5P2) is a lipid messenger that regulates a wide variety of cellular functions. The majority of cellular PI4,5P2 is generated by isoforms of the type I phosphatidylinositol phosphate kinases (PIPKI) that are generated from three genes, and each PIPKI isoform has a unique distribution and function in cells. It has been shown that the signaling specificity of PI4,5P2 can be determined by a physical association of PIPKs with PI4,5P2 effectors. IQGAP1 is newly identified as an interactor of multiple isoforms of PIPKs. Considering the versatile roles of IQGAP1 in cellular signaling pathways, IQGAP1 may confer isoform-specific roles of PIPKs in distinct cellular locations. In this mini review, the emerging roles of PIPKs that are regulated by an association with IQGAP1 will be summarized. Focuses will be on cell migration, vesicle trafficking, cell signaling, and nuclear events.

Emerging roles of PtdIns(4,5)P2--beyond the plasma membrane.

Phosphoinositides are a collection of lipid messengers that regulate most subcellular processes. Amongst the seven phosphoinositide species, the roles for phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] at the plasma membrane, such as in endocytosis, exocytosis, actin polymerization and focal adhesion assembly, have been extensively studied. Recent studies have argued for the existence of PtdIns(4,5)P2 at multiple intracellular compartments, including the nucleus, endosomes, lysosomes, autolysosomes, autophagic precursor membranes, ER, mitochondria and the Golgi complex. Although the generation, regulation and functions of PtdIns(4,5)P2 are less well-defined in most other intracellular compartments, accumulating evidence demonstrates crucial roles for PtdIns(4,5)P2 in endolysosomal trafficking, endosomal recycling, as well as autophagosomal pathways, which are the focus of this Commentary. We summarize and discuss how phosphatidylinositol phosphate kinases, PtdIns(4,5)P2 and PtdIns(4,5)P2-effectors regulate these intracellular protein and membrane trafficking events.

Phosphatidylinositol Phosphate 5-Kinase Iγ and Phosphoinositide 3-Kinase/Akt Signaling Couple to Promote Oncogenic Growth.

The assembly of signaling complexes at the plasma membrane is required for the initiation and propagation of cellular signaling upon cell activation. The class I PI3K and the serine/threonine-specific protein kinase Akt signaling pathways (PI3K/Akt) are often activated in tumors. These pathways are initiated by the generation of phosphatidylinositol 3,4,5-triphosphate (PIP3) by PI3K-mediated phosphorylation of phosphatidylinositol 4,5-biphosphate (PIP2), synthesized by phosphatidylinositol 4-phosphate 5-kinase (PIPKI) enzymes. The mechanism of how tumor cells recruit and organize the PIP2-synthesizing enzymes with PI3K in the plasma membrane for activation of PI3K/Akt signaling is not defined. Here, we demonstrated a role for the phosphatidylinositol 4-phosphate 5-kinase Iγ (PIPKIγ) in PI3K/Akt signaling. PIPKIγ is overexpressed in triple-negative breast cancers. Loss of PIPKIγ or its focal adhesion-targeting variant, PIPKIγi2, impaired PI3K/Akt activation upon stimulation with growth factors or extracellular matrix proteins in different tumor cells. PIPKIγi2 assembles into a complex containing Src and PI3K; Src was required for the recruitment of PI3K enzyme into the complex. PIPKIγi2 interaction with Src and its lipid kinase activity were required for promoting PI3K/Akt signaling. These results define a mechanism by which PIPKIγi2 and PI3K are integrated into a complex regulated by Src, resulting in the spatial generation of PIP2, which is the substrate PI3K required for PIP3 generation and subsequent Akt activation. This study elucidates the mechanism by which PIP2-generating enzyme controls Akt activation upstream of a PI3K enzyme. This pathway may represent a signaling nexus required for the survival and growth of metastasizing and circulating tumor cells in vivo.

PIP kinases define PI4,5P2signaling specificity by association with effectors.

Phosphatidylinositol 4,5-bisphosphate (PI4,5P2) is an essential lipid messenger with roles in all eukaryotes and most aspects of human physiology. By controlling the targeting and activity of its effectors, PI4,5P2modulates processes, such as cell migration, vesicular trafficking, cellular morphogenesis, signaling and gene expression. In cells, PI4,5P2has a much higher concentration than other phosphoinositide species and its total content is largely unchanged in response to extracellular stimuli. The discovery of a vast array of PI4,5P2 binding proteins is consistent with data showing that the majority of cellular PI4,5P2is sequestered. This supports a mechanism where PI4,5P2functions as a localized and highly specific messenger. Further support of this mechanism comes from the de novo synthesis of PI4,5P2which is often linked with PIP kinase interaction with PI4,5P2effectors and is a mechanism to define specificity of PI4,5P2signaling. The association of PI4,5P2-generating enzymes with PI4,5P2effectors regulate effector function both temporally and spatially in cells. In this review, the PI4,5P2effectors whose functions are tightly regulated by associations with PI4,5P2-generating enzymes will be discussed. This article is part of a Special Issue entitled Phosphoinositides.

Isoform 5 of PIPKIγ regulates the endosomal trafficking and degradation of E-cadherin.

Phosphatidylinositol phosphate kinases (PIPKs) have distinct cellular targeting, allowing for site-specific synthesis of phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] to activate specific signaling cascades required for cellular processes. Several C-terminal splice variants of PIPKIγ (also known as PIP5K1C) exist, and have been implicated in a multitude of cellular roles. PI(4,5)P2 serves as a fundamental regulator of E-cadherin transport, and PI(4,5)P2-generating enzymes are important signaling relays in these pathways. We present evidence that the isoform 5 splice variant of PIPKIγ (PIPKIγi5) associates with E-cadherin and promotes its lysosomal degradation. Additionally, we show that the endosomal trafficking proteins SNX5 and SNX6 associate with PIPKIγi5 and inhibit PIPKIγi5-mediated E-cadherin degradation. Following HGF stimulation, activated Src directly phosphorylates PIPKIγi5. Phosphorylation of the PIPKIγi5 C-terminus regulates its association with SNX5 and, consequently, E-cadherin degradation. Additionally, this PIPKIγi5-mediated pathway requires Rab7 to promote degradation of internalized E-cadherin. Taken together, the data indicate that PIPKIγi5 and SNX5 are crucial regulators of E-cadherin sorting and degradation. PIPKIγi5, SNX and phosphoinositide regulation of lysosomal sorting represent a novel area of PI(4,5)P2 signaling and research. PIPKIγi5 regulation of E-cadherin sorting for degradation might have broad implications in development and tissue maintenance, and enhanced PIPKIγi5 function might have pathogenic consequences due to downregulation of E-cadherin.