Changes of ornithine decarboxylase activity and polyamine content upon differentiation of mouse NB-15 neuroblastoma cells

Aminohexanoic hydroxamate is a potent inducer of the differentiation of mouse neuroblastoma cells

Deoxyhypusine synthase is the key enzyme for modifying a lysine residue to hypusine in the cellular protein eukaryotic initiation factor 5A (eIF-5A). Deletion of the deoxyhypusine synthase or the eIF-5A gene in yeast produces lethal phenotype. Inhibition of deoxyhypusine synthase by 1-guanidino-7-aminoheptane (GC7) suppresses tumor cell growth. Hypusine formation represents one of the most specific polyamine-dependent biochemical reactions. In view of the importance of polyamines in growth regulation and cancer biology, deoxyhypusine synthase has been considered to be a good target for chemotherapeutic drug design. Using GC7 as a prototype we have synthesized and tested three classes of diamine analogs, namely, guanidino-, pyrimidino-, and hydroxamate derivatives, as potential inhibitors for deoxyhypusine synthase. Our study shows that (i) among all the compounds tested, GC7 remained to be the most potent inhibitor for deoxyhypusine synthase; (ii) N,N'-bispyrimidino-1, 9-diaminononane, although a poor inhibitor of deoxyhypusine synthase, was a potent growth inhibitor; and (iii) one of the hydroxamate derivatives, 6-aminohexanoic hydroxamate (HC6), prominently induced the differentiation of mouse neuroblastoma cells at sub-millimolar concentrations. Interestingly, other hydroxamates with different chain length were not nearly as effective as HC6 in inducing neuroblastoma cell differentiation. The effect of HC6 was also unique in that it could induce neurite outgrowth and the expression of neuron-specific genes such as synapsin I and MAP-2 in neuroblastoma cells in the absence of other promoting agents such as cAMP. The effect of HC6 on neuroblastoma cell differentiation was comparable with, or better than that of N(6),O(2)'-dibutyryl cAMP (Bt(2)cAMP), a standard reagent commonly used for inducing the differentiation of mouse and human neuroblastoma cells in culture.

Acetylcholinesterase inhibitor treatment delays recovery from axotomy in cultured dorsal root ganglion neurons

We have previously reported that dorsal root ganglion neurons cultured in the presence of the highly specific, reversible acetylcholinesterase inhibitor 1,5-bis-(4-allyldimethylammoniumphenyl) pentan-3-one dibromide (BW284c51), showed significantly reduced neurite outgrowth and contained massive perikaryal inclusions of neurofilaments. In the present report we have more closely examined these changes in a time course study over a 21-day culture period using a combined morphological, immunocytochemical and enzymatic approach and additionally, describe, the effects of acetylcholinesterase inhibitor treatment on the state of neurofilament phosphorylation. Finally, we have examined the effects of co-administration of N6,2'-0-dibutyryladenosine 3':5'-cyclic monophosphate (dbcAMP) with BW284c51. At 1 day in culture, both control and treated cells displayed eccentrically located nuclei, numerous polysomes and perikaryal accumulations of neurofilaments which were immunoreactive with both phosphorylation- and nonphosphorylation-dependent neurofilament antibodies. These cytological changes, which are common features of the chromatolytic reaction following axotomy in vivo, rapidly resolved in the control neurons, where by 7 days in culture, the neurofilament accumulations had completely disappeared and neurite outgrowth was robust. In contrast, inhibitor-treated neurons retained the post-axotomy features up to 21 days and had significantly reduced neurite outgrowth. In addition, we have investigated a possible role of cyclic adenosine monophosphate (cAMP) in the recovery process since it has been shown to enhance neuritic outgrowth in cultured neurons. Our results demonstrate that the addition of dbcAMP, a membrane permeable analog of cAMP, significantly enhanced neuritic outgrowth and accelerated the recovery of BW284c51-treated dorsal root ganglion cells, as gauged by the disappearance of the axotomy-related cytological changes. Treatment with dbcAMP also increased acetylcholinesterase activity which has been positively correlated with neurite outgrowth both in vivo and in vitro. Together, these observations suggest that acetylcholinesterase has a non-cholinolytic, neurotrophic role in neuronal regeneration and development.

Polyamine profiles and growth properties of ornithine decarboxylase overexpressing MCF-7 breast cancer cells in culture

To determine the direct influence of the polyamine (PA) pathway on breast cancer phenotype, we employed a transfection approach to induce overexpression of the PA biosynthetic enzyme ornithine decarboxylase (ODC) in the hormone-responsive MCF-7 breast cancer cell line. Using a modified calcium phosphate method and an ODC cDNA coding for a truncated and more stable enzyme, we were able to achieve a moderate to marked degree of ODC overexpression (up to 150-fold) in a transient transfection system. ODC-overexpressing MCF-7 cells exhibited a selective increase in cellular putrescine content, while the levels of spermidine and spermine remained unaffected. Under defined culture conditions, overexpression of ODC resulted in a consistent but modest increase in [3H]thymidine incorporation into DNA which was similar in the presence and absence of 17-beta-estradiol, TGF-alpha, and IGF-I. In the presence of serum, the effect of ODC overexpression on basal [3H]-thymidine incorporation into DNA was inconsistent, possibly as a result of subtle differences in culture conditions. Overall, our results support the hypothesis that activation of the PA biosynthetic pathway may confer a growth advantage to breast cancer cells.

Differentiation of a mouse neuroblastoma variant cell line whose ornithine decarboxylase gene has been amplified

Differentiation of mouse neuroblastoma cells has been shown to be accompanied by changes in polyamine metabolism and a decrease in polyamine content. We have previously shown that alpha-difluoromethyl ornithine, a suicide inhibitor of ornithine decarboxylase (ODC, EC 4.1.1.17) and suboptimal concentrations of dibutyryl cAMP (0.1 to 0.2 mM) are effective in inducing the differentiation of mouse Neuro-2a (N2a) neuroblastoma cells. Exogenously added putrescine or spermidine can block the action of DFMO and dibutyryl cAMP, suggesting that polyamines may play a regulatory role in neuroblastoma differentiation. We have now isolated from N2a cells a clonal variant line, DF-40, whose ODC gene has been amplified by 40-fold. The DF-40 cells overproduced the ODC enzyme and contained very high levels of putrescine, spermidine and spermine. Treatment of DF-40 cells with dibutyryl cAMP or DFMO/dibutyryl cAMP led to a more than 80% reduction in polyamine content. Such a decrease did not cause the DF-40 cells to differentiate. Polyamine content in the treated DF-40 cells was still comparable or higher than that in the undifferentiated N2a cells. In contrast, serum-deprivation induced full differentiation of DF-40 cells. Levels of polyamine in the differentiated DF-40 cells, however, were also found to be comparable to that in the undifferentiated N2a cells. Exogenously added polyamines could not block the differentiation of DF-40 cells induced by serum-deprivation, suggesting that the action of polyamines in regulating neuroblastoma differentiation may depend on the presence of serum factors.

Polyamine involvement in the secretion and action of TGF-alpha in hormone sensitive human breast cancer cells in culture

These experiments were designed to test polyamine (PA) involvement in the secretion and action of transforming growth factor alpha (TGF-alpha) in hormone responsive MCF-7 breast cancer cells in liquid culture. At the same time, we evaluated the influence of culture conditions (with serum vs. serum depleted) and subclonality of MCF-7 cells on PA involvement in estrogen (E2) and TGF-alpha stimulated cell proliferation. Despite inducing a profound suppression of cellular PA levels and inhibiting basal and E2-stimulated growth, administration of the PA synthesis inhibitor alpha-difluoromethylornithine (DFMO) did not influence either basal or E2-induced TGF-alpha secretion. In the same experiments, on the other hand, addition of DFMO completely blocked the growth stimulatory effect of exogenous TGF-alpha. However, when the culture conditions were changed to serum-free medium, TGF-alpha and E2-induced cell proliferation was affected modestly or not at all by DFMO administration, despite similar suppression of cellular ornithine decarboxylase (ODC) activity and PA levels. In addition, different clones of MCF-7 cells differed in their sensitivity to the antiproliferative effect of DFMO as well as in basal levels of ODC activity and PA. We conclude that PAs are not involved in basal or E2-stimulated TGF-alpha secretion in MCF-7 breast cancer cells. On the other hand, PAs do seem to be important mediators of TGF-alpha and E2-induced breast cancer cell proliferation, though the degree of such involvement appears to be influenced by serum factors and clonal variability of MCF-7 cells.

The in vitro differentiation of pleomorphic Trypanosoma brucei from bloodstream into procyclic form requires neither intermediary nor short-stumpy stage

Our studies on the in vitro differentiation of a pleomorphic Trypanosoma brucei strain TREU667 indicate that the parasite differentiates directly from long-slender into procyclic form when incubated in Cunningham's medium at 26 degrees C. The intermediary and the short-stumpy bloodstream forms harvested from infected mice can also differentiate directly into procylic form in vitro with time courses similar to that for the long-slender form. Thus, none of the three bloodstream forms appear to be significantly better preadapted for differentiation. Tricarboxylic acid (TCA) cycle intermediates cis-aconitate and L-citrate can shorten the initial lag phase of the differentiation, but an essential trigger appears to be the temperature shift from 37 degrees C to 26 degrees C, when other TCA cycle intermediates such as L-proline, L-malate, alpha-ketoglutarate, fumarate and succinate are present in Cunningham's medium. The ornithine decarboxylase (ODC) activity in T. brucei showed a gradual increase and the ODC mRNA level remained constant during the differentiation. DL-alpha-Difluoromethylornithine (DFMO), putrescine, dibutyryl cAMP and theophylline all exerted no discernible effect on the in vitro process, which suggests that neither cAMP increase nor polyamine depletion could be counted among the triggers of T. brucei differentiation. A monomorphic T. brucei strain EATRO110 was tested in the same medium at 26 degrees C but was unable to differentiate.

Selectivity of polyamine involvement in hormone action on normal and neoplastic target tissues of the rat

The present experiments were designed to evaluate the polyamine involvement in hormonal actions on proliferation and receptor content of neoplastic tissue (hormone-responsive breast cancer) as well as on growth of normal endocrine target tissue (uterus) in the same animals. Administration of estradiol and perphenazine (to stimulate endogenous prolactin release) stimulated N-nitrosomethyl-urea (NMU)-induced rat mammary tumor growth following ovariectomy-induced tumor regression. Such hormonal activation of breast cancer growth was completely abolished by treatment with alpha-difluoromethyl-ornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, which lowered tumor content of polyamines. The growth inhibitory effect of DFMO was partially reversible by exogenous putrescine administration. In contrast, the rise in cytosolic content of progesterone receptors induced by hormonal treatment was not affected by suppression of tumor polyamine levels by DFMO. Similarly, DFMO administration failed to influence the hormone-induced increase in uterine weight in the same animals. Thus, our data suggest selectivity of polyamine involvement in hormone actions, which, in our experimental system, seems to be restricted to the endocrine control of neoplastic cell proliferation.

Isolation and characterization of an 18 kDa hypusine-containing protein from cultured NB-15 mouse neuroblastoma cells

An 18 kDa protein can be metabolically labeled by [3H]putrescine or [3H]spermidine in various mammalian cells. The labeling is due to a post-translational modification of one lysine residue to hypusine using the aminobutyl moiety derived from spermidine. In view of the lack of knowledge of the function of this spermidine-modified protein, we decided to use the radioactivity associated with the [3H]spermidine-labeled 18 kDa protein as a tracer to develop a simple procedure for purifying this protein from cultured cells. We first screened more than 15 different affinity adsorbents for their ability to bind the labeled 18 kDa protein. This approach enabled us to develop a four-step procedure to purify the labeled 18 kDa protein from NB-15 mouse neuroblastoma cells. The procedure, including a Cibacron Blue column, an omega-aminooctyl-agarose, a Sepharose G-50, and a Mono Q column, resulted in an 800-fold purification of the labeled 18 kDa protein. Two-dimensional gel analysis of fractions enriched in the labeled 18 kDa protein revealed (i) the presence of isoforms of hypusine-containing 18 kDa protein, with pI values ranging from 4.7 to 5.2, and (ii) the presence of an additional labeled protein with an apparent molecular mass of 22 kDa and a pI value of 5.0. The labeling intensity of the 22 kDa protein, however, was less than 5% of that of the 18 kDa protein. Peptide map analysis, using the V-8 proteinase digestion method, indicated that the 18 kDa hypusine-containing protein obtained from NB-15 cells was similar to eukaryotic initiation factor 4D isolated from rabbit reticulocytes.

Polyamine metabolism in an obligately alkalophilic Bacillus alcalophilus that grows at pH 11.0

Bacillus alcalophilus, an obligately alkalophilic bacterium that grows at pH 11.0, has an intracellular pH of 9.5 or less. Unlike all other living organisms, polyamines (putrescine, spermidine and spermine) in B. alcalophilus, if present, will be largely unprotonated. HPLC analysis indicated that spermidine is the major polyamine in B. alcalophilus, accounting for more than 90% of total polyamines, and the level of spermidine varies during growth. Ornithine decarboxylase activity was not detectable in B. alcalophilus under all conditions examined. When [3H]arginine was added to the culture medium, the radioactivity can be recovered from polyamine pool; the distribution is 3% for putrescine, 94% for spermidine, and 3% for spermine, suggesting the presence of arginine pathway for polyamine biosynthesis. The polyamine transport system in B. alcalphilus appears to be Na+-dependent and is highly sensitive to the inhibition of gramicidin S and valinomycin.

Changes of serum-induced ornithine decarboxylase activity and putrescine content during aging of IMR-90 human diploid fibroblasts

The roles of ornithine decarboxylase (ODC, EC 4.1.1.17) and polyamines in cellular aging were investigated by examining serum-induced changes of these parameters in quiescent IMR-90 human diploid fibroblasts as a function of their population doubling level (PDL) and in human progeria fibroblasts. Serum stimulation caused increases of ODC and DNA synthesis in IMR-90 human diploid fibroblasts, with maximal values occurring, respectively, 10 hr and 22 hr after serum stimulation. Both serum-induced ODC activity and DNA synthesis in IMR-90 cells were found to be inversely related to their PDL. Maximal ODC activity and DNA synthesis in young cells (PDL = approximately 18-22) were, respectively, five-fold and six-fold greater than that in old cells (PDL = approximately 50-55), which in turn were comparable or slightly higher than that in progeria fibroblasts. Polyamine contents (putrescine, spermidine, and spermine) in quiescent IMR-90 cells did not show significant PDL-dependency. The putrescine and spermine contents in quiescent progeria cells were comparable to those in quiescent IMR-90 cells. The spermidine content in quiescent progeria cells, however, was extremely low, less than half of that in quiescent IMR-90 cells. Serum stimulation caused a marked increase in putrescine content in young cells but not in old cells or in progeria cells. The spermidine and the spermine content in IMR-90 cells, either young or old, and in progeria cells did not change significantly after serum stimulation. Our study indicated that aging of IMR-90 human diploid fibroblasts was accompanied by specific changes of polyamine metabolism, namely, the serum-induced ODC activity and putrescine accumulation. These changes were also observed in progeria fibroblasts derived from patients with Hutchinson-Gilford syndrome.

Adipose cell differentiation: evidence for a two-step process in the polyamine-dependent Ob1754 clonal line

A subclone of preadipocyte Ob17 cells has been isolated (Ob1754 clonal line). Confluent Ob1754 cells treated with an inhibitor of spermidine and spermine synthesis, methylglyoxal bis(guanylhydrazone), were totally dependent upon putrescine addition for the expression of glycerol-3-phosphate dehydrogenase which behaved as a late marker of adipose conversion. Under these conditions, the early expression of lipoprotein lipase during growth arrest remained unchanged. Studies at the mRNA level showed that the expression of unidentified pOb24 and pGH3 mRNAs, which was parallel to that of lipoprotein lipase, is independent of polyamine addition whereas the late emergence of glycerol-3-phosphate dehydrogenase mRNA was putrescine-dependent and co-ordinated with the expression of pAL422 mRNA encoding for a myelin-P2 homologue [Bernlohr, Angus, Lane, Bolanowski & Kelly (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 5468-5472]. The appearance of lipoprotein lipase preceded DNA synthesis and post-confluent mitoses which were both putrescine-dependent and which took place before the appearance of glycerol-3-phosphate dehydrogenase. Thus the adipose conversion of Ob1754 cells involves the expression of at least two separate sets of markers which are differently regulated.

Erythroid differentiation of cultured murine erythroleukemia cells by the spermine analogue canavalmine

Canavalmine, an analogue of spermine, induced erythroid differentiation of murine erythroleukemia cells 745A, as evidenced by benzidine staining and heme content of cultured cells. Benzidine-positive cells synthesizing hemoglobin appeared on day 4 after addition of 250 microM canavalmine. The canavalmine-induced cell differentiation was inhibited by the addition of agents which alter the structure of the cell membrane, such as local anesthetics (procainamide and lidocaine) or Ca2+ antagonists (nifedipine and verapamil) at dosages not toxic for the cell growth. Canavalmine did not significantly affect the levels of conjugated polyamines in the acid-insoluble fraction of the cells. In contrast, the level of free spermidine in the acid-soluble fraction greatly decreased during the 18 h after canavalmine treatment. Putrescine and spermidine, when added externally to the growth medium, showed dose-dependent inhibition of canavalmine-induced cell differentiation. Neither cadaverine nor spermine had any significant effect. These results suggest that not only structural change of cell membrane but alteration of the polyamine metabolism, especially a regulation of the cellular level of free spermidine, might have a key importance in erythroid differentiation of murine erythroleukemia cells induced by canavalmine.

Differences in the reduction kinetics of incorporated spin labels in undifferentiated and differentiated mouse neuroblastoma cells

Significant differences in the rate of reduction of two spin labels, 5-doxylstearic acid and TEMPOL, in the undifferentiated and differentiated NB-15 mouse neuroblastoma cells were demonstrated by using electron paramagnetic resonance (EPR) spectroscopy. The half-time (T1/2) values for decay of the EPR signal of 5-doxylstearic acid in the undifferentiated and differentiated neuroblastoma cells were 70 min and 290 min, respectively. The T1/2 values of TEMPOL in the undifferentiated and differentiated cells were 18 min and 34 min, respectively. The cellular reductant was characterized as non-protein-bound sulfhydryl groups. A corresponding difference in the cellular non-protein-bound sulfhydryl content, 19.30 nmol/mg protein for the undifferentiated cells and 6.78 nmol/mg protein for the differentiated cells, was observed. Comparison of the reduction rates of TEMPOL, 5-doxylstearic acid and 16-doxylstearic acid in the undifferentiated NB-15 cells suggested that the permeation of non-protein-bound sulfhydryl compounds from the cytosol to membrane may be responsible for the reduction of the lipid-soluble stearic acid spin labels.

Lack of detectable polyamines in an extremely halophilic bacterium

Polyamines (putrescine, spermidine, spermine and other analogs) were not detectable by the dansylation procedure coupled with HPLC analysis in an extremely halophilic bacterium, Halobacterium halobium. Based on the detection limit of this analytical method, we estimated that the polyamine content in H. halobium, if present, was less than 0.06% of that of E. coli. Putrescine uptake and the metabolic conversion of ornithine or arginine to polyamines were negligible in this bacterium. In a H. halobium cell-free extract, a saturated amount of KC1 was needed for poly(U) directed polyphenylalanine synthesis; neither putrescine nor spermidine could replace KC1. These results suggest that polyamines may play an insignificant role in the growth of this halophilic bacterium.

Rat uterine polyamine biosynthetic decarboxylase activities following multiple injections of estradiol-17 beta and/or estriol

A single injection of 0.5 micrograms estradiol-17 beta (E2) plus 0.5 micrograms estriol (E3) stimulated a different pattern in 22-24 day-old rat uterine ornithine decarboxylase (ODC) and S-adenosyl methionine decarboxylase (SAMDC) activities than was induced by either a single injection of 0.5 micrograms E2 or multiple injections of 0.5 micrograms E3. Differences included alterations in enzyme activity peak timing as well as activity duration. Every 3 hour injections of 0.05 micrograms E2 induced maximum uterine ODC activity at 4, 24, 32, and 40 hours, intermediate activity at 48, 64, and 72 hours as well as a small peak by 56 hours. When 0.05 micrograms E2 plus 0.05 micrograms E3 were injected simultaneously every 3 hours, the ODC activity pattern was similar except that activity fell to intermediate levels by 40 hours. It is suggested that E3 alterations of E2 induced uterine enzyme activities (when monitored at frequent intervals) could be physiological alterations in uterine growth responses due to E2-E3 hormone interactions. However, there appeared to be no differences between E2 or E2 plus E3 induction of DNA synthesis and luminal epithelial cell height and cross-sectional area or ODC and SAMDC activities when measured at 24, 48, or 72 hours.

Spermine specifically inhibits the phosphorylation of an 11,000-dalton nuclear protein in various cultured mammalian cell lines

The effect of polyamines (putrescine, spermidine and spermine) on endogenous protein phosphorylation in mouse neuroblastoma cells was investigated by using techniques of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The results indicated that spermine at 1mM completely inhibited the phosphorylation of the 11,000-dalton and 120,000-dalton proteins in nuclear fractions. The inhibition of the phosphorylation of the 11,000-dalton but not the 120,000-dalton protein by spermine was also observed in five other cell lines examined and appeared to be a general phenomenon. The inhibitory effect of spermine on the phosphorylation of the 11,000-dalton protein was specific, other cations such as ammonium chloride, arginine, putrescine, cyclen and trien were ineffective at equal molar or much higher concentrations.

Transglutaminase catalyzed incorporation of putrescine into surface proteins of mouse neuroblastoma cells

Transglutaminase, purified from guinea pig liver, was used to catalyze the incorporation of [14C]putrescine into exposed surface proteins of intact mouse neuroblastoma cells. This method specifically labeled two surface proteins (Mr = 92 000 and 76 000) in the N-18 mouse neuroblastoma cells and three surface proteins (Mr = 92 000, 76 000, and 72 000) in the NB-15 mouse neuroblastoma cells. In addition, transglutaminase also catalyzed cross-linking reactions of exposed surface proteins. In both the N-18 and NB-15 cells, differentiation was accompanied by a 2-fold increase of specific radioactivity incorporated into trichloroacetic acid insoluble cellular material, suggesting that the differentiated mouse neuroblastoma cells may possess greater amount of accessible peptide-bound glutaminyl residues on their surface than their malignant counterparts. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorographic method revealed that while the [14C]putrescine-labeled protein patterns of undifferentiated and differentiated mouse neuroblastoma cells were similar, the intensity of labeling of individual bands was specifically modulated by cell differentiation.