Lipid kinases play crucial and multiple roles in membrane trafficking and signaling

Membrane Recognition and Binding by the Phosphatidylinositol Phosphate Kinase PIP5K1A: A Multiscale Simulation Study

Phosphatidylinositol phosphates (PIPs) are lipid signaling molecules that play key roles in many cellular processes. PIP5K1A kinase catalyzes phosphorylation of PI4P to form PIP₂, which in turn interacts with membrane and membrane-associated proteins. We explore the mechanism of membrane binding by the PIP5K1A kinase using a multiscale molecular dynamics approach. Coarse-grained simulations show binding of monomeric PIP5K1A to a model cell membrane containing PI4P. PIP5K1A did not bind to zwitterionic or anionic membranes lacking PIP molecules. Initial encounter of kinase and bilayer was followed by reorientation to enable productive binding to the PI4P-containing membrane. The simulations suggest that unstructured regions may be important for the preferred orientation for membrane binding. Atomistic simulations indicated that the dimeric kinase could not bind to the membrane via both active sites at the same time, suggesting a conformational change in the protein and/or bilayer distortion may be needed for dual-site binding to occur.

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PIP5K1A kinase interacts with PIP-containing membranes via its activation loop

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PIP5K1A does not bind to zwitterionic or anionic membranes lacking PIP molecules

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Initial encounter of protein and bilayer is followed by reorientation and binding

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Dimeric PIP5K1A binds with membrane contacts via only one catalytic site at a time

Unraveling the Function of Lemur Tyrosine Kinase 2 Network

Lemur Tyrosine Kinase 2 (LMTK2) is a recently cloned transmembrane protein, actually a serine/threonine kinase named after the Madagascar primate lemur due to the long intracellular C-terminal tail. LMTK2 is relatively little known, compared to other kinases but its role has been increasingly recognized. Published data show that LMTK2 regulates key cellular events, including endocytic trafficking, nerve growth factor signaling, apoptosis, and Cl^- transport. Abnormalities in the expression and function of LMTK2 are associated with human disease, such as neurodegeneration, cancer and infertility. We summarized the current state of knowledge on LMTK2 structure, regulation, interactome, intracellular localization, and tissue expression and point out future research directions to better understand the role of LMTK2.

Discovery of a Potent, Orally Bioavailable PI4KIIIβ Inhibitor (UCB9608) Able To Significantly Prolong Allogeneic Organ Engraftment in Vivo

The primary target of a novel series of immunosuppressive 7-piperazin-1-ylthiazolo[5,4- d]pyrimidin-5-amines was identified as the lipid kinase, PI4KIIIβ. Evaluation of the series highlighted their poor solubility and unwanted off-target activities. A medicinal chemistry strategy was put in place to optimize physicochemical properties within the series, while maintaining potency and improving selectivity over other lipid kinases. Compound 22 was initially identified and profiled in vivo, before further modifications led to the discovery of 44 (UCB9608), a vastly more soluble, selective compound with improved metabolic stability and excellent pharmacokinetic profile. A co-crystal structure of 44 with PI4KIIIβ was solved, confirming the binding mode of this class of inhibitor. The much-improved in vivo profile of 44 positions it as an ideal tool compound to further establish the link between PI4KIIIβ inhibition and prolonged allogeneic organ engraftment, and suppression of immune responses in vivo.

The human kinome and kinase inhibition

Protein and lipid kinases play key regulatory roles in a number of biological processes. Unsurprisingly, activating mutations in kinases have been linked to a number of disorders and diseases, most notably cancers. Thus, kinases have emerged as promising clinical targets. There are more than 500 human protein kinases and about 20 lipid kinases. Most protein kinases share a highly conserved domain, the eukaryotic protein kinase (ePK) domain, which contains the ATP and substrate-binding sites. Many inhibitors in clinical use bind to the highly conserved ATP binding site. For this reason, many kinase inhibitors are not exclusively selective for their intended targets. Furthermore, despite the current interest in kinase inhibitors, very few kinases implicated in disease have validated inhibitors. This unit describes the human kinome, ePK structure, and types of kinase inhibitors, focusing on methods to identify potent and selective kinase inhibitors.

Insulin clearance: confirmation as a highly heritable trait, and genome-wide linkage analysis

AIMS/HYPOTHESIS

We have previously documented a high heritability of insulin clearance in a Hispanic cohort. Here, our goal was to confirm the high heritability in a second cohort and search for genetic loci contributing to insulin clearance.

METHODS

Hyperinsulinaemic-euglycaemic clamps were performed in 513 participants from 140 Hispanic families. Heritability was estimated for clamp-derived insulin clearance and a two-phase genome-wide linkage scan was conducted using a variance components approach. Linkage peaks were further investigated by candidate gene association analysis in two cohorts.

RESULTS

The covariate-adjusted heritability of insulin clearance was 73%, indicating that the majority of the phenotypic variance is due to genetic factors. In the Phase 1 linkage scan, no signals with a logarithm of odds (LOD) score >2 were detected. In the Phase 2 scan, two linkage peaks with an LOD >2 for insulin clearance were identified on chromosomes 15 (LOD 3.62) and 20 (LOD 2.43). These loci harbour several promising candidate genes for insulin clearance, with 12 single nucleotide polymorphisms (SNPs) on chromosome 15 and six SNPs on chromosome 20 being associated with insulin clearance in both Hispanic cohorts.

CONCLUSIONS/INTERPRETATION

In a second Hispanic cohort, we confirmed that insulin clearance is a highly heritable trait and identified chromosomal loci that harbour genes regulating insulin clearance. The identification of such genes may improve our understanding of how the body clears insulin, thus leading to improved risk assessment, diagnosis, prevention and therapy of diabetes, as well as of other hyperinsulinaemic disorders, such as the metabolic syndrome and polycystic ovary syndrome.

Phosphatidylinositol-4-phosphate-5-kinase alpha deficiency alters dynamics of glucose-stimulated insulin release to improve glucohomeostasis and decrease obesity in mice

OBJECTIVE

Phosphatidylinositol-4-phosphate-5-kinase (PI4P5K) has been proposed to facilitate regulated exocytosis and specifically insulin secretion by generating phosphatidylinositol-4,5-bisphosphate (PIP(2)). We sought to examine the role of the α isoform of PI4P5K in glucohomeostasis and insulin secretion.

RESEARCH DESIGN AND METHODS

The response of PI4P5Kα(-/-) mice to glucose challenge and a type 2-like diabetes-inducing high-fat diet was examined in vivo. Glucose-stimulated responses and PI4P5Kα(-/-) pancreatic islets and β-cells were characterized in culture.

RESULTS

We show that PI4P5Kα(-/-) mice exhibit increased first-phase insulin release and improved glucose clearance, and resist high-fat diet-induced development of type 2-like diabetes and obesity. PI4P5Kα(-/-) pancreatic islets cultured in vitro exhibited decreased numbers of insulin granules docked at the plasma membrane and released less insulin under quiescent conditions, but then secreted similar amounts of insulin on glucose stimulation. Stimulation-dependent PIP(2) depletion occurred on the plasma membrane of the PI4P5Kα(-/-) pancreatic β-cells, accompanied by a near-total loss of cortical F-actin, which was already decreased in the PI4P5Kα(-/-) β-cells under resting conditions.

CONCLUSIONS

Our findings suggest that PI4P5Kα plays a complex role in restricting insulin release from pancreatic β-cells through helping to maintain plasma membrane PIP(2) levels and integrity of the actin cytoskeleton under both basal and stimulatory conditions. The increased first-phase glucose-stimulated release of insulin observed on the normal diet may underlie the partial protection against the elevated serum glucose and obesity seen in type 2 diabetes-like model systems.