Modulation of delta opioid agonist-induced antinociception by repeated morphine pretreatment in rhesus monkeys

AIMS

Repeated treatment with morphine increases antinociceptive effects of delta opioid agonists in rodents by a mechanism that may involve increased cell-surface expression of delta receptors. The present study evaluated effects of repeated morphine treatment on behavioral effects of the delta agonist SNC80 and the mu agonist fentanyl in rhesus monkeys.

MAIN METHODS

In an assay of schedule-controlled responding, three monkeys responded for food reinforcement under a fixed-ratio 30 schedule. In an assay of thermal nociception, tail-withdrawal latencies were evaluated in three monkeys using thermal stimulus intensities of 48 and 54 degrees C. In both assays, the effects of SNC80 (0.032-3.2mg/kg) and fentanyl (0.001-0.056 mg/kg) were evaluated after repeated treatment with saline or a regimen of morphine doses modeled on the regimen that enhanced delta agonist antinociception and apparent delta receptor availability in previous rodent studies.

KEY FINDINGS

Both SNC80 and fentanyl dose-dependently decreased rates of schedule-controlled responding, and repeated morphine treatment did not significantly alter these effects. In the assay of thermal nociception, SNC80 had little effect on tail-withdrawal latencies from water heated to 48 or 54 degrees C, whereas fentanyl increased tail-withdrawal latencies at both temperatures. Repeated morphine tended to increase the antinociceptive effects of SNC80 and to decrease the antinociceptive effects of fentanyl, but these effects of repeated morphine were small and were significant only at the higher stimulus intensity (54 degrees C).

SIGNIFICANCE

These results provide limited support for the proposition that prior stimulation of mu receptors selectively increases the antinociceptive effects of delta agonists in rhesus monkeys.

Reversal of the deoxyhypusine synthesis reaction. Generation of spermidine or homospermidine from deoxyhypusine by deoxyhypusine synthase

Deoxyhypusine synthase catalyzes the first step in hypusine (N epsilon-(4-amino-2-hydroxybutyl)lysine) synthesis in a single cellular protein, eIF5A precursor. The synthesis of deoxyhypusine catalyzed by this enzyme involves transfer of the 4-aminobutyl moiety of spermidine to a specific lysine residue in the eIF5A precursor protein to form a deoxyhypusine-containing eIF5A intermediate, eIF5A(Dhp). We recently discovered the efficient reversal of deoxyhypusine synthesis. When eIF5A([3H]Dhp), radiolabeled in the 4-aminobutyl portion of its deoxyhypusine residue, was incubated with human deoxyhypusine synthase, NAD, and 1,3-diaminopropane, [3H]spermidine was formed by a rapid transfer of the radiolabeled 4-aminobutyl side chain of the [3H]deoxyhypusine residue to 1,3-diaminopropane. No reversal was observed with [3H]hypusine protein, suggesting that hydroxylation at the 4-aminobutyl side chain of the deoxyhypusine residue prevents deoxyhypusine synthase-mediated reversal of the modification. Purified human deoxyhypusine synthase also exhibited homospermidine synthesis activity when incubated with spermidine, NAD, and putrescine. Thus it was found that [14C]putrescine can replace eIF5A precursor protein as an acceptor of the 4-aminobutyl moiety of spermidine to form radiolabeled homospermidine. The Km value for putrescine (1.12 mM) as a 4-aminobutyl acceptor, however, is much higher than that for eIF5A precursor (1.5 microM). Using [14C]putrescine as an acceptor, various spermidine analogs were evaluated as donor substrates for human deoxyhypusine synthase. Comparison of spermidine analogs as inhibitors of deoxyhypusine synthesis, as donor substrates for synthesis of deoxyhypusine (or its analog), and for synthesis of homospermidine (or its analog) provides new insights into the intricate specificity of this enzyme and versatility of the deoxyhypusine synthase reaction.

N(epsilon)-(gamma-L-glutamyl)-L-lysine (GGEL) is increased in cerebrospinal fluid of patients with Huntington's disease

Pathological-length polyglutamine (Q(n)) expansions, such as those that occur in the huntingtin protein (htt) in Huntington's disease (HD), are excellent substrates for tissue transglutaminase in vitro, and transglutaminase activity is increased in post-mortem HD brain. However, direct evidence for the participation of tissue transglutaminase (or other transglutaminases) in HD patients in vivo is scarce. We now report that levels of N(epsilon)-(gamma-L-glutamyl)-L-lysine (GGEL)--a 'marker' isodipeptide produced by the transglutaminase reaction--are elevated in the CSF of HD patients (708 +/- 41 pmol/mL, SEM, n = 36) vs. control CSF (228 +/- 36, n = 27); p < 0.0001. These data support the hypothesis that transglutaminase activity is increased in HD brain in vivo.

Branched-chain and unsaturated 1,7-diaminoheptane derivatives as deoxyhypusine synthase inhibitors

Deoxyhypusine synthase catalyzes the first step in the posttranslational biosynthesis of the unusual amino acid hypusine [N epsilon-(4-amino-2-hydroxybutyl)lysine] in eukaryotic translation initiation factor 5A (eIF-5A). eIF-5A and its single hypusine residue are essential for cell proliferation. Two series of 1,7-diaminoheptane derivatives were prepared and tested as inhibitors of human deoxyhypusine synthase. These include branched-chain saturated derivatives and both branched- and straight-chain unsaturated derivatives providing size and positional variation in branching and different torsional constraints. Of the branched-chain compounds, 7-amino-1-guanidinooctane (39) proved to be the most potent inhibitor in vitro (IC50, 34 nM), while 1,7-diamino-trans-hept-3-ene (20a) displayed the greatest inhibition (IC50, 0.7 microM) among the unsaturated compounds. Compound 39 also provided effective inhibition of hypusine production in Chinese hamster ovary cells in culture. Considerations of the in vitro inhibition data reported here, along with earlier findings, allowed some speculation concerning the conformation of the substrate spermidine during its productive interaction at the active site of deoxyhypusine synthase.

Enzyme-substrate intermediate formation at lysine 329 of human deoxyhypusine synthase

Deoxyhypusine (Nepsilon-(4-aminobutyl)lysine) is the key intermediate in the posttranslational synthesis of the unique amino acid, hypusine (Nepsilon-(4-amino-2-hydroxybutyl)lysine). Deoxyhypusine synthase catalyzes the formation of deoxyhypusine by conjugation of the butylamine moiety of spermidine to the epsilon-amino group of one specific lysine residue of the eukaryotic translation initiation factor 5A (eIF-5A) precursor protein. However, in the absence of the eIF-5A precursor, catalysis involves only the NAD-dependent cleavage of spermidine to generate 1,3-diaminopropane and a putative 4-carbon amine intermediate that gives rise to Delta1-pyrroline. We have obtained evidence for a covalent enzyme-substrate intermediate that accumulates in the absence of the eIF-5A precursor. Incubation of human recombinant enzyme with [1, 8-3H]spermidine and NAD, followed by reduction with NaBH3CN, resulted in specific radiolabeling of the enzyme. The radioactive component in the reduced enzyme intermediate was identified as deoxyhypusine and was shown to occur at a single locus. The fact that labeled deoxyhypusine was found after treatment with a reducing agent suggests an intermediate with the butylamine moiety derived from spermidine attached through an imine linkage to the epsilon-amino group of a specific lysine residue of the enzyme. This residue has been identified as lysine 329. Separate experiments showing efficient transfer of labeled butylamine moiety from enzyme intermediate to eIF-5A precursor strongly support a reaction mechanism involving an imine intermediate.

Phospho-beta-glucosidase from Fusobacterium mortiferum: purification, cloning, and inactivation by 6-phosphoglucono-delta-lactone

6-Phosphoryl-beta-D-glucopyranosyl:6-phosphoglucohydrolase (P-beta-glucosidase, EC 3.2.1.86) has been purified from Fusobacterium mortiferum. Assays for enzyme activity and results from Western immunoblots showed that P-beta-glucosidase (Mr, 53,000; pI, 4.5) was induced by growth of F. mortiferum on beta-glucosides. The novel chromogenic and fluorogenic substrates, p-nitrophenyl-beta-D-glucopyranoside-6-phosphate (pNPbetaGlc6P) and 4-methylumbelliferyl-beta-D-glucopyranoside-6-phosphate (4MUbetaGlc6P), respectively, were used for the assay of P-beta-glucosidase activity. The enzyme hydrolyzed several P-beta-glucosides, including the isomeric disaccharide phosphates cellobiose-6-phosphate, gentiobiose-6-phosphate, sophorose-6-phosphate, and laminaribiose-6-phosphate, to yield glucose-6-phosphate and appropriate aglycons. The kinetic parameters for each substrate are reported. P-beta-glucosidase from F. mortiferum was inactivated by 6-phosphoglucono-delta-lactone (P-glucono-delta-lactone) derived via oxidation of glucose 6-phosphate. The pbgA gene that encodes P-beta-glucosidase from F. mortiferum has been cloned and sequenced. The first 42 residues deduced from the nucleotide sequence matched those determined for the N terminus by automated Edman degradation of the purified enzyme. From the predicted sequence of 466 amino acids, two catalytically important glutamyl residues have been identified. Comparative alignment of the amino acid sequences of P-beta-glucosidase from Escherichia coli and F. mortiferum indicates potential binding sites for the inhibitory P-glucono-delta-lactone to the enzyme from F. mortiferum.

Diamine and triamine analogs and derivatives as inhibitors of deoxyhypusine synthase: synthesis and biological activity

Deoxyhypusine synthase catalyzes the initial step in the posttranslational formation of the amino acid hypusine [N epsilon-(4-amino-2-hydroxybutyl)lysine] in eukaryotic initiation factor 5A (eIF-5A). eIF-5A and its hypusine modification are believed to be essential for cell growth. A number of compounds related to diamines and triamines were synthesized and tested as inhibitors of this enzyme. The findings indicate that the long chain triamines 2a and 2b and their guanyl derivatives 3a, 3b, 4a, and 4b exert inhibition by binding to enzyme through only a portion of their structures at any one time. The inhibition exhibited by N-ethyl-1,7-diaminoheptane 20 and its guanyl derivative 21 supports this notion and is evidence for participation of the secondary amino group in binding to enzyme. There is preliminary evidence that amidino and isothiuronium groups may also serve as basic centers for binding to enzyme. Few of the compounds tested here were comparable in inhibitory potency to 1-guanidino-7-aminoheptane (GC7) the most effective known inhibitor of deoxhypusine synthase, and none proved nearly as efficient as GC7 in inhibiting the enzyme in Chinese hamster ovary cells. Hence, unlike the antiproliferative effect of GC7, for which there is evidence of cause by interference with deoxhypusine synthase catalysis (Park, M. H.; Wolff, E. C.; Lee, Y. B.; Folk, J. E. J. Biol. Chem. 269, 1994, 27827-27832), the effective growth arrest exerted by several of the newly synthesized compounds cannot be attributed to inhibition of hypusine synthesis.

Identification of YHR068w in Saccharomyces cerevisiae chromosome VIII as a gene for deoxyhypusine synthase. Expression and characterization of the enzyme

Deoxyhypusine synthase catalyzes the formation of deoxyhypusine, the first step in hypusine biosynthesis. Amino acid sequences of five tryptic peptides from rat deoxyhypusine synthase were found to match partially the deduced amino acid sequence of the open reading frame of gene YHR068w of Saccharomyces cerevisiae chromosome VIII (AC:U00061). In order to determine whether the product of this gene corresponds to yeast deoxyhypusine synthase,a 1.17-kilobase pair cDNA with an identical nucleotide sequence to that of the YHR068w coding region was obtained from S. cerevisiae cDNA by polymerase chain reaction and was expressed in Escherichia coli B strain BL21 (DE3). The recombinant protein was found mostly in the E. coli cytosol fraction and comprised approximately 20% of the total soluble protein. The purified form of the expressed protein effectively catalyzed the formation of deoxyhypusine in yeast eIF-5A precursors as well as in human precursor and in those from Chinese hamster ovary cells. The molecular mass of the enzyme was estimated to be 172,000 +/- 4,300 Da by equilibrium centrifugation. The mass of its polypeptide subunit was determined to be approximately 43,000 Da, in close agreement with that calculated for the coding region of the YHRO68w gene. These findings show that this gene is a coding sequence for yeast deoxyhypusine synthase and that the product of this gene exists in a tetrameric form.

Purification from Fusobacterium mortiferum ATCC 25557 of a 6-phosphoryl-O-alpha-D-glucopyranosyl:6-phosphoglucohydrolase that hydrolyzes maltose 6-phosphate and related phospho-alpha-D-glucosides

6-Phosphoryl-O-alpha-D-glucopyranosyl:6-phosphoglucohydrolase (6-phospho-alpha-glucosidase) has been purified from Fusobacterium mortiferum ATCC 25557. p-Nitrophenyl-alpha-D-glucopyranoside 6-phosphate (pNP alpha Glc6P) served as the chromogenic substrate for detection and assay of enzyme activity. The O2-sensitive, metal-dependent phospho-alpha-glucosidase was stabilized during purification by inclusion of dithiothreitol and Mn2+ ion in chromatography buffers. Various 6-phosphoryl-O-alpha-linked glucosides, including maltose 6-phosphate, pNP alpha Glc6P, trehalose 6-phosphate, and sucrose 6-phosphate, were hydrolyzed by the enzyme to yield D-glucose 6-phosphate and aglycone moieties in a 1:1 molar ratio. 6-Phospho-alpha-glucosidase (M(r) of approximately 49,000; pI of approximately 4.9) is activated by Fe2+, Mn2+, Co2+, and Ni2+, and the maximum rate of pNP alpha Glc6P hydrolysis occurs at 40 degrees C within the pH range 7.0 to 7.5. The sequence of the first 32 amino acids of 6-phospho-alpha-glucosidase exhibits 67% identity (90% similarity) to that deduced for the N terminus of a putative phospho-beta-glucosidase (designated ORF f212) encoded by glvG in Escherichia coli. Western blots involving highly specific polyclonal antibody against 6-phospho-alpha-glucosidase and spectrophotometric analyses with pNP alpha Glc6P revealed only low levels of the enzyme in glucose-, mannose-, or fructose-grown cells of F. mortiferum. Synthesis of 6-phospho-alpha-glucosidase increased dramatically during growth of the organism on alpha-glucosides, such as maltose, alpha-methylglucoside, trehalose, turanose, and palatinose.

Deoxyhypusine synthase from rat testis: purification and characterization

Deoxyhypusine synthase is the first enzyme involved in the post-translational formation of hypusine, a unique amino acid that occurs at one position in a single cellular protein, eukaryotic translation initiation factor 5A (eIF-5A). This NAD-dependent enzyme catalyzes the formation of deoxyhypusine by transfer of the butylamine portion of spermidine to the epsilon-amino group of a specific lysine residue in the eIF-5A precursor. Its purification from rat testis was accomplished by ammonium sulfate fractionation and successive ion-exchange chromatographic steps, followed by chromatofocusing on a hydrophilic resin (Mono P). A pI of 4.7 was determined by isoelectric focusing. Amino acid sequences of five tryptic peptides of the pure enzyme did not correspond to any sequences in the protein data banks. The enzyme migrates as a single band on SDS-polyacrylamide gel electrophoresis with an apparent monomer molecular mass of approximately 42,000 Da. Matrix-assisted laser desorption mass spectrometry gave a monomer mass of 40,800 Da. There is evidence, however, that the active enzyme exists as a tetramer of this subunit. Rabbit polyclonal antibodies to the 42-kDa protein precipitated deoxyhypusine synthase activity. The enzyme shows a strict specificity for NAD. Purified deoxyhypusine synthase catalyzes the overall synthesis of deoxyhypusine and, in the absence of the eIF-5A precursor, catalyzes the cleavage of spermidine.

Specific inhibition of eIF-5A and collagen hydroxylation by a single agent. Antiproliferative and fibrosuppressive effects on smooth muscle cells from human coronary arteries

Restenosis occurs in 35% of patients within months after balloon angioplasty, due to a fibroproliferative response to vascular injury. These studies describe a combined fibrosuppressive/antiproliferative strategy on smooth muscle cells cultured from human primary atherosclerotic and restenotic coronary arteries and from normal rat aortas. L-Mimosine suppressed the posttranslational hydroxylation of the precursors for collagen and for eukaryotic initiation factor-5A (eIF-5A) by directly inhibiting the specific protein hydroxylases involved, prolyl 4-hydroxylase (E.C. 1.14.11.2) and deoxyhypusyl hydroxylase (E.C. 1.14.99.29), respectively. Inhibition of deoxyhypusyl hydroxylation correlated with a dose-dependent inhibition of DNA synthesis. Inhibition of prolyl hydroxylation caused a dose-dependent reduction in the secretion of hydroxyproline-containing protein and decreased the formation of procollagen types I and III. The antifibroproliferative action could not be attributed to nonspecific or toxic effects of mimosine, appeared to be selective for the hydroxylation step in the biosynthesis of the procollagens and of eIF-5A, and was reversible upon removal of the compound. The strategy of targeting these two protein hydroxylases has important implications for the pathophysiology of restenosis and for the development of agents to control fibroproliferative diseases.

Antiproliferative effects of inhibitors of deoxyhypusine synthase. Inhibition of growth of Chinese hamster ovary cells by guanyl diamines

Certain guanyl diamines are effective inhibitors of deoxyhypusine synthase (Jakus, J., Wolff, E. C., Park, M. H., and Folk, J. E. (1993) J. Biol. Chem. 268, 13151-13159), the first enzyme involved in the biosynthesis of the unusual amino acid hypusine (N epsilon-(4-amino-2-hydroxybutyl)lysine). Evidence that hypusine is implicated in cell growth prompted this study of the cellular effects of these inhibitors. In Chinese hamster ovary (CHO) cells, inhibition of hypusine biosynthesis followed by progressive arrest in cellular proliferation was observed with both N-mono- and N,N'-bisguanyl derivatives of 1,6-diaminohexane, 1,7-diaminoheptane, and 1,8-diaminooctane. Cells treated with these compounds showed no significant change in polyamine distribution, suggesting that the observed growth inhibition is not mediated through an interference with polyamine metabolism. N1-guanyl-1,7-diaminoheptane, the most potent inhibitor of deoxyhypusine synthase both in vitro and in cells, exhibited the highest antiproliferative activity toward CHO cells. No early cytotoxic effects were observed with this inhibitor, and its antiproliferative activity appeared to be reversible. Transport studies showed that N1-guanyl-1,7-diaminoheptane is actively taken up by the polyamine transport system. Mutant CHO cells defective in polyamine transport were found to be resistant to growth inhibition by this compound. The findings suggest that the antiproliferative effect of N1-guanyl-1,7-diaminoheptane is exerted intracellularly through inhibition of hypusine synthesis.

Inhibition of the G1-S transition of the cell cycle by inhibitors of deoxyhypusine hydroxylation

The formation of the unusual amino-acid hypusine in eIF-5A (eukaryotic initiation factor 5A) is associated with cellular proliferation. We used a panel of compounds, including mimosine, to probe the relationship between the exit from the G1 phase of the cell cycle, i.e., the onset of DNA replication, and the formation of hypusine by the enzyme deoxyhypusyl hydroxylase (DOHH). These two parameters displayed the same dose dependency and structure-activity relationship. Only compounds that inhibited DOHH also suppressed proliferation. This effect was observed: (i) in spontaneously proliferating, virally transformed, and mitogen-stimulated cells; (ii) for both anchorage-dependent and anchorage-independent proliferation; and (iii) with normal and malignant cell lines. DOHH reactivation occurred rapidly after inhibitor withdrawal and correlated with synchronized entry into S. The changes in the expression of specific genes during the G1-to-S transition mimicked the physiological pattern. These findings suggest that hypusine formation in eIF-5A which occurs in a specific, invariant sequence motif acquired early in evolution, may be involved in the G1-to-S transition in the eukaryotic cells tested.

Is hypusine essential for eukaryotic cell proliferation?

Hypusine [N epsilon-(4-amino-2-hydroxybutyl)-L-lysine] is a most remarkable amino acid, occurring in all eukaryotic cells, yet occupying only a single position in one protein, eukaryotic protein synthesis initiation factor 5A (eIF-5A). The unusual structure of hypusine, its derivation from the polyamine spermidine, and its increased formation in response to growth stimulation, as well as its limited occurrence in the highly conserved amino acid sequence of eIF-5A, have aroused keen interest in the biological significance of its existence and in its relationship to eIF-5A function.

Features of the spermidine-binding site of deoxyhypusine synthase as derived from inhibition studies. Effective inhibition by bis- and mono-guanylated diamines and polyamines

Several types of basic compounds structurally related to spermidine, one of the substrates for deoxyhypusine synthase, were tested as inhibitors of this enzyme. The results indicate that inhibitory compounds associate with the enzyme at the site of spermidine binding and must possess two charged primary amino or guanidino groups, or one of each. The efficiency of inhibition is related to the maximum possible distance between the primary amino groups and is adversely affected by substitutions on the secondary amino group or in the carbon chains of polyamines. The mono-guanyl derivatives are much more effective inhibitors than the parent amines or their bis-guanylated counterparts, N1-guanyl-1,7-diaminoheptane being the most effective compound with a Ki value of about 10 nM. Based on these observations we have proposed a model for the spermidine-binding site of deoxyhypusine synthase. Studies with Chinese hamster ovary cells reveal a direct correlation between prevention of hypusine formation by several guanyldiamines and their in vitro inhibition of deoxyhypusine synthase. This evidence for disruption of the initial step in the post-translational maturation of eukaryotic initiation factor 5A provides a basis for the potential control of protein biosynthesis and cell proliferation.

Hypusine: its post-translational formation in eukaryotic initiation factor 5A and its potential role in cellular regulation

The amino acid, hypusine [N epsilon-(4-amino-2-hydroxybutyl) lysine], a unique component of one cellular protein, eukaryotic translation initiation factor 5A (eIF-5A, old terminology eIF-4D), is formed post-translationally in two enzymatic steps: (i) transfer of the 4-aminobutyl moiety of the polyamine spermidine to the epsilon-amino group of a single specific lysine residue in the eIF-5A precursor protein to form an intermediate, deoxyhypusine, and (ii) subsequent hydroxylation in this 4-aminobutyl portion. Hypusine is produced soon after the translation of eIF-5A mRNA; the modification is essentially irreversible. Hypusine is found in all eukaryotes examined as well as in archaebacteria; it does not occur in eubacteria. The protein containing hypusine from each species displays a high degree of amino acid identity; the sequence of amino acids surrounding the hypusine residue is strictly conserved, suggesting the importance of the hypusine modification throughout evolution. Expression of one of the two yeast eIF-5A genes is required for survival and the lysine codon at the site of hypusine synthesis is vital for yeast growth. The precise cellular function of eIF-5A remains to be elucidated; however, eIF-5A stimulates methionyl-puromycin synthesis in a model assay for translation initiation and eIF-5A precursors containing lysine in place of hypusine are inactive in this assay. This provides evidence that the hypusine modification is needed for eIF-5A activity. In view of the important role of hypusine in eIF-5A and because of the narrow specificities of the enzymes involved in formation of this unusual amino acid, the hypusine biosynthetic steps offer promising targets for intervention in cellular proliferation. Spermidine analogs that are inhibitors of deoxyhypusine synthase in vitro also cause inhibition of hypusine formation in cells, together with a reduction in protein synthesis and in cell growth. In addition, certain metal chelating inhibitors of deoxyhypusine hydroxylase exhibit anti-proliferative effects by arresting mammalian cells at the G1/S boundary of the cell cycle. These results lay the foundation for the potential regulation of cellular events through the application of specific and potent inhibitors of hypusine biosynthesis.

Hypusine: its post-translational formation in eukaryotic initiation factor 5A and its potential role in cellular regulation

The amino acid, hypusine [N epsilon-(4-amino-2-hydroxybutyl) lysine], a unique component of one cellular protein, eukaryotic translation initiation factor 5A (eIF-5A, old terminology eIF-4D), is formed post-translationally in two enzymatic steps: (i) transfer of the 4-aminobutyl moiety of the polyamine spermidine to the epsilon-amino group of a single specific lysine residue in the eIF-5A precursor protein to form an intermediate, deoxyhypusine, and (ii) subsequent hydroxylation in this 4-aminobutyl portion. Hypusine is produced soon after the translation of eIF-5A mRNA; the modification is essentially irreversible. Hypusine is found in all eukaryotes examined as well as in archaebacteria; it does not occur in eubacteria. The protein containing hypusine from each species displays a high degree of amino acid identity; the sequence of amino acids surrounding the hypusine residue is strictly conserved, suggesting the importance of the hypusine modification throughout evolution. Expression of one of the two yeast eIF-5A genes is required for survival and the lysine codon at the site of hypusine synthesis is vital for yeast growth. The precise cellular function of eIF-5A remains to be elucidated; however, eIF-5A stimulates methionyl-puromycin synthesis in a model assay for translation initiation and eIF-5A precursors containing lysine in place of hypusine are inactive in this assay. This provides evidence that the hypusine modification is needed for eIF-5A activity. In view of the important role of hypusine in eIF-5A and because of the narrow specificities of the enzymes involved in formation of this unusual amino acid, the hypusine biosynthetic steps offer promising targets for intervention in cellular proliferation. Spermidine analogs that are inhibitors of deoxyhypusine synthase in vitro also cause inhibition of hypusine formation in cells, together with a reduction in protein synthesis and in cell growth. In addition, certain metal chelating inhibitors of deoxyhypusine hydroxylase exhibit anti-proliferative effects by arresting mammalian cells at the G1/S boundary of the cell cycle. These results lay the foundation for the potential regulation of cellular events through the application of specific and potent inhibitors of hypusine biosynthesis.

Comparison of the activities of variant forms of eIF-4D. The requirement for hypusine or deoxyhypusine

Eukaryotic protein synthesis initiation factor 4D (eIF-4D) (current nomenclature, eIF-5A) contains the unique amino acid hypusine (N epsilon-(4-amino-2-hydroxybutyl)lysine). The first step in hypusine biosynthesis, i.e. the formation of the intermediate, deoxyhypusine (N epsilon-(4-aminobutyl)lysine), was carried out in vitro using spermidine, deoxyhypusine synthase, and ec-eIF-4D(Lys), an eIF-4D precursor prepared by over-expression of human eIF-4D cDNA in Escherichia coli. In a parallel reaction, using N-(3-aminopropyl)cadaverine in place of spermidine, a variant form of eIF-4D containing homodeoxyhypusine (N epsilon-(5-aminopentyl)lysine) was prepared. Evidence that N-(3-aminopropyl)cadaverine can also act as the amine substrate for deoxyhypusine synthase in intact cells was obtained by incubating putrescine- and spermidine-depleted Chinese hamster ovary cells with [3H]cadaverine. In these cells, in which [3H]cadaverine is readily converted to N-(3-aminopropyl) [3H]cadaverine, small amounts of [3H]homodeoxyhypusine and another 3H-labeled compound, presumed to be N epsilon-(5-amino-2-hydroxy[3H]pentyl)lysine, were found. eIF-4D stimulates methionyl-puromycin synthesis, an in vitro model assay for translation initiation. Whereas the unmodified precursor ec-eIF-4D(Lys) appeared inactive, the deoxyhypusine-containing form provided a significant degree of stimulation. The variant form containing homodeoxyhypusine, on the other hand, showed little or no activity. These findings emphasize the importance of hypusine or deoxyhypusine for the biological activity of eIF-4D and demonstrate the influence of both the length and chemical nature of its amino alkyl side chain.

The active site of deoxyhypusyl hydroxylase: use of catecholpeptides and their component chelator and peptide moieties as molecular probes

The final step of hypusine formation in the eukaryotic translation initiation factor 4D (eIF-4D) is mediated by the enzyme deoxyhypusyl hydroxylase. In an effort to find specific inhibitors for this enzyme, we have studied the effects of two catecholpeptides, N alpha-acetyl-N delta-(3,4-dihydroxybenzoyl)-L-Orn-L-Pro-Gly (compound I) and N alpha-acetyl-N delta-(2,3-dihydroxybenzoyl)-L-Orn-L-Pro-Gly (compound II). Their structures were designed for anchorage to the enzyme s active site, utilizing the catechol-mediated chelation of a putative, enzyme-bound metal ion. Both compounds were found to strongly inhibit hypusine formation in vitro. Compound I was about seven times more potent than compound II, whereas the component peptide itself showed no intrinsic inhibitory activity even at concentrations as high as 1 mM. When used in conjugation with a chelating catechol moiety, however, it gave a 17- and an 8-fold enhancement of the half-maximal inhibition mediated by the chelating moieties per se, i.e. the 3,4- and the 2,3-dihydroxybenzoyl esters, respectively. The mode of inhibition by compound I was competitive with respect to the unhydroxylated precursor of eIF-4D and showed a Ki value of 32 microM +/- 3.4 microM. These catecholpeptides are the most efficient peptide antagonists of deoxyhypusyl hydroxylase known at present. They allow an assessment of the enzyme's active site organization and provide the first experimental evidence that a metal ion constitutes an integral part of its catalytic center.

Eukaryotic initiation factor 5A: the molecular form of the hypusine-containing protein from human erythrocytes

Eukaryotic initiation factor 5A (eIF-5A, formerly known as eIF-4D) purified from human erythrocytes has been found to have a monomeric molecular weight between 17,500 and 18,000. In this study, using exclusion chromatography and analytical ultracentrifugation, we demonstrate that eIF-5A normally exists as a dimer in solution and appears to be capable of undergoing reversible association to form higher polymers.

Protransglutaminase E from guinea pig skin. Isolation and partial characterization

We have isolated protransglutaminase E, the zymogen form of epidermal transglutaminase E, from the skin of the adult guinea pig. This zymogen is the source of the large majority of soluble transglutaminase activity of skin. A molecular weight value for protransglutaminase E of 77,800 +/- 700, estimated by sedimentation equilibrium, is in close agreement with the apparent values determined by exclusion chromatography and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Treatment of the proenzyme with dispase, proteinase K, trypsin, or thrombin produces active enzyme. The enzyme, transglutaminase E, formed by the action of dispase, was observed to exist in the native state as a molecule indistinguishable in size from the zymogen. Under denaturing conditions, however, the enzyme dissociates into two fragments with molecular weights of 50,000 and 27,000. The observation that reducing agents are not needed for this dissociation suggests a noncovalent association of the two peptide chains in the native enzyme. Evidence that the catalytically essential -SH group of the enzyme residues in the Mr 50,000 fragment and that only the Mr 27,000 fragment possesses an unmasked amino terminus provides the basis for a proposed model of zymogen activation. Whether the noncatalytic fragment plays a role in catalysis is not known because separation of the fragments of native enzyme was not achieved.

N1N8-bis(gamma-glutamyl)spermidine cross-linking in epidermal-cell envelopes. Comparison of cross-link levels in normal and psoriatic cell envelopes

N1N8-Bis(gamma-glutamyl)spermidine was found in exhaustive proteolytic digests of isolated cell envelopes from human epidermis at levels comparable with those of epsilon-(gamma-glutamyl)lysine. Significantly higher than normal amounts of these compounds, particularly the bis(gamma-glutamyl)polyamine, were observed in envelopes from afflicted areas (scales) of psoriatic patients. These findings support the notions that N1N8-bis(gamma-glutamyl)spermidine, like epsilon-(gamma-glutamyl)lysine, functions in cell envelopes as an enzyme-generated protein cross-link and stabilizing force and that individuals with the chronic, recurrent skin disease, psoriasis, exhibit in involved epidermis abnormal cell-envelope-protein cross-linking.

Cleavage of spermidine as the first step in deoxyhypusine synthesis. The role of NAD

The biosynthesis of deoxyhypusine (N-(4-aminobutyl)lysine) occurs by the transfer of the 4-aminobutyl moiety of spermidine to a specific lysine residue in a precursor of eukaryotic translation initiation factor 4D (eIF-4D). Deoxyhypusine synthase, the enzyme that catalyzes this reaction, was purified approximately 700-fold from rat testis. The Km values for the substrates, spermidine, the eIF-4-D precursor protein, and NAD+, were estimated as approximately 1, 0.08, and 30 microM, respectively. After incubation of partially purified enzyme with [1,8-3H]spermidine, NAD+, and the eIF-4D precursor, equal amounts of radioactivity were found in free 1,3-diaminopropane and in protein-bound deoxyhypusine. However, when the protein substrate (eIF-4D precursor) was omitted, radioactivity was found in 1,3-diaminopropane and in delta 1-pyrroline in nearly equal quantities, providing evidence that the cleavage of spermidine occurs, albeit at a slower rate, in the absence of the eIF-4D precursor. That NAD+, which is required for this reaction, functions as the hydrogen acceptor was demonstrated by the fact that radioactivity from spermidine labeled with 3H at position 5 is found in NADH as well as in delta 1-pyrroline. Transfer of this hydrogen from spermidine to the re face of the nicotinamide ring of NAD+, as determined by the use of dehydrogenases of known stereospecificity, defines the first step of deoxyhypusine synthesis as a pro-R, or A, stereospecific dehydrogenation. Based on these findings, an enzyme mechanism involving imine intermediate formation is proposed.

High-performance liquid chromatographic method for determination of hypusine and deoxyhypusine

A selective and sensitive reversed-phase high-performance liquid chromatographic method is described for the determination of the amino acid hypusine which occurs ubiquitously in mammalian cells and for the simultaneous measurement of its immediate precursor deoxyhypusine. These amino acids, after their ion-exchange separation from the bulk of other amino acids in protein hydrolysates, are derivatized with o-phthalaldehyde and the fluorescent derivatives are separated by reverse-phase liquid chromatography. The sensitivity of this method allows detection of less than 5 pmol of each of these unusual amino acids. The method is applied to the determination of hypusine and deoxyhypusine in acid hydrolysates of cultured cells and tissues.

Inhibition of deoxyhypusine hydroxylase by polyamines and by a deoxyhypusine peptide

The inhibition of deoxyhypusine hydroxylase was studied in vitro. Of the polyamines tested, spermine and its homologue thermine exhibited the strongest inhibition against the enzyme from rat testis. Kinetic analysis revealed that the inhibition by spermine was competitive (Ki, 0.25 +/- 0.02 mM) with respect to the deoxyhypusine protein substrate. Spermidine and its homologue caldine were also inhibitors, but less potent ones than spermine. The spermidine analogues with one or both primary amino groups replaced by the cyano group did not inhibit. A number of diamines, including putrescine, were found to display little or no inhibition. The observed effects of naturally occurring polyamines on deoxyhypusine hydroxylase activity is consistent with a suggestion of regulation of this enzymic activity by cellular levels of polyamines. A synthetic peptide Lys-Thr-Gly-deoxyhypusine-His-Gly-His-Ala-Lys, the amino acid sequence of which corresponds to that surrounding hypusine in eukaryotic initiation factor 4D, was found to display competitive-type inhibition (Ki, 0.44 +/- 0.02 mM) against deoxyhypusine hydroxylase from Chinese hamster ovary cells. Free hypusine and deoxyhypusine, on the other hand, possessed no inhibitory properties. A peptide analogous to the deoxyhypusine nonapeptide with lysine in place of deoxyhypusine had little effect on enzyme activity. The preparation of a derivative of deoxyhypusine, suitably protected for use in the solid-phase synthesis of deoxyhypusine peptides, is described.

High-performance liquid chromatographic method for the determination of epsilon-(gamma-glutamyl)lysine and mono- and bis-gamma-glutamyl derivatives of putrescine and spermidine

A sensitive, simple, and rapid high-performance liquid chromatographic (HPLC) method is reported for the determination of epsilon-(gamma-glutamyl)lysine and certain gamma-glutamylpolyamines in selected fractions from ion-exchange chromatograms of protein digests. The method involves pre-column derivatization of the gamma-glutamylamine conjugates with o-phthalaldehyde, linear-gradient reversed-phase HPLC separation, and fluorimetric detection. The gradient used was designed to provide a means of avoiding a desalting step, while maintaining proper chromatographic performance. gamma-Glutamylamines in amounts from 0.1 to 1 nmol display linear concentration-response relationships. The detection limits are approximately 10 and 200 pmol per mg of protein for the gamma-glutamylpolyamines and for epsilon-(gamma-glutamyl)lysine, respectively. The use of the method is exemplified by an analysis of the epidermal cell envelope from the skin of a newborn mouse.

Epidermal and hair follicle transglutaminases. Partial characterization of soluble enzymes in newborn mouse skin

Treatment of skins of newborn mice with the neutral protease Dispase in order to separate dermis and epidermis causes pronounced changes in the levels of transglutaminase activity in the epidermis. Two soluble transglutaminases, one anionic enzyme and one cationic enzyme, of Mr approximately 90,000 and approximately 50,000, respectively, are extracted from epidermis; and the activities of both enzymes increase as a function of the time of Dispase treatment of skin. When the anionic Mr approximately 90,000 enzyme is incubated with Dispase after its chromatographic isolation from epidermal extracts, it is converted to a lower molecular weight enzyme. Hair follicles isolated from dermis prepared by a 12-h Dispase treatment of the skin of newborn mice contain two soluble cationic transglutaminases, one of which is indistinguishable from that of epidermis and the other which is not seen in epidermis. Both of these hair follicle enzymes are of Mr approximately 50,000 and appear to exist in monomeric form. They have been partially purified. Based upon these findings, we suggest that transglutaminase processing and control occur during normal differentiation of keratinocytes in epidermis and of hair follicle epidermal cells in dermis and that production of the proper forms of the enzyme may be essential to the formation of mature cornified envelopes and hair shafts, respectively.

Free and protein-conjugated polyamines in mouse epidermal cells. Effect of high calcium and retinoic acid

We have investigated polyamine metabolism in primary cultures of mouse epidermal cells. These cells, which grow at low Ca2+ levels as a monolayer with characteristics of basal cells, terminally differentiate when the extracellular Ca2+ level is raised above 1 mM. The cellular levels of free polyamines were measured, and, after incubation of cell cultures with [3H]putrescine, the distribution of label in both acid-soluble and acid-insoluble cellular components was examined. Free polyamine levels were reduced in cells induced to differentiate. Treatment with retinoic acid, which prevents differentiation and causes increased proliferation, resulted in an increase in free putrescine. Upon adjustment of the calcium concentration to a level that induces differentiation, the enzyme transglutaminase was activated, and a concomitant increase in the level of both protein-bound mono- and bis-gamma-glutamyl derivatives of putrescine and spermidine was observed. Isolation of a material of apparent molecular weight about 6000 which contains only mono-gamma-glutamylpolyamines and the finding of both mono- and bis-gamma-glutamylpolyamines in the protein fraction containing cornified cell envelopes provided the basis for speculation on polyamines in envelope formation. Our data suggest that polyamines play a role during epidermal cell differentiation through transglutaminase-mediated post-translational modification.

Covalent incorporation of polyamines as gamma-glutamyl derivatives into CHO cell protein

The possible role of polyamines in the covalent modification of proteins in CHO cells was investigated by metabolic labeling with [3H]putrescine. A single radiolabeled protein band with an apparent relative molecular mass of 18,000 Da was observed by SDS-polyacrylamide gel electrophoresis. Almost all the radioactivity covalently linked to this protein was recovered as hypusine. The labeling of this protein was increased several-fold when cells were cultured with alpha-difluoromethylornithine (DFMO) or with this drug plus methylglyoxal bis(guanylhydrazone) (MGBG), as a result of increase in specific radioactivity of the hypusine immediate precursor, spermidine. Also labeled under the latter condition were other cellular proteins. These were aggregates on the top both of the stacking gel and of the running gel, and protein-like materials with relative molecular masses of 36 and 8 kDa. The radioactivity covalently associated with these proteins was recovered after acid hydrolysis as polyamines. The identification of gamma-glutamylputrescine and gamma-glutamylspermidines in proteolytic digests of the acid-insoluble fraction of treated cells indicates that polyamines are covalently linked to these cellular protein. Several possible cellular functions of gamma-glutamylpolyamine protein components are discussed.

Modulation of cellular transglutaminase: protease-induced activation

Multiple molecular forms of transglutaminase are found in cells and each form is widely distributed. We find a 95 K dalton enzyme associated with membrane fractions. A 50 K dalton enzyme occurs primarily in epidermis and hair follicles. Cells after treatment with proteases show greater transglutaminase activity. The activated enzyme in rat chondrosarcoma cells is one of 95 K daltons, whereas mouse epidermal cells and rabbit endometrium cells after protease activation display enzymes of both 95 K daltons and 50 K daltons. The 95 K dalton enzyme, but not that of 80 K daltons, can be activated by proteases or sulfhydryl compounds after cell lysis. In cells that undergo terminal differentiation, e.g., reticulocytes, megakaryocytes, monocytes, chondrocytes, and epidermal cells, the forms of transglutaminase are modulated. Our findings suggest that these modulations in differentiating cells are the results of transglutaminase post-translational modifications that cause pronounced changes in catalytic activity.

Identification of a substrate site for liver transglutaminase on the aminopropeptide of type III collagen

The aminopropeptide of type III collagen incorporates [3H]putrescine in the presence of liver transglutaminase, and the change in incorporation with concentration indicates one binding site on each of the Mr = 15,000 subunits of the peptide. At low concentrations the incorporation was comparable to that of dimethyl casein and much greater than actin or fibrinogen. Cleavage and Edman degradation of the aminopropeptide identified the major putrescine-binding site as glutamine in position 14. The surrounding amino acid sequence (Leu-Gly-Gln-Ser) shows homology with some synthetic peptide substrates of transglutaminase.

Biosynthetic labeling of hypusine in mammalian cells. Carbon-hydrogen bond fissions revealed by dual labeling

Using a dual-label technique in which 3H- and 14C-labeled forms of putrescine and of spermidine were employed as biosynthetic precursors of hypusine, two -C-H bond cleavages were detected during production of this unique amino acid in Chinese hamster ovary cells. One of these cleavages occurs at C-1 of the 4-aminobutyl group during its transfer from the secondary amine nitrogen of spermidine to the nitrogen at the epsilon-position of a specific lysine residue in the polypeptide precursor of eukaryotic initiation factor 4D. Breakage of the other -C-H bond takes place at C-2 in this aminobutyl segment after it has been coupled to lysine to form the intermediate deoxyhypusine residue. Hydroxylation at this carbon atom, which constitutes the last step in hypusine biosynthesis, is the cause of bond cleavage. The data obtained are consistent with a notion that no additional -C-H bond fissions occur during hypusine biosynthesis. Our findings permit suggestion of a mechanism for enzymic aminobutyl group transfer in which 4-aminobutyraldehyde produced by oxidative cleavage of spermidine is coupled with the epsilon-amino group of a specific lysine residue to form an enzyme-bound imine intermediate.

Indirect assays for deoxyhypusine hydroxylase using dual-label ratio changes and oxidative release of radioactivity

Two procedures for rapid assay of deoxyhypusine hydroxylase activity are described. One of these assays measures changes in the 3H:14C ratio of dual-labeled protein that results from the release of tritium from a specific position in the side chain of the 3H,14C-labeled constituent amino acid deoxyhypusine upon its conversion to [3H,14C]hypusine. The other assay relies upon release of radioactivity from product protein by periodate oxidation of the radiolabeled side chain of component hypusine. The good correspondence of each of these assays with the ion exchange chromatographic method which measures hypusine and deoxyhypusine in acid hydrolysates of protein indicates that each provides a valid means of determining deoxyhypusine hydroxylase activity.

Deoxyhypusine hydroxylase from rat testis. Partial purification and characterization

Deoxyhypusine hydroxylase, the enzyme that catalyzes the formation of hypusine from deoxyhypusine in eukaryotic initiation factor 4D, has been partially purified from rat testis. The partially purified enzyme requires only the addition of certain sulfhydryl compounds for catalytic activity, dithiothreitol being the most effective. Its lack of dependency on the alpha-keto acid-dependent dioxygenase cofactors, Fe2+, alpha-ketoglutarate, and ascorbic acid, its failure to decarboxylate stoichiometrically alpha-ketoglutarate with deoxyhypusine hydroxylation, and its strong and specific inhibition by Fe2+ all suggest a catalytic mechanism of this enzyme unlike that of the prolyl and lysyl hydroxylases.

Activation of transglutaminase and production of protein-bound gamma-glutamylhistamine in stimulated mouse mast cells

The identification of transglutaminase in the growth-factor-dependent mouse mast cell line PT18 was accomplished through its characteristic catalytic properties (specificity, calcium dependency, and inhibition by iodoacetamide); and by both immunoprecipitation and Western blot analysis using affinity purified antibody. The enzymatic activity in these cells increased in association with the release of histamine from the cells induced by an IgE-dependent mechanism or by exposure to the ionophores A23187 or Br-x537A. The increase in transglutaminase activity was paralleled by a marked increase in the level of protein-bound gamma-glutamylhistamine, determined in radiolabeled form in mast cells that were either metabolically labeled with [3H]histidine or incubated with [3H]histamine before degranulation. The highest level of bound gamma-glutamylhistamine was found in the immunologically stimulated cells. Enzymatic activity and the gamma-glutamyl derivative were associated primarily with the cells, both before and after stimulation. Separation of gamma-glutamylhistamine in a proteolytic digest of these cells was carried out using a combination of ion exchange chromatography and high performance liquid chromatography. The gamma-glutamyl compound was identified and quantitated through the enzymatic production of histamine with the use of gamma-glutamylamine cyclotransferase, an enzyme specific for the disassembly of gamma-glutamylamines.

The biosynthesis of hypusine (N epsilon-(4-amino-2-hydroxybutyl)lysine). Alignment of the butylamine segment and source of the secondary amino nitrogen

The unusual amino acid hypusine is produced in a single protein of mammalian cells by a novel posttranslational event in which a lysine residue is conjugated with the four-carbon moiety from the polyamine spermidine to form an intermediate deoxyhypusine, and in which this intermediate is subsequently hydroxylated. Specifically isotopically labeled precursors of hypusine were used to identify the biosynthetic origin of some of the atoms of hypusine and thus to provide further insight into the mechanism of this in vivo chemical modification reaction. Radiolabel from [1,4-3H] putrescine, [1,8-3H]spermidine, and [5-3H]spermidine entered hypusine during growth of Chinese hamster ovary cells. The occurrence of this label at positions 1 and 4, at position 4, and at position 1, respectively, in the 4-amino-2-hydroxybutyl portion of hypusine revealed an alignment of atoms identical to that in the butylamine segment of spermidine. Growth of cells with [epsilon-15N]lysine as the source of lysine yielded hypusine enriched in 15N, whereas only isotope-free hypusine during growth by [4-15N]spermidine. These was found in cells whose spermidine was replaced during growth by [4-15N]spermidine. These findings are in accordance with a proposal that the first phase of hypusine biosynthesis, the production of intermediate deoxyhypusine, occurs through transfer of the butylamine moiety from spermidine to the epsilon-amino nitrogen of protein-bound lysine. The technique of thermospray high-performance liquid chromatography/mass spectrometry provided positive identification of 15N in hypusine through final separation and on-column direct analysis of this amino acid. Methods of preparation are given for spermidine of high specific radioactivity, labeled specifically at position 5 with 3H, and for spermidine with 15N at the 4-position.