Insulin is the primary hormone involved in glucose homeostasis, and impairment of insulin action and/or secretion has a critical role in the pathogenesis of diabetes mellitus. Type-II SH2-domain-containing inositol 5-phosphatase, or 'SHIP2', is a member of the inositol polyphosphate 5-phosphatase family. In vitro studies have shown that SHIP2, in response to stimulation by numerous growth factors and insulin, is closely linked to signalling events mediated by both phosphoinositide-3-OH kinase and Ras/mitogen-activated protein kinase. Here we report the generation of mice lacking the SHIP2 gene. Loss of SHIP2 leads to increased sensitivity to insulin, which is characterized by severe neonatal hypoglycaemia, deregulated expression of the genes involved in gluconeogenesis, and perinatal death. Adult mice that are heterozygous for the SHIP2 mutation have increased glucose tolerance and insulin sensitivity associated with an increased recruitment of the GLUT4 glucose transporter and increased glycogen synthesis in skeletal muscles. Our results show that SHIP2 is a potent negative regulator of insulin signalling and insulin sensitivity in vivo.

Highlights d C-terminal helix alteration unfolds APOL1, increasing APOL1 interaction with APOL3 d APOL3 binds to NCS-1, promoting NCS-1-PI4KB interaction and PI4KB activation d C-terminal APOL1 variants interfere with APOL3-NCS-1 interaction, inactivating PI4KB d PI4KB inactivation occurs in podocytes from kidney disease patients with APOL1 variants

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Inositol 1,4,5-trisphosphate (Ins(1,4,5)P(3)) is phosphorylated by Ins(1,4,5)P(3) 3-kinase, generating inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P(4)). The physiological function of Ins(1,3,4,5)P(4) is still unclear, but it has been reported to be a potential modulator of calcium mobilization. Disruption of the gene encoding the ubiquitously expressed Ins(1,4,5)P(3) 3-kinase isoform B (Itpkb) in mice caused a severe T cell deficiency due to major alterations in thymocyte responsiveness and selection. However, we were unable to detect substantial defects in Ins(1,4,5)P(3) amounts or calcium mobilization in Itpkb(-/-) thymocytes. These data indicate that Itpkb and Ins(1,3,4,5)P(4) define an essential signaling pathway for T cell precursor responsiveness and development.

Somatostatin limits cell growth by inhibiting the proliferative activity of growth factor receptors. In this study, it is shown that in pituitary tumor cells, the somatostatin analogue octreotide produces its antiproliferative action by inducing the expression the tumor suppressor gene Zac1. ZAC/Zac1 induces cell cycle arrest and apoptosis and is highly expressed in normal pituitary, mammary, and ovarian glands but is down-regulated in pituitary, breast, and ovarian tumors. Knocking down Zac1 by RNA interference abolished the antiproliferative effect of octreotide in pituitary tumor cells, indicating that Zac1 is necessary for the action of octreotide. The effect of octreotide on Zac1 expression was pertussis toxin sensitive and was abolished after transfection with a dominant negative vector for SHP-1. Zac1 is a target of the phosphatidylinositol 3-kinase (PI3K) survival pathway. Octreotide treatment decreased the tyrosine phosphorylation levels of the PI3K regulatory subunit p85, induced dephosphorylation of phosphoinositidedependent kinase 1 (PDK1) and Akt, and activated glycogen synthase kinase 3B (GSKB). Therefore, in pituitary tumor cells, somatostatin analogues produce their antiproliferative action by acting on the PI3K/Akt signaling pathway and increasing

The consequences of the rapid 3-phosphorylation of inositol 1,4,5-trisphosphate (IP 3 ) to produce inositol 1,3,4,5-tetrakisphosphate (IP 4 ) via the action of IP 3 3-kinases involve the control of calcium signals. Using green fluorescent protein constructs of full-length and truncated IP 3 3-kinase isoform A expressed in HeLa cells, COS-7 cells, and primary neuronal cultures, we have defined a novel N-terminal 66-amino acid F-actin-binding region that localizes the kinase to dendritic spines. The region is necessary and sufficient for binding Factin and consists of a proline-rich stretch followed by a predicted ␣-helix. We also localized endogenous IP 3 3-kinase A to the dendritic spines of pyramidal neurons in primary hippocampal cultures, where it is co-localized postsynaptically with calcium/calmodulin-dependent protein kinase II. Our experiments suggest a link between inositol phosphate metabolism, calcium signaling, and the actin cytoskeleton in dendritic spines. The phosphorylation of IP 3 in dendritic spines to produce IP 4 is likely to be important for modulating the compartmentalization of calcium at synapses.Inositol 1,4,5-trisphosphate (IP 3 ) 1 signals in neurons are terminated predominantly via the action of calcium-stimulated IP 3 3-kinases (IP3kins) (1). These enzymes produce 1,3,4,5-tetrakisphosphate (IP 4 ), which does not gate IP 3 receptor calcium channels and may have signaling properties of its own (2-4). Brain has more IP3kin activity than other tissues (5), and this is due to the concentration of the A isoform in the dendrites of principal neurons, such as cerebellar Purkinje cells, hippocampal CA1 pyramidal cells, and dentate gyrus granule cells (6 -8). Targeted disruption of IP3kin A isoform (IP3kinA) produces mice with enhanced long term potentiation but normal spatial learning (9). By contrast, injecting IP 4 into pyramidal neurons prior to tetanic stimulation strengthens the long term potentiation via a mechanism that involves the enhancement of voltage-activated calcium channels by IP 4 (10).IP3kins are members of the inositol polyphosphate kinase family, which consists of proteins sharing a conserved C-terminal catalytic region (4, 11). Animal IP3kins are the only inositol polyphosphate kinases thought to be regulated by calcium, both via direct interaction with calmodulin and by phosphorylation by calmodulin-dependent kinase II (CaMKII) (12)(13)(14). The B isoform of IP3kin, which is expressed in most cells and in glia in brain (5, 15), is localized to internal membranes of the endoplasmic reticulum and Golgi apparatus, where it is poised to regulate IP 3 concentrations near calcium stores (16). In contrast, nothing is known about targeting mechanisms for isoform A in neurons.Based on purification of the bovine and rat brain enzyme, IP3kinA activity and protein have been described as cytosolic (17)(18)(19), in contrast to type I 5-phosphatase that appears to be mostly membrane-bound (20). Immunocytochemical studies employing antibodies against the purified rat brain enzyme reveale...

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN), a phosphoinositide 3-phosphatase, is an important regulator of insulin-dependent signaling. The loss or impairment of PTEN results in an antidiabetic impact, which led to the suggestion that PTEN could be an important target for drugs against type II diabetes. Here we report the design and validation of a small- molecule inhibitor of PTEN. Compared with other cysteine-based phosphatases, PTEN has a much wider active site cleft enabling it to bind the PtdIns(3,4,5)P3 substrate. We have exploited this feature in the design of vanadate scaffolds complexed to a range of different organic ligands, some of which show potent inhibitory activity. A vanadyl complexed to hydroxypicolinic acid was found to be a highly potent and specific inhibitor of PTEN that increases cellular PtdIns(3,4,5)P3 levels, phosphorylation of Akt, and glucose uptake in adipocytes at nanomolar concentrations. The findings presented here demonstrate the applicability of a novel and specific chemical inhibitor against PTEN in research and drug development.

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