Effects of electro-mechanical uncouplers, hormonal stimulation and pacing rate on the stability and function of cultured rabbit myocardial slices

Introduction: Recent advances have enabled organotypic culture of beating human myocardial slices that are stable for weeks. However, human myocardial samples are rare, exhibit high variability and frequently originate from diseased hearts. Thus, there is a need to adapt long-term slice culture for animal myocardium. When applied to animal cardiac slices, studies in healthy or genetically modified myocardium will be possible. We present the culture of slices from rabbit hearts, which resemble the human heart in microstructure, electrophysiology and excitation-contraction coupling. Methods: Left ventricular myocardium from New Zealand White rabbits was cut using a vibratome and cultured in biomimetic chambers for up to 7 days (d). Electro-mechanical uncoupling agents 2,3-butanedione monoxime (BDM) and cytochalasin D (CytoD) were added during initiation of culture and effects on myocyte survival were quantified. We investigated pacing rates (0.5 Hz, 1 Hz, and 2 Hz) and hormonal supplements (cortisol, T3, catecholamines) at physiological plasma concentrations. T3 was buffered using BSA. Contractile force was recorded continuously. Glucose consumption and lactate production were measured. Whole-slice Ca2+ transients and action potentials were recorded. Effects of culture on microstructure were investigated with confocal microscopy and image analysis. Results: Protocols for human myocardial culture resulted in sustained contracture and myocyte death in rabbit slices within 24 h, which could be prevented by transient application of a combination of BDM and CytoD. Cortisol stabilized contraction amplitude and kinetics in culture. T3 and catecholaminergic stimulation did not further improve stability. T3 and higher pacing rates increased metabolic rate and lactate production. T3 stabilized the response to β-adrenergic stimulation over 7 d. Pacing rates above 1 Hz resulted in progredient decline in contraction force. Image analysis revealed no changes in volume fractions of cardiomyocytes or measures of fibrosis over 7 d. Ca2+ transient amplitudes and responsiveness to isoprenaline were comparable after 1 d and 7 d, while Ca2+ transient duration was prolonged after 7 d in culture. Conclusions: A workflow for rabbit myocardial culture has been established, preserving function for up to 7 d. This research underscores the importance of glucocorticoid signaling in maintaining tissue function and extending culture duration. Furthermore, BDM and CytoD appear to protect from tissue damage during the initiation phase of tissue culture.

A network of p73, p53 and Egr1 is required for efficient apoptosis in tumor cells

p73, a transcription factor rarely mutated in cancer, regulates a subset of p53 target genes that cause cells to respond to genotoxic stress by growth arrest and apoptosis. p73 is produced in two main forms; only TAp73 reiterates the roles of p53, while DeltaNp73 can be oncogenic in character. We show that the TAp73 form produced by TP73 P1 promoter has five distinct Egr1-binding sites, each contributing to the transcriptional upregulation of TAp73 by Egr1 in several cell types. In contrast, TP73 P2 promoter transcribes DeltaNp73, is not induced by Egr1, but is induced by TAp73 and p53. Induction of TAp73 by genotoxic stress requires Egr1 in mouse in vivo. Newly discovered non-consensus p53-binding sites in p73, p53 and Egr1 promoters reveal inter-regulating networks and sustained expression by feedback loops in response to stress, resulting in prolonged expression of the p53 family of genes and efficient apoptosis.

The Egr-1 transcription factor directly activates PTEN during irradiation-induced signalling

The PTEN tumour suppressor and pro-apoptotic gene is frequently mutated in human cancers. We show that PTEN transcription is upregulated by Egr-1 after irradiation in wild-type, but not egr-1-/-, mice in vivo. We found that Egr-1 specifically binds to the PTEN 5' untranslated region, which contains a functional GCGGCGGCG Egr-1-binding site. Inducing Egr-1 by exposing cells to ultraviolet light upregulates expression of PTEN messenger RNA and protein, and leads to apoptosis. egr-1-/- cells, which cannot upregulate PTEN expression after irradiation, are resistant to ultraviolet-light-induced apoptosis. Therefore, Egr-1 can directly regulate PTEN, triggering the initial step in this apoptotic pathway. Loss of Egr-1 expression, which often occurs in human cancers, could deregulate the PTEN gene and contribute to the radiation resistance of some cancer cells.

Focal adhesion kinase and Src mediate integrin regulation of insulin receptor phosphorylation

We show here that phosphorylation of the insulin receptor and insulin receptor substrate-1 is increased when suspended cells are replated on fibronectin. This is not due to decreased numbers of cell surface receptors, alteration of insulin binding, or stimulation of a phosphatase activity in non-adherent cells. Expression of Src together with focal adhesion kinase (FAK) in suspended cells restores insulin-induced receptor autophosphorylation to levels observed in fibronectin-attached cells. Conversely, expression of dominant-negative mutants of either Src or FAK abolishes potentiation of insulin receptor phosphorylation by cell adhesion. The results suggest that both Src and FAK participate in integrin-mediated regulation of insulin receptor signal.

Surfing the insulin signaling web

The diverse biological actions of insulin and insulin-like growth factor I (IGF-I) are initiated by binding of the polypeptides to their respective cell surface tyrosine kinase receptors. These activated receptors phosphorylate a series of endogenous substrates on tyrosine, amongst which the insulin receptor substrate (IRS) proteins are the best characterized. Their phosphotyrosine-containing motifs become binding sites for Src homology 2 (SH2) domains on proteins such as SH2 domain-containing protein-tyrosine-phosphatase (SHP)-2/Syp, growth factor receptor bound-2 protein, (Grb-2), and phosphatidyl inositol 3 kinase (PI3 kinase), which participate in activation of specific signaling cascades. However, the IRS molecules are not only platforms for signaling molecules, they also orchestrate the generation of signal specificity, integration of signals induced by several extracellular stimuli, and signal termination and modulation. An extensive review is beyond the scope of the present article, which will be centered on our own contribution and reflect our biases.

[Technological advances in immuno-oncology: from fundamental concepts to patient immunological monitoring]

Over the past decade, cancer immunology has known several advances due to both basic research and new technologies recently developed in this field. This review will illustrate the impact of some new immunological technologies and how the latter resulted in the exploration of new territories in cancer immunology and the emergence of new concepts that allowed to revisit the immunosurveillance concept and permitted to improve the patient monitoring.

Effects of alcohol ethoxylate and pluronic detergents on the development of pasture bloat in cattle and sheep

A series of studies was conducted to determine the efficacy and possible modes of action of a water-soluble mixture of alcohol ethoxylate and pluronic detergents (AEPD; Blocare 4511, ANCARE, Auckland, NZ) in preventing pasture bloat in ruminants grazing or fed freshly harvested alfalfa. Ten cannulated Suffolk wethers were offered freshly harvested alfalfa; five were given a daily intraruminal dose of 40 ml of 50% AEPD (vol/vol) 1 h before feeding, and five (controls) were dosed with water. Viscosity of ruminal fluid was reduced (P < 0.001) in AEPD-treated wethers, relative to the controls, for the first 2 h after feeding but not at 4 h after feeding and beyond. Treatment with AEPD did not affect dry matter (DM) intake, digestibility of DM, acid detergent fiber, or neutral detergent fiber, or N digestion and retention, implying that AEPD likely would not affect milk production. In a crossover grazing study, five of the wethers were given AEPD in drinking water (0.1%, vol/vol); treatment with AEPD was 100% effective for preventing bloat in sheep grazing early-bloom alfalfa for 4 h daily. Replicate grazing studies were conducted with cattle in Lethbridge, AB; Lacombe, AB; and Kamloops, BC. Treated animals received AEPD in the water (0.06%, vol/vol) and grazed vegetative alfalfa for 6 h daily. As it did with sheep, AEPD treatment effectively precluded the bloat observed in control animals. Consequently, AEPD may be a valuable tool for alfalfa pasture-based dairy production although further study is required to develop an integrated model for optimal administration under a variety of climatic conditions.

Cell adhesion regulates ubiquitin-mediated degradation of the platelet-derived growth factor receptor beta

Cross-talk between integrin-mediated adhesion and growth factors has been described in many recent studies; however, the underlying mechanisms remain incompletely understood. We report here that detachment of cells from the extracellular matrix induced a decrease in both the autophosphorylation and protein levels of the platelet-derived growth factor receptor beta (PDGF-R beta), which was completely reversed upon replating cells on fibronectin. The effect occurred in all cells examined but to a greater extent in primary fibroblasts compared with established cell lines. Decreased PDGF-R levels in suspended cells correlated with ubiquitination of the PDGF-R and was blocked by treatment with inhibitors of the proteasome pathway. Unlike PDGF-induced down-regulation, detachment-induced degradation did not require receptor autophosphorylation, internalization, or tyrosine kinase activity. We conclude that cell detachment results in cellular desensitization to PDGF that is mediated by degradation of the PDGF-R via a novel ubiquitin-dependent pathway.

Cell adhesion and focal adhesion kinase regulate insulin receptor substrate-1 expression

Integrins are transmembrane receptors involved in interactions between cells and extracellular matrix proteins. Here we show that cell adhesion regulates insulin receptor substrate-1 (IRS-1) mRNA synthesis. When fibroblasts are held in suspension, lower levels of IRS-1 mRNA, but not of IRS-2 mRNA, are detected, and this effect is due to the negative regulation of IRS-1 transcription rather than to decreased mRNA stability. Upon fibronectin- or vitronectin-mediated integrin stimulation, the level of IRS-1 mRNA was restored within 4 h. The focal adhesion kinase (FAK) is known to be activated upon integrin stimulation, and we found that IRS-1 was not expressed in FAK(-)(/-) cells. Stable re-expression of epitope-tagged FAK in FAK(-)(/-) fibroblasts (DA2 cells) restored normal levels of IRS-1 expression, confirming that IRS-1 mRNA expression is regulated by FAK. It is known that integrins activate the JNK pathway. However, in adherent FAK(-)(/-) cells, we failed to detect activation of JNK, whereas JNK was stimulated in DA2 cells. This confirms the role of FAK in integrin-induced JNK stimulation. FAK-independent stimulation of JNK with anisomycin treatment both in FAK(-)(/-) cells and in suspended FAK(+/+) cells confirmed that IRS-1 mRNA transcription can be partially regulated by JNK. We suggest that integrins can modulate insulin and insulin-like growth factor-1 signaling pathways by regulating the levels of IRS-1 in cells and that FAK-mediated signaling to JNK is one pathway involved in this process.

Monitoring cellular responses to Listeria monocytogenes with oligonucleotide arrays

Listeria monocytogenes is a pathogenic intracellular microorganism whose infection induces pleiotropic biological changes associated with host cell gene expression regulation. Here we define the gene expression profiles of the human promyelocytic THP1 cell line before and after L. monocytogenes infection. Gene expression was measured on a large scale via oligonucleotide microarrays with probe sets corresponding to 6,800 human genes. We assessed and discussed the reproducibility of the hybridization signatures. In addition to oligonucleotide arrays, we also performed the large scale gene expression measurement with two high-density membranes, assaying for 588 and 18,376 human genes, respectively. This work allowed the reproducible identification of 74 up-regulated RNAs and 23 down-regulated RNAs as a consequence of L. monocytogenes infection of THP1. The reliability of these data was reinforced by performing independent infections. Some of these detected RNAs were consistent with previous results, while some newly identified RNAs encode gene products that may play key roles in L. monocytogenes infection. These findings will undoubtedly enhance the understanding of L. monocytogenes molecular physiology and may help identify new therapeutic targets.

LiMn2O4low-temperature phase: synchrotron and neutron diffraction study

The structural evolution of LiMn2O4spinel was followed from 320 K down to 10 K. The structural transformation, recently studied down to 230 K [Rodriguez-Carvajal, Rousse, Masquelier & Hervieu (1998).Phys. Rev. Lett.81, 4660–4663], takes place near room temperature with a significant hysteresis: the high-temperature cubic phase transforms to a superstructure orthorhombic cell. The present study indicates that the nuclear structure is stable down to 10 K, while neutron diffraction patterns below 80 K show the rise of a magnetic ordering in the spinel phase. From Mn—O bond-length analysis of the MnO6octahedra, a temperature-independent charge ordering in the structure can be deduced.

A direct estimate of the human alphabeta T cell receptor diversity

Generation and maintenance of an effective repertoire of T cell antigen receptors are essential to the immune system, yet the number of distinct T cell receptors (TCRs) expressed by the estimated 10(12) T cells in the human body is not known. In this study, TCR gene amplification and sequencing showed that there are about 10(6) different beta chains in the blood, each pairing, on the average, with at least 25 different alpha chains. In the memory subset, the diversity decreased to 1 x 10(5) to 2 x 10(5) different beta chains, each pairing with only a single alpha chain. Thus, the naïve repertoire is highly diverse, whereas the memory compartment, here one-third of the T cell population, contributes less than 1 percent of the total diversity.

Interactions between mitogenic stimuli, or, a thousand and one connections

Signals from G-protein-coupled receptors, tyrosine kinase receptors and integrins cooperate to determine cell growth. Work over the past two years has shown that this cooperation is based on crosstalk involving both receptors and their downstream signaling pathways. These interactions enable cells to integrate information from multiple stimuli that regulate cell cycle progression.

Insulin receptor substrate-1 as a signaling molecule for focal adhesion kinase pp125(FAK) and pp60(src)

Insulin receptor substrate-1 (IRS-1) is a major substrate of insulin and insulin-like growth factor-I receptors, which upon phosphorylation on tyrosine docks several signaling molecules. Recently, IRS-1 was found to interact with alphav beta3 integrins upon insulin stimulation. Integrins are transmembrane proteins that play an important role in adhesion between cells and between cells and extracellular matrix. One of the major proteins implicated in integrin signaling is pp125(FAK), a cytosolic tyrosine kinase, which upon integrin engagement becomes tyrosine-phosphorylated and subsequently binds to c-Src. Here, we established a mammalian two-hybrid system to show that pp125(FAK) binds to IRS-1. This association depends largely on the C terminus of pp125(FAK) but not on pp125(FAK) tyrosine kinase activity. Furthermore, we observed co-immunoprecipitation of pp125(FAK) with IRS-1 in 293 cells, suggesting a possible biological function of this association. When IRS-1 was expressed in 293 cells together with pp125(FAK) or Src, we found extensive IRS-1 tyrosine phosphorylation. In pp125(FAK)-expressing cells, this was concomitant with increased association of IRS-1 with Src homology 2-containing proteins such as growth factor receptor-bound protein 2, phosphatidylinositol (PI) 3-kinase p85alpha subunit, and Src homology 2-containing protein-tyrosine phosphatase-2. In addition, pp125(FAK)-induced association of IRS-1 with PI 3-kinase resulted in increased PI 3-kinase activity. In contrast, no change in mitogen-activated protein kinase activity was observed, indicating that pp125(FAK)-induced association between IRS-1 and growth factor receptor-bound protein 2 does not affect the mitogen-activated protein kinase pathway. Moreover, we found that engagement of integrins induced IRS-1 tyrosine phosphorylation. Considering our results together, we suggest that integrins and insulin/insulin-like growth factor-I receptor signaling pathways converge at an early point in the signaling cascade, which is the IRS-1 protein.

[Guidelines for the evaluation of internal quality control of smears for screening of uterine cancer in France in the structures of Pathologic Anatomy and Cytology. French Association for Quality Assurance in Pathologic Anatomy and Cytology (AFAQAP)--Commission for cervical smears]

A national organized mass-screening effective programme is the only way to reduce the risk of cervical cancer, if properly organized and correlated with a system of Quality Assurance. Since 1900, an Association for Quality Assurance was created by the French pathologists, named "AFAQAP". These pathologists thus demonstrated their interest in this kind of action that should be effective if women and clinicians are also implied. The pathologists have concluded the first part of their programme with these French guidelines for internal quality control of pap smears.

Dynamin associates with Src-Homology Collagen (Shc) and becomes tyrosine phosphorylated in response to insulin

The activated insulin receptor phosphorylates docking proteins such as Src-Homology Collagen (Shc) and Insulin Receptor Substrate-1 (IRS-1), which then bind several proteins that contain a Src-Homology 2 (SH2) domain. Both Shc and IRS-1 associate with Growth Factor Receptor-Bound protein 2 (Grb2), an adaptor molecule. The hormone-receptor complex is then rapidly internalized through coated-pits. Dynamin, a 100 kDa protein with GTPase activity, is thought to play a crucial role in receptor-mediated endocytosis. In this study, we show that insulin induces tyrosine phosphorylation of dynamin in cells overexpressing human insulin receptors. Phosphorylation is observed rapidly, i.e. within 1 minute of insulin treatment. Moreover, exposure of cells to the hormone leads to co-immunoprecipitation of dynamin with Shc and with insulin receptor. Since dynamin constitutively associates with Grb2, it could be recruited to the insulin signaling complex through binding of Grb2 to tyrosine-phosphorylated Shc.

[Tyrosine kinase: implications in tumor pathology and therapeutic perspectives]

The tyrosine kinase family includes growth factor receptor and cytoplasmic enzymes. It plays a key role in normal cell division and abnormal cell proliferation and differentiation. The most common tyrosine kinases are the epidermal-growth factor (EGFR) and platelet-derived growth factor (PDGF) receptors, and a chromosome Philadelphia product, the Bcr-abl oncogene. Many studies have attempted to correlate clinical evolution of tumors with tyrosine kinase expression. However, clinical application of these new prognostic factors has not yet been demonstrated. More recently, tyrosine-phosphorylation inhibitors (tryphostin) have been developed in phase I studies. Results that were obtained show some objective responses in patients with glioblastoma and polymetastatic cancer. Another approach to block tyrosine kinase expression is the use of monoclonal antibodies. Trials using such antibodies have shown interesting preliminary results.

p125Fak focal adhesion kinase is a substrate for the insulin and insulin-like growth factor-I tyrosine kinase receptors

The focal adhesion kinase p125(Fak) is a widely expressed cytosolic tyrosine kinase, which is involved in integrin signaling and in signal transduction of a number of growth factors. In contrast to tyrosine kinase receptors such as the platelet-derived growth factor and the hepatocyte growth factor receptors, which induce p125(Fak) phosphorylation, insulin has been shown to promote its dephosphorylation. In this study, we compared p125(Fak) phosphorylation in insulin-stimulated cells maintained in suspension or in an adhesion state. We found that, in nonattached cells, insulin promotes p125(Fak) phosphorylation, whereas dephosphorylation occurred in attached cells. This was observed in Rat-1 fibroblasts overexpressing the insulin receptor, as well as in Hep G2 hepatocytes and in 3T3-L1 adipocytes expressing more natural levels of insulin receptors. Insulin-induced p125(Fak) phosphorylation correlated with an increase in paxillin phosphorylation, indicating that p125(Fak) kinase activity may be stimulated by insulin. Mixing of purified insulin or insulin-like growth factor-I (IGF-I) receptors with p125(Fak) resulted in an increase in p125(Fak) phosphorylation. Using a kinase-deficient p125(Fak) mutant, we found that this protein is a direct substrate of the insulin and IGF-I receptor tyrosine kinases. This view is supported by two additional findings. (i) A peptide corresponding to p125(Fak) sequence comprising amino acids 568-582, which contains tyrosines 576 and 577 of the kinase domain regulatory loop, is phosphorylated by the insulin receptor; and (ii) p125(Fak) phosphorylation by the insulin receptor is prevented by addition of this peptide. Finally, we observed that p125(Fak) phosphorylation by the receptor results in its activation. Our results show that the nature of the cross-talk between the insulin/IGF-I receptors and p125(Fak) is dependent on the cell architecture, and hence the interaction of the insulin/IGF-I signaling system with the integrin system will vary accordingly.

Interaction of Janus kinases JAK-1 and JAK-2 with the insulin receptor and the insulin-like growth factor-1 receptor

Insulin and insulin-like growth factor-1 (IGF-1) treatment of cells overexpressing the insulin receptor or the IGF-1 receptor promotes phosphorylation and activation of Janus kinases JAK-1 and JAK-2 but not of TYK-2. With insulin, we observed maximal phosphorylation of JAK-1 within 2 min (5.2 +/- 0.6-fold) and maximal phosphorylation of JAK-2 within 10 min (2.4 +/- 0.6-fold). In cells incubated with IGF-1, we found maximal phosphorylation of JAK-2 within 2 min (1.9 +/- 0.2-fold) and of JAK-1 within 5 min (4.5 +/- 0.4-fold). The JAKs from insulin- or IGF-1-stimulated cells were activated, as shown by their autophosphorylation in vitro. Moreover, they were able to phosphorylate in vitro native insulin receptor substrate (IRS)-1 and a fragment of IRS-2 (GST-IRS-2591-786). Comparison of 32P-peptide maps of IRS-1 phosphorylated in vitro by the insulin receptor vs. JAK-1 showed the occurrence of different phosphopeptides, suggesting that different sites are likely to be phosphorylated by the two kinases. Finally, coprecipitation of receptors and JAK-1 was seen, and phosphorylation of both receptors was found to be necessary for receptor binding to JAK-1. Two domains of JAK- 1 are involved in the formation of the complex between receptor and JAK-1, i.e. the N-terminal portion containing JH7 and JH6 domains, and the C-terminal kinase domain (JH1 domain). Taking our data together, we conclude that: 1) insulin and IGF-1 lead to phosphorylation and activation of JAK-1 and JAK-2 in intact cells; 2) phosphorylation of IRS-I by JAK-1 seems to occur on sites different from those phosphorylated by the insulin receptor; 3) JAK-1 interacts directly with phosphorylated insulin and IGF-1 receptors; and 4) the JH7-JH6 and JH1 domains of JAK-1 are responsible for the interaction with insulin and IGF-1 receptors.

Tyr624 and Tyr628 in insulin receptor substrate-2 mediate its association with the insulin receptor

In addition to the pleckstrin homology domain and the phosphotyrosine binding domain in insulin receptor substrate (IRS)-1 and IRS-2, a region between amino acids 591 and 786 in IRS-2 (IRS-2-(591-786)) binds to the insulin receptor. Based on peptide competition studies, this region interacts with the phosphorylated regulatory loop of the insulin receptor; we designate this region the kinase regulatory loop binding (KRLB) domain. Two tyrosine residues in the KRLB domain at positions 624 and 628 are crucial for this interaction. Phosphorylation of tyrosine residues in the KRLB domain by the insulin receptor inhibits the binding to the receptor. These results reveal a novel mechanism regulating the interaction of the insulin receptor and IRS-2 that may distinguish the signal of IRS-2 from IRS-1.

The effect of cyclic adenosine monophosphate on the mitogen-activated protein kinase pathway depends on both the cell type and the type of tyrosine kinase-receptor

The mitogen-activated protein kinase (MAP kinase) is a key participant in growth factor-stimulated intracellular events such as proliferation and differentiation. We and others have previously described a cross-talk between the MAP kinase pathway and the cAMP pathway. Indeed, in several cell lines and, in particular in fibroblasts, an increase in the level of cAMP produced an inhibition of MAP kinase together with decreased cell proliferation. In contrast, in PC12 cells, cAMP induced an increase in the NGF-induced activation of MAP kinase concomitantly with augmented NGF-induced differentiation. Therefore, it has been proposed that the cellular context is important for the nature of the cAMP effects on growth factor-stimulated MAP kinase activity. Here we show that the type of tyrosine kinase receptor stimulated also participates in the nature of the cAMP effect. Thus, in NIH3T3 fibroblasts expressing NGF receptors (NIH3T3/trk cells) we found that cAMP potentiates NGF-stimulated ERK1 and MEK1 activities, whereas in NIH3T3 fibroblasts expressing insulin receptors (NIH3T3/IR cells) we saw no effect of cAMP on the activation of insulin-stimulated ERK1 and MEK1. In PC12 cells and in Rat1 fibroblasts expressing insulin receptors (PC12/IR and Rat1/IR cells) we observed, respectively, a potentiation and an inhibition of insulin-stimulated ERK1 activity. In addition, cAMP does not seem to modify the basal nor growth factor-stimulated She or IRS-1 tyrosine phosphorylation in the different cell lines studied. Finally, we observed that cAMP inhibited serum- and insulin-induced, but not NGF-induced, cell proliferation in NIH3T3 cells. However, cAMP potentiated insulin-stimulated cell differentiation in PC12/IR cells. These results led us to conclude that the cAMP effect on cell proliferation in NIH3T3 fibroblasts and PC12/IR cells appears to be correlated, in part, with the effect of cAMP on the MAP kinase pathway, but by itself this pathway cannot fully account for these observations.

Role of the insulin receptor C-terminal acidic domain in the modulation of the receptor kinase by polybasic effectors

Basic polymers such as polylysine have been found to activate insulin receptor autophosphorylation and kinase activity toward substrates. It was suggested that acidic receptor domains may be involved in the interaction of the receptor with these basic effectors. In a previous study, we have shown that the receptor acid-rich C-terminal sequence, including residues 1270-1280, is involved in the regulation of the receptor kinase activity. Moreover, this domain may be the site of interaction with histone, which is a modulator of the receptor kinase. In this study, we investigated whether the insulin receptor domain comprising amino acids 1270-1280 is involved in the interaction with polybasic effectors. We used anti-peptide serum directed to this sequence, and basic activators such as polylysine, polyarginine and protamine sulfate. Our antibodies inhibit polylysine-induced receptor autophosphorylation, whereas they have no effect on receptor phosphorylation stimulated by concanavalin A which is a non-basic activator of the insulin receptor. Polylysine-induced receptor aggregation was blocked by the antibodies (Fab fragments or whole Ig), indicating that competition occurs between the antibody and polylysine at the level of their binding site to the receptor. Finally, we observed a direct interaction of the 125I-peptide corresponding to receptor sequence 1270-1280 with the basic polymers in dot-blot experiments. Interestingly, the peptide did not bind spermine, a basic molecule which is not an activator of the insulin receptor kinase. Our data indicate that the insulin receptor C-terminal acidic domain including residues 1270-1280 is involved in the interaction of polylysine and other polybasic molecules with the receptor. Since this receptor region has been implicated in the regulation of the receptor kinase activity, we propose that interaction of basic effectors with this domain may be responsible for their activating properties.

Insulin receptor-induced phosphorylation of cellular and synthetic substrates is regulated by the receptor beta-subunit C-terminus

The transmembrane beta-subunits of the insulin receptor possess hormone-sensitive tyrosine kinase activity. To study the role of the C-terminus domain, a rabbit antipeptide antibody directed to the 1294-1317 domain was produced. The antipeptide antibody inhibited the receptor-induced phosphorylation of poly (Glu, Tyr) and synthetic peptides corresponding to the receptor autophosphorylation sites. In contrast, the same antibody did not inhibit receptor autophosphorylation. The kinetic parameters of the poly(Glu, Tyr) phosphorylation reaction indicated that the antibody interfered with the receptor enzymatic site. Concerning the insulin receptor cellular substrates, the anti-(1294-1317) antibody inhibited Src homology/collagen and IRS-1 phosphorylation. The extent of inhibition was 52% for Src homology/collagen phosphorylation and 30% for IRS-1 phosphorylation. From our data, we conclude that a similar regulation of insulin receptor-induced phosphorylation of artificial and cellular insulin receptor substrates can be generated at the level of the receptor beta-subunit C-terminus.

A conformational change in the beta-subunit of the insulin-like growth factor I receptor identified by antipeptide antibodies

Insulin-like growth factor I (IGF-I) binding to its receptor results in receptor autophosphorylation and phosphorylation of several cellular substrates. The mechanism by which binding of the ligand to the extracellular receptor domain activates the intracellular kinase remains to be defined. Using polyclonal antibodies against four regions of the IGF-I receptor, we searched for putative conformational changes occurring in purified receptors. We studied the ability of the antipeptide antibodies to immunoprecipitate the native, ligand-occupied, or autophosphorylated IGF-I receptor. We found that the antipeptide antibody directed to the sequence 985-998 of the kinase domain immunoprecipitated the phosphorylated receptor, but not the native or the ligand-occupied receptor. By contrast, the antibody against the sequence 950-957 of the juxtamembrane domain immunoprecipitated the three receptor forms. The difference between phosphorylated receptors and unphosphorylated receptors was not observed in Western blot experiments, indicating that the conformational modification of the receptors is not detected upon unfolding. These data demonstrate that the IGF-I receptor undergoes an autophosphorylation-induced conformational change detectable in the kinase domain. Our work provides evidence that conformational changes induced by autophosphorylation may be a common activation mechanism for tyrosine kinase receptors.

Involvement of Janus kinases in the insulin signaling pathway

The adaptor molecule growth-factor-receptor-bound protein-2 (Grb2) plays a role in insulin action since it links tyrosine phosphorylated IRS-1 and Shc to the guanine-nucleotide-exchange factor, Sos, which initiates the mitogen-activated-protein (MAP) kinase cascade by producing Ras-GTP. Both IRS-1 and Shc are phosphorylated by the insulin-receptor tyrosine kinase. In the present study, we have investigated whether the tyrosine kinases of the Janus kinase family (JAK) could be involved in insulin signaling by acting on Grb2. In fibroblasts over-expressing insulin receptors we observed that two tyrosine-phosphorylated proteins interact with Grb2 and with a mutant of Grb2, which lacks the Src homology 2 (SH2) domain, indicating that these proteins associate with the SH3 domains of Grb2. Further, we found that both JAK1 and JAK2 constitutively associate with Grb2, through interaction with the SH3 domains of Grb2. Finally, insulin appears to induce the tyrosine phosphorylation of JAK1, but does not modify the tyrosine phosphorylation state of JAK2. In conclusion, our results suggest that the JAK proteins could participate in insulin signal transduction, and could therefore constitute an alternative pathway for mediating some of the pleiotropic responses induced by insulin.

Interaction of the C-terminal acidic domain of the insulin receptor with histone modulates the receptor kinase activity

In this study, we investigated the role of the insulin receptor domain 1270-1280, an acid-rich sequence located in the receptor C-terminus. Antipeptide IgG raised against this sequence were obtained and used to analyze their effect on receptor function. Antipeptide IgG inhibited receptor autophosphorylation at Tyr1146, Tyr1150 and Tyr1151. These sites are known to be key modulators of the receptor activity. Autophosphorylation at other sites may also have been inhibited. The antipeptide antibody decreased the receptor kinase activity measured with poly(Glu80Tyr20) and a synthetic peptide corresponding to the proreceptor sequence 1142-1158. We provide evidence that the effect of the antibody on substrate phosphorylation may result from the control of the phosphorylation level of the receptor. Concerning the action of the antipeptide IgG on the receptor kinase activity, histone did not behave similarly to poly(Glu80Tyr20). The antibody recognizing sequence 1270-1280 competed with histone for an overlapping binding site. Histone also modulated insulin receptor autophosphorylation, supporting the idea that interference with domain 1270-1280 alters the receptor kinase. Our data suggest that the acidic region including residues 1270-1280 of the insulin receptor C-terminus is involved in the following events: (a) receptor binding with histone, an exogenous substrate of the receptor kinase, and (b) the regulation of receptor autophosphorylation and kinase activity. Based on these observations, we would like to propose that this insulin receptor domain could interact with cellular proteins modulating the receptor kinase.

The insulin receptor C-terminus is involved in regulation of the receptor kinase activity

During the insulin receptor activation process, ligand binding and autophosphorylation induce two distinct conformational changes in the C-terminal domain of the receptor beta-subunit. To analyze the role of this domain and the involvement of the C-terminal autophosphorylation sites (Tyr1316 and Tyr1322) in receptor activation, we used (i) antipeptide antibodies against three different C-terminal sequences (1270-1281, 1294-1317, and 1309-1326) and (ii) an insulin receptor mutant (Y/F2) where Tyr1316 and Tyr1322 have been replaced by Phe. We show that the autophosphorylation-induced C-terminal conformational change is preserved in the Y/F2 receptor, indicating that this change is not induced by phosphorylation of the C-terminal sites but most likely by phosphorylation of the major sites in the kinase domain (Tyr1146, Tyr1150, and Tyr1151). Binding of antipeptide antibodies to the C-terminal domain modulated (activated or inhibited) both mutant and wild-type receptor-mediated phosphorylation of poly(Glu/Tyr). In contrast to the wild-type receptor, Y/F2 exhibited the same C-terminal configuration before and after insulin binding, evidencing that mutation of Tyr1316 and Tyr1322 introduced conformational changes in the C-terminus. Finally, the mutant receptor was 2-fold more active than the wild-type receptor for poly(Glu/Tyr) phosphorylation. In conclusion, the whole C-terminal region of the insulin receptor beta-subunit is likely to exert a regulatory influence on the receptor kinase activity. Perturbations of the C-terminal region, such as binding of antipeptides or mutation of Tyr1316 and Tyr1322, provoke alterations at the receptor kinase level, leading to activation or inhibition of the enzymic activity.

Antibodies to the extracellular receptor domain restore the hormone-insensitive kinase and conformation of the mutant insulin receptor valine 382

A mutation substituting a valine for phenylalanine at residue 382 in the insulin receptor alpha-subunit has been found in two sisters with a genetic form of extreme insulin resistance. This receptor mutation impairs the ability of the hormone to activate autophosphorylation of solubilized receptors and phosphorylation of substrates (Accili, D., Mosthaf, L., Ullrich, A., and Taylor, S. I. (1991) J. Biol. Chem. 266, 434-439). We have previously demonstrated that in native receptors insulin induces a conformational change in the receptor beta-subunit, which is thought to be necessary for receptor activation (Baron, V., Gautier, N., Komoriya, A., Hainaut, P., Scimeca, J. C., Mervic, M., Lavielle, S., Dolais-Kitabgi, J., and Van Obberghen, E. (1990) Biochemistry 29, 4634-4641). Hence, it was thought that a defect in this conformational change might explain the functional defect of the mutant receptor. This appears to be the case, as we demonstrate here that the mutant receptor is locked in its inactive configuration. However, we found two monoclonal antibodies, directed to the extracellular domain, which are capable of restoring the mutant receptor kinase activity. The activation of the mutant receptor was accompanied by restoration of conformational changes in the beta-subunit C terminus. From these data, we draw the two following conclusions. (i) A causal link exists between receptor kinase activation and the occurrence of conformational changes. (ii) Ligands other than insulin, such as antibodies, which perturb the extracellular domain, can function as alternative ways to restore the mutant receptor kinase.

The insulin receptor activation process involves localized conformational changes

The molecular process by which insulin binding to the receptor alpha-subunit induces activation of the receptor beta-subunit with ensuing substrate phosphorylation remains unclear. In this study, we aimed at approaching this molecular mechanism of signal transduction and at delineating the cytoplasmic domains implied in this process. To do this, we used antipeptide antibodies to the following sequences of the receptor beta-subunit: (i) positions 962-972 in the juxtamembrane domain, (ii) positions 1247-1261 at the end of the kinase domain, and (iii) positions 1294-1317 and (iv) positions 1309-1326, both in the receptor C terminus. We have previously shown that insulin binding to its receptor induces a conformational change in the beta-subunit C terminus. Here, we demonstrate that receptor autophosphorylation induces an additional conformational change. This process appears to be distinct from the one produced by ligand binding and can be detected in at least three different beta-subunit regions: the juxtamembrane domain, the kinase domain, and the C terminus. Hence, the cytoplasmic part of the receptor beta-subunit appears to undergo an extended conformational change upon autophosphorylation. By contrast, the insulin-induced change does not affect the juxtamembrane domain 962-972 nor the kinase domain 1247-1261 and may be limited to the receptor C terminus. Further, we show that the hormone-dependent conformational change is maintained in a kinase-deficient receptor due to a mutation at lysine 1018. Therefore, during receptor activation, the ligand-induced change could precede ATP binding and receptor autophosphorylation. We propose that insulin binding leads to a transient receptor form that may allow ATP binding and, subsequently, autophosphorylation. The second conformational change could unmask substrate-binding sites and stabilize the receptor in an active conformation.

Potential involvement of the carboxy-terminus of the Glut 1 transporter in glucose transport

The role of the carboxy-terminal domain of the Glut 1 glucose transporter was investigated using an antipeptide antibody to the C-terminal part of the molecule. The study was performed in fibroblasts transfected with the cDNA coding for the human insulin receptor. These cells acutely respond to insulin for glucose transport. Using antipeptide antibodies to Glut 1 and Glut 4, we first established that these cells expressed only Glut 1. Then, to define the role of the C-terminal part of Glut 1 in glucose transport, the antibodies were loaded into the cells by electroporation. When anti-Glut 1 immunoglobulins were introduced into the cells, a 60% increase in basal deoxyglucose and 3-O-methylglucose transport was observed compared to that in cells electroporated with nonimmune immunoglobulins. The stimulatory action of the antipeptide was not due to an increase in the total amount of transporters. It was found only at low glucose concentrations, suggesting that the affinity of the transporter, rather than its maximal capacity, was changed. Finally, the effect of antibody was additive to that of insulin. The interaction between the anti-Glut 1 antibody and the carboxy-tail of the transporter seems to lead to an increase in the intrinsic activity of the transporter, suggesting that this part of the molecule could be implicated in the regulation of glucose uptake.

Antipeptide antibody to the insulin-like growth factor-I receptor sequence 1232-1246 inhibits the receptor kinase activity

To approach the question of why insulin-like growth factor-I (IGF-I) and insulin have different physiological actions, we developed antibodies directed against cytoplasmic regions of the IGF-I receptor exhibiting a low degree of homology with the corresponding sequences of the insulin receptor. We found that an antipeptide antibody directed against the beta-subunit carboxyl-terminal sequence (1232-1246) of the IGF-I receptor significantly reduced the in vitro receptor autophosphorylation. The ability of the synthetic peptide corresponding to the IGF-I receptor sequence 1232-1246 to abolish this inhibitory effect reflects the specific nature of the antibody interaction with the targeted domain in the receptor. Antipeptide antibody to IGF-I receptor sequence 1232-1246 also decreased receptor phosphorylation activity toward the exogenous substrate poly(Glu/Tyr). The reduction in poly(Glu/Tyr) phosphorylation was seen even when the antibody was incubated with a receptor previously activated and phosphorylated. Therefore, the inhibitory action on substrate phosphorylation is likely to be unrelated to the antibody reduction of receptor autophosphorylation but rather results from a global decrease in receptor enzymatic activity. The effect of the antipeptide antibody on receptor tyrosine kinase cannot be accounted for by a lowering of the receptor Km for ATP or of its affinity for the substrate poly(Glu/Tyr). Moreover, the interaction of the antibody with the receptor had no repercussion on the ligand binding site as shown by the unaltered IGF-I binding. Taken together our data suggest that the beta-subunit carboxyl-terminal domain of the IGF-I receptor plays a key role in regulating its kinase activity and that the particular sequence recognized by our antipeptide antibody could be involved in negative regulation of receptor functioning.

The carboxyl-terminal domain of the insulin receptor: its potential role in growth-promoting effects

The role of the insulin receptor carboxyl-terminal domain in regulation of insulin signal transduction was studied with antipeptide antibodies against the sequence 1321-1338, which contains two autophosphorylation sites, tyrosine 1328 and tyrosine 1334. The antibodies were introduced by electroporation in murine fibroblasts transfected with an expression plasmid encoding the human insulin receptor. We found that introduction of these antipeptides into cells stimulated cellular proliferation, compared to cells loaded with nonimmune Ig. In contrast, neither glucose transport nor amino acid transport was stimulated by the antibodies. Despite its stimulatory effect on cell growth, the injected antipeptide did not enhance phosphorylation of ribosomal protein S6. In vitro, anti-C1 antipeptide stimulated insulin receptor autophosphorylation but did not increase receptor-mediated phosphorylation of the copolymer (glutamate/tyrosine, 4/1), while histone phosphorylation was increased. We interpret our results to mean that perturbation of the receptor C-terminus could lead to phosphorylation of selected substrates, which may be involved in cell growth regulation. Taken together, our data suggest that (i) insulin receptor mediated stimulation of cell growth and stimulation of ribosomal protein S6 phosphorylation result from divergent signaling pathways and (ii) the insulin receptor C-terminal domain exerts an inhibition on the growth signal mediated by the receptor. This inhibition appears to be released upon insulin binding to receptor or by interaction of the antipeptide with the receptor.

Insulin and insulin-like-growth-factor-I (IGF-I) receptors in Xenopus laevis oocytes. Comparison with insulin receptors from liver and muscle

Insulin and insulin-like-growth-factor-I (IGF-I) receptors were partially purified from full-grown (stages V-VI) Xenopus laevis oocytes by affinity chromatography on wheat-germ agglutinin-agarose. Competitive-binding assays revealed high-affinity binding sites for both insulin and IGF-I (Kd = 2.5 x 10(-10) M and 8 x 10(-10) M respectively). However, IGF-I receptors were about 15 times more abundant than insulin receptors (22.5 x 10(11) versus 1.5 x 10(11)/mg of protein). Moreover, comparison of intact and collagenase-treated oocytes showed that most of the insulin receptors were in the oocyte envelopes, whereas IGF-I receptors were essentially at the oocyte surface. Oocyte receptors were composed of alpha-subunits of approximately 130 kDa and a doublet of beta-subunits of 95 and 105 kDa, which both had ligand-induced phosphorylation patterns compatible with IGF-I receptor beta-subunits. Accordingly, the receptor tyrosine kinase was stimulated at low IGF-I concentrations [half-maximally effective concentration (EC50) approximately 0.5-1 nM], and at higher insulin concentrations (EC50 approximately 20-50 nM). Partially purified glycoproteins from Xenopus liver and muscle contained mainly receptors of the insulin-receptor type, with alpha-subunits of 140 kDa in liver and 125 kDa in muscle, and doublets of beta-subunits of 92-98 kDa in liver and 85-94 kDa in muscle. Immunoprecipitation of receptors from oocytes, liver and muscle by receptor-specific anti-peptide antibodies suggested that the beta-subunit heterogeneity resulted from the existence of two distinct IGF-I receptors in oocytes and of two distinct insulin receptors in both liver and muscle. In the different tissues, the two receptor subtypes differed at least by their beta-subunit C-terminal region.

Insulin binding to its receptor induces a conformational change in the receptor C-terminus

Antibodies against peptides corresponding to sequences in the C-terminus of the insulin receptor beta-subunit were used to approach the putative role of this receptor domain in signal generation. Two sequences were chosen and correspond to peptide C1, comprising amino acids 1309-1326, and peptide C2, comprising amino acids 1294-1317. The two antibodies produced distinct immunoprecipitation patterns as a function of the insulin receptor form and recognized changes in the insulin receptor molecule induced by ligand binding and autophosphorylation. Both antipeptides, anti-C1 and anti-C2, showed an important decrease in their recognition capacity for the receptor occupied by insulin when compared to the empty receptor. Further, anti-C1 had a lower affinity for the phosphorylated receptor compared to the unphosphorylated receptor and failed to recognize a fraction of the phosphoreceptor population. In contrast, anti-C2 had similar affinities for the phosphorylated and unphosphorylated receptors but was unable to interact with part of the unphosphorylated receptors. Finally, using immunoblotting of the receptor to analyze the denatured molecules, we showed that the phosphorylation-induced changes detected by anti-C1 are retained, suggesting that they are likely not of a conformational nature. In contrast, the insulin-induced changes in the receptor molecule disappear with receptor denaturation which points to their reversible nature. We conclude from these data that (i) antipeptides against the receptor C-terminal sequence are able to distinguish between phosphorylated and unphosphorylated receptor forms and (ii) binding of insulin to its receptor leads to a reversible, phosphorylation-independent, and possibly conformational change at the level of the receptor C-terminal domain.

Antibodies to insulin receptor tyrosine kinase stimulate its activity towards exogenous substrates without inducing receptor autophosphorylation

Anti-peptide antibodies directed against a highly-conserved sequence of the insulin receptor tyrosine kinase domain have been used to study the relationship between this specific region and kinase activation. Antibodies have been prepared by the injection into a rabbit of a synthetic peptide (P2) corresponding to residues 1110-1125 of the proreceptor. The peptide exhibits 88-95% sequence similarity with the corresponding sequence in the v-ros protein and in receptors for epidermal growth factor and for insulin-like growth factor 1. Two antibodies with different specificities could be separated from total antiserum obtained after immunization with P2. One antibody [anti-(P-Tyr)] cross-reacted with phosphotyrosine and immunoprecipitated solely autophosphorylated receptors. This antibody was shown to increase or decrease the receptor tyrosine kinase activity depending on its concentration. In all circumstances receptor autophosphorylation and substrate phosphorylation were modulated in a parallel fashion. The second antibody (anti-P2) failed to immunoprecipitate the insulin receptor, but was found to interact with both the peptide and the receptor by e.l.i.s.a. assay. Using a tyrosine co-polymer we found that anti-P2 activated the insulin receptor kinase leading to substrate phosphorylation at a level similar to that observed with insulin. This effect was additive to the hormonal effect. In contrast, receptor autophosphorylation was not modified by the anti-peptide. The differential effect of this anti-peptide further supports the idea that receptor autophosphorylation and kinase activity towards exogenous substrates might be independently regulated. Finally, our data suggest that conformational changes in the receptor tyrosine kinase domain may be sufficient for activation of its enzymic activity.

Use of an anti-insulin receptor antibody to discriminate between metabolic and mitogenic effects of insulin: correlation with receptor autophosphorylation

In a previous report we described the properties of a rabbit anti-insulin receptor antibody (RAIR-IgG) and its effects on the autophosphorylation and kinase activity of human insulin receptors. The present study was carried out on the hepatoma cell line Fao. We tested the mimetic effects of RAIR-IgG on different biological parameters known to be stimulated by insulin, receptor autophosphorylation and kinase activity. RAIR-IgG stimulated the metabolic effects (glucose and amino acid transport) but, unlike insulin, was unable to promote cell proliferation. These data clearly demonstrated the existence of two distinctly controlled pathways in the mediation of the hormonal response. When we investigated the effects of this antibody at the molecular level we found that in a cell-free system RAIR-IgG weakly stimulated receptor autophosphorylation on non-regulatory sites and failed to stimulate tyrosine kinase activity toward exogenous substrates. Accordingly, RAIR-IgG did not stimulate receptor autophosphorylation in 32P-labelled intact cells. Interestingly, under similar conditions RAIR-IgG elicited ribosomal S6 protein phosphorylation, as did insulin. The possibility that RAIR-IgG activated a cryptic tyrosine kinase activity is discussed.