Discovery and functional characterization of a novel small molecule inhibitor of the intracellular phosphatase, SHIP2.

BACKGROUND AND PURPOSE: The lipid phosphatase known as SH2 domain-containing inositol 5'-phosphatase 2 (SHIP2) plays an important role in the regulation of the intracellular insulin signalling pathway. Recent studies have suggested that inhibition of SHIP2 could produce significant benefits in treatment of type 2 diabetes. However, there were no small molecule SHIP2 inhibitors and we, therefore, aimed to identify this type of compound. EXPERIMENTAL APPROACH: The phosphatase assay with malachite green was used for high-throughput screening. The pharmacological profiles of suitable compounds were further characterized in phosphatase assays, cellular assays and oral administration in normal and diabetic (db/db) mice. KEY RESULTS: During high-throughput screening, AS1949490 was identified as a potent SHIP2 inhibitor (IC(50)= 0.62 microM for SHIP2). This compound was also selective for SHIP2 relative to other intracellular phosphatases. In L6 myotubes, AS1949490 increased the phosphorylation of Akt, glucose consumption and glucose uptake. In FAO hepatocytes, AS1949490 suppressed gluconeogenesis. Acute administration of AS1949490 inhibited the expression of gluconeogenic genes in the livers of normal mice. Chronic treatment of diabetic db/db mice with AS1949490 significantly lowered the plasma glucose level and improved glucose intolerance. These in vivo effects were based in part on the activation of intracellular insulin signalling pathways in the liver. CONCLUSIONS AND IMPLICATIONS: This is the first report of a small molecule inhibitor of SHIP2. This compound will help to elucidate the physiological functions of SHIP2 and its involvement in various diseases, such as type 2 diabetes.

NF-kappaB activation by camptothecin. A linkage between nuclear DNA damage and cytoplasmic signaling events.

Activation of the transcription factor NF-kappaB by extracellular signals involves its release from the inhibitor protein IkappaBalpha in the cytoplasm and subsequent nuclear translocation. NF-kappaB can also be activated by the anticancer agent camptothecin (CPT), which inhibits DNA topoisomerase (Topo) I activity and causes DNA double-strand breaks during DNA replication to induce S phase-dependent cytotoxicity. Here we show that CPT activates NF-kappaB by a mechanism that is dependent on initial nuclear DNA damage followed by cytoplasmic signaling events. NF-kappaB activation by CPT is dramatically diminished in cytoplasts and in CEM/C2 cells expressing a mutant Topo I protein that fails to bind CPT. This response is intensified in S phase cell populations and is prevented by the DNA polymerase inhibitor aphidicolin. In addition, CPT activation of NF-kappaB involves degradation of cytoplasmic IkappaBalpha by the ubiquitin-proteasome pathway in a manner that depends on the IkappaB kinase complex. Finally, inhibition of NF-kappaB activation augments CPT-induced apoptosis. These findings elucidate the progression of signaling events that initiates in the nucleus with CPT-Topo I interaction and continues in the cytoplasm resulting in degradation of IkappaBalpha and nuclear translocation of NF-kappaB to attenuate the apoptotic response.

TRAF6 is a signal transducer for interleukin-1.

Many cytokines signal through different cell-surface receptors to activate the transcription factor NF-kappaB. Members of the TRAF protein family have been implicated in the activation of NF-kappaB by the tumour-necrosis factor (TNF)-receptor superfamily. Here we report the identification of a new TRAF family member, designated TRAF6. When overexpressed in human 293 cells, TRAF6 activates NF-kappaB. A dominant-negative mutant of TRAF6 inhibits NF-kappaB activation signalled by interleukin-1 (IL-1) but not by TNF. IL-1 treatment of 293 cells induces the association of TRAF6 with IRAK, a serine/threonine kinase that is rapidly recruited to the IL-1 receptor after IL-1 induction. These findings indicate that TRAF proteins may function as signal transducers for distinct receptor families and that TRAF6 participates in IL-1 signalling.

Molecular characterization of an insect transferrin and its selective incorporation into eggs during oogenesis.

A protein with a molecular mass of 65 kDa that was specifically taken up into eggs was purified from the hemolymph of adult female Sarcophaga peregrina flies. From cDNA analysis, this protein was shown to be a Sarcophaga transferrin. Unlike mammalian transferrin, the similarity between its N-terminal and C-terminal halves was only 19%, and it was suggested to conjugate one iron atom/molecule in its N-terminal half. Sarcophaga transferrin was found to transport iron ions into eggs during oogenesis and deliver them to another protein, thought to be ferritin. No significant activation of the transferrin gene was detected during embryogenesis, so probably maternal transferrin is used as an intercellular or intracellular iron-transporter during embryogenesis of this insect.

Purification and molecular cloning of cDNA for an inducible antibacterial protein of larvae of a coleopteran insect, Holotrichia diomphalia.

Injection of Escherichia coli into larvae of the coleopteran Holotrichia diomphalia results in the appearance of antibacterial activity in the hemolymph. An antibacterial protein, named holotricin 2, was purified from larvae of this insect and characterized. A cDNA clone for holotricin 2 was isolated and its complete sequence was determined. This protein was found to inhibit the growth of Gram-negative bacteria and to consist of 72-amino acid residues with no cysteine residues. Its amino acid sequence is similar to that of coleoptericine, an antibacterial protein isolated from larvae of the coleopteran Zophobas atratus.

Evidence for an increase in positive surface charge and an increase in susceptibility to trypsin of Sarcophaga lectin (from the flesh fly, Sarcophaga peregrina) on its interaction with galactose, a hapten sugar of the lectin.

When Sarcophaga lectin (from the flesh fly, Sarcophaga peregrina), an insect humoral lectin, was eluted from a column of DEAE-cellulose in the presence of galactose (a hapten sugar of this lectin), it emerged at a lower salt concentration than when galactose was absent. In the presence of galactose the lectin was, in addition, more susceptible to trypsin digestion. The lectin was found to have an affinity for basic proteins such as histone H3 and sarcotoxin IA, but this property was lost in the presence of galactose. These results suggested that the lectin changes its conformation on interaction with galactose. This change is suggested to result in the exposure of some hidden lysine and/or arginine residues.