Effect of urethan on the induction of ornithine decarboxylase in regenerating rat liver

The effect of urethan on the induction of ornithine decarboxylase in the early stage of the regeneration of rat liver was studied. The induced activity of ornithine decarboxylase was suppressed by administration of urethan immediately after partial hepatectomy. Although ornithine decarboxylase was induced biphasically by partial hepatectomy, a single intraperitoneal injection of urethan resulted in the reduction of both phases. However, the ornithine decarboxylase activity induced by glucocorticoids and growth hormone was not suppressed by urethan. The increased level of 3′,5′-cyclic adenosine monophosphate induced by partial hepatectomy was also reduced by urethan and this suppression was proportional to the suppression of ornithine decarboxylase activity. Reversal of the urethan-induced suppression of ornithine decarboxylase by administration of dibutyryl 3′,5′-cyclic adenosine monophosphate was also observed.     

Effect of urethan on the induction of ornithine decarboxylase in regenerating rat liver.

The effect of urethan on the induction of ornithine decarboxylase in the early stage of the regeneration of rat liver was studied. The induced activity of ornithine decarboxylase was suppressed by administration of urethan immediately after partial hepatectomy. Although ornithine decarboxylase was induced biphasically by partial hepatectomy, a single intraperitoneal injection of urethan resulted in the reduction of both phases. However, the ornithine decarboxylase activity induced by glucocorticoids and growth hormone was not suppressed by urethan. The increased level of 3',5'-cyclic adenosine monophosphate induced by partial hepatectomy was also reduced by urethan and this suppression was proportional to the suppression of ornithine decarboxylase activity. Reversal of the urethan-induced suppression of ornithine decarboxylase by administration of dibutyryl 3',5'-cyclic adenosine monophosphate was also observed.     

Effects of Ca2+ ionophore A23187, 1,2-dioctanoylglycerol, and dibutyryl cAMP on the activity and expression of ornithine decarboxylase in guinea pig lymphocytes

The Ca2+ ionophore A23187 induced small increases in ornithine decarboxylase activity and ornithine decarboxylase mRNA in guinea pig lymphocytes. 1,2-Dioctanoylglycerol potentiated the A23187-induced ornithine decarboxylase activity and the accumulation of mRNA for this enzyme. Dibutyryl cAMP also potentiated the enzyme activity, but had little effect on the accumulation of mRNA. 1,2-Dioctanoylglycerol and 12-O-tetradecanoylphorbol-13-acetate potentiated ornithine decarboxylase activity that had been increased by treatment with both A23187 and dibutyryl cAMP with a consistent increase in the ornithine decarboxylase mRNA. However, dibutyryl cAMP augmented ornithine decarboxylase activity that had been increased by the combination of A23187 and 1,2-dioctanoylglycerol without affecting the ornithine decarboxylase mRNA level. These results suggest that the protein kinase C and cyclic AMP pathways are involved in the enhancement of ornithine decarboxylase activity in guinea pig lymphocytes, but that the mechanisms of the enhancement differ for each pathway, the former increasing the ornithine decarboxylase mRNA level, but not the latter.     

Regulation of polyamine biosynthesis in normal and transformed hamster cells in culture

Several aspects of polyamine biosynthesis were compared in low-passage hamster embryo fibroblasts and transformed hamster fibroblasts. Earlier studies had demonstrated a larger and longer-lasting induction of ornithine decarboxylase activity in transformed cells than in hamster embryo fibroblasts. The increases in intracellular polyamine concentrations after serum stimulation were much greater in chemically transformed HE68BP cells than in normal hamster fibroblasts. Treatment of confluent cultures with the tumor promoter, 12-O-tetradecanoylphorbol-13-acetate, greatly potentiated ornithine decarboxylase induction by fresh medium in HE68BP cells, but not in hamster fibroblasts. A similar synergistic effect was observed when transformed cells, but not normal cells, were treated with the combination of insulin and promoter. HE68BP cells were capable of growth in medium containing serum concentrations as low as 0.5%, whereas only concentrations of 5% or more supported the growth of hamster embryo fibroblasts. Low serum concentrations induced ornithine decarboxylase in HE68BP cells but not in normal cells, and a given serum concentration always produced a greater induction of ornithine decarboxylase in transformed than in normal cells.Another enzyme involved in polyamine synthesis, $\text{S-}\text{adenosyl-}\text{L}\text{-methionine}$ decarboxylase was induced in normal and transformed cells by serum-containing medium or tetradecanoylphorbol acetate, but in contrast to ornithine decarboxylase, no synergistic effect was seen in transformed cells exposed to the combination of fresh medium and the tumor promoter. A macromolecular inhibitor of ornithine decarboxylase was readily detected in hamster fibroblast cultures treated with high concentrations of putrescine, but little or none of this inhibitor was found in HE68BP cultures. In both cell types, however, serum induction of ornithine decarboxylase was inhibited under conditions of excess putrescine.The results demonstrate several differences between normal and transformed hamster cells in the regulation of polyamine synthesis.     

Modulation of ornithine decarboxylase activity and ornithine decarboxylase-antizyme complex in rat heart by hormone and putrescine treatment

Ornithine decarboxylase was present in a cryptic, complexed form in an amount approximately equivalent to that of free ornithine decarboxylase activity in adult rat heart. Addition of isoproterenol (10 mg/kg) caused a notable rise in ornithine decarboxylase activity and a simultaneous decrease in the amount of the complexed enzyme. During the period of ornithine decarboxylase decay, when cardiac putrescine content had reached high values, the level of the complex increased above that of the control. Administration of putrescine (1.5 mmol/kg, twice) or dexamethasone (4 mg/kg) produced a decrease of heart ornithine decarboxylase activity, while it did not remarkably affect the level of complexed ornithine decarboxylase, therefore raising significantly the ratio of bound to total ornithine decarboxylase. Putrescine also elicited the appearance of free antizyme, concomitantly with the disappearance of free ornithine decarboxylase activity after 3-4 h of treatment. These results indicate that a significant amount of ornithine decarboxylase occurs in an inactive form in the heart under physiological conditions and that its absolute and relative levels may vary following stimuli which affect heart ornithine decarboxylase activity.     

Trypanosoma brucei ornithine decarboxylase: enzyme purification, characterization, and expression in Escherichia coli

Ornithine decarboxylase from the African trypanosome is an important target for antitrypanosomal chemotherapy. Despite this, the enzyme had not been previously purified or extensively characterized as it is a very low level protein. In this paper we describe the purification of Trypanosoma brucei brucei ornithine decarboxylase from bloodstream form trypomastigotes by 107,000-fold to a specific activity of 2.7 x 10(6) nmol CO2/h/mg of protein in the parasite. T. brucei ornithine decarboxylase had a native molecular weight of 90,000 and a subunit molecular weight of 45,000. The isoelectric point of the protein was 5.0. The Km for ornithine was 280 microM and the Ki for the irreversible inhibitor alpha-difluoromethylornithine (DFMO) was 220 microM with a half-time of inactivation at saturating DFMO concentration of 2.7 min. T. brucei ornithine decarboxylase appears similar to mouse ornithine decarboxylase, further supporting our previous suggestion that the selective toxicity of DFMO to the parasite is not due to catalytic differences between the two proteins. Although a small quantity of T. brucei ornithine decarboxylase was purified from T. brucei, extensive structural and kinetic studies will require a more ample source of the enzyme. We therefore expressed our previously cloned T. brucei ornithine decarboxylase gene in Escherichia coli using a vector that contains an inducible lambda promoter. T. brucei ornithine decarboxylase activity was induced in E. coli to levels that were 50 to 200 fold of that present in the long-slender bloodstream form of T. brucei. Ornithine decarboxylase activity in the crude E. coli lysate was 1500-6000 nmol of CO2/h/mg of protein and represented 0.05-0.2% of the total cell protein. The recombinant T. brucei ornithine decarboxylase was purified to apparent homogeneity from the transformed E. coli. The purified recombinant enzyme had kinetic and physical properties essentially identical to those of the native enzyme.     

Regulation of ornithine decarboxylase synthesis. Effect of a nutritional deficiency of vitamin B6

In vitamin B₆ deficiency there is an increase in the activity of the pyridoxal phosphate dependent enzyme ornithine decarboxylase. In the rat liver: the apoenzyme and holoenzyme activity increased 1.6 and 4 fold respectively. Concomitantly, putrescine and spermidine concentrations were halved. The lack of correspondence between product concentration and enzymic activity suggests a control mechanism other than ornithine decarboxylase activity.     

Polyamine and amino acid content, and activity of polyamine-synthesizing decarboxylases, in liver of streptozotocin-induced diabetic and insulin-treated diabetic rats

1. Concentrations of polyamines, amino acids, glycogen, nucleic acids and protein, and activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, were measured in livers from control, streptozotocin-diabetic and insulin-treated diabetic rats. 2. Total DNA per liver and protein per mg of DNA were unaffected by diabetes, whereas RNA per mg of DNA and glycogen per g of liver were decreased. Insulin treatment of diabetic rats induced both hypertrophy and hyperplasia, as indicated by an increase in all four of these constituents to or above control values. 3. Spermidine content was increased in the livers of diabetic rats, despite the decrease in RNA, but it was further increased by insulin treatment. Spermine content was decreased by diabetes, but was unchanged by insulin treatment. Thus the ratio spermidine/spermine in the adult diabetic rat was more typical of that seen in younger rats, whereas insulin treatment resulted in a ratio similar to that seen in rapidly growing tissues. 4. Ornithine decarboxylase activity was variable in the diabetic rat, showing a positive correlation with endogenous ornithine concentrations. This correlation was not seen in control or insulin-treated rats. Insulin caused a significant increase in ornithine decarboxylase activity relative to control or diabetic rats. 5. S-Adenosylmethionine decarboxylase activity was increased approx. 2-fold by diabetes and was not further affected by insulin. 6. Hepatic concentrations of the glucogenic amino acids, alanine, glutamine and glycine were decreased by diabetes. Their concentrations and that of glutamate were increased by injection of insulin. Concentrations of ornithine, proline, leucine, isoleucine and valine were increased in livers of diabetic rats and were decreased by insulin. Diabetes caused a decrease in hepatic concentration of serine, threonine, lysine and histidine. Insulin had no effect on serine, lysine and histidine, but caused a further fall in the concentration of threonine.     

Effect of 1,3-diaminopropane on ornithine decarboxylase enzyme protein in thioacetamide-treated rat liver.

A radioimmunoassay for ornithine decarboxylase was used to study the regulation of this enzyme in rat liver. The antiserum used reacts with ornithine decarboxylase from mouse, human or rat cells. Rat liver ornithine decarboxylase enzyme activity and enzyme protein (as determined by radioimmunoassay) were measured in thioacetamide-treated rats at various times after administration of 1,3-diaminopropane. Enzyme activity declined rapidly after 1,3-diaminopropane treatment as did the amount of enzyme protein, although the disappearance of enzyme activity slightly preceded the loss of immunoreactive protein. The loss of enzyme protein after cycloheximide treatment also occurred rapidly, but was significantly slower than that seen with 1,3-diaminopropane. When 1,3-diaminopropane and cycloheximide were injected simultaneously, the rate of disappearance of enzyme activity and enzyme protein was the same as that seen with cycloheximide alone. These results show that the rapid loss in enzyme activity after 1,3-diaminopropane treatment is primarily due to a loss in enzyme protein and that protein synthesis is needed in order for 1,3-diaminopropane to exert its full effect. A macromolecular inhibitor of ornithine decarboxylase that has been termed antizyme is induced in response to 1,3-diaminopropane, but our results indicate that the loss of enzyme activity is not due to the accumulation of inactive ornithine decarboxylase-antizyme complexes. It is possible that the antizyme enhances the degradation of the enzyme protein. Control experiments demonstrated that the antiserum used would have detected any inactive antizyme-ornithine decarboxylase complexes present in liver since addition of antizyme to ornithine decarboxylase in vitro did not affect the amount of ornithine decarboxylase detected in our radioimmunoassay. Anti-(ornithine decarboxylase) antibodies may be useful in the purification of antizyme since the antizyme-ornithine decarboxylase complex can be immunoprecipitated, and antizyme released from the precipitate with 0.3 M-NaCl.     

Regulation of ornithine decarboxylase activity by amino acids, cyclic AMP and luteinizing hormone in cultured mammalian cells

Any one of five amino acis (alanine, asparagine, glutamine, glycine, and serine) is an essential requirement for the induction of ornithine decarboxylase (EC 4.1.1.17) in cultured chinese hamster ovary (CHO) cells maintained with a salts/glucose, medium. Each of these amino acids induced a striking activation of ornithine decarboxylase in the presence of dibutyryl cyclic AMP and luteinizing hormone. The effect of the other amino acids was considerably less or negligible. The active amino acids at optimal concentrations (10 mM) induced only a 10-20 fold enhancement of enzyme activity alone, while in the presence of dibutyryl cyclic AMP, ornithine decarboxylase activity was increased 40-50 fold within 7-8 h. Of the hormones and drugs tested, luteinizing hormone resulted in the highest (300-500 fold) induction of ornithine decarboxylase with optimal concentrations of dibutyryl cyclic AMP and asparagnine. Omission of dibutyryl cyclic AMP reduced this maximal activation to one half while optimal levels of luteinizing hormone alone caused no enhancement of ornithine decarboxylase activity. The induction of ornithine decarboxylase elicited by dibutyryl cyclic AMP, amino acid and luteinizing hormone was diminished about 50% with inhibitors of RNA and protein synthesis. The specific amino acid requirements for ornithine decarboxylase induction in chinese hamster ovary cells was similar to the requirements for induction in two other transformed cell lines. Understanding the mechanism of enzyme induction requires an identification of the essential components of the regulatory system. The essential requirement for enzyme induction is one of five amino acids. The induction of ornithine decarboxylase by dibutyryl cyclic AMP and luteinizing hormone was additive in the presence of an active amino acid.     

Investigation of structure and rate of synthesis of ornithine decarboxylase protein in mouse kidney

An immunoblotting technique was used to study the forms of ornithine decarboxylase present in androgen-induced mouse kidney. Two forms were detected which differed slightly in isoelectric point but not in subunit molecular weight (approximately 55 000). Both forms were enzymatically active and could be labeled by reaction with radioactive alpha-(difluoromethyl)-ornithine, an enzyme-activated irreversible inhibitor. On storage of crude kidney homogenates or partially purified preparations of ornithine decarboxylase, the enzyme protein was degraded to a smaller size (Mr approximately 53 000) without substantial loss of enzyme activity. The synthesis and degradation of ornithine decarboxylase protein were studied by labeling the protein by intraperitoneal injection of [35S]methionine and immunoprecipitation using both monoclonal and polyclonal antibodies. The fraction of total protein synthesis represented by renal ornithine decarboxylase was increased at least 25-fold by testosterone treatment of female mice and was found to be about 1.1% in the fully induced androgen-treated female. Both forms of the enzyme were rapidly labeled in vivo, and the immunoprecipitable ornithine decarboxylase protein was almost completely lost after 4-h exposure to cycloheximide, confirming directly the very rapid turnover of this enzyme. Treatment with 1,3-diaminopropane which is known to cause a great reduction in ornithine decarboxylase activity did not greatly selectively inhibit the synthesis of the enzyme. However, 1,3-diaminopropane did produce an increase in the rate of degradation of ornithine decarboxylase and a general reduction in protein synthesis. These two factors, therefore, appear to be responsible for the loss of ornithine decarboxylase activity and protein in response to 1,3-diaminopropane.     

Induction of ornithine decarboxylase by 12-O-tetradecanoylphorbol 13-acetate in hamster fibroblasts. Relationship between levels of enzyme activity, immunoreactive protein, and RNA during the induction process

Phorbol ester tumor promoters and growth factors rapidly stimulate ornithine decarboxylase activity in the transformed hamster fibroblast line HE68BP. We report here a close correspondence between the time courses and magnitudes of induction of ornithine decarboxylase activity and immunoreactive ornithine decarboxylase protein following treatment of HE68BP cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) and/or refeeding with fresh medium. Cycloheximide addition to induced cells caused a rapid fall in the levels of both ornithine decarboxylase activity and ornithine decarboxylase protein. Northern blot analysis of RNA isolated from HE68BP cells indicated that treatment with TPA and fresh medium increased the amount of two species of mRNA of lengths 2.4 and 2.1 kilobase. This increased accumulation of ornithine decarboxylase mRNA corresponded temporally to that observed at the protein level, with a 15-fold maximal induction 7 h after treatment followed by a rapid decline in hybridizable RNA. These data indicate that stimulation of ornithine decarboxylase activity by TPA or refeeding involves changes in levels of ornithine decarboxylase mRNA as well as changes in the rate of synthesis of ornithine decarboxylase protein.     

Limitations of the Moeller lysine and ornithine decarboxylase tests.

A total of 40 fecal and environmental isolates, including 26 Escherichia coli strains, 9 members of the genus Klebsiella, and 5 members of the genus Enterobacter, were tested by enzyme assay for their endogenous and induced levels of lysine decarboxylase and ornithine decarboxylase when grown in Moeller decarboxylase medium. All of the coliforms examined had measurable lysine decarboxylase and ornithine decarboxylase activities whether or not they were positive in the Moeller test. In general, the Moeller lysine decarboxylase test reflected the inducibility of lysine decarboxylase whereas the Moeller ornithine decarboxylase test did not relect the inducibility of ornithine decarboxylase. Neither test measured the amount of intracellular enzyme; rather, they indicated whether the amount of polyamine liberated was sufficient to raise the pH of the culture medium above 7. Changing the growth conditions (i.e., the concentrations of glucose, lysine, and amino acids other than lysine) greatly influenced the lysine decarboxylase activity in coliforms. The limitations on the interpretation of the Moeller test results are discussed.     

Limitations of the Moeller lysine and ornithine decarboxylase tests.

A total of 40 fecal and environmental isolates, including 26 Escherichia coli strains, 9 members of the genus Klebsiella, and 5 members of the genus Enterobacter, were tested by enzyme assay for their endogenous and induced levels of lysine decarboxylase and ornithine decarboxylase when grown in Moeller decarboxylase medium. All of the coliforms examined had measurable lysine decarboxylase and ornithine decarboxylase activities whether or not they were positive in the Moeller test. In general, the Moeller lysine decarboxylase test reflected the inducibility of lysine decarboxylase whereas the Moeller ornithine decarboxylase test did not relect the inducibility of ornithine decarboxylase. Neither test measured the amount of intracellular enzyme; rather, they indicated whether the amount of polyamine liberated was sufficient to raise the pH of the culture medium above 7. Changing the growth conditions (i.e., the concentrations of glucose, lysine, and amino acids other than lysine) greatly influenced the lysine decarboxylase activity in coliforms. The limitations on the interpretation of the Moeller test results are discussed.     

Regulation of the activity of ornithine decarboxylase and S-adenosylmethionine decarboxylase in mammary gland and liver of lactating rats. Effects of starvation, prolactin and insulin deficiency.

1. Starvation caused a marked decrease in the activity of ornithine decarboxylase in mammary gland, together with a lesser decrease in the activity of S-adenosylmethionine decarboxylase and a marked fall in milk production. Liver ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were unaffected. 2. Refeeding for 2.5 h was without effect on ornithine decarboxylase in mammary gland, but it returned the S-adenosylmethionine decarboxylase activity in mammary gland to control values and elevated both ornithine decarboxylase and S-adenosylmethionine decarboxylase in liver. 3. Refeeding for 5 h returned the activity of ornithine decarboxylase in mammary gland to fed-state values and resulted in further increases in S-adenosylmethionine decarboxylase in mammary gland and liver and in ornithine decarboxylase in liver. 4. Prolactin deficiency in fed rats resulted in decreased milk production and decreased activity of ornithine decarboxylase in mammary gland. The increase in ornithine decarboxylase activity normally seen after refeeding starved rats for 5 h was completely blocked by prolactin deficiency. 5. In fed rats, injection of streptozotocin 2.5 h before death caused a decrease in the activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase in mammary gland, which could be reversed by simultaneous injection of insulin. Insulin deficiency also prevented the increase in S-adenosylmethionine decarboxylase in liver and mammary gland normally observed after refeeding starved rats for 2.5 h.     

Osmotically induced changes in the ornithine decarboxylase activity of Dictyostelium discoideum.

Myxamoebae of Dictyostelium discoideum from exponentially growing cultures showed altered ornithine decarboxylase activity upon external osmotic perturbation. On transfer to hypotonic NaCl solutions (20 mosmol/kg), cells showed high enzyme activity which was relatively independent of the concentration of the coenzyme pyridoxal phosphate (assay concentrations, 5 and 200 microM). In hypertonic solution (400 mosmol/kg) cells had a reduced level of ornithine decarboxylase activity which was dependent on the coenzyme concentration. The changes in activity were freely reversible in further external osmotic manipulation. The response to osmotic change occurred rapidly, within a few minutes. The changes still occurred at 7 degrees C but 2 mM sodium azide prevented the formation of the high activity form, although this effect was reversed when azide was removed. Cycloheximide had no effect on the osmotically induced changes. Addition of putrescine caused ornithine decarboxylase eventually to the converted to the low-activity form regardless of the osmolality of the solution. The characteristic cofactor concentration dependence of the high- and low-activity form were retained on storage of the cell extracts. No evidence was found for diffusible effectors which stabilized one or the other form of the activity. The enzymes responsible for the two forms were of the same molecular size as judged by gel filtration, and the activities had similar thermostabilities. The results are interpreted in terms of an osmotically induced interconversion of two forms of a single ornithine decarboxylase.     

Decarboxylation of arginine and ornithine by arginine decarboxylase purified from cucumber (Cucumis sativus) seedlings

A purified preparation of arginine decarboxylase fromCucumis sativus seedlings displayed ornithine decarboxylase activity as well. The two decarboxylase activities associated with the single protein responded differentially to agmatine, putrescine andPi. While agmatine was inhibitory (50 %) to arginine decarboxylase activity, ornithine decarboxylase activity was stimulated by about 3-fold by the guanido arnine. Agmatine-stimulation of ornithine decarboxylase activity was only observed at higher concentrations of the amine. Inorganic phosphate enhanced arginine decarboxylase activity (2-fold) but ornithine decarboxylase activity was largely uninfluenced. Although both arginine and ornithine decarboxylase activities were inhibited by putrescine, ornithine decarboxylase activity was profoundly curtailed even at 1 mM concentration of the diamine. The enzyme-activated irreversible inhibitor for mammalian ornithine decarboxylase,viz. α-difluoromethyl ornithine, dramatically enhanced arginine decarboxylase activity (3–4 fold), whereas ornithine decarboxylase activity was partially (50%) inhibited by this inhibitor. At substrate level concentrations, the decarboxylation of arginine was not influenced by ornithine andvice-versa. Preliminary evidence for the existence of a specific inhibitor of ornithine decarboxylase activity in the crude extracts of the plant is presented. The above results suggest that these two amino acids could be decarboxylated at two different catalytic sites on a single protein.     

Hormonal control of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase during development of the rat epididymis

The specific activities of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase were determined during growth of the rat epididymis. Ornithine decarboxylase activity was first detectable on day 21 and increased 10-fold in both the head and tail of epididymis prior to their rapid growth responses. Hypophysectomy reduced ornithine decarboxylase activity to undetectable levels, but enzyme activity was restored by treatment with gonadotropins or testosterone. Testosterone also induced a precocious 10-fold increase of epididymal ornithine decarboxylase in the pre-pubertal rat. In contrast, the specific activity of S-adenosyl-L-methionine decarboxylase changed little during development and merely doubled in response to hormonal treatments. The results describe a pattern of changes in these enzyme activities during hormone-dependent development of the epididymis, and suggest that ornithine decarboxylase is the rate-limiting activity in the regulation of spermidine biosynthesis by testosterone in this organ.     

Ornithine decarboxylase activity in relation to DNA synthesis in mouse interfollicular epidermis and hair follicles.

The relationship between ornithine decarboxylase (L-ornithine carboxylyase, EC 4.1.1.17) activity and DNA synthetic activity was studied in mouse epidermis. Interfollicular epidermis and hair follicles were investigated separately. It was found that, in hair follicles, the variations of DNA replicative activity, which are reflected in the cyclic growth of hair, are paralleled by corresponding changes in ornithine decarboxylase activity. In both interfollicular epidermis and hair follicles, stimulation of DNA synthetic activity by plucking of hair induced a rapid and marked increase in ornithine decarboxylase activity. The relationship of steady-state and induced ornithine decarboxylase activity to DNA synthetic activity was compared in hair follicles and interfollicular epidermis. A correlation between the activity of this enzyme and DNA replication was found thereby in each of these tissues.     

Polyamine depletion enhances the roscovitine-induced apoptosis through the activation of mitochondria in HCT116 colon carcinoma cells

Small molecule inhibitors of cyclin-dependent kinases (CDKs) show high therapeutic potential in various cancer types which are characterized by the accumulation of transformed cells due to impaired apoptotic machinery. Roscovitine, a CDK inhibitor showed to be a potent apoptotic inducer in several cancer cells. Polyamines, putrescine, spermidine and spermine, are biogenic amines involved in many cellular processes, including apoptosis. In this study, we explored the potential role of polyamines in roscovitine-induced apoptosis in HCT116 colon cancer cells. Roscovitine induced apoptosis by activating mitochondrial pathway caspases and modulating the expression of Bcl-2 family members. Depletion of polyamines by treatment with difluoromethylornithine (DFMO) increased roscovitine-induced apoptosis. Transient silencing of ornithine decarboxylase, polyamine biosynthesis enzyme and special target of DFMO also increased roscovitine-induced apoptosis in HCT116 cells. Interestingly, additional putrescine treatment was found pro-apoptotic due to the presence of non-functional ornithine decarboxylase (ODC). Finally, roscovitine altered polyamine catabolic pathway and led to decrease in putrescine and spermidine levels. Therefore, the metabolic regulation of polyamines may dictate the power of roscovitine induced apoptotic responses in HCT116 colon cancer cells.