Calcium and microtubule dependence for increased ornithine decarboxylase activity stimulated by beta-adrenergic agonists, dibutyryl cyclic AMP, or serum in a rat astrocytoma cell line

Interleukin-6 promotes microtubule stability in axons via Stat3 protein-protein interactions

The interleukin-6 (IL-6) family of cytokines and its downstream effector, STAT3, are important mediators of neuronal health, repair, and disease throughout the CNS, including the visual system. Here, we elucidate a transcription-independent mechanism for the neuropoietic activities of IL-6 related to axon development, regeneration, and repair. We examined the outcome of IL-6 deficiency on structure and function of retinal ganglion cell (RGC) axons, which form the optic projection. We found that IL-6 deficiency substantially delays anterograde axon transport in vivo. The reduced rate of axon transport is accompanied by changes in morphology, structure, and post-translational modification of microtubules. In vivo and in vitro studies in mice and swine revealed that IL-6-dependent microtubule phenotypes arise from protein-protein interactions between STAT3 and stathmin. As in tumor cells and T cells, this STAT3-stathmin interaction stabilizes microtubules in RGCs. Thus, this IL-6-STAT3-dependent mechanism for axon architecture is likely a fundamental mechanism for microtubule stability systemically.

Induction of ornithine decarboxylase activity in isolated chicken osteoblasts by parathyroid hormone: the role of cAMP and calcium

We investigated the role of cAMP and Ca2+ as mediators in parathyroid hormone (PTH)-induced ornithine decarboxylase (ODC) activity in primary cultures of chicken osteoblasts. We present evidence that the induction of ODC activity by PTH is most likely a receptor-mediated process and that cAMP is a mediator. However, using three different approaches we have strong indications that cAMP is not the exclusive mediator of PTH-induced ODC activity. First, when the dose-response curve of PTH-induced ODC activity is compared with that of PTH-stimulated cAMP production, the ED50 for cAMP production is about five times as high as that for the induction of ODC activity. Second, 1 mM 9-(tetrahydro-2-furanyl) adenine (SQ 22.536) almost completely inhibited PTH-stimulated cAMP production whereas there was only a small inhibitory effect on PTH-induced ODC activity. Third, some PTH fragments unable to stimulate cAMP production were still able to induce ODC activity. We therefore propose that apart from cAMP, an additional messenger, most likely Ca2+, must be present. Evidence for this concept are the observations that substances affecting extracellular and intracellular Ca2+ levels (EGTA, A23187, CoCl2, verapamil) or antagonizing calmodulin (Trifluoroperazin, Compound 48/80) also strongly affect PTH-induced ODC activity. These effects could not be explained by a positive interaction of Ca2+ with the hormone-stimulated cAMP system as 2 mM EGTA strongly enhanced PTH-stimulated cAMP production but at the same time completely inhibited PTH-induced ODC activity. A similar dissociation between hormone-induced cAMP production and induction of ODC activity was found with the Ca2+ -ionophore A23187 (10(-7) M) which significantly inhibited PTH-stimulated cAMP production but strongly enhanced PTH-induced ODC activity. Our results suggest that intracellular Ca2+, and possibly calmodulin, in addition to cAMP, are involved in PTH-induced ODC activity in chicken osteoblasts. Most probably Ca2+ is the initial messenger and cAMP acts in a coordinate pattern as a synarchic messenger making the induction of ODC activity by PTH more sensitive to Ca2+. Furthermore, the present findings are in agreement with our concept of the existence of two receptors or two receptor-sites for PTH on osteoblasts. One receptor is coupled to the production of cAMP and is presumably activated when the first two aminoacids of the NH2-terminus of the hormone are present and the other, suggested to be responsible for the increase in intracellular Ca2+, is thought to be activated by a region of the hormone sequence between amino acid 3 and 34.(ABSTRACT TRUNCATED AT 250 WORDS)

Synergistic stimulation of S-adenosylmethionine decarboxylase activity by Ca2+ ionophore A23187, cholera toxin and 1-oleoyl-2-acetylglycerol

The Ca2+ ionophore A23187 induced S-adenosylmethionine decarboxylase in guinea-pig lymphocytes, and cholera toxin stimulated the induction synergistically. The activator of protein kinase C, 1-oleoyl-2-acetylglycerol, did not induce S-adenosylmethionine decarboxylase activity but potentiated the enzyme activity induced by A23187 or by A23187 and cholera toxin. The addition of both A23187 and cholera toxin induced S-adenosylmethionine decarboxylase, but the further addition of 1-oleoyl-2-acetylglycerol or 12-O-tetradecanoylphorbol 13-acetate did not potentiate the enzyme induction in protein kinase-C-down-regulated cells that had been treated with 12-O-tetradecanoylphorbol 13-acetate for 18 h. These results suggest that a Ca2+-dependent pathway, other than that for protein kinase C, is essential for the induction of S-adenosylmethionine decarboxylase and that a cAMP-dependent pathway and also protein kinase C are involved in the potentiation of the induction.

Polyamines mediate uncontrolled calcium entry and cell damage in rat heart in the calcium paradox

Brief perfusion of heart with calcium-free medium renders myocardial cells calcium-sensitive so that readmission of calcium results in uncontrolled Ca2+ entry and acute massive cell injury (calcium paradox). We investigated the hypothesis that polyamines may be involved in the mediation of abnormal Ca2+ influx and cell damage in the calcium paradox. The isolated perfused rat heart was used for these studies. Calcium-free perfusion promptly (less than 5 min) decreased the levels of polyamines and the activity of their rate-regulating synthetic enzyme, ornithine decarboxylase (ODC), and calcium reperfusion abruptly (less than 15-180 s) increased these components. alpha-Difluoromethylornithine (DFMO), a specific suicide inhibitor of ODC, suppressed the calcium reperfusion-induced increase in polyamines and the concomitant increase in myocardial cellular 45Ca influx, loss of contractility, release of cytosolic enzymes, myoglobin, and protein, and structural lesions. Putrescine, the product of ODC activity, nullified DFMO inhibition and restored the calcium reperfusion-induced increment in polyamines and the full expression of the calcium paradox. Putrescine itself enhanced the reperfusion-evoked release of myoglobin and protein in the absence of DFMO. Hypothermia blocked the changes in heart ODC and polyamines induced by calcium-free perfusion and calcium reperfusion and prevented the calcium paradox. These results indicate that rapid Ca2+-directed changes in ODC activity and polyamine levels are essential for triggering excessive transsarcolemmal transport of Ca2+ and explosive myocardial cell injury in the calcium paradox.

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.

Beta-adrenergic stimulation inhibits calcium efflux and alters the morphology of cultured arterial muscle cells

Beta-adrenoreceptor stimulation with isoproterenol (IP) rapidly and reversibly rounded and arborized smooth muscle cells (SMC) cultured from rat aorta. The arborized SMC remained firmly attached to the substratum via a network of long, dendritelike processes. Arborization of the SMC correlated closely with increases in cellular cAMP produced by IP and a variety of other compounds. The intracellular calcium antagonist 8-(N,N-diethylamino)-octyl-3,4,5-trimethoxybenzoate (TMB-8) also rounded and arborized the SMC. Antitubulin compounds potently blocked arborized by IP, dibutyryl cAMP, and TMB-8. The release of cell-bound 45Ca2+ was followed in the presence and absence of IP. IP strikingly increased the amount of 45Ca2+ that remained cell bound between 20 and 120 min. Propranolol and colchicine prevented IP from inhibiting the release of cell-bound 45Ca2+. These results suggest that the modulation of Ca2+ transport is involved in the arborization of cultured SMC by cAMP.

The role of polyamines in somatomedin-stimulated differentiation of L6 myoblasts

The somatomedins are potent stimulators of proliferation and differentiation of cultured myoblasts. In studies on the mechanism(s) of these actions, we have measured the activities of ornithine decarboxylase (ODC), an enzyme associated with rapid cell proliferation, and creatine kinase (CK), a biochemical marker for muscle differentiation, after treatment of L6 myoblast cultures with Multiplication Stimulating Activity (MSA), a member of the somatomedin family of insulinlike growth factors. ODC levels reached a peak 24 hours after MSA addition (before any detectable differentiation of the myoblasts) and then decreased as differentiation commenced and CK activity increased. Addition of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, caused a dramatic decrease in differentiation. Measurement of 3H-thymidine incorporation, DNA content, and cell number established that the effect of DFMO on differentiation was not a simple consequence of its antiproliferative actions. Cellular levels of putrescine and spermidine (but not spermine) decreased substantially following addition of DFMO to the cultures. The inhibitory effects of DFMO were abolished upon addition of exogenous polyamines to the medium. However, addition of polyamines in the absence of MSA or DFMO did not mimic the stimulation of differentiation by MSA. We conclude that polyamines play an essential role in the stimulation of L6 myoblast differentiation by somatomedins, but they are not sufficient to effect this stimulation.

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.

Sulindac for polyposis of the colon

Four members of a Gardner's syndrome family had rectal and colon polyposis treated with nonsteroid anti-inflammatory drugs. Three of these patients had had subtotal colectomy and ileoproctostomy and the residual polyps arose in the rectal mucosa. The polyps almost completely disappeared when sulindac was administered. Indomethacin therapy over the course of a preceding year was ineffective in one of these patients. One patient (case 4) had diffuse polyposis in an intact colon. After sulindac therapy for a year, only three small mucosal polyps could be identified by air contrast barium enema and colonoscopic examination. These observations confirm those of Pollard and Luckert [1,2] on rats with chemically induced polyposis of the intestinal tract.

Interplay of cyclic AMP and microtubules in modulating the initiation of DNA synthesis in 3T3 cells

The results presented here show that disruption of the microtubule network acts synergistically with cAMP-elevating agents to stimulate the entry into DNA synthesis of 3T3 cells. Antimicrotubule agents and increased cAMP levels require an additional growth-promoting factor for inducing initiation of DNA synthesis; such requirement can be furnished by insulin, vasopressin, epidermal growth factor, platelet-derived growth factor, or fibroblast-derived growth factor. The involvement of the microtubules is indicated by the fact that enhancement of the DNA synthetic response was demonstrated with the chemically diverse agents colchicine, nocodazole, vinblastine, or demecolcine, all of which elicited the response in a dose-dependent manner. We verified that colchicine and nocodazole, at the doses used in this study, induced microtubule disassembly in the absence as well as in the presence of cAMP-elevating agents as judged by measurement of [3H]colchicine binding of total and pelletable tubulin. The involvement of cAMP was revealed by increasing its endogenous production by cholera toxin or by treatment with 8BrcAMP. The enhancing effects of antimicrotubule drugs and cAMP-elevating agents could be demonstrated by incorporation of [3H]thymidine into acid-insoluble material, autoradiography of labeled nuclei, or flow cytofluorometric analysis. The addition of antimicrotubule drugs does not increase the intracellular level of cAMP nor does addition of cAMP-elevating agents promote disassembly of microtubules (as judged by measuring [3H]colchicine binding of total and pelletable tubulin) in 3T3 cells. In view of these findings and the striking synergistic effects between these agents in stimulating DNA synthesis in the presence of a peptide growth factor, we conclude that increased cAMP levels and a disrupted microtubule network regulate independent pathways involved in proliferative response.

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.

Induction of ornithine decarboxylase in guinea pig lymphocytes by the divalent cation ionophore A 23187. Effect of dibutyryladenosine 3',5'-monophosphate

The divalent cation ionophore, A23187, at a concentration of 0.25 microgram/ml, enhanced influx of Ca2+, activity of ornithine decarboxylase and incorporation of [3H]thymidine into DNA of guinea pig lymphocytes. Combined treatment of cells with A23187 and dibutyryladenosine 3',5'-monophosphate (Bt2cAMP) augmented these three events. A23187 at a concentration of 0.06 microgram/ml was insufficient for induction of ornithine decarboxylase stimulated neither Ca2+ influx nor [3H]thymidine incorporation, but stimulated Ca2+ efflux. A23187 (0.06 microgram/ml) in combination with Bt2cAMP caused a marked induction of ornithine decarboxylase and stimulation of [3H]thymidine incorporation into DNA. When the time of Bt2cAMP addition was delayed after A23187, the stimulation of ornithine decarboxylase activity decreased. Washout of Bt2cAMP from cell culture earlier than 4 h of incubation caused a reduction in the stimulatory effect of Bt2cAMP. These results suggest that raising concentrations of cytoplasmic Ca2+ and cellular cAMP are important to some initial events leading to induction of ornithine decarboxylase and these biochemical changes are obligatory sequential steps for stimulation of DNA synthesis.

Cell cycle changes in the adenylate cyclase of C6 glioma cells

The adenylate cyclase of C6 glioma cell cultures was characterized for sensitivity to the beta-adrenergic agonist isoproterenol, as well as fluoride, and GTP as a function of the cell cycle. The mitotic phase of the cell cycle was emphasized because both the basal cellular cyclic AMP level and the intact C6 cell's capacity to accumulate cyclic AMP in response to isoproterenol decreased during mitosis. Basal and stimulated adenylate cyclase activities in mitotic cells were decreased relative to the enzyme activities in the G1, S, and G2 phases of the cell cycle. Analysis of the beta-adrenergic receptor using the radioligand(-)[3H]dihydroalprenolol showed that neither ligand affinity nor receptor density changed during the cell cycle, indicating that the reduced adenylate cyclase activity of the mitotic C6 cell was not caused by alterations in this hormone receptor. The reduction in the mitotic cell's basal adenylate cyclase activity was more prominent than the decrease in isoproterenol-, fluoride, or GTP-stimulated activities suggesting that the effectiveness of these enzymes activators (i.e., the efficiency of the coupling mechanism) was not attenuated during mitosis. These studies indicate that the intrinsic catalytic capacity (not the beta-adrenergic receptor or the coupling mechanism) of the C6 adenylate cyclase complex is reduced during mitosis and contributes to the mitotic cell's inability to accumulate and maintain the cyclic AMP concentration at the interphase level.

Role of calcium in the modulation of ornithine decarboxylase activity in isolated pig granulosa cells in vitro

We examined the role of Ca(2+) in the control of basal and hormone-stimulated ornithine decarboxylase activity in isolated pig granulosa cells maintained under chemically defined conditions in vitro. Omission of Ca(2+) from the incubation medium (measured Ca(2+) concentration 5mum) decreased basal enzymic activity, and significantly (P<0.01) impaired the response to maximally stimulating doses of either lutropin or follitropin. No significant alteration occurred in the concentration of either gonadotropin required to elicit half-maximal effects. The addition of EGTA (1.27-2.0mm) to chelate residual extracellular Ca(2+) further decreased hormone-induced rises in ornithine decarboxylase activity. Despite the presence of 1.27mm concentrations of extracellular Ca(2+), the administration of presumptive Ca(2+) antagonists, believed to impair trans-membrane Ca(2+) influx [verapamil (10-100mum), nifedipine (1-100mum) or CoCl(2) (1mm)] suppressed hormone-stimulated ornithine decarboxylase activity. The inhibitory effects of verapamil or of Ca(2+) omission from the medium were not overcome by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (0.25mm), or by cholera toxin, or by an exogenously supplied cyclic AMP analogue, 8-bromo cyclic AMP. Conversely, micromolar concentrations of a putative bivalent-cation ionophore, A23187, increased significantly the stimulation of ornithine decarboxylase activity by saturating concentrations of lutropin or 8-bromo cyclic AMP. Thus the present observations implicate Ca(2+) ions in the modulation of hormone action and cellular function in normal ovarian cells.

Reverse transformation of vole cells transformed by avian sarcoma virus containing the src gene

Vole cells transformed by avian sarcoma virus carrying the src gene lose their fibroblastic morphology, the organized cytoskeletal system of the normal fibroblastic cell, the typical fibronectin deposit around the cell membrane, and the ability to shut off multiplication when suspended in liquid medium. All of these transformation characteristics are reversed by treatment with cAMP derivatives. Moreover, the cAMP treatment does not cause loss of activity of the src gene product. These data imply that cAMP exerts its effect at or after the point in the metabolic pathway affected by the src gene product, pp60src. Presumably, the decision to adopt the transformed or the normal state is determined by the degree to which the src gene or cAMP-mediated kinase activities respectively predominante in the cell. The development of all four transformation characteristics as a result of introduction of the src gene, and their coordinate reversal by cAMP derivatives, supports the previous thesis that in the normal vole or CHO fibroblast all four properties are part of a common regulatory system.