The role of calcium in the induction of ornithine decarboxylase in rat HTC cells

Increased spermidine or spermine level is essential for hepatocyte growth factor-induced DNA synthesis in cultured rat hepatocytes

BACKGROUND/AIMS

Hepatocyte growth factor is a potent mitogen for mature hepatocytes and seems to act as a trigger for liver regeneration. Hepatocyte growth factor was first purified from human and rabbit plasma and rat platelets. Additionally, putrescine, spermidine, and spermine are widely distributed in many different cells; intracellular concentrations of these polyamines are closely related to cell proliferation. The present study examined whether polyamine metabolism is involved in hepatocyte growth factor-induced DNA synthesis in primary cultured rat hepatocytes.

METHODS

Hepatocytes were isolated from rats by the collagenase perfusion method. Ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were measured as the release of 14CO2 from L-[1-14C]ornithine and S-adenosyl-L-[carboxyl-14C]methionine, respectively.

RESULTS

alpha-Difluoromethylornithine inhibited hepatocyte growth factor-induced DNA synthesis by only 21%. On the other hand, methylglyoxal bis(guanylhydrazone) completely inhibited hepatocyte growth factor-induced DNA synthesis to nontreated control level. The inhibitory effect of methylglyoxal bis(guanylhydrazone) on hepatocyte growth factor-induced DNA synthesis was reversed by exogenously added spermidine or spermine.

CONCLUSIONS

Spermidine or spermine is essential for hepatocyte growth factor-induced DNA synthesis in primary cultured rat hepatocytes.

Correlations between developmental ornithine decarboxylase gene expression and enzyme activity in the rat brain

The rise and decline in cerebral ODC activity during specific stages of development has been attributed to cytoplasmic intermediates which regulate ornithine decarboxylase activity. Here we examine whether transcriptional regulation contributes to the production of the developmental profiles of ODC activity. Postnatal cerebellar and neocortical tissue were obtained from Long-Evans hooded rats at postnatal days (PND) 5, 10, 15, 20, 25, 30, 90 and probed for ODC and actin gene expression, by Northern analysis. Our results indicate that ODC gene expression in the cerebellum was elevated at PND 5 and 10 followed by a gradual drop to the adult low levels by PND 20. By contrast, high levels of ODC gene expression in the neocortex were seen at PND 5 with an abrupt decrease at day 10 to low adult levels. The expression of the ODC gene in the neocortex follows closely the pattern for the ODC enzyme activity; however, it tends to remain elevated longer in the cerebellum. The levels of actin gene expression exhibited a distinct developmental profile in the postnatally developing cerebellum. However, actin mRNA levels remained unchanged in the neocortex, consistent with the prenatal development of this region. Our findings suggest that ODC gene expression may play an important role in the production of the ontogenetic patterns of ODC activity.

Independent actions of asparagine and high levels of free Ca2+ in the induction of ornithine decarboxylase

During growth stimulation of cells, Ca2+ and amino acids of the A, ASC and N transport systems are important for the induction of ornithine decarboxylase (ODC, L-ornithine carboxylase, EC 4.1.1.17). In order to clarify the relationship between Ca2+ and amino acids, we studied the induction of ODC by asparagine under three different Ca2+ states in H-35 rat hepatoma cells. First, in normal cells, extracellular Ca2+ above 0.1 mM and 10 mM asparagine separately stimulated ODC activity and their effects were approximately additive. In these normal cells, asparagine could act in the absence of medium Ca2+. TMB-8, a sequestered-Ca2+ release antagonist, had no effect on ODC induction whilst the asparagine action is sensitive to treatment with W7, a Ca-calmodulin antagonist, or lanthanum, a Ca2+ antagonist. Secondly, in cells treated with 0.5 mM EGTA in Ca(2+)-free medium, the asparagine action on ODC induction was blocked but the inhibition could be reversed by the addition of Ca2+ to the medium. Thirdly, ionomycin treatment in the absence of medium Ca2+ did not block the asparagine effect. Furthermore, in ionomycin-treated cells, the presence of high levels of medium Ca2+ increased ODC activity, but this increase was additive to, and could not replace, the action of asparagine. Our results indicate that the asparagine action does not depend on an increase of intracellular free-Ca2+.

Involvement of cAMP and calcium in the induction of ornithine decarboxylase activity in an osteoblast cell line

The role of cAMP and calcium in the induction of ornithine decarboxylase (ODC, E.C.4.1.1.17) activity in the osteogenic sarcoma cell line, UMR 106-01, was studied, with particular interest for parathyroid hormone (PTH). PTH and forskolin dose-dependently induced the ODC activity and the cAMP production. Protein synthesis is involved in the effect of PTH and forskolin on ODC activity but not on cAMP production. Using quin2 we showed that 20 nM PTH and 10 microM forskolin increased the intracellular ionized calcium concentration ([Ca2+]i), thereby offering the possibility for calcium to play a role as cellular mediator in the action of PTH and forskolin in bone. Data obtained with A23187 showed that solely an increase of the [Ca2+]i is not sufficient to stimulate basal or potentiate PTH- and forskolin-induced ODC activity. However, the effects of calcium channel blockers and EGTA on basal and PTH- and forskolin-induced ODC activity point to a specific role for calcium. Moreover, the effects of calcium channel blockers and EGTA on basal and PTH- and forskolin-induced cAMP production indicate that the involvement of calcium in the induction of ODC activity is primarily located at another site than the adenylate cyclase. These data indicate that calcium is involved in the control of basal ODC activity. Furthermore, these data suggest that both cAMP and calcium are involved in the induction of ODC activity by PTH and forskolin. More precisely, ODC activity in UMR 106-01 cells can be induced by PTH and forskolin via a calcium-dependent cAMP messenger system.

An in situ assay system to measure ornithine decarboxylase activity in primary cultures of chicken osteoblasts: effects of bone-seeking hormones

We present a rapid and uncomplicated in situ assay for measuring ornithine decarboxylase activity in small cell quantities. This method is more economic than the in situ methods described by others. In addition, our system is faster and less complicated since it avoids manipulation of the CO2-trapping paper. Applying this method we demonstrate that parathyroid hormone, PGE1, and other inducers of intracellular cAMP levels, like IBMX and forskolin can induce ODC activity in primary cultures of chicken osteoblasts. Salmon calcitonin does not induce ODC activity, and 1.25 (OH)2D3 at higher concentrations can even give an inhibition of ODC activity. We confirm the recent findings that ODC activity is also dependent on calcium.

Synergistic induction of ornithine decarboxylase by diacylglycerol, A23187, and cholera toxin in guinea pig lymphocytes

When guinea pig lymphocytes were cultured with 1-oleoyl-2-acetyl-glycerol (OAG), A23187, and cholera toxin, ornithine decarboxylase activity was induced synergistically, peaking at 6 h. Addition of 12-O-tetradecanoyl-phorbol 13-acetate (TPA), A23187, and dibutyryl cAMP caused the same kind of induction. Cholera toxin potentiated the ability of A23187 to induce ornithine decarboxylase, but not that of OAG. Dibutyryl cAMP augmented the induction caused by A23187 but not by TPA. These results suggest that both the activation of Ca++-sensitive, phospholipid-dependent protein kinase (protein kinase C) and the increase in intracellular levels of Ca++ and cAMP are necessary for this induction. cAMP may potentiate the induction by modulating a Ca++ messenger system other than that for protein kinase C activation.

Induction of ornithine decarboxylase in guinea-pig lymphocytes. Synergistic effect of diacylglycerol and calcium

Calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), N-(6-aminohexyl)-1-naphthalenesulfonamide (W-5) and trifluoperazine inhibited ornithine decarboxylase induction in lymphocytes activated with phytohemagglutinin or inophore A23187. W-7, a more potent calmodulin antagonist than W-5, suppressed ornithine decarboxylase induction in a higher extent than did W-5. These results suggest that calmodulin may play an important role in ornithine decarboxylase induction in the activated lymphocytes. However, the extent of ornithine decarboxylase induction was greater in cells pretreated with Clostridium phospholipase C and then incubated with ionophore A23187 than in cells incubated with ionophore A23187 without the pretreatment. Moreover, combined treatment of cells with ionophore A23187 and tumor promotor, phorbol 12-myristate 13-acetate, caused synergistic induction of ornithine decarboxylase activity. These results, taken together, suggest that both activations of Ca2+-activated phospholipid-dependent protein kinase by diacylglycerol and of calmodulin-dependent function resulted from an elevation of cytosolic Ca2+ concentration may operate in the induction of ornithine decarboxylase in the activated lymphocytes.

Dissociation of RNA synthesis from the calcium requirement for serum-increased ornithine decarboxylase activity in rat glioma cells

When C6-2B rat glioma cells were stimulated with calf serum in the presence of calcium, ornithine decarboxylase activity increased maximally in 6-8 h after an initial 2-3 h lag period wherein RNA synthesis occurred. The increase of ornithine decarboxylase activity in serum-stimulated C6-2B cells was prevented by the calcium chelator EGTA, but EGTA had no effect upon RNA synthesis as judged by [3H]uridine incorporation into RNA. In addition, the calcium requirement for increased ornithine decarboxylase activity was temporally distal to the lag period. EGTA appeared to inhibit the synthesis of ornithine decarboxylase, because the half-life values of ornithine decarboxylase activity were similar (37-47 min) in the presence of EGTA or protein synthesis inhibitors such as cycloheximide or emetine. Also, calcium readdition rapidly reversed EGTA inhibition of ornithine decarboxylase activity by a mechanism which could be blocked by cycloheximide.

Induction of brain ornithine decarboxylase during recovery from metabolic, mechanical, thermal, or chemical injury

Metabolic, mechanical, thermal, and chemical injury induced ornithine decarboxylase (ODC) activity in rat brain. A two- to sixfold increase in ODC activity was measured at 5-9 h after different modes of injury to the brain. During the early phase of recovery from transient ischemia, when average protein synthesis was less than 50% of control, ODC activity was increased nearly fivefold. The rise in activity could be blocked by anisomycin, or reduced by intracerebral injections of actinomycin D. Drilling burr holes into the skull, injection of the vehicle for actinomycin D, hyperthermia, and freezing lesions all caused increased ODC activity. Neurotoxic chemicals (ammonia, methionine sulfoximine, acrylamide, carbon tetrachloride, and anisomycin) also increased brain ODC activity, whereas other chemicals (mannitol and valine) did not. Treatments known to stimulate the synthesis of heat shock proteins (carotid occlusion, hyperthermia, Cd2+, canavanine, and ethanol) induced ODC activity in the liver, whereas only hyperthermia and ethanol caused significant increases in spleen ODC activity. All increases in ODC activity were blocked by difluoromethylornithine, an irreversible inhibitor of ODC. The cellular response to noxious or stressful stimuli includes the synthesis of a small number of proteins of unknown functions; ODC may be one of these "heat shock" or "trauma" proteins.

Calcium stimulates ornithine decarboxylase activity in cultured mammalian epithelial cells

Ornithine decarboxylase (ODC) activity usually rises to a peak a few hours after a trophic stimulus. The stimulation of ODC has been shown to depend on extracellular calcium in several in vitro eukaryotic systems. We have investigated the effect of calcium concentration on ODC activity and have found that ODC is stimulated when CaCl2 alone is added to calcium-deprived cells. Epithelial cells from calf esophagus were cultured and grown until stratified. Replacement of medium with fresh serum-free medium resulted in stimulation of ODC activity, which peaked at 4 hours and declined to basal level by 10 hours. Subsequent depletion of Ca2+ either by addition of ethylene glycol bis (beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) or by replacement of medium with Ca2+-free medium, resulted in obliteration of ODC activity 4 hours later. Conversely, cultures in which medium was replaced with Ca2+-free medium and at 10 hours were repleted with Ca2+ (either by addition of CaCl2 or by replacement of medium with Ca2+-containing medium) exhibited a pronounced elevation of ODC activity 4 hours later. ODC activity peaked at 6 hours after the addition of CaCl2 and declined by 8 hours. The effect was elicited by a wide range of concentrations of added Ca2+ from 0.1 mM to 4.0 mM, but was maximal at 1.0 mM. ODC activity was totally abolished if either cycloheximide (10 micrograms/ml) or putrescine (10 mM) was added to cultures immediately prior to Ca2+ addition. Actinomycin D (2, 5, or 10 micrograms/ml) added 30 minutes before Ca2+ did not prevent the stimulation of ODC by added Ca2+. Stimulation by Ca2+ is dependent on (1) absence of Ca2+ during the initial 10-hour incubation and (2) duration of incubation in Ca2+-free medium prior to Ca2+ replenishment. The results indicate that Ca2+ can increase ODC in epithelial cells exposed to Ca2+-depleted medium and that the increase in ODC depends on protein synthesis but is not inhibited by actinomycin D.

Involvement of calcium ions in the activation of ornithine decarboxylase by isoprenaline evaluated 'in situ' in the perfused rat heart

Ornithine decarboxylase activity evaluated during the perfusion of isolated rat hearts by a method 'in situ' was rapidly increased when the hearts were infused with isoprenaline (isoproterenol). Omission of Ca2+ from the perfusion medium or the administration of verapamil to the perfused hearts decreased the isoprenaline-stimulated ornithine decarboxylase activity, whereas a marked stimulatory effect was registered when the hearts were perfused with the Ca2+ ionophore A23187.