Biomedical subjects

M A Desiderio

Publications and source records attributed to M A Desiderio.

At least 19 recordsLinked to original sources

PubMed2004

Hepatocyte growth factor-activated NF-kappaB regulates HIF-1 activity and ODC expression, implicated in survival, differently in different carcinoma cell lines.

Hepatocyte growth factor (HGF)-stimulated Met signaling influences tumor survival, growth and progression, all processes involving the transcription factor NF-kappaB. NF-kappaB plays a complex role in the control of survival due to the influence of cellular factors acting downstream. We undertook a comparative investigation of two human breast carcinoma cells with different grades of malignancy and HepG2 hepatoma cells, which present a biphasic response to HGF (proliferation followed by apoptosis). We found evidence that HGF induced gene patterns characteristic of survival rather than apoptosis depending on the cell type. The ability of NF-kappaB to regulate expression of hypoxia-inducible factor-1alpha (HIF-1alpha), a survival/anti-apoptotic gene in cancer, seemed to be critical. In the HepG2 and MCF-7 (low invasive breast carcinoma) cell lines increased transcription and translation were responsible for HIF-1alpha induction after HGF. The regulation by NF-kappaB was mainly at the level of the 5'-UTR of the HIF-1alpha message. HIF-1 (alpha/beta heterodimer) was likely to transactivate Mcl-1, another anti-apoptotic gene. Opposite results were observed in MDA-MB-231 cells (highly invasive breast carcinoma), which have high NF-kappaB activity, further inducible by HGF, because HIF-1alpha mRNA expression and HIF-1 transactivating capacity were HGF-insensitive while the alpha subunit seemed to be degraded after HGF. However, ornithine decarboxylase (ODC) and heme oxygenase mRNA expression persistently increased. By transiently transfecting two ODC gene reporters we demonstrated that ODC is a target gene of NF-kappaB in HGF-treated tumor cells. By regulating HIF-1 activity and specific gene expression downstream, NF-kappaB may influence the survival threshold, with an impact on the fate of carcinoma cells after prolonged HGF treatment.

Breast Neoplasms↗

PubMed2000

Hepatocyte growth factor signal coupling to various transcription factors depends on triggering of Met receptor and protein kinase transducers in human hepatoma cells HepG2.

Hepatocyte growth factor (HGF) regulates a wide variety of biological activities by binding to the tyrosine kinase receptor Met. In HGF-treated hepatocarcinoma cells, we observed a biphasic activation of AP-1 and AP-2 transcription factors. For NF-kappaB complex the p50-p50 homodimer was activated before the p50-p65 heterodimer, and c-Myc/Max DNA-binding activity increased thereafter. Since these transcription factors are responders to mitogenic stimulation through protein kinase transducers, we tested the effects of inhibitors of these enzymes on the DNA binding after HGF treatment. Inhibition of protein kinase C (PKC) with H7 strikingly activated NF-kappaB above the values observed after HGF alone. Under this inhibitory condition, Met tyrosine phosphorylation was elevated as though the phosphorylation-dependent activity of the receptor was partially blocked by activation of PKC due to HGF. NF-kappaB DNA binding seems to be related to Met triggering by HGF since it was largely prevented by genistein treatment, which blocks receptor activity. Phosphatidylinositol 3-kinase seems to be involved in AP-1 binding activity stimulated by HGF. It is noteworthy that Met is responsive to HGF stimulating postreceptor signaling, which converges on the activation of transcription factors acting coordinately to regulate target gene expression.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1999

Influence of polyamines on DNA binding of heat shock and activator protein 1 transcription factors induced by heat shock.

Polyamine depletion, obtained in FAO cells with specific inhibitors of biosynthetic enzymes, prevents or decreases the accumulation of hsp 70 mRNA following heat shock [Desiderio et al., Hepatology 24 (1996) 150-156]. The present study shows that under conditions of spermidine depletion caused by alpha-difluoromethylornithine, the DNA binding capacity of the transcription factor HSF induced by heat shock undergoes a severe and prompt deactivation. Replenishment of the spermidine pool before heat shock re-establishes the DNA binding activity of HSF and the inducibility of hsp 70 mRNA. Similar to HSF, but with a different time-course, the DNA binding of the transcription factor AP-1 activated by heat shock is also impaired in spermidine-depleted cells and reversed by exogenous spermidine. STAT3 provides an example of a transcription factor slightly activated by heat shock but insensitive to polyamine decrease.

Animals↗

PubMed1998

Inhibition of proteasome function prevents thymocyte apoptosis: involvement of ornithine decarboxylase.

We have previously shown that polyamine levels rapidly decrease in thymocytes undergoing apoptosis, and that ornithine decarboxylase increases early but too transiently to maintain elevated polyamine levels. These data led us to suppose that a precocious ornithine decarboxylase degradation might be responsible for the imbalance of polyamine metabolism. Ornithine decarboxylase is known to be degraded by the cytosolic 26S proteasome that plays an essential role in thymocyte apoptosis. In this paper we demonstrate that the inhibition of proteasome function preserves ornithine decarboxylase activity and prevents thymocytes from undergoing apoptosis after dexamethasone treatment. Since intracellular polyamine levels are also preserved, ornithine decarboxylase seems to be functionally active in maintaining polyamine homeostasis after proteasome inhibition in thymocytes. Our proposed role for the proteasome in quiescent cells upon an apoptotic stimulus is to degrade proteins like ornithine decarboxylase that are involved in the control of the cell cycle and cell survival.

Animals↗

PubMed1998

Hepatocyte growth factor-induced expression of ornithine decarboxylase, c-met, and c-myc is differently affected by protein kinase inhibitors in human hepatoma cells HepG2.

Binding of hepatocyte growth factor (HGF) to its receptor Met induces autophosphorylation and activation of the tyrosine kinase activity. In HGF-treated HepG2 cells, we studied: (i) the expression patterns of early (c-myc, c-jun, and c-fos) and delayed-early (ornithine decarboxylase and c-met) response genes and (ii) the possible involvement of protein kinase transducers in the control of the expression of c-met and of other genes eventually induced downstream. c-met and c-myc mRNAs peaked 1-2 h after HGF, while c-jun and c-fos mRNAs slightly increased at 1 h. Ornithine decarboxylase activity was induced earlier (4 h) than the mRNA (8-10 h). The transducers involved in HGF-triggered gene inductions were investigated using different protein kinase inhibitors: genistein for the receptor tyrosine kinase, herbimycin A for the nonreceptor tyrosine kinase (pp60(c-src)), wortmannin for phosphatidylinositol 3-kinase (PI3K) and H7 for protein kinase C (PKC). The similarity of responses to PKC inhibition led to suppose that c-myc and ornithine decarboxylase mRNAs were induced sequentially along the same transduction pathway triggered by HGF. Ornithine decarboxylase activity seemed to be largely regulated by phosphorylation(s). The mRNA expression of c-jun was likely to undergo a negative regulation through a mechanism involving PI3K, while that of c-met seemed to be almost independent from various protein kinases (PI3K, pp60(c-src), and PKC).

Cyclic AMP-Dependent Protein Kinases↗

PubMed1998

Regulation of spermidine/spermine N1-acetyltransferase expression by cytokines and polyamines in human hepatocarcinoma cells (HepG2).

Spermidine/spermine N1-acetyltransferase (cSAT), a key enzyme in polyamine degradation, is induced by various hepatotoxins and liver tumor promoters. In this paper we demonstrate that physiological factors, such as cytokines, control cSAT expression in HepG2 human hepatocarcinoma cells. Hepatocyte growth factor (HGF) induced the cSAT mRNA precursor (3.5 kb) at 4 h. The mature form of mRNA (1.3 kb) increased 6-8-fold between 8 and 10 h, and remained elevated until 18 h. An increase in cSAT activity (2-fold) and high levels of N1-acetylspermidine were observed concomitantly. Interleukin-1 beta (IL-1 beta) enhanced cSAT expression (both mRNA and enzyme activity) similar to HGF, while tumor necrosis factor-alpha (TNF-alpha) was less effective. This system also provides a useful means for examining the involvement of negative and positive changes of polyamines in the induction of cSAT and c-jun, a gene that participates in the control of cSAT expression. alpha-Difluoromethylornithine (DFMO) pretreatment, by lowering putrescine and spermidine in HGF- or IL-1 beta-treated cells, prevented the induction of cSAT. This effect was reversed by exogenous putrescine or spermidine. IL-1 beta induced c-jun mRNA more than HGF. DFMO prevented almost completely the enhancement of c-jun mRNA expression by IL-1 beta, and this effect was reversed by exogenous putrescine or spermidine. Therefore, we suggest that cSAT and c-jun expression is specifically regulated by polyamine-mediated mechanisms in IL-1 beta treated HepG2 cells. Since cSAT is inducibile by cytokines that control tumor metabolism and growth as well as tumor-host interaction, we hypothesize an involvement of cSAT in hepatoma growth.

Acetyltransferases↗

PubMed1997

Treatment with inhibitors of polyamine biosynthesis, which selectively lower intracellular spermine, does not affect the activity of alkylating agents but antagonizes the cytotoxicity of DNA topoisomerase II inhibitors.

Inhibitors of ornithine decarboxylase (ODC), such as alpha-difluoromethylornithine (DFMO), may influence the cytotoxicity of anti-tumour agents that interact with DNA. Intracellular levels of putrescine and spermidine were markedly reduced by ODC inhibitors while the level of spermine, which is the main polyamine in nuclei, was unchanged. By combining a novel inhibitor of ODC, such as (2R, 5R)-6-heptyne-2,5-diamine (MDL 72.175, MAP), with an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), such as 5'-[[(Z)-4-aminobut-2-enyl]methylamino]-5'-deoxyadenosine (MDL 73.811, AbeAdo), spermine was selectively depleted in a human ovarian cancer cell line OVCAR-3 (i.e. spermine became almost undetectable whereas the levels of spermidine and putrescine were not affected). The depletion of spermine blocked DNA synthesis with a consequent accumulation of cells in the G1 phase of the cell cycle. Pretreatment with MAP plus AbeAdo did not change the cytotoxicity of alkylating agents, such as L-phenylalanine mustard (L-PAM), 1,4-bis(2'-chloroethyl)-1,4-diazabicyclo-[2.2.1] heptane diperchlorate (DABIS), 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), cis-diamminedichloroplatinum (II) (cis-DDP), N-deformyl-N-[4-N-N,N-bis (2-chloroethylamino)benzoyl] (tallimustine) or CC-1065, whereas it markedly reduced the cytotoxicity of DNA topoisomerase II inhibitors, such as doxorubicin (DX) and 4'-demethylepipodophyllotoxin-5-(4,6-O)-ethylidene- beta-D-glycopyranoside (VP-16). The addition of spermine before drug treatment restored the sensitivity to the DNA topoisomerase II inhibitors, thus indicating that the reduced effect was related to the intracellular spermine level. The reason for the reduction in cytotoxicity is unclear, but it does not appear to be related to a cell cycle effect or to a decrease in the intracellular level of DNA topoisomerase II. Drugs that modify polyamine biosynthesis are under early clinical development as potential new anti-tumour agents. These findings illustrate the need for caution in combining such drugs with DNA topoisomerase II inhibitors.

Alkynes↗

PubMed1996

Effects of polyamine imbalance on the induction of stress genes in hepatocarcinoma cells exposed to heat shock.

The expression of hsp70-the inducible member of the corresponding heat shock gene family-of the oxidative stress marker gene heme oxygenase (HOx), and of the immediate early response genes c-fos and c-jun has been studied in FAO hepatocarcinoma cells depleted of polyamines and exposed to heat shock. Depletion of polyamines was obtained in short-term experiments (24-48 hours) by the use of alpha difluoromethylornithine (DFMO), a classical inhibitor of ornithine decarboxylase (ODC), or of the combination of the newly available inhibitors of ODC and S-adenosylmethionine decarboxylase, i.e., (2R,5R)-hept-6-yne-2,5-diamine (MAP) and 5'{[(Z)-4-aminobut-2-enyl]methylanino}-5-deoxyadeno-si ne (AbeAdo). Under our experimental conditions polyamine imbalance was realized without appreciable growth-related genes. Decreases of putrescine and spermidine 48 hours after DFMO prevented the induction of hsp70 messenger RNA (mRNA), whereas depletion spermidine and spermine obtained with MAP/AbeAdo decreased intensity and duration of post-heat shock accumulation of hsp70 mRNA. Inductions of HOx, c-jun and c-fos were also inhibited. Because MAP/AbeAdo caused also an intracelluar accumulation of putrescine, we tested the effect of exogenous putrescine, which was found to stabilize the mRNAs for hsp70 and c-jun. Hsp70 and HOx are thought to play a protective role, and the proteins of c-jun and c-fos constitute the transcription factor activator protein-1, which is involved in the transcription of many defensive products. Therefore, the integrity of polyamine pool seems to be a necessary permissive condition for an effective response of the cells to adverse environmental changes.

Animals↗

PubMed1995

Is polyamine decrease a common feature of apoptosis? Evidence from gamma rays- and heat shock-induced cell death.

Here we report that in rat thymocytes undergoing apoptosis upon two different stimuli, such as heat shock treatment and gamma irradiation, an early mRNA accumulation of ornithine decarboxylase (ODC)--the rate-limiting enzyme of polyamine biosynthesis--was followed by a very marked increase in ODC activity (28-40 and 6-8-fold, respectively). However, polyamine levels started to decrease before the appearance of DNA laddering, being putrescine and spermidine strongly diminished (8-12 hs), and spermine even depleted (12 hs). Taken together with our previous data on another model of apoptosis, i.e., glucocorticoid-induced cell death (Desiderio et al., Cell Growth Differ. 6: 505-513, 1995), these results suggest that an imbalance of polyamine metabolism, i.e., a strong activation of ODC and a paradoxical decrease of the intracellular polyamine content, might be a general feature of the apoptotic process.

Analysis of Variance↗

PubMed1995

Involvement of ornithine decarboxylase and polyamines in glucocorticoid-induced apoptosis of rat thymocytes.

Ornithine decarboxylase (ODC), the first and rate-limiting enzyme of polyamine metabolism, has been shown to be required for entry into and progression through the cell cycle. However, the role of ODC and polyamines in apoptosis remains to be determined. We have examined ODC expression and polyamine levels in thymocytes activated to undergo apoptosis by dexamethasone treatment. We have demonstrated a rapid and reversible induction of ODC (mRNA and activity), as previously reported for the mRNA expression of other "early" genes, c-fos, c-jun, and c-myc, in the same experimental model. Surprisingly, polyamine levels diminished progressively starting at 2-4 h after dexamethasone treatment, and spermine was depleted at 8-12 h. This seemed to be relevant since increasing the intracellular polyamine levels by exogenous spermine administration prevented the DNA "laddering" (2-4 h) and the DNA loss from the nucleus (8-18 h) due to dexamethasone treatment. Moreover, the activities of spermidine/spermine N1-acetyltransferase, which controls the cytosolic polyamine interconversion pathway, and of spermidine N8-acetyltransferase, which regulates the nuclear pool and functions of polyamines, were measured in apoptotic cells. Spermidine/spermine N1-acetyltransferase activity progressively increased and might be responsible for spermidine and spermine excretion as acetyl derivatives. In contrast, spermidine N8-acetyltransferase activity remained unchanged. A completely different scenario was observed in proliferating concanavalin A-treated thymocytes, studied for comparison. In this case, polyamine levels increased, remaining at high values until 12 h. This is likely a consequence of the rapid and prolonged induction of ODC (mRNA and activity), accompanied by that of spermidine/spermine N1-acetyltransferase (mRNA and activity).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyltransferases↗

PubMed1994

Expression patterns of ornithine decarboxylase and c-met in growing Yoshida AH-130 hepatoma.

The expression of the two proto-oncogenes ornithine decarboxylase and c-met was examined during various phases of growth of Yoshida AH-130 ascites hepatoma. Ornithine decarboxylase (ODC) and c-met mRNA levels declined progressively from day 5 (exponential growth-phase) until day 14 (quasi-stationary growth-phase). Transcription rate for both the genes remained constant between days 5 and 10, while decreasing at day 14. ODC activity was consistent with ODC mRNA level during hepatoma growth. In host liver, ODC mRNA accumulated 5 and 14 days after tumor transplantation, while c-met mRNA level was elevated until day 10 and diminished at day 14. ODC activity triplicated at day 14 in host liver. The progressive decline in the expression of ODC and c-met observed in hepatoma might be one of the mechanisms important for the control of tumor growth.

Animals↗

PubMed1994

Expression of spermidine/spermine N1-acetyltransferase in growing Yoshida AH-130 hepatoma cells.

Activity and messenger RNA levels of spermidine/spermine N1-acetyltransferase, the rate-limiting enzyme of the polyamine interconversion pathway, were investigated in host liver and in Yoshida AH-130 ascites hepatoma cells as a function of tumor growth phases. Enzyme activity reached maximal values at day 10 in host liver (2.0-fold increase) and at days 10 and 14 in hepatoma cells (4.2- and 5.4-fold increases)--that is, when the cellular growth was nearly arrested. At day 10 the messenger RNA levels of spermidine/spermine N1-acetyltransferase were augmented concomitantly; they were about two and four times higher, respectively, in host liver and tumor cells than in control liver. The in vitro transcription rate seemed to be constant during hepatoma cell growth. Treatment of the animals with N1,N2-bis-(2,3-butadienyl)-1,4-butanediamine (MDL 72527), a specific inhibitor of polyamine oxidase, caused large accumulation of N1-acetylspermidine in hepatoma cells and in the ascitic fluid; the maximal values were reached at day 14. The levels of putrescine in inhibitor-treated rats decreased in hepatoma cells (day 5) and in ascitic fluid (days 5 and 14), whereas values of spermidine and spermine remained unchanged. The proposed role for spermidine/spermine N1-acetyltransferase-enhanced expression is to regulate the cellular polyamine pool by causing their excretion as acetylderivatives from tumor cells into the ascitic fluid, even if putrescine seems also to be excreted. Eventual repeat uptake of putrescine by hepatoma cells could contribute to the control of cellular polyamine levels.

Acetyltransferases↗

PubMed1994

Expression of a growth arrest specific gene (gas-6) during liver regeneration: molecular mechanisms and signalling pathways.

A set of growth arrest-specific (gas) genes negatively regulated by serum has been identified. To define the role of gas genes in a model of cell proliferation in vivo we analyzed the expression of one of these genes (gas-6) during liver regeneration after partial hepatectomy (PH). We found that gas-6 mRNA was down-regulated 4 hours after PH, within the G0 to G1 transition. Later on, gas-6 mRNA increased over the level found in normal liver with a peak at 16 hours, before the onset of DNA synthesis. This surge was probably triggered by an inflammatory response caused by the surgical trauma, because an increase of similar extent occurring with the same time course was present in livers of sham-operated and turpentine-treated rats. Comparison of mRNA steady state levels with nuclear transcription rates indicated that gas-6 expression is post-transcriptionally regulated. As we found that down-regulation of gas-6 expression was prevented by treatment with Actinomycin D, a labile protein might be involved in the determination of gas-6 mRNA stability. To investigate the mitogenic signals controlling gas-6 expression during liver regeneration we treated hepatectomized rats with a specific alpha-1-adrenoceptor blocker (prazosin) as well as with drugs which modify intracellular calcium levels. The decrease of gas-6 mRNA 4 hours after PH was prevented by prazosin and by neomycin, an inhibitor of calcium release from endogenous stores. These findings suggest that down-regulation of gas-6 expression during hepatic regeneration is triggered by catecholamines interaction with alpha-1-adrenergic receptors and by subsequent calcium release. In addition we found that the rise of gas-6 gene expression occurring at 16 hours after PH was not affected by prazosin but was inhibited by trifluoperazine. Therefore, we suggest that up-regulation of gas-6 gene expression is mediated by the interaction of calcium with calmodulin, independently of catecholamines.

Animals↗

PubMed1993

Cytosolic and nuclear spermidine acetyltransferases in growing NIH 3T3 fibroblasts stimulated with serum or polyamines: relationship to polyamine-biosynthetic decarboxylases and histone acetyltransferase.

The expression (mRNA level of enzymic activity) of cytosolic and nuclear spermidine acetyltransferases was studied in NIH 3T3 fibroblasts, either (1) serum-starved and stimulated to grow by serum refeeding, or (2) treated with inhibitors of ornithine decarboxylase (ODC) (MDL 72.175) and S-adenosylmethionine decarboxylase (AdoMetDC) (MDL 73.811) and stimulated to grow by spermidine. Expression of the known growth-regulated genes for ODC, AdoMetDC and histone acetyltransferase was also examined. The mRNA for spermidine/spermine N1-acetyltransferase (SAT) accumulated after serum refeeding (between 6 and 16 h) and even more after spermidine addition (16 h). Histone acetyltransferase activity increased after both growth stimuli, whereas spermidine N8-acetyltransferase activity remained unchanged. After serum stimulation, the ODC mRNA level and activity rose between 6 and 16 h, whereas AdoMetDC mRNA accumulation occurred later (16 h) than the increase in enzyme activity (6 h). Stimulation of ODC and AdoMetDC activities was suppressed by the inhibitors added alone or in combination with spermidine, whereas mRNA accumulation was down-regulated by spermidine. These results indicate that the expression of SAT was growth-controlled and that SAT mRNA level was regulated by polyamines.

3T3 Cells↗

PubMed1992

Opposite responses of nuclear spermidine N8-acetyltransferase and histone acetyltransferase activities to regenerative stimuli in rat liver.

Experiments performed in different models of hepatic regeneration at the time of maximal DNA synthesis, determined by thymidine kinase activity assay, demonstrated that spermidine N8-acetyltransferase activity increased 48 hr after CCl4 administration (2-fold), 72 hr after CCl4 plus phenobarbital (3-fold) and 24 hr after partial hepatectomy (4.5-fold). On the contrary, at these times histone acetyltransferase activity diminished (approximately twofold) and was unchanged compared with control values in the liver of hepatotoxin-treated and hepatectomized rats, respectively. Histone acetylation was, however, enhanced 1.5-fold before the onset of DNA replication (14 hr), and 3.4-fold after the peak of DNA synthesis (32 hr) in the liver of hepatectomized rats. alpha-Difluoromethylornithine, a specific and irreversible inhibitor of ornithine decarboxylase that was administered to hepatectomized rats, blocked polyamine synthesis, thymidine kinase activity and consequently liver regeneration 24 hr after the surgery. In those conditions, spermidine N8-acetyltransferase activity was decreased approximately twofold, whereas histone acetyltransferase activity was elevated approximately twofold. All these effects were reversed by putrescine coadministration. Altogether, these findings showed that nuclear spermidine N8-acetyltransferase and histone acetyltransferase activities were regulated in opposite ways during the processes associated with liver regeneration. Moreover, they suggested that the polyamines themselves might have a direct or indirect role in this regulation.

Acetyltransferases↗

PubMed1992

Spermidine nuclear acetylation in rat hepatocytes and in logarithmically growing rat hepatoma cells: comparison with histone acetylation.

Spermidine acetylation has been studied in nuclear homogenates and in entire nuclei from rat hepatocytes and rat hepatoma tissue culture (HTC) cells, isolated at different stages of logarithmic growth, and compared to histone acetylation. Under all experimental conditions, N8-acetylspermidine was the predominant product of the reaction (90%). Unlike histone, spermidine acetylation in HTC cell and hepatocyte entire nuclei was almost absent or strikingly reduced relative to acetylation using nuclear homogenates as the enzyme sources. This was due to the lack of a free minor pool of spermidine, most likely lost during the purification of entire nuclei. Thus, preincubation of intact nuclei in the presence of spermidine restored activities to values observed using nuclear sonicates. Spermidine acetylation in HTC cell nuclei fluctuated moderately during cell growth, being stimulated immediately after initiation of proliferation and decreasing progressively as cultures reached high cell density. This pattern corroborated that of N8-acetylspermidine intracellular accumulation induced by culturing cells in the presence of 1 mM 7-amino-2-heptanone, a competitive inhibitor of N8-acetylspermidine deacetylase. Histone acetylation during HTC cell growth was not markedly different qualitatively from that of spermidine. Moreover, spermidine and histone acetylations in hepatocyte nuclei were of the same order of magnitude as those seen in rat hepatoma cell nuclei. Finally, inhibition of deacetylation of N8-acetylspermidine had no apparent deleterious effects on cell and growth. It remains to be determined whether the acetylation step is of higher physiological importance, in particular, and as discussed in nuclear spermidine turnover.

Acetylation↗

PubMed1990

Effect of adrenergic and Ca2+ antagonists on increased ornithine decarboxylase expression in regenerating rat liver.

Partial hepatectomy (PH) (70% resection) causes within 4 hr an accumulation of ornithine decarboxylase (EC 4.1.1.17, ODC) mRNAs concomitant with an increase in ODC activity, maximum values being observed at 8 and 16 hr, respectively. In the early hours of hepatic regeneration, enhancement of transcriptional-rate of ODC gene, demonstrated by nuclear run-on analysis, can account for the accumulation of ODC mRNAs. The involvement of catecholamines in these processes is demonstrated by using prazosin and propranolol, specific antagonists of alpha 1 and beta adrenoceptors, respectively. Prazosin reduces almost completely the rise of ODC activity at 4 hr, without affecting mRNA levels. At 16 hr, enzyme activity and mRNAs increase, however, over the values observed in regenerating liver of prazosin-untreated animals. These findings suggest that alpha 1-receptor activation triggers positive control signals for ODC gene expression at the early time of liver regeneration and, on the contrary, negative signals at later times by mainly post-transcriptional and transcriptional mechanisms, respectively. Propranolol reduces similarly the initial 4 hr-rise of ODC activity. These results indicate that activation of both alpha 1- and beta-adrenoceptors causes the large increase in ODC activity. Pharmacological manipulation of intracellular Ca2+ levels by verapamil, a Ca2(+)-channel blocker, or neomycin, an inhibitor of Ca2+ release from endogenous stores, diminishes ODC activity at 4 and 16 hr after PH. ODC mRNA levels, which are not modified at 4 hr, increase over the values of partially hepatectomized rat liver at 16 hr. Trifluoperazine inhibits both ODC activity and mRNA accumulation at the times studied. As a working hypothesis it is proposed that Ca2(+)-mediated processes induced by catecholamines are involved in ODC gene expression during the prereplicative phase of liver regeneration.

Adrenergic alpha-Antagonists↗

PubMed1990

Diamine oxidase activity in a model of multistep hepatocarcinogenesis.

Treatment of rats with a complete hepatocarcinogenic regimen (diethylnitrosamine, 2-acetylaminofluorene and partial hepatectomy) produced a prolonged stimulation of diamine oxidase activity in liver, which showed early and persistent preneoplastic nodules. Diethylnitrosamine or partial hepatectomy tested separately caused a transient increase in enzyme activity. Early nodules, which were positive for gamma-glutamyltransferase activity, and hepatomas showed diamine oxidase activity of approximately 5- and 13-fold that of control liver, respectively. These results indicate an activation of terminal catabolism of polyamines in preneoplastic nodules and in hepatomas.

2-Acetylaminofluorene↗