Enhanced expression of insulin receptor substrate-2 and activation of protein kinase B/Akt in regenerating pancreatic duct epithelium of 60 %-partial pancreatectomy rats

AIMS/HYPOTHESIS

Early compensatory mechanisms of regeneration following partial pancreatectomy involve ductal proliferation and, subsequently, differentiation into acinar and endocrine cell types, although it is not clear how these processes are regulated. We investigated the expression and roles of insulin receptor substrate-2 (IRS-2) and protein kinase B/Akt (Akt) in pancreatic regeneration that starts with the common duct epithelium using a non-diabetic model of beta cell adaptation and mass expansion, 60 %-pancreatectomy rats.

METHODS

We used confocal immunofluorescence microscopy to study IRS-2 and Akt expression and activation in pancreatic common ducts at intervals after surgery. These proteins were studied in relation to proliferation markers and insulin immunostaining.

RESULTS

In pancreatectomized rats, a short-term increase in proliferation was observed in the common duct epithelial lining ( approximately 4-fold) compared with sham-operated control rats which correlated with about a 1.8-fold increase in IRS-2 immunoreactivity 2 days after surgery. Interspersed with proliferating cells of the common duct, evaginations were rare single and clustered insulin immunopositive cells which expressed high levels of IRS-2 immunoreactivity. Epithelium of duct evaginations from 2-day post-Px rats exhibited striking phospho-Akt staining ( approximately 3.5-fold above control rats) without any detectable changes in total Akt staining.

CONCLUSION/INTERPRETATION

Our data suggest that IRS-2 plays an important role in pancreatic regeneration and growth by mediating duct proliferation and by maintaining the differentiated beta cell. The restricted staining pattern of phospho-Akt to cells of the common duct evaginations suggests that it has a role in regulating post-mitotic events related to cell-specific gene expression or survival or both.

[Research on automatic diagnosis system of electrocardiogram]

The duration of QRS wave, P wave and T wave of ECG can be computerized and auto-detected with digital signal process and wave recognition technology. It can diagnose 15 kinds of abnormal ECG such as ventricular presystole automatically and print out corresponding diagnosis reports. In order to verify the system's stability and creditability, we used American MIT-BIH database to test our algorithms and got a good result.

[Effect of dynorphin A1-13 on C6 glioma cells swelling induced by glutamate]

AIM AND METHOD

To explore the cell mechanism of brain edema and the effect of dynorphin A1-13 on swelling of C6 glioma cells. Water content of cell are studied by using 3-O-methyl-D-glucose.

RESULTS

(1) Glutamate (0.5, 1.0, 10.0 mmol/L) increased the water content of C6 glioma at an hour. (2) Dynorphin A1-13 could significantly decrease the increasing in water content of C6 glioma cells induced by glutamate. (3) nor-BNI, a antagonist, could inhibit the effect of dynorphin A1-13 on water content of swelling C6 glioma cells.

CONCLUSION

Glutamate could induce the swelling of C6 glioma cells. Dynorphin A1-13 could reduce C6 glioma cells swelling induced by glutamate via kappa opioid receptor.

Neurite morphogenesis of identified visual interneurons and its relationship to photoreceptor synaptogenesis in the flies, Musca domestica and Drosophila melanogaster

The first neuropile, or lamina, of the fly's optic lobe comprises a model set of identified neurons that are arrayed in cylindrical modules, called cartridges. The cartridge acquires adult form only in the second half of the fly's pupal life. All cells are by then correctly located within each of the lamina's cartridges (Drosophila, Musca), becoming invested by glial cells after 75% of pupal development (P + 75%). In adult cartridges, two lamina cells, L1 and L2, receive input from photoreceptor terminals R1-R6, at so-called tetrad synapses that form in the pupa when these cells' dendrites contact R1-R6. Single-section electron microscopy (EM, Drosophila) and serial-EM reconstructions of L1 and L2 (Musca) reveal relationships between the morphogenesis of L1/L2 dendrites and the formation of tetrads. Neurite outgrowth is initially (P + 55%) random and neurites are unbranched; many neurites invaginate surrounding terminals of R1-R6 but, later, embrace the outer surfaces of these. The maximum profusion of neurites at P + 74% coincides with peak numbers of nascent tetrads; neurites then branch vertically, in the lamina's depth. Later, neurites failing to reach R1-R6's outer surfaces regress. Down the length of their axons, L1 and L2's neurites initially form a random sequence, L1 partnering L1 as often as L2, etc., but beginning at P + 74%, L1 partners L2, and L2 partners L1, with progressive strictness. L1 has more neurites overall than L2. These observations are consistent with the following hypotheses: a neurite only survives if it contacts a presynaptic site; a synapse only survives if it progressively acquires the appropriate number and combination of postsynaptic neurites, culminating in a tetrad; an interaction exists between the neurites of L1 and L2, so that the growth of one respects the pattern of growth of the other.

[Derivative gas chromatographic analysis of fructooligosaccharide in fermented sucrose]

As a new sweetener, fructooligosaccharide is paid more and more attention for its health improvement property. It includes trisaccharide, tetrasaccharide and pentasaccharide, and can be produced from sucrose by the fermentation of microorganism. In order to analyze the content of fructooligosaccharide in fermented sugar by gas chromatography, fructooligosaccharide was transformed into trimethylsilyl derivatives. Based on the modified gas chromatograph SP2308, and under the chosen chromatographic conditions with 0.53 mm capillary column of OV-101, the contents of fructose, glucose, sucrose and fructooligosaccharide were determined by programmed temperature chromatography. The recovery of fructooligosaccharide was satisfactory.

Insulin-induced insulin receptor substrate-1 degradation is mediated by the proteasome degradation pathway

Insulin receptor substrate (IRS) proteins are important intracellular molecules that mediate insulin receptor tyrosine kinase signaling. A decreased content of IRS proteins has been found in insulin-resistant states in animals, humans, and cultured cells under various conditions. However, the molecular mechanism that controls cellular levels of IRS proteins is unknown. We report that chronic insulin treatment induces the degradation of IRS-1, but not IRS-2, protein in cultured cells. The insulin-induced degradation of IRS-1 can be prevented by pretreatment with lactacystin, a specific inhibitor for proteasome degradation. These data demonstrate, for the first time, that insulin-induced degradation of IRS-1 is mediated by the proteasome degradation pathway. IRS-2 can escape from the insulin-induced proteasome degradation, suggesting the existence of specific structural requirements for this degradation process.

Identification of enhanced serine kinase activity in insulin resistance

Insulin receptor substrate (IRS) proteins play a crucial role as signaling molecules in insulin action. Serine phosphorylation of IRS proteins has been hypothesized as a cause of attenuating insulin signaling. The current study investigated serine kinase activity toward IRS-1 in several models of insulin resistance. An in vitro kinase assay was developed that used partially purified cell lysates as a kinase and glutathione S-transferase fusion proteins that contained various of IRS-1 fragments as substrates. Elevated serine kinase activity was detected in Chinese hamster ovary/insulin receptor (IR)/IRS-1 cells and 3T3-L1 adipocytes chronically treated with insulin, and in liver and muscle of obese JCR:LA-cp rats. It phosphorylated the 526-859 amino acid region of IRS-1, whereas phosphorylation of the 2-516 and 900-1235 amino acid regions was not altered. Phosphopeptide mapping of the 526-859 region of IRS-1 showed three major phosphopeptides (P1, P2, and P3) with different patterns of phosphorylation depending on the source of serine kinase activity. P1 and P2 were strongly phosphorylated when the kinase activity was prepared from insulin-resistant Chinese hamster ovary/IR/IRS-1 cells, weakly phosphorylated by the kinase activity from insulin-resistant 3T3-L1 adipocytes, and barely phosphorylated when the extract was derived from insulin-resistant liver. In contrast, P3 was phosphorylated by the serine kinase activity prepared from all insulin-resistant cells and tissues of animals. P1 and P2 phosphorylation can be explained by mitogen-activated protein kinase activity based on the phosphopeptide map generated by recombinant ERK2. In contrast, mitogen-activated protein kinase failed to phosphorylate the P3 peptide, suggesting that another serine kinase regulates this modification of IRS-1 in insulin-resistant state.

Developmental anatomy of the Drosophila brain: neuroanatomy is gene expression

On-line databases of anatomical information are being compiled for a number of genetically manipulable organisms, including the fruit fly, Drosophila melanogaster. Based on the success of the molecular databases that preceded them, they face formidable problems in data cataloguing, storage, and retrieval. The prospect for such databases, which is apparent already, is to alter permanently the approach to neuroanatomy in such species. Experience with Drosophila indicates the possibility to arbitrate controversies over and, in some cases, to redefine the borders drawn in the brain by conventional neuroanatomical methods. Two publications in this issue of Journal of Comparative Neurology by Nassif et al. and by Hartenstein et al. highlight one of the first demonstrations of a further opportunity in Drosophila. In some cases, it is already possible to suggest how individual cellular elements--neurons, tracts, and neuropil regions--might be traced from the time when they first express a precocious marker, such as the product of the fasciclin-II gene, through the metamorphic pupal stage, and into the adult. In this way, it becomes possible to identify the structures of the adult brain from the time of their first emergence in the embryo and to follow their transitional positions throughout the course of development. Critical in this process is the neuroanatomical organization of the larval brain, which contains not only the fully functional central nervous system of the larva but also the developing elements of the adult brain, because this holds the key to understanding both the cellular elements that are inherited from the embryo and the elements that are in the process of forming the adult nervous system.

A rapid method for combined laser scanning confocal microscopic and electron microscopic visualization of biocytin or neurobiotin-labeled neurons

Intracellular recording and dye filling are widely used to correlate the morphology of a neuron with its physiology. With laser scanning confocal microscopy, the complex shapes of labeled neurons in three dimensions can be reconstructed rapidly, but this requires fluorescent dyes. These dyes are neither permanent nor electron dense and therefore do not allow investigation by electron microscopy. Here we report a technique that quickly and easily converts a fluorescent label into a more stable and electron-dense stain. With this technique, a neuron is filled with Neurobiotin or biocytin, reacted with fluorophore-conjugated avidin, and imaged by confocal microscopy. To permit long-term storage or EM study, the fluorescent label is then converted to a stable electron-dense material by a single-step conversion using a commercially available ABC kit. We find that the method, which apparently relies on recognition of avidin's excess biotin binding sites by the biotin-peroxidase conjugate, is both faster and less labor intensive than photo-oxidation procedures in common use. The technique is readily adaptable to immunocytochemistry with biotinylated probes, as we demonstrate using anti-serotonin as an example.

Mechanism of the dynorphin-induced dualistic effect on free intracellular Ca2+ concentration in cultured rat spinal neurons

In order to study the different mechanisms of dynorphin spinal analgesia and neurotoxicity at low and high doses, the effects of various concentrations of dynorphin A-(1-17) on the free intracellular Ca2+ concentration ([Ca2+]i) in the cultured rat spinal neurons were studied using single cell microspectrofluorimetry. While dynorphin A-(1-17) 0.1-100 microM had no significant effect on basal [Ca2+]i, dynorphin A-(1-17) 0.1 and 1 microM significantly decreased the high KCl-evoked peak [Ca2+]i by 94% and 83% respectively. Dynorphin A-(1-17) 10 and 100 microM did not affect the peak [Ca2+]i following K+ depolarization, but in all these neurons there was a sustained and irreversible rise in [Ca2+]i following high-K+ challenge. Pretreatment with the specific kappa-opioid receptor antagonist nor-binaltorphimine 10 microM, but not the competitive NMDA receptor antagonist, DL-2-amino-5-phosphonovalerate (APV) 10 microM, significantly blocked the inhibitory effect of dynorphin A-(1-17) 0.1 microM on peak [Ca2+]i. However, APV 10 microM and nor-binaltorphimine 10 microM significantly antagonized the sustained rise in [Ca2+]i induced by a high concentration of dynorphin A-(1-17) 10 microM. Furthermore, in the presence, and following the addition, of increasing concentrations of dynorphin A-(1-17) (0.1, 1, 10 and 100 microM), the high concentrations of dynorphin A-(1-17) failed to produce a sustained rise in peak [Ca2+]i. These results suggested that dynorphin exerted a dualistic modulatory effect on [Ca2+]i in cultured rat spinal neurons, inducing a sustained and irreversible intracellular Ca2+ overload via activation of both NMDA and kappa-opioid receptors at higher concentrations, but inhibiting depolarization-evoked Ca2+ influx via kappa-opioid but not NMDA receptors at lower concentrations. Serial addition of graded concentrations of dynorphin A-(1-17) prevented the effect of high concentrations of dynorphin A-(1-17) on [Ca2+]i.

The 60 kDa insulin receptor substrate functions like an IRS protein (pp60IRS3) in adipose cells

The 60 kDa insulin receptor substrate in rat adipocytes that binds to the PI-3 kinase displays several functional characteristics in common with the IRS proteins; so we propose the name pp60(IRS3) to distinguish it from other tyrosine phosphorylated proteins of similar size. During insulin stimulation, p85 associated with pp60(IRS3) more rapidly than with IRS-1 or IRS-2. In mice lacking IRS-1, p85 associated more strongly with pp60(IRS3) than with IRS-2, suggesting that pp60(IRS3) provides an alternate pathway in these cells. Synthetic peptides containing two phosphorylated YMPM motifs displace pp60(IRS3) and IRS-1 from alphap85 immune complexes, suggesting that pp60(IRS3), like IRS-1, engages both SH2 domains in p85. Moreover, pp60(IRS3) binds to immobilized peptides containing a phosphorylated NPXY motif, suggesting that it contains a PTB domain with similar specificity to that in IRS-1. The cloning of pp60(IRS3) will reveal a new member of the IRS protein family which mediates insulin receptor signals in a narrow range of tissues.

Synaptic organization of the uniglomerular projection neurons of the antennal lobe of the moth Manduca sexta: a laser scanning confocal and electron microscopic study

The detailed branching pattern and synaptic organization of the uniglomerular projection neurons of the antennal lobe, the first processing center of the olfactory pathway, of the moth Manduca sexta were studied with laser scanning confocal microscopy and a technique combining laser scanning confocal microscopy and electron microscopy. Uniglomerular projection neurons, identified electrophysiologically or morphologically, were stained intracellularly with neurobiotin or biocytin. Brains containing the injected neurons were treated with streptavidin-immunogold to label the injected material for electron microscopy and with Cy3-streptavidin to label the neurons with fluorescence for laser scanning confocal microscopy, and then embedded in Epon. Labeled neurons were imaged and reconstructed with laser scanning confocal microscopy (based on the retained fluorescence of the labeled neuron in the Epon block), and thin sections were cut at selected optical levels for correlation of light microscopic data and electron microscopic detail. Each neuron had a cell body in one of the three cell-body clusters of the antennal lobe, a primary neurite that extended across the coarse neuropil at the center of the antennal lobe and then formed a dense tuft of processes within a single glomerulus, and an axon that emanated from the primary neurite and projected from the antennal lobe via the antenno-cerebral tract to the lateral horn of the ipsilateral protocerebrum and, collaterally, to the calyces of the mushroom body. In the electron microscope, the fine dendritic branches in the apical zones of the glomeruli, where sensory axons terminate, were found to receive many input synapses. In deeper layers across the glomeruli, the processes participated in both input and output synapses, and the bases of the glomeruli, the most proximal, thickest branches formed output synapses. In both of the protocerebral areas in which axonal branches terminated, those branches formed exclusively output synapses. Our findings indicate that, in addition to conveying olfactory information to the protocerebrum, uniglomerular projection neurons in the antennal lobes of M. sexta participate in local intraglomerular synaptic circuitry.

Organization of the antennal motor system in the sphinx moth Manduca sexta

The antennae of the sphinx moth Manduca sexta are multimodal sense organs, each comprising three segments: scape, pedicel, and flagellum. Each antenna is moved by two systems of muscles, one controlling the movement of the scape and consisting of five muscles situated in the head capsule (extrinsic muscles), and the other system located within the scape (intrinsic muscles) and consisting of four muscles that move the pedicel. At least seven motoneurons innervate the extrinsic muscles, and at least five motoneurons innervate the intrinsic muscles. The dendritic fields of the antennal motoneurons overlap one another extensively and are located in the neuropil of the antennal mechanosensory and motor center. The density of motoneuronal arborizations is greatest in the lateral part of this neuropil region and decreases more medially. None of the motoneurons exhibits a contralateral projection. The cell bodies of motoneurons innervating the extrinsic muscles are distributed throughout an arching band of neuronal somata dorsal and dorsolateral to the neuropil of the antennal mechanosensory and motor center, whereas the cell bodies of motoneurons innervating the intrinsic muscles reside mainly among the neuronal somata situated dorsolateral to that neuropil.

The IRS-2 gene on murine chromosome 8 encodes a unique signaling adapter for insulin and cytokine action

Signal transduction by insulin and IGF-1, several interleukins (IL-2, IL-4, IL-9, IL-13), interferons, GH, and other cytokines involves IRS proteins, which link the receptors for these factors to signaling molecules with Src homology-2 domains (SH2-proteins). We recently reported the amino acid sequence of murine IRS-2; in order to examine a potential genetic role for this molecule in disease, we isolated the murine IRS-2 gene and compared the expression pattern of IRS-2 against IRS-1. Like IRS-1, IRS-2 is encoded by a single exon. Whereas IRS-1 is located on murine chromosome 1, IRS-2 is located on murine chromosome 8 near the insulin receptor. IRS-2 is expressed together with IRS-1 in many cells and tissues; however, IRS-2 predominates in murine hematopoietic cells where it may be essential for cytokine signaling; IRS-1 predominates in adipocytes and differentiated 3T3-L1 cells where it contributes to the normal insulin response. In 32D cells, IRS-1 and IRS-2 undergo differential tyrosine phosphorylation during insulin or IL-4 stimulation, as assessed indirectly by interaction with various recombinant SH2 domains. Thus, signaling specificity through the IRS proteins may be accomplished by specific expression patterns and distinct phosphorylation patterns during interaction with various activated receptors.

Activity blockade does not prevent the construction of olfactory glomeruli in the moth Manduca sexta

During metamorphic development, the arrival at the olfactory (antennal) lobe of olfactory receptor axons initiates the process of glomerulus formation. The glomeruli are discrete spheroidal regions of neuropil that are the sites of synaptic interactions among receptor neurons and their target antennal-lobe neurons. The process of glomerulus formation begins as groups of receptor axons form protoglomeruli. These dense clusters of terminal branches mostly are discrete entities from the time they can be recognized, although a few branches from neighboring protoglomeruli overlap laterally. A previous study by Schweitzer et al. [Schweitzer E. S., Sanes J. R. and Hildebrand J. G. (1976) Ontogeny of electroantennogram responses in the moth, Manduca sexta. J. Insect Physiol. 22, 955-960] has shown that odor-induced activity in the receptor neurons can be detected first in recordings from the axons in the antennal nerve only in the last few days of metamorphic development and thus could not influence the process of glomerulus formation. In this study, we have tested directly the possibility that an earlier presence of spontaneous activity in either the receptor axons or the antennal-lobe neurons could affect the process. Tetrodotoxin, a Na(+)-channel blocker, was injected into the hemolymph prior to the onset of glomerulus formation to block any spontaneous Na(+)-dependent activity. Subsequent intracellular recordings from antennal-lobe neurons revealed no spike activity. Comparison with vehicle-injected control animals at stages during and after glomerulus formation revealed no differences in the localization of receptor-axon terminal branches in the glomeruli, in the border of glial cells that forms around each glomerulus, or in the morphology of the tufted glomerular arbors of one of the antennal-lobe neurons. We conclude that: (1) the process of glomerulus formation is largely independent of activity; and (2) glomeruli as modular units of the CNS more closely resemble cortical barrels than cortical columns, both in their ontogeny and in the lack of an obvious effect of activity on the morphology of the neurons arborizing within them.

Cross-talk between the insulin and angiotensin signaling systems

Angiotensin II (AII), acting via its G-protein linked receptor, is an important regulator of cardiac, vascular, and renal function. Following injection of AII into rats, we find that there is also a rapid tyrosine phosphorylation of the major insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) in the heart. This phenomenon appears to involve JAK2 tyrosine kinase, which associates with the AT1 receptor and IRS-1/IRS-2 after AII stimulation. AII-induced phosphorylation leads to binding of phosphatidylinositol 3-kinase (PI 3-kinase) to IRS-1 and IRS-2; however, in contrast to other ligands, AII injection results in an acute inhibition of both basal and insulin-stimulated PI 3-kinase activity. The latter occurs without any reduction in insulin receptor or IRS phosphorylation or in the interaction of the p85 and p110 subunits of PI 3-kinase with each other or with IRS-1/IRS-2. These effects of AII are inhibited by AT1 receptor antagonists. Thus, there is direct cross-talk between insulin and AII signaling pathways at the level of both tyrosine phosphorylation and PI 3-kinase activation. These interactions may play an important role in the association of insulin resistance, hypertension, and cardiovascular disease.

Combining laser scanning confocal microscopy and electron microscopy in studies of the insect nervous system

Experimentally determining the synaptic interconnections between neurons in the nervous system is laborious and difficult in any animal species, but especially so in many invertebrates, including insects, where neurons generally have large, finely branching neuritic trees that form both pre- and postsynaptic specializations in dense neuropils with other neuritic trees. Electron microscopy is needed to identify synapses, but correlation of synapse type and location with the overall branching patterns of neurons, which are visible readily only in the light microscope or through extensive reconstruction of serial electron-microscope sections, is very difficult. In this paper, we present a simple method that we have developed (Sun et al. (1995) J. Histochem. Cytochem., 43: 329-335) that combines laser scanning confocal microscopy and electron microscopy for the study of synaptic relationships of neurons in the antennal lobe, the first central neuropil in the olfactory pathway, of the moth Manduca sexta. Briefly, neurons are labeled by intracellular injection with neurobiotin or biocytin, and then processed with a gold-particle tag for electron microscopic study and a fluorescent tag for confocal microscopy, and embedded in plastic. The fluorescence of the labeled neuron in the plastic blocks is imaged in three dimensions with laser scanning confocal microscopy and then the neuron is thin-sectioned at precisely chosen depths for electron microscopic study. The fluorescence pattern can be monitored repeatedly between episodes of thin-sectioning, and subtraction of a fluorescence image from the previous fluorescence image reveals which fluorescent processes have been sectioned. In this way, electron microscopic detail can be mapped onto a three-dimensional light microscopic image of the neuron.

YMXM motifs and signaling by an insulin receptor substrate 1 molecule without tyrosine phosphorylation sites

Tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) by the activated receptors for insulin, IGF-1, and various cytokines creates binding sites for signaling proteins with Src homology 2 domains (SH2 proteins). Determining the role of specific SH2 proteins during insulin signaling has been difficult because IRS-1 possesses as many as 18 potential tyrosine phosphorylation sites, several of which contain redundant motifs. Using 32D cells, which contain no endogenous IRS proteins, we compared the signaling ability of an IRS-1 molecule in which 18 potential tyrosine phosphorylation sites were replaced by phenylalanine (IRS-1(F18)) with two derivative molecules which retained three YMXM motifs (IRS-1(3YMXM)) or the two COOH-terminal SHP2-Fyn binding sites (IRS-1(YCT)). During insulin stimulation, IRS-1(F18) failed to undergo tyrosine phosphorylation or mediate activation of the phosphotidylinositol (PI) 3'-kinase or p70(s6k); IRS-1(YCT) was tyrosine phosphorylated but also failed to mediate these signaling events. Neither IRS-1(3YMXM) nor IRS-1(YCT) mediated activation of mitogen-activated protein kinases. IRS-1(F18) and IRS-1(YCT) partially mediated similar levels of insulin-stimulated mitogenesis at high insulin concentrations, however, suggesting that IRS-1 contains phosphotyrosine-independent elements which effect mitogenic signals, and that the sites in IRS-l(YCT) do not augment this signal. IRS-1(3YMXM) mediated the maximal mitogenic response to insulin, although the response to insulin was more sensitive with wild-type IRS-1. By contrast, the association of IRS-1(3YMXM) with PI 3'-kinase was more sensitive to insulin than the association with IRS-1. Thus, the binding of SH2 proteins (such as PI 3'-kinase) by YMXM motifs in IRS-1 is an important element in the mitogenic response, but other elements are essential for full mitogenic sensitivity.

The Fyn tyrosine kinase binds Irs-1 and forms a distinct signaling complex during insulin stimulation

Irs-proteins link the receptors for insulin/IGF-1, growth hormones, and several interleukins and interferons to signaling proteins that contain Src homology-2 (SH2). To identify new Irs-1-binding proteins, we screened a mouse embryo expression library with recombinant [32P]Irs-1, which revealed a specific association between p59fyn and Irs-1. The SH2 domain in p59fyn bound to phosphorylated Tyr895 and Tyr1172, which are located in YXX(L/I) motifs. Mutation of p59fyn at the COOH-terminal tyrosine phosphorylation site (Tyr531) enhanced its binding to Irs-1 during insulin stimulation. Binding experiments with various SH2 protein revealed that Grb-2 was largely excluded from Irs-1 complexes containing p59fyn, whereas Grb-2 and p85 occurred in the same Irs-1 complex. By comparison with the insulin receptor, p59fyn kinase phosphorylated a unique cohort of tyrosine residues in Irs-1. These results outline a role for p59fyn or other related Src-kinases during insulin and cytokine signaling.

The Drosophila insulin receptor activates multiple signaling pathways but requires insulin receptor substrate proteins for DNA synthesis

The Drosophila insulin receptor (DIR) contains a 368-amino-acid COOH-terminal extension that contains several tyrosine phosphorylation sites in YXXM motifs. This extension is absent from the human insulin receptor but resembles a region in insulin receptor substrate (IRS) proteins which binds to the phosphatidylinositol (PI) 3-kinase and mediates mitogenesis. The function of a chimeric DIR containing the human insulin receptor binding domain (hDIR) was investigated in 32D cells, which contain few insulin receptors and no IRS proteins. Insulin stimulated tyrosine autophosphorylation of the human insulin receptor and hDIR, and both receptors mediated tyrosine phosphorylation of Shc and activated mitogen-activated protein kinase. IRS-1 was required by the human insulin receptor to activate PI 3-kinase and p70s6k, whereas hDIR associated with PI 3-kinase and activated p70s6k without IRS-1. However, both receptors required IRS-1 to mediate insulin-stimulated mitogenesis. These data demonstrate that the DIR possesses additional signaling capabilities compared with its mammalian counterpart but still requires IRS-1 for the complete insulin response in mammalian cells.

The type I interferon receptor mediates tyrosine phosphorylation of insulin receptor substrate 2

Binding of interferon alpha (IFN alpha) to its receptor induces activation of the Tyk-2 and Jak-1 tyrosine kinases and tyrosine phosphorylation of multiple downstream signaling elements, including the Stat components of the interferon-stimulated gene factor 3 (ISGF-3). IFN alpha also induces tyrosine phosphorylation of IRS-1, the principle substrate of the insulin receptor. In this study we demonstrate that various Type I IFNs rapidly stimulate tyrosine phosphorylation of IRS-2. This is significant since IRS-2 is the major IRS protein found in hematopoietic cells. The IFN alpha-induced phosphorylated form of IRS-2 associates with the p85 regulatory subunit of the phosphatidylinositol 3'-kinase, suggesting that this kinase participates in an IFN alpha-signaling cascade downstream of IRS-2. We also provide evidence for an interaction of IRS-2 with Tyk-2, suggesting that Tyk-2 is the kinase that phosphorylates this protein during IFN alpha stimulation. A conserved region in the pleckstrin homology domain of IRS-2 may be required for the interaction of IRS-2 with Tyk-2, as shown by the selective binding of glutathione S-transferase (GST) fusion proteins containing the IRS-2-IH1PH or IRS-1-IH1PH domains to Tyk-2 but not other Janus kinases in vitro.

Interleukins 2, 4, 7, and 15 stimulate tyrosine phosphorylation of insulin receptor substrates 1 and 2 in T cells. Potential role of JAK kinases

The signaling molecules insulin receptor substrate (IRS)-1 and the newly described IRS-2 (4PS) molecule are major insulin and interleukin 4 (IL-4)-dependent phosphoproteins. We report here that IL-2, IL-7, and IL-15, as well as IL-4, rapidly stimulate the tyrosine phosphorylation of IRS-1 and IRS-2 in human peripheral blood T cells, NK cells, and in lymphoid cell lines. In addition, we show that the Janus kinases, JAK1 and JAK3, associate with IRS-1 and IRS-2 in T cells. Coexpression studies demonstrate that these kinases can tyrosine-phosphorylate IRS-2, suggesting a possible mechanism by which cytokine receptors may induce the tyrosine phosphorylation of IRS-1 and IRS-2. We further demonstrate that the p85 subunit of phosphoinositol 3-kinase associates with IRS-1 in response to IL-2 and IL-4 in T cells. Therefore, these data indicate that IRS-1 and IRS-2 may have important roles in T lymphocyte activation not only in response to IL-4, but also in response to IL-2, IL-7, and IL-15.

The insulin receptor substrate-1-related 4PS substrate but not the interleukin-2R gamma chain is involved in interleukin-13-mediated signal transduction

Interleukin-13 (IL-13) induced a potent mitogenic response in IL-3-dependent TF-1 cells and DNA synthesis to a lesser extent in MO7E and FDC-P1 cells. IL-13 stimulation of these lines, like IL-4 and insulin-like growth factor-1 (IGF-1), resulted in tyrosine phosphorylation of a 170-kD substrate. The tyrosine-phosphorylated 170-kD substrate strongly associated with the 85-kD subunit of phosphoinositol-3 (PI-3) kinase and with Grb-2. Anti-4PS serum readily detected the 170-kD substrate in lysates from both TF-1 and FDC-P1 cells stimulated with IL-13 or IL-4. These data provide evidence that IL-13 induces tyrosine phosphorylation of the 4PS substrate, providing an essential interface between the IL-13 receptor and signaling molecules containing SH2 domains. IL-13 and IL-4 stimulation of murine L cell fibroblasts, which endogenously express the IL-4 receptor (IL-4R alpha) and lack expression of the IL-2 receptor gamma subunit (IL-2R gamma), resulted in tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1)/4PS. Enhanced tyrosine phosphorylation of IRS-1/4PS was observed in response to IL-4, but not IL-13 treatment of L cells transfected with the IL-2R gamma chain. These results indicate that IL-13 does not use the IL-2R gamma subunit in its receptor complex and that expression of IL-2R gamma enhances, but is not absolutely required for mediating IL-4-induced tyrosine phosphorylation of IRS-1/4PS.

4PS/insulin receptor substrate (IRS)-2 is the alternative substrate of the insulin receptor in IRS-1-deficient mice

Insulin receptor substrate-1 (IRS-1) is the major cytoplasmic substrate of the insulin and insulin-like growth factor (IGF)-1 receptors. Transgenic mice lacking IRS-1 are resistant to insulin and IGF-1, but exhibit significant residual insulin action which corresponds to the presence of an alternative high molecular weight substrate in liver and muscle. Recently, Sun et al. (Sun, X.-J., Wang, L.-M., Zhang, Y., Yenush, L. P., Myers, M. G., Jr., Glasheen, E., Lane, W.S., Pierce, J. H., and White, M. F. (1995) Nature 377, 173-177) purified and cloned 4PS, the major substrate of the IL-4 receptor-associated tyrosine kinase in myeloid cells, which has significant structural similarity to IRS-1. To determine if 4PS is the alternative substrate of the insulin receptor in IRS-1-deficient mice, we performed immunoprecipitation, immunoblotting, and phosphatidylinositol (PI) 3-kinase assays using specific antibodies to 4PS. Following insulin stimulation, 4PS is rapidly phosphorylated in liver and muscle, binds to the p85 subunit of PI 3-kinase, and activates the enzyme. Insulin stimulation also results in the association of 4PS with Grb 2 in both liver and muscle. In IRS-1-deficient mice, both the phosphorylation of 4PS and associated PI 3-kinase activity are enhanced, without an increase in protein expression. Immunodepletion of 4PS from liver and muscle homogenates removes most of the phosphotyrosine-associated PI 3-kinase activity in IRS-1-deficient mice. Thus, 4PS is the primary alternative substrate, i.e. IRS-2, which plays a major role in physiologic insulin signal transduction via both PI 3-kinase activation and Grb 2/Sos association. In IRS-1-deficient mice, 4PS/IRS-2 provides signal transduction to these two major pathways of insulin signaling.