多胺代谢与大鼠心肌缺血再灌注损伤关系的实验研究

目的 观察缺血再灌注不同时期大鼠心肌多胺代谢变化规律,探讨多胺代谢与心肌缺血再灌注损伤的关系.方法 采用结扎冠状动脉方法复制大鼠在体心肌缺血再灌注损伤模型,应用逆转录聚合酶链反应(RT-PCR)、Western免疫印迹(Western blot)方法分别测定正常、缺血再灌注2 h、6 h、12 h和24 h时心肌鸟氨酸脱羧酶(ODC)和精胺/精脒乙酰转移酶(SSAT)mRNA的转录和蛋白表达水平,并用高效液相色谱仪测定多胺含量变化.结果 心肌缺血再灌注后ODC和SSAT mRNA的转录和蛋白表达均上调,至再灌注24 h时,与假手术组比,ODC mRNA和SSAT mRNA转录分别增加了3.1倍和3.8倍(P＜0.01),ODC和SSAT的蛋白表达分别增加了3.1倍和2.9倍(P＜0.01).精胺、精脒和多胺总代谢池含量减少,至再灌注24 h时,分别比假手术组少了33.6%、35.3%和32.9%,而腐胺多了58.9%(P＜0.01).结论 心肌缺血再灌注损伤可导致多胺代谢失衡,二者密切相关.     

Gossypol activates pancreatic polyamine catabolism in normal rats and induces acute pancreatitis in transgenic rats over-expressing spermidine/spermine N1-acetyltransferase

BACKGROUND: The male antifertility agent gossypol has been reported to induce spermidine/spermine N1-acetyltransferase (SSAT) in canine prostate cells. As SSAT is the rate-controlling enzyme in the catabolism of the polyamines and is involved in the development of acute pancreatitis in a recent transgenic rat model, we exposed normal and transgenic rats over-expressing SSAT to gossypol to evaluate its effect on pancreatic polyamine metabolism and organ integrity. METHODS: Pancreatic SSAT activity, polyamine pools, pancreatic histology and plasma 2-amylase activity were determined after different doses of gossypol. RESULTS: Gossypol increased pancreatic putrescine and decreased spermidine and spermine pools in normal rats accompanied by tissue oedema and significantly elevated plasma amylase activity. In transgenic rats, the drug strikingly induced SSAT, profoundly depleted the higher polyamines and caused distinct pancreatitis. The combination of gossypol at doses harmless to transgenic pancreas with an inhibitor of polyamine oxidase caused massive synergistic induction of SSAT, profound depletion of the polyamine pools and acute pancreatitis. CONCLUSIONS: The results indicate that gossypol induces pancreatitis through an activation of polyamine catabolism.     

Polyamine synthesis and transport inhibition in a human anaplastic thyroid carcinoma cell line in vitro and as xenograft tumors.

Polyamines are essential cellular components for neoplastic transformation and cell proliferation. Antineoplastic efforts that inhibit polyamine synthesis are insufficient to induce cytotoxicity, due to compensatory induction of polyamine transport. Treatment of an anaplastic human thyroid carcinoma cell line (DRO90-1) with a novel polymeric spermine conjugate (polyspermine; PSpm) caused in vitro cytotoxicity and inhibited the growth of xenograft tumors at low concentrations. Similar in vitro antineoplastic effects were noted with two other human anaplastic thyroid carcinoma cell lines. This coincided with inhibition of polyamine uptake and synthetic enzyme activities, with reduced ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAM-DC) but increased spermidine/spermine N1-acetyltransferase (SSAT) activities, as measured in DRO90-1 cells. In subsequent studies using these cells, PSpm was effective in reducing the intracellular levels of all polyamines in vitro, resulting in cytotoxicity that was not reversed by administration of extracellular polyamines. Low-dose PSpm inhibited tumor growth in vivo, but high doses of PSpm potentiated xenograft tumor growth. PSpm degradation products produced with in vivo treatment may be produced that function as substrates for polyamine biosynthesis. These studies suggest that polyamine metabolism inhibition is a viable target for antineoplastic therapy of anaplastic thyroid carcinoma, although the in vivo response to PSpm suggests that this agent will have limited clinical utility.     

Gossypol Activates Pancreatic Polyamine Catabolism in Normal Rats and Induces Acute Pancreatitis in Transgenic Rats Over-expressing Spermidine/Spermine N 1 -Acetyltransferase

Background: The male antifertility agent gossypol has been reported to induce spermidine/spermine N 1 -acetyltransferase (SSAT) in canine prostate cells. As SSAT is the rate-controlling enzyme in the catabolism of the polyamines and is involved in the development of acute pancreatitis in a recent transgenic rat model, we exposed normal and transgenic rats over-expressing SSAT to gossypol to evaluate its effect on pancreatic polyamine metabolism and organ integrity. Methods: Pancreatic SSAT activity, polyamine pools, pancreatic histology and plasma &#33 -amylase activity were determined after different doses of gossypol. Results: Gossypol increased pancreatic putrescine and decreased spermidine and spermine pools in normal rats accompanied by tissue oedema and significantly elevated plasma amylase activity. In transgenic rats, the drug strikingly induced SSAT, profoundly depleted the higher polyamines and caused distinct pancreatitis. The combination of gossypol at doses harmless to transgenic pancreas with an inhibitor of polyamine oxidase caused massive synergistic induction of SSAT, profound depletion of the polyamine pools and acute pancreatitis. Conclusions: The results indicate that gossypol induces pancreatitis through an activation of polyamine catabolism.     

Polyamine levels of human colorectal adenocarcinomas are correlated with tumor stage and grade

BACKGROUND AND AIMS: Cellular proliferation and differentiation are regulated by polyamines and their rate-limiting enzyme ornithine decarboxylase (ODC), both of which are correlated with tumor growth, but their role in differentiation is less clear. We investigated the correlation of ODC activity and polyamine levels with tumor stage and grade with respect to sample recruitment. PATIENTS AND METHODS: We determined ODC activity ([(14)C]CO(2) release), polyamines (HPLC), and histological staging and grading (TNM classification) of tissue samples from 64 patients with colorectal adenocarcinomas. RESULTS: We found the concentrations of putrescine, spermidine, and N(1)-acetyl-spermidine and the ODC activity in tumor tissue to be twice as high as in adjacent normal mucosa. A critical parameter affecting ODC activity was ischemic time, which significantly reduced ODC activity levels in tumors (threefold) and in the surrounding normal tissue (ninefold) when the ischemic period exceeded 1 h. By contrast, polyamine content was not affected by ischemia. Total polyamine and spermine concentrations were higher in T3 and T4 than in T2 tumors, but putrescine was higher in T4 than in T3 and T2 tumors. There were significantly higher levels of total polyamines and spermine in moderately differentiated (G2) than in poorly differentiated (G3) tumors. CONCLUSION: The lower spermidine/spermine ratio in G2 (0.44) compared with that in G3 (0.64) tumors suggests the involvement of the polyamines in colonic cell differentiation. Polyamine content is thus correlated with the tumor stage.     

Age-related changes in polyamine biosynthesis after fasting and refeeding

The effect of aging on ornithine decarboxylase (ODC) activity and polyamine biosynthesis in the proximal small intestine was studied in two groups of male Fisher 344 rats (young [4-month old] and aged [26- to 27-month old]) using a fasting and refeeding model. In control (nonfasted) rats, levels of polyamines (putrescine, spermidine and spermine) and ODC activity were significantly higher in aged compared with young rats. In aged rats, fasting significantly reduced the levels of putrescine by 41%, spermidine by 23%, and spermine by 11%; however, fasting had no effect on polyamine levels in young rats. ODC activity was decreased 75% in young and 50% in aged rats after fasting compared with the respective age-matched controls. Conversely, 2 h after reinstituting a chow diet increased ODC activity by 17-fold in young rats but only 8-fold in aged rats. Putrescine levels were also increased in both age groups after refeeding; however, similar to ODC activity, these increases were much less in aged rats. In addition, spermidine and spermine levels remained significantly depressed in the aged groups even after 24 h of refeeding. These findings suggest that the normal rigid control of gut polyamine biosynthesis and proliferation noted in young rats is markedly altered with aging.     

Aging and intestinal polyamine metabolism in the rat

Hyperproliferation and delayed expression of enzyme activity occur in small intestinal enterocytes of aging rats, and starvation and refeeding result in impaired control of these processes. Since altered polyamine metabolism may accompany changes in enterocyte proliferation, we studied the effects of nutrient manipulation upon cell numbers, ornithine decarboxylase (ODC) activity and polyamine content in jejunum and ileum of 4- to 5- and 26- to 27-month Fischer rats. In both groups, cell numbers fell during starvation and and increased during refeeding. Crypt cell hyperplasia was found in aging animals. Jejunal putrescine, spermine and spermidine content were greater in older rats, fell during starvation, and rose during refeeding. Ileal ODC activity was 66% greater in the aging rats, but jejunal ODC activity was modestly increased in young animals. Intestinal polyamine content correlates with proliferative changes and polyamine metabolism responds appropriately to nutrient manipulation during aging. Dissociation of ODC activity and polyamine content in aging jejunum probably occurred because enterocyte differentiation was delayed. Investigation of intestinal polyamine metabolism may be useful in elucidating deranged proliferative activities found in the intestine of aging rodents.     

Decreased ornithine decarboxylase activity in the kidneys of Dahl salt-sensitive rats.

To assess the roles of polyamines (putrescine, spermidine, and spermine) and ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine synthesis, in the development of salt-sensitive hypertension, we evaluated activity and expression of ODC, urinary polyamine excretion, and antizyme (endogenous ODC inhibitor protein) expression in Dahl salt-sensitive (SS) and salt-resistant (SR) rats after they were fed on a low (0.3%) or high (4%) salt diet for 4 weeks. We also examined the effects of spermidine and difluoromethylornithine (DFMO: a specific inhibitor of ODC) on the systolic blood pressure and ODC protein expression in SS rats fed a high salt diet. Renal ODC activity and urinary polyamine excretion in SS rats were lower than those in SR rats after 4 weeks treatment with a low or high salt diet. The renal ODC protein expression of SS rats was paradoxically increased as compared to the SR group. A high salt diet did not alter ODC activity but increased ODC protein only in SS rats. ODC mRNA and antizyme protein expressions were not significantly different among the four groups. Spermidine supplementation attenuated and DFMO exaggerated hypertension in SS rats fed a high salt diet. Spermidine down-regulated and DFMO up-regulated renal ODC protein in SS rats on a high salt diet. ODC activity was decreased but protein was paradoxically increased in kidneys of SS rats. ODC protein was suggested to increase in compensation for the inhibition of its activity. Impaired ODC activity and polyamine production in the kidney may exaggerate salt-sensitive hypertension in SS rats.     

Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain.

The cellular responses to hypoxia are poorly understood. To test the hypothesis that ornithine decarboxylase (ODC; L-ornithine carboxy-lyase; EC 4.1.1.17) activity and polyamine concentrations change in response to acute hypoxia, we performed the following studies. Pregnant Sprague-Dawley rats inspired various O2 concentrations (9-21%) for various time periods (0.5-48 h) from days 15 to 21 of gestation. In fetal brains we measured the activity of ODC, ODC mRNA, and polyamines. In response to 4-h acute mild hypoxia, ODC activity in fetal rat brain (cerebrum, cerebellum, and hippocampus) increased to 330-450% from control values (P < 0.001), after which it declined to control levels in 6-8 h. The 4-h ODC response varied inversely with inspired O2 concentration and was not mimicked by beta 2 agonist or blocked by beta 2-antagonist administration. The ODC response was associated with an increase in fetal brain putrescine concentration to 190% above control at 4-6 h (P < 0.01) and an increase in the polyamines spermidine and spermine to about 115% above control at 6-8 h. We also observed that ODC mRNA increased significantly after 2-4 h of hypoxia. ODC activity and polyamine concentrations appear to be useful enzymatic markers for fetal brain hypoxia. The magnitude and time course of the acute hypoxic ODC increase were similar to responses to extracellular signals that result in differentiation or cell growth. Thus, the well-defined and regulated ODC activity response may represent a protective mechanism in brain to hypoxia.     

Polyamines in 1 alpha, 25-dihydroxycholecalciferol-induced differentiation of human promyelocytic leukemia cells, HL-60

The human promyelocytic leukemia cell line, HL-60, differentiated into macrophage/monocytes in the presence of 1 alpha,25-dihydroxycholecalciferol [1 alpha,25(OH)2D3], as assessed by the percentage of morphologically mature cells and their ability to reduce nitroblue tetrazolium. In this study of the mechanism involved, the activities of ornithine decarboxylase and spermidine/spermine-N1-acetyltransferase (SAT), the rate-limiting enzymes of polyamine metabolism, as well as the cellular levels of polyamine were measured. ODC activity reached a peak 24 h after the addition of 1 alpha,25(OH)2D3 and then decreased, while SAT activity gradually increased as differentiation commenced. An increase in putrescine and decreases in spermidine and spermine were also observed. Addition of alpha-difluoromethylornithine, an irreversible inhibitor of ODC, with or without methylglyoxalbis(guanylhydrazone), an inhibitor of S-adenosylmethionine decarboxylase, caused no effect on 1 alpha,25(OH)2D3-induced cell differentiation, although the cellular levels of putrescine and spermidine decreased markedly. Addition of alpha-difluoromethylornithine markedly suppressed cell proliferation; this effect was reversed by the addition of exogenous putrescine. Addition of exogenous spermidine or spermine to overcome activation of SAT also had no effect on 1 alpha,25(OH)2D3-induced cell differentiation. These results suggest both that polyamine metabolism is not important in 1 alpha,25(OH)2D3-induced differentiation of HL-60 cells, but that it is intimately involved in the proliferation of these cells.     

Stimulation of polyamine biosynthesis by follicle-stimulating hormone in serum-free cultures of rat Sertoli cells

Sertoli cells derived from 21-day-old rats were cultured in serum-free Ham's F-10 medium to allow a direct investigation of the effects of FSH on polyamine (PA) biosynthesis in a defined culture system. After 48 h in culture, the basal cellular content consisted predominantly of spermine (1.1 nmol/mg protein) with substantially lower amounts of spermidine (0.1 nmol/mg protein) and undetectable amounts of putrescine. Upon the addition of ovine FSH (3 X 10(-9) M), cellular spermine content became significantly elevated above the control value as early as 1 h after treatment, reaching a 2.5-fold stimulation by 4 h. Spermidine was also elevated by 4 h after FSH treatment, but remained less than 20% of the spermine concentration. At no time did the cellular content of putrescine increase to measurable levels. Extended time-course studies demonstrated that the FSH-induced cellular increase in spermine and spermidine content persisted up to 24 h during the continuous presence of FSH. Bu2cAMP (5 mM) invoked similar changes in PA levels when measured at 4, 8, and 24 h. Ornithine decarboxylase (ODC) activity, which catalyzes the production of putrescine, was increased by FSH in a temporal fashion similar to that of spermine production. Addition of alpha-difluoromethylornithine, an irreversible inhibitor of ODC, blocked increases in both ODC activity and PA in cells stimulated with FSH or Bu2cAMP. Pulse-chase experiments using [3H]ornithine demonstrate that putrescine is initially synthesized, and is subsequently converted to spermidine and spermine. These studies suggest that regulation of PA biosynthesis by FSH is largely expressed as increases in spermine, and to a lesser extent spermidine, suggesting that the more complex PAs may be involved in the regulation of Sertoli cell function.     

Structures of wild-type and mutant human spermidine/spermine N1-acetyltransferase, a potential therapeutic drug target

Spermidine/spermine N1-acetyltransferase (SSAT) is a key enzyme in the control of polyamine levels in human cells, as acetylation of spermidine and spermine triggers export or degradation. Increased intracellular polyamine levels accompany several types of cancers as well as other human diseases, and compounds that affect the expression, activity, or stability of SSAT are being explored as potential therapeutic drugs. We have expressed human SSAT from the cloned cDNA in Escherichia coli and have determined high-resolution structures of wild-type and mutant SSAT, as the free dimer and in binary and ternary complexes with CoA, acetyl-CoA (AcCoA), spermine, and the inhibitor N1,N11bis-(ethyl)-norspermine (BE-3-3-3). These structures show details of binding sites for cofactor, substrates, and inhibitor and provide a framework to understand enzymatic activity, mutations, and the action of potential drugs. Two dimer conformations were observed: a symmetric form with two open surface channels capable of binding substrate or cofactor, and an asymmetric form in which only one of the surface channels appears capable of binding and acetylating polyamines. SSAT was found to self-acetylate lysine-26 in the presence of AcCoA and absence of substrate, a reaction apparently catalzyed by AcCoA bound in the second channel of the asymmetric dimer. These unexpected and intriguing complexities seem likely to have some as yet undefined role in regulating SSAT activity or stability as a part of polyamine homeostasis. Sequence signatures group SSAT with proteins that appear to have thialysine Nepsilon-acetyltransferase activity.     

Role of polyamines in isoproterenol-induced cardiac hypertrophy: effects of alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase

DFMO is a selective irreversible inhibitor of ornithine decarboxylase (ODC), the initial enzyme in the polyamine biosynthetic pathway. DFMO was utilized to determine the role of polyamines in isoproterenol (ISO)-induced cardiac hypertrophy. Daily subcutaneous administration of 200 mg/kg of DFMO reduced cardiac putrescine levels but did not significantly alter the basal levels of spermidine or spermine, nor was normal cardiac growth affected. ISO-induced cardiac hypertrophy was accompanied by increased putrescine and spermidine levels but spermine was not significantly altered. DFMO reversed the ISO-induced increases in putrescine and inhibited or attenuated both the increases in spermidine content and the cardiac hypertrophy. Although normal ODC activity appears not to be necessary for the maintenance of basal levels of polyamines or for normal cardiac growth, sustained inhibition of ODC interferes with ISO-induced elevations of putrescine, spermidine and heart weight.     

Intracellular polyamine levels of intestinal epithelial cells in inflammatory bowel disease

Polyamines and their acetylated derivatives are a prerequisite for cellular metabolism and considered to be essential for proliferation and differentiation of the rapidly renewing intestinal mucosa. However, their role during mucosal inflammation is less clear. Polyamine concentrations were determined in isolated colonic epithelial cells (CECs) from endoscopic biopsies from 26 patients with inflammatory bowel disease (IBD) and 40 controls as well as colon samples from mice with and without acute or chronic dextran sodium sulfate (DSS)-induced colitis. In patients with ulcerative colitis, CEC spermidine and N8-acetylspermidine levels were significantly enhanced and spermine levels were reduced compared with healthy controls. A correlation of polyamine levels of patients with IBD with their corresponding inflammatory index revealed that increased concentrations of spermidine, N8-acetylspermidine, and N1-acetylspermine were found in CECs from the most severe inflamed mucosal areas. Using acute and chronic DSS colitis as a model of mucosal inflammation, we found enhanced levels of spermidine and spermine in acute colitis, whereas in chronic inflammation, CEC spermine concentrations were decreased. Our data indicate a lack of the anti-inflammatory polyamine spermine in severe ulcerative colitis and chronic DSS colitis, which may aggravate the disease. Increased spermidine and N8-acetylspermidine levels reflect increased uptake and metabolism likely due to accelerated proliferation and regeneration of CECs.     

Polyamines,diamine oxidase,and ornithine decarboxylase activity in colorectal cancer and in normal surrounding mucosa

We investigated the polyamine levels [putrescine (Put), spermidine (Spd), and spermine (Spm)] and their metabolism by simultaneously considering the ornithine decarboxylase (ODC) and diamine oxidase (DAO) activities in human colorectal cancer and in normal surrounding tissue. Single and total polyamine levels were significantly higher in the neoplastic tissue than in the surrounding mucosa from the same patients. Furthermore, the ODC activity was significantly higher and the DAO activity significantly lower in the neoplastic tissue than in the surrounding mucosa. Polyamine levels and enzymatic activities did not correlate with the clinical and histologic characteristics of patients. In normal tissue samples, no correlation was found between single and total polyamine levels and enzymatic activities (both DAO and ODC). On the contrary, in colorectal neoplastic samples, significant and positive correlations were found between the levels of total polyamines, Spd, and Spm and the ODC activity. In the same specimens, DAO activity was related to Spd levels and the Spd/Spm ratio, but, in those cases, the correlation was negative. Thus, our findings suggest that, during the neoplastic growth of the colorectal mucosa, the balance between polyamine degradation and biosynthesis is disengaged from the control exerted by the two enzymes.     

Activation of polyamine catabolism in transgenic rats induces acute pancreatitis

Polyamines are required for optimal growth and function of cells. Regulation of their cellular homeostasis is therefore tightly controlled. The key regulatory enzyme for polyamine catabolism is the spermidine/spermine N(1)-acetyltransferase (SSAT). Depletion of cellular polyamines has been associated with inhibition of growth and programmed cell death. To investigate the physiological function SSAT, we generated a transgenic rat line overexpressing the SSAT gene under the control of the inducible mouse metallothionein I promoter. Administration of zinc resulted in a marked induction of pancreatic SSAT, overaccumulation of putrescine, and appearance of N(1)-acetylspermidine with extensive depletion of spermidine and spermine in transgenic animals. The activation of pancreatic polyamine catabolism resulted in acute pancreatitis. In nontransgenic animals, an equal dose of zinc did not affect pancreatic polyamine pools, nor did it induce pancreatitis. Acetylated polyamines, products of the SSAT-catalyzed reaction, are metabolized further by the polyamine oxidase (PAO) generating hydrogen peroxide, which might cause or contribute to the pancreatic inflammatory process. Administration of specific PAO inhibitor, MDL72527 [N(1),N(2)-bis(2,3-butadienyl)-1,4-butanediamine], however, did not affect the histological score of the pancreatitis. Induction of SSAT by the polyamine analogue N(1),N(11)-diethylnorspermine reduced pancreatic polyamines levels only moderately and without signs of organ inflammation. In contrast, the combination of N(1), N(11)-diethylnorspermine with MDL72527 dramatically activated SSAT, causing profound depletion of pancreatic polyamines and acute pancreatitis. These results demonstrate that acute induction of SSAT leads to pancreatic inflammation, suggesting that sufficient pools of higher polyamine levels are essential to maintain pancreatic integrity. This inflammatory process is independent of the production of hydrogen peroxide by PAO.     

Interleukin-1beta induces elevation of spermidine/spermine N1-acetyltransferase activity and an increase in the amount of putrescine in synovial adherent cells from patients with rheumatoid arthritis

OBJECTIVE: To investigate polyamine metabolism in rheumatoid synovial adherent cells stimulated by interleukin- 1beta (IL-1beta). METHODS: Synovial adherent cells obtained from patients with rheumatoid arthritis (RA) were cultured and incubated in the presence or absence of human recombinant IL-1beta at a concentration of 10 ng/ml for 24 h. The cellular contents of polyamines as well as the activities of spermidine/spermine N1-acetyltransferase (SAT) and ornithine decarboxylase (ODC) were measured. RESULTS: Polyamines in synovial adherent cells decreased significantly after 24 h incubation in the absence of IL-1beta. However, in the presence of IL-Ibeta, putrescine and N'-acetylspermidine increased significantly. No significant difference was observed between the amount of spermidine in synovial adherent cells incubated with and without IL-1beta. Spermine and N8-acetylspermidine in synovial adherent cells incubated with IL-1beta decreased significantly more than in synovial adherent cells incubated without. SAT activity reached a peak 12 h after the addition of IL-1beta and then decreased, while the ODC activity did not increase. SAT activity was elevated by the addition of IL-1beta in a dose dependent manner. CONCLUSION: An increase in the putrescine level in rheumatoid synovial adherent cells as a result of the elevation of SAT activity induced by IL-1beta may play a role in RA.     

The alpha9beta1 integrin enhances cell migration by polyamine-mediated modulation of an inward-rectifier potassium channel

The alpha9beta1 integrin accelerates cell migration through binding of spermidine/spermine acetyltransferase (SSAT) to the alpha9 cytoplasmic domain. We now show that SSAT enhances alpha9-mediated migration specifically through catabolism of spermidine and/or spermine. Because spermine and spermidine are effective blockers of K(+) ion efflux through inward-rectifier K(+) (Kir) channels, we examined the involvement of Kir channels in this pathway. The Kir channel inhibitor, barium, or knockdown of a single subunit, Kir4.2, specifically inhibited alpha9-dependent cell migration. alpha9beta1 and Kir4.2 colocalized in focal adhesions at the leading edge of migrating cells and inhibition or knockdown of Kir4.2 caused reduced persistence and an increased number of lamellipodial extensions in cells migrating on an alpha9beta1 ligand. These results identify a pathway through which the alpha9 integrin subunit stimulates cell migration by localized polyamine catabolism and modulation of Kir channel function.     

Hormonal control of polyamine levels in bovine adrenocortical cells

The implication of polyamines in cellular growth and differentiation processes and the existence of a polyamine-mediated protein phosphorylation system in adrenocortical cells suggest that polyamines may be examined as potential intracellular messengers in the pleiotypic action of ACTH. Bovine adrenocortical cells in culture exhibit a specific, energy-dependent, partly sodium-supported, inward polyamine transport system, independent of the A, L, and N aminoacid uptake systems. Steroidogenic concentrations of ACTH (10(-12) to 10(-9)M) induced a rapid activation of the polyamine uptake, resulting in a 2- to 3-fold increase in intracellular polyamine content, over 1 h. The ACTH dose-response curves for steroidogenic activity and for polyamine uptake were similar. Other adrenocortical effectors such as angiotensin II, acetylcholine, and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) activated polyamine uptake with a pattern parallel to their steroidogenic potency (i.e. ACTH greater than angiotensin II greater than acetylcholine, TPA). Steroidogenic concentrations of 8-bromo-cAMP displayed no effect on the adrenocortical polyamine uptake, suggesting that cAMP does not mediate this action of ACTH. On the other hand, ACTH induced a large increase in ornithine decarboxylase (ODC) activity in bovine adrenocortical cells, after a 6- to 8-h lag period, resulting in an average 2-fold increase in cell putrescine, spermidine, and spermine content. However, when the cells were previously polyamine loaded, ACTH-dependent ODC induction was suppressed. Adrenocortical cell polyamine content thus appears to be under hormonal control. ACTH may act through two possible pathways: 1) the rapid activation of the cell polyamine accumulation from an extracellular source and 2) the delayed increase in polyamine biosynthesis secondary to induction of ODC activity, when the cells are relatively depleted of the polyamines. These observations suggest that polyamines may function as intracellular messengers for some of the ACTH effects in bovine adrenocortical cells.     

Prolactin and polyamine catabolism: specific effect on polyamine oxidase activity in rat thymus

Much evidence suggests that prolactin has an immunoregulatory function and that its effects on cells of the immune system depend on the level and specific forms of the receptors present on the target cells. The effect of administration of prolactin on polyamine catabolism was investigated in thymus of male intact rats by measuring the activities of spermidine/spermine N(1)-acetyltransferase and polyamine oxidase, because of the relationships between polyamines (especially putrescine) and the immune system. The administration of prolactin to rats resulted in the rapid induction of spermidine/spermine N(1)-acetyltransferase activity in the thymus (1.6-times the level of control rats, within 4 h), and in a marked decrease in polyamine oxidase activity at 24 h. The changes in enzyme activities were accompanied by an increase in putrescine concentration and a decrease in spermidine and spermine concentrations. In the spleen, prolactin increased SAT activity only 24 h after administration and was ineffective on PAO activity.