Mutations in human GLUD2 glutamate dehydrogenase affecting basal activity and regulation

Glutamate dehydrogenase (GDH) in human exists in GLUD1 and GLUD2 gene-encoded isoforms (hGDH1 and hGDH2, respectively), differing in their regulation and tissue expression pattern. Whereas hGDH1 is subject to GTP control, hGDH2 uses for its regulation, a novel molecular mechanism not requiring GTP. This is based on the ability of hGDH2 to maintain a baseline activity of <10% of its capacity subject to full activation by rising ADP/ l -leucine levels. Here we studied further the molecular mechanisms regulating hGDH2 function by creating and analyzing hGDH2 mutants harboring single amino acid substitutions in the regulatory domain (antenna, pivot helix) of the protein. Five hGDH2 mutants were obtained: two with an amino acid change (Gln441Arg, Ser445Leu) in the antenna, two (Lys450Glu, His454Tyr) in the pivot helix, and one (Ser448Pro) in the junction between the two structures. Functional analyses revealed that, while the antenna mutations increased basal enzyme activity without affecting its allosteric properties, the pivot helix mutations drastically reduced basal activity and impaired enzyme regulation. On the other hand, the Ser448Pro mutation reduced basal activity but did not alter allosteric regulation. Also, compared with wild-type hGDH2, the antenna mutants were relatively thermostable, whereas the pivot helix mutants were extremely heat labile. Hence, the present data further our understanding of the molecular mechanisms involved in the function and stability of hGDH2, an enzyme thought to be of importance for nerve tissue biology.     

The human GLUD2 glutamate dehydrogenase and its regulation in health and disease

Whereas glutamate dehydrogenase in most mammals (hGDH1 in the human) is encoded by a single functional GLUD1 gene expressed widely, humans and other primates have acquired through retroposition an X-linked GLUD2 gene that encodes a highly homologous isoenzyme (hGDH2) expressed in testis and brain. Using an antibody specific for hGDH2, we showed that hGDH2 is expressed in testicular Sertoli cells and in cerebral cortical astrocytes. Although hGDH1 and hGDH2 have similar catalytic properties, they differ markedly in their regulatory profile. While hGDH1 is potently inhibited by GTP and may be controlled by the need of the cell for ATP, hGDH2 has dissociated its function from GTP and may metabolize glutamate even when the Krebs cycle generates GTP amounts sufficient to inactivate hGDH1. As astrocytes are known to provide neurons with lactate that largely derives from the Krebs cycle via conversion of glutamate to α-ketoglutarate, the selective expression of hGDH2 may facilitate metabolic recycling processes essential for glutamatergic transmission. As there is evidence for deregulation of glutamate metabolism in degenerative neurologic disorders, we sequenced GLUD1 and GLUD2 genes in neurologic patients and found that a rare T1492G variation in GLUD2 that results in substitution of Ala for Ser445 in the regulatory domain of hGDH2 interacted significantly with Parkinson's disease (PD) onset. Thus, in two independent Greek and one North American PD cohorts, Ser445Ala hemizygous males, but not heterozygous females, developed PD 6-13 years earlier than subjects with other genotypes. The Ala445-hGDH2 variant shows enhanced catalytic activity that is resistant to modulation by GTP, but sensitive to inhibition by estrogens. These observations are thought to suggest that enhanced glutamate oxidation by the Ala445-hGDH2 variant accelerates nigral cell degeneration in hemizygous males and that inhibition of the overactive enzyme by estrogens protects heterozygous females. We then evaluated the interaction of estrogens and neuroleptic agents (haloperidol and perphenazine) with the wild-type hGDH1 and hGDH2 and found that both inhibited hGDH2 more potently than hGDH1 and that the evolutionary Arg443Ser substitution was largely responsible for this sensitivity. Hence, the properties acquired by hGDH2 during its evolution have made the enzyme a selective target for neuroactive steroids and drugs, providing new means for therapeutic interventions in disorders linked to deregulation of this enzyme.     

New positive allosteric modulators of the metabotropic glutamate receptor 2 (mGluR2): identification and synthesis of N-propyl-8-chloro-6-substituted isoquinolones

A series of N-propyl-8-chloro-6-substituted isoquinolones was identified as positive allosteric modulators of metabotropic glutamate receptor 2 (mGluR2 PAM) via high throughput screening (HTS). The subsequent synthesis and initial SAR exploration that led to the identification of compound 28 is described.     

Study of structure-function relationships in human glutamate dehydrogenases reveals novel molecular mechanisms for the regulation of the nerve tissue-specific (GLUD2) isoenzyme

In mammalian brain, glutamate dehydrogenase (GDH) is located predominantly in astrocytes, where is thought to play a role in transmitter glutamate's metabolism. Human GDH exists in GLUD1 (housekeeping) and GLUD2 (nerve tissue-specific) isoforms, which share all but 15 out of their 505 amino acids. The GLUD1 GDH is potently inhibited by GTP, whereas the GLUD2 enzyme is resistant to this compound. On the other hand, the GLUD2 isoform assumes in the absence of GTP a conformational state associated with little catalytic activity, but it remains amenable to full activation by ADP and/or L-leucine. Site-directed mutagenesis of the GLUD1 gene at sites that differ from the corresponding residues of the GLUD2 gene showed that replacement of Gly456 by Ala made the enzyme resistant to GTP (IC(50)=2.8+/-0.15 microM) compared to the wild-type GDH (IC(50)=0.19+/-0.01 microM). In addition, substitution of Ser for Arg443 virtually abolished basal activity and rendered the enzyme dependent on ADP for its function. These properties may permit the neural enzyme to be recruited under conditions of low energy charge (high ADP:ATP ratio), similar to those that prevail in synaptic astrocytes during intense glutamatergic transmission. Hence, substitution of Ser for Arg443 and Ala for Gly456 are the main evolutionary changes that led to the adaptation of the GLUD2 GDH to the unique metabolic needs of the nerve tissue.     

Discovery of dual positive allosteric modulators (PAMs) of the metabotropic glutamate 2 receptor and CysLT1 antagonists for treating migraine headache

Pyridylmethylsulfonamide series were the first reported example of positive allosteric modulators (PAM) of the mGlu₂ receptor. The hydroxyacetophenone scaffold is a second series of mGlu₂ PAMs we have identified. This series of molecules are potent mGlu₂ potentiators and possess significant CysLT1 (cysteinyl leukotriene receptor 1) antagonist activity, showing in vivo efficacy in a dural plasma protein extravasation (PPE) model of migraine. In this paper, we describe the dual SAR, pharmacokinetics and preclinical in vivo efficacy data for a tetrazole containing hydroxyacetophenone scaffold.     

The complex regulation of human glud1 and glud2 glutamate dehydrogenases and its implications in nerve tissue biology

Mammalian glutamate dehydrogenase (GDH) is a housekeeping mitochondrial enzyme (hGDH1 in the human) that catalyses the reversible inter-conversion of glutamate to α-ketoglutarate and ammonia, thus interconnecting amino acid and carbohydrate metabolism. It displays an energy sensing mechanism, which permits enzyme activation under low cellular energy states. As GDH is at the crossroads of important metabolic pathways, a tight control of its activity is essential. Indeed, to fulfill its role in metabolism and cellular energetics, mammalian GDH has evolved into a highly regulated enzyme subject to allosteric modulation by diverse compounds. The recent emergence (<23million years ago) in apes and humans of a hGDH2 isoenzyme with distinct regulatory properties, as well as, the detection of gain-of-function variants in hGDH1 and hGDH2 that affect the nervous system, have introduced additional complexities. The properties of the two highly homologous human GDHs were studied using purified recombinant hGDH1 and hGDH2 obtained by expression of the corresponding cDNAs in Sf21 cells. Results showed that, in contrast to hGDH1 that maintains substantial basal activity (35-40% of its maximal capacity), hGDH2 displays low basal activity (3-8% of maximal) that is remarkably responsive to activation by rising levels of ADP and/or l-leucine. This is primarily due to the Arg443Ser evolutionary change, which also made hGDH2 markedly sensitive to estrogens and neuroleptic drugs. In contrast to hGDH1, which is subject to potent GTP inhibition, hGDH2 has dissociated its function from this energy switch, being able to metabolize glutamate even when the Krebs cycle generates GTP levels sufficient to inactivate the housekeeping hGDH1. Our data also show that spermidine, a polyamine thought to reduce oxidative stress and to prolong survival, and EGCG, a green tea polyphenol, inhibit hGDH2 at lower concentrations than hGDH1. The implications of these findings in nerve tissue biology are discussed.     

Second extracellular loop of human glucagon-like peptide-1 receptor (GLP-1R) differentially regulates orthosteric but not allosteric agonist binding and function

The glucagon-like peptide-1 receptor (GLP-1R) is a prototypical family B G protein-coupled receptor that exhibits physiologically important pleiotropic coupling and ligand-dependent signal bias. In our accompanying article (Koole, C., Wootten, D., Simms, J., Miller, L. J., Christopoulos, A., and Sexton, P. M. (2012) J. Biol. Chem. 287, 3642-3658), we demonstrate, through alanine-scanning mutagenesis, a key role for extracellular loop (ECL) 2 of the receptor in propagating activation transition mediated by GLP-1 peptides that occurs in a peptide- and pathway-dependent manner for cAMP formation, intracellular (Ca(2+)(i)) mobilization, and phosphorylation of extracellular signal-regulated kinases 1 and 2 (pERK1/2). In this study, we examine the effect of ECL2 mutations on the binding and signaling of the peptide mimetics, exendin-4 and oxyntomodulin, as well as small molecule allosteric agonist 6,7-dichloro-2-methylsulfonyl-3-tert-butylaminoquinoxaline (compound 2). Lys-288, Cys-296, Trp-297, and Asn-300 were globally important for peptide signaling and also had critical roles in governing signal bias of the receptor. Peptide-specific effects on relative efficacy and signal bias were most commonly observed for residues 301-305, although R299A mutation also caused significantly different effects for individual peptides. Met-303 was more important for exendin-4 and oxyntomodulin action than those of GLP-1 peptides. Globally, ECL2 mutation was more detrimental to exendin-4-mediated Ca(2+)i release than GLP-1(7-36)-NH(2), providing additional evidence for subtle differences in receptor activation by these two peptides. Unlike peptide activation of the GLP-1R, ECL2 mutations had only limited impact on compound 2 mediated cAMP and pERK responses, consistent with this ligand having a distinct mechanism for receptor activation. These data suggest a critical role of ECL2 of the GLP-1R in the activation transition of the receptor by peptide agonists.     

Substitution of Ser for Arg-443 in the regulatory domain of human housekeeping (GLUD1) glutamate dehydrogenase virtually abolishes basal activity and markedly alters the activation of the enzyme by ADP and L-leucine

Human glutamate dehydrogenase (GDH) exists in GLUD1 (housekeeping) and in GLUD2-specified (brain-specific) isoforms, which differ markedly in their basal activity and allosteric regulation. To determine the structural basis of these functional differences, we mutagenized the GLUD1 GDH at four residues that differ from those of the GLUD2 isoenzyme. Functional analyses revealed that substitution of Ser for Arg-443 (but not substitution of Thr for Ser-331, Leu for Met-370, or Leu for Met-415) virtually abolished basal activity and totally abrogated the activation of the enzyme by l-leucine (1-10 mm) in the absence of other effectors. However, when ADP (0.025-0.1 mm) was present in the reaction mixture, l-leucine (0.3-6.0 mm) activated the mutant enzyme up to >2,000%. The R443S mutant was much less sensitive to ADP (SC(50) = 383.9 +/- 14.6 microm) than the GLUD1 GDH (SC(50) = 31.7 +/- 4.2 microm; p < 0.001); however, at 1 mm ADP the V(max) for the mutant (136.67 micromol min(-1) mg(-1)) was comparable with that of the GLUD1 GDH (152.95 micromol min(-1) mg(-1)). Varying the composition and the pH of the reaction buffer differentially affected the mutant and the wild-type GDH. Arg-443 lies in the "antenna" structure, in a helix that undergoes major conformational changes during catalysis and is involved in intersubunit communication. Its replacement by Ser is sufficient to impair both the catalytic and the allosteric function of human GDH.     

缺氧诱导因子-1和缺氧诱导因子-2：结构、功能及调节

缺氧诱导因子-1（HIF-1）和缺氧诱导因子-2（HIF-2）是细胞应对缺氧时关键的转录因子,在生物体生理及病理过程中有重要的作用。HIF由一个α亚基和一个β亚基组成二聚体。在蛋白水平上,HIF的稳定性及转录活性受到多种机制的调控,除为人所熟知的O2/PHDs/pVHL降解途径及FIH-1羟基化作用外,分别针对HIF-1α和HIF-2α的特异性调控机制也相继被报道。从HIF-1α和HIF-2α的蛋白结构、稳定性调控、转录激活功能以及两者在细胞代谢、肿瘤发生中的作用等方面对两者的相似性和差异性进行综述。     

The 2'-O- and 3'-O-Cy3-EDA-ATP(ADP) complexes with myosin subfragment-1 are spectroscopically distinct

Ribose-modified highly-fluorescent sulfoindocyanine ATP and ADP analogs, 2'(3')-O-Cy3-EDA-AT(D)P, with kinetics similar to AT(D)P, enable myosin and actomyosin ATPase enzymology with single substrate molecules. Stopped-flow studies recording both fluorescence and anisotropy during binding to skeletal muscle myosin subfragment-1 (S1) and subsequent single-turnover decay of steady-state intermediates showed that on complex formation, 2'-O- isomer fluorescence quenched by 5%, anisotropy increased from 0.208 to 0.357, and then decayed with turnover rate k(cat) 0.07 s(-1); however, 3'-O- isomer fluorescence increased 77%, and anisotropy from 0.202 to 0.389, but k(cat) was 0.03 s(-1). Cy3-EDA-ADP.S1 complexes with vanadate (V(i)) were studied kinetically and by time-resolved fluorometry as stable analogs of the steady-state intermediates. Upon formation of the 3'-O-Cy3-EDA-ADP.S1.V(i) complex fluorescence doubled and anisotropy increased to 0.372; for the 2'-O- isomer, anisotropy increased to 0.343 but fluorescence only 6%. Average fluorescent lifetimes of 2'-O- and 3'-O-Cy3-EDA-ADP.S1.V(i) complexes, 0.9 and 1.85 ns, compare with approximately 0.7 ns for free analogs. Dynamic polarization shows rotational correlation times higher than 100 ns for both Cy3-EDA-ADP.S1.V(i) complexes, but the 2'-O-isomer only has also a 0.2-ns component. Thus, when bound, 3'-O-Cy3-EDA-ADP's fluorescence is twofold brighter with motion more restricted and turnover slower than the 2'-O-isomer; these data are relevant for applications of these analogs in single molecule studies.     

CB1 receptors diminish both Ca(2+) influx and glutamate release through two different mechanisms active in distinct populations of cerebrocortical nerve terminals

We have investigated the mechanisms by which activation of cannabinoid receptors reduces glutamate release from cerebrocortical nerve terminals. Glutamate release evoked by depolarization of nerve terminals with high KCl (30 mmol/L) involves N and P/Q type Ca(2+)channel activation. However, this release of glutamate is independent of Na(+) or K(+) channel activation as it was unaffected by blockers of these channels (tetrodotoxin -TTX- or tetraethylammonium TEA). Under these conditions in which only Ca(2+) channels contribute to pre-synaptic activity, the activation of cannabinoid receptors with WIN55,212-2 moderately reduced glutamate release (26.4 +/- 1.2%) by a mechanism that in this in vitro model is resistant to TTX and consistent with the inhibition of Ca(2+) channels. However, when nerve terminals are stimulated with low KCl concentrations (5-10 mmol/L) glutamate release is affected by both Ca(2+) antagonists and also by TTX and TEA, indicating the participation of Na(+) and K(+) channel firing in addition to Ca(2+) channel activation. Interestingly, stimulation of nerve terminals with low KCl concentrations uncovered a mechanism that further inhibited glutamate release (81.78 +/- 4.9%) and that was fully reversed by TEA. This additional mechanism is TTX-sensitive and consistent with the activation of K(+) channels. Furthermore, Ca(2+) imaging of single boutons demonstrated that the two pre-synaptic mechanisms by which cannabinoid receptors reduce glutamate release operate in distinct populations of nerve terminals.     

Molecular docking simulations of steroid substrates into human cytosolic hydroxysteroid dehydrogenases (AKR1C1 and AKR1C2): insights into positional and stereochemical preferences

AKR1C1 and AKR1C2 are human cytosolic hydroxysteroid dehydrogenases, which play pivotal roles in the metabolism and action of natural and synthetic steroid hormones. The two enzymes are highly homologous, and have distinct positional and stereochemical preferences with various substrates. We performed molecular docking simulations of three steroid substrates, including an androgen (5alpha-dihydrotestosterone, DHT), a progestin (progesterone, PRO), and a synthetic hormone ([7alpha,17alpha]-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one or tibolone, TIB), into the active sites of the two enzymes. For each substrate and enzyme pair, the activity inferred by the "productive" docking models (in which the spatial arrangement of the steroid and the cofactor would permit a reaction) matched the experimentally observed positional and stereochemical outcome. These productive conformations were energetically and statistically favored except for TIB and PRO with AKR1C2, where experimentally strong substrate inhibition and low activity were observed, respectively. Results showed that (i) a 3-ketosteroid (DHT) and a 20-ketosteroid (PRO) were reduced by AKR1C1 since the carbonyl groups could occupy the same position by "backwards" binding of steroids; (ii) 3alpha-reduced (DHT) and 3beta-reduced (TIB) products were formed by AKR1C2 since the angular methyl groups of the steroids were inverted by "upside-down" binding of steroids; and (iii) the 3beta- and 3alpha-reduction of DHT by AKR1C1 and AKR1C2, respectively occurred since the steroids employed a "swinging" motion to present opposite faces to the cofactor. Favorable nonproductive modes were observed with all substrates in both enzymes in which the steroid was bound at a "near-entry" position and/or an "in-middle" position, which may influence the reaction coordinate.     

(2'-5')An-dependent endoribonuclease: enzyme levels are regulated by IFN beta, IFN gamma, and cell culture conditions

The levels of a (2'-5')An-dependent endonuclease (RNase L) were determined in extracts prepared from murine L cells and Ehrlich ascites tumor (EAT) cells by measuring specific binding of protein to a labeled derivative of (2'-5')An, (2'-5')A3[32P]pCp. RNase L levels were found to depend both on interferon (IFN) treatment and on cell growth conditions. Treatment of murine L cells and EAT cells with 100-2,000 IRU IFN beta or IFN gamma resulted in a similar 2-4-fold increase in the levels of RNase L when cells were present at low density. The levels of RNase L were also shown to increase 2-3-fold as cells approached saturation density. Serum-starved cells also displayed relatively high levels of RNase L. RNase L levels in cells maintained at high cell density did not change appreciably following treatment with IFN beta or IFN gamma. Regulation of RNase L levels by cell growth conditions as well as by IFN beta or IFN gamma treatment suggests that RNase L may play an important role in regulating the levels of cellular mRNAs as well as acting to degrade viral RNAs.     

Induction of lacI mutations in Big Blue Rat-2 cells treated with 1-(2-hydroxyethyl)-1-nitrosourea: a model system for the analysis of mutagenic potential of the hydroxyethyl adducts produced by 1,3-bis (2-chloroethyl)-1-nitrosourea.

We have investigated the genotoxic effects of 1-(2-hydroxyethyl)-1-nitrosourea (HENU). We have chosen this agent because of its demonstrated ability to produce N7-(2-hydroxyethyl) guanine (N7-HOEtG) and O⁶-(2-hydroxyethyl) 2′-deoxyguanosine (O⁶-HOEtdG); two of the DNA alkylation products produced by 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU). For these studies, we have used the Big Blue Rat-2 cell line that contains a lambda/lacI shuttle vector. Treatment of these cells with HENU produced a dose dependent increase in the levels of N7-HOEtG and O⁶-HOEtdG as quantified by HPLC with electrochemical detection. Treatment of Big Blue Rat-2 cells with either 0, 1 or 5 mM HENU resulted in mutation frequencies of 7.2±2.2×10⁻⁵, 45.2±2.9×10⁻⁵ and 120.3±24.4×10⁻⁵, respectively. Comparison of the mutation frequencies demonstrates that 1 and 5 mM HENU treatments have increased the mutation frequency by 6- and 16-fold, respectively. This increase in mutation frequency was statistically significant (P<0.001). Sequence analysis of HENU-induced mutations have revealed primarily G:C→A:T transitions (52%) and a significant number of A:T→T:A transversions (16%). We propose that the observed G:C→A:T transitions are produced by the DNA alkylation product O⁶-HOEtdG. These results suggest that the formation of O⁶-HOEtdG by BCNU treatment contributes to its observed mutagenic properties.     

Phosphorylation of recombinant human spermidine/spermine N(1)-acetyltransferase by CK1 and modulation of its binding to mitochondria: a comparison with CK2.

Cytosolic spermidine/spermine acetyltransferase (SSAT) catalyzes the acetylation of the N(1)-propylamino groups of spermine and spermidine. The enzyme has a very short half-life and is rapidly induced by various stimuli. Once acetylated, these polyamines are subjected to the action of polyamine oxidase, which, besides initiating polyamine catabolism, may produce reactive oxygen species that in turn trigger modifications in subcellular compartments such as mitochondria. The present work evaluates the ability of the cAMP-independent Ser/Thr-protein kinase CK1 to phosphorylate SSAT. Results demonstrate that SSAT is phosphorylated by CK1, in sites distinct from those phosphorylated by CK2. Moreover, both phosphorylation processes are involved in the uptake of SSAT into rat liver mitochondria. Although CK2 is less effective than CK1 in phosphorylating SSAT, CK2 phosphorylation is much more powerful in preventing binding of SSAT to mitochondrial structures. These results suggest the involvement of CK1- and CK2-mediated SSAT phosphorylation in regulating the contents of polyamines and SSAT itself within subcellular compartments and implicate SSAT and polyamines as indirect modulators of progression through the cell cycle.     

Expression and function of P2X(7) receptor and CD39/Entpd1 in patients with type 2 diabetes and their association with biochemical parameters

Chronic inflammation is an important contributor to the insulin resistance observed in type 2 diabetes (T2D). We evaluated the expression and function of the P2X₇ receptor and CD39/Entpd1, molecules involved in the cellular regulation of inflammation, in peripheral blood mononuclear cells from T2D patients, and their correlation with the concentration of HbA1c in blood. T2D patients with deficient metabolic control (DC) showed increased proportion of P2X₇⁺ cells compared with healthy individuals; T2D-DC subjects also displayed higher proportion of CD14⁺, CD4⁺ and CD19⁺ subpopulations of P2X₇⁺ cells when compared with T2D patients with acceptable metabolic control. A significant association was observed between the proportion of P2X₇⁺CD14⁺ cells and blood concentration of LDL-c. In addition, the percentages of CD39⁺ cells and CD39⁺CD19⁺ cells were significantly associated with HbA1c and fasting plasma glucose levels. No changes were observed in the function of P2X₇⁺ cells from T2D patients; however, enhanced CD39/Entpd1 enzyme activity and low serum levels of IL-17 were detected. Therefore, CD39⁺ cells could have a balancing regulatory role in the inflammatory process observed in patients with T2D.     

Up-regulation and sustained activation of Stat1 are essential for interferon-gamma (IFN-gamma)-induced dual oxidase 2 (Duox2) and dual oxidase A2 (DuoxA2) expression in human pancreatic cancer cell lines

Dual oxidase 2 is a member of the NADPH oxidase (Nox) gene family that plays a critical role in the biosynthesis of thyroid hormone as well as in the inflammatory response of the upper airway mucosa and in wound healing, presumably through its ability to generate reactive oxygen species, including H2O2. The recently discovered overexpression of Duox2 in gastrointestinal malignancies, as well as our limited understanding of the regulation of Duox2 expression, led us to examine the effect of cytokines and growth factors on Duox2 in human tumor cells. We found that exposure of human pancreatic cancer cells to IFN-γ (but not other agents) produced a profound up-regulation of the expression of Duox2, and its cognate maturation factor DuoxA2, but not other members of the Nox family. Furthermore, increased Duox2/DuoxA2 expression was closely associated with a significant increase in the production of both intracellular reactive oxygen species and extracellular H2O2. Examination of IFN-γ-mediated signaling events demonstrated that in addition to the canonical Jak-Stat1 pathway, IFN-γ activated the p38-MAPK pathway in pancreatic cancer cells, and both played an important role in the induction of Duox2 by IFN-γ. Duox2 up-regulation following IFN-γ exposure is also directly associated with the binding of Stat1 to elements of the Duox2 promoter. Our findings suggest that the pro-inflammatory cytokine IFN-γ initiates a Duox2-mediated reactive oxygen cascade in human pancreatic cancer cells; reactive oxygen species production in this setting could contribute to the pathophysiologic characteristics of these tumors.     

Different mechanisms are involved in intracellular calcium increase by insulin-like growth factors 1 and 2 in articular chondrocytes: Voltage-gated calcium channels,and/or phospholipase C coupled to a pertussis-sensitive G-protein

This study describes the mechanisms involved in the IGF-1 and IGF-2-induced increases in intracellular calcium concentration [Ca²⁺]i in cultured chondrocytes and the involvement of type 1 IGF receptors. It shows that IGF-1, IGF-2, and insulin increased the cytosolic free calcium concentration [Ca²⁺]i in a dose-dependent manner, with a plateau from 25 to 100 ng/ml for both IGF-1 and IGF-2 and from 1 to 2 μg/ml for insulin. The effect of IGF-1 was twice as great as the one of IGF-2, and the effect of insulin was 40% lower than IGF-1 effect. Two different mechanisms are involved in the intracellular [Ca²⁺]i increase. 1) IGF-1 and insulin but not IGF-2 involved a Ca²⁺ influx through voltage-gated calcium channels: pretreatment of the cells by EGTA and verapamil diminished the IGF-1 or insulin-induced[Ca²⁺]i but did not block the effect of IGF-2.2)IGF-1, IGF-2, and insulin also induced a Ca²⁺ mobilization from the endoplasmic reticulum: phospholipase C (PLC) inhihitors, neomycin, or U-73122 partially blocked the intracellular [Ca²⁺]i increase induced by IGF-1 and insulin and totally inhibited the effect of IGF-2. This Ca²⁺ mobilization was pertussis toxin (PTX) dependent, suggesting an activation of a PLC coupled to a PTX-sensitive G-protein. Lastly, preincubation of the cells with IGF₁ receptor antibodies diminished the IGF-1-induced Ca²⁺ spike and totally abolished the Ca²⁺ influx, but did not modify the effect of IGF-2. These results suggest that IGF-1 action on Ca²⁺ influx involves the IGF₁ receptor, while part of IGF-1 and all of IGF-2 Ca²⁺ mobilization do not implicate this receptor. J. Cell. Biochem. 64:414–422. © 1997 Wiley-Liss, Inc.