EGF stimulates polyamine uptake in Caco-2 cells

Spermine, a molecular switch regulating EGFR, integrin β3, Src, and FAK scaffolding

Intracellular polyamine levels are highly regulated by the activity of ornithine decarboxylase (ODC), which catalyzes the first rate-limiting reaction in polyamine biosynthesis, producing putrescine, which is subsequently converted to spermidine and spermine. We have shown that polyamines regulate proliferation, migration, and apoptosis in intestinal epithelial cells. Polyamines regulate key signaling events at the level of the EGFR and Src. However, the precise mechanism of action of polyamines is unknown. In the present study, we demonstrate that ODC localizes in lamellipodia and in adhesion plaques during cell spreading. Spermine regulates EGF-induced migration by modulating the interaction of the EGFR with Src. The EGFR interacted with integrin β3, Src, and focal adhesion kinase (FAK). Active Src (pY418-Src) localized with FAK during spreading and migration. Spermine prevented EGF-induced binding of the EGFR with integrin β3, Src, and FAK. Activation of Src and FAK was necessary for EGF-induced migration in HEK293 cells. EGFR-mediated Src activation in live HEK293 cells using a FRET based Src reporter showed that polyamine depletion significantly increased Src kinase activity. In vitro binding studies showed that spermine directly binds Src, and preferentially interacts with the SH2 domain of Src. The physical interaction between Src and the EGFR was severely attenuated by spermine. Therefore, spermine acts as a molecular switch in regulating EGFR-Src coupling both physically and functionally. Upon activation of the EGFR, integrin β3, FAK and Src are recruited to EGFR leading to the trans-activation of both the EGFR and Src and to the Src-mediated phosphorylation of FAK. The activation of FAK induced Rho-GTPases and subsequently migration. This is the first study to define mechanistically how polyamines modulate Src function at the molecular level.

Activated K-RAS increases polyamine uptake in human colon cancer cells through modulation of caveolar endocytosis

Endocytic pathways have been implicated in polyamine transport in mammalian cells, but specific mechanisms have not been described. We have shown that expression of a dominant negative (DN) form of the GTPase Dynamin, but not Eps15, diminished polyamine uptake in colon cancer cells indicating a caveolar and nonclathrin uptake mode. Polyamines co-sediment with lipid raft/caveolin-1 rich fractions, of the plasma membrane in a sucrose density gradient. Knock down of caveolin-1 significantly increased polyamine uptake. Conversely, ectopic expression of this protein resulted in diminished polyamine uptake. We also found that presence of an activated K-RAS oncogene significantly increased polyamine uptake by colon cancer cells. This effect is through an increase in caveolin-1 phosphorylation at tyrosine residue 14. Caveolin-1 is a negative regulator of caveolar endocytosis and phosphorylation in a K-RAS dependent manner leads to an increase in caveolar endocytosis. In cells expressing wild type K-RAS, addition of exogenous uPA was sufficient to stimulate caveolar endocytosis of polyamines. This effect was abrogated by the addition of a SRC kinase inhibitor. These data indicate that polyamine transport follows a dynamin-dependent and clathrin-independent endocytic uptake route, and this route is positively regulated by the oncogenic expression of K-RAS in a caveolin-1 dependent manner.

Biological significance of dietary polyamines

Polyamines are classically known by their names of putrescine, spermine, and spermidine. They are synthesized endogenously from ornithine and are interconvertible. In addition, an exogenous supply of polyamines is provided by dietary intake and by intestinal absorption from the products of bacterial metabolism. Polyamine uptake occurs almost entirely in the gut, and afterward the various forms are metabolized in different tissues under the strict regulation of ornithine decarboxylase, which is the first enzyme involved in their synthesis. Polyamines are eliminated from the organism by means of oxidation reactions, appearing in urine in all their metabolic forms. Polyamines play an important role in regulating cell growth and proliferation, the stabilization of negative charges of DNA, RNA transcription, protein synthesis, apoptosis, and the regulation of the immune response. They are components of breast milk and might be important in neonatal gut maturation, for which reason the possible supplementation of infant formulas with these compounds is under study.

Disturbed keratinocyte differentiation in transgenic mice and organotypic keratinocyte cultures as a result of spermidine/spermine N-acetyltransferase overexpression

Overexpression of the rate-limiting enzyme in polyamine catabolism spermidine/spermine N1-acetyltransferase (SSAT) in transgenic (Tg) mouse leads to accumulation of putrescine in the skin and permanent hair loss at the age of 3 wk. The hair follicles of these mice are replaced by dermal cysts and epidermal utriculi. Increased putrescine production is also seen in hyperproliferative cutaneous disorders such as in psoriasis. These disorders are characterized by delayed onset of epidermal differentiation characterized as reduced expression of terminal differentiation markers such as cytokeratins 1/10, and filaggrin and persisting expression of basal cell cytokeratins 5/14 in the suprabasal layers. The use of these markers in immunohistological analysis of SSAT Tg skin clearly showed signs of disturbed differentiation. To exclude the possibility that changes in differentiation originated from underlying connective tissue, we introduced SSAT gene into an established rat epidermal cell line. Organotypic cultures derived from the transfected cells displayed similar changes in their differentiation pattern as keratinocytes in Tg skin. The role of accumulated putrescine in cutaneous changes of SSAT Tg mice was verified by an experiment in which putrescine level was reduced by systemic putrescine biosynthesis inhibition. The putrescine reduction was sufficient to alleviate the cutaneous changes to such an extent that distinct hair regrowth could be seen. These results suggest that the cutaneous changes of SSAT Tg animals are due to disorders of the keratinocyte differentiation. Moreover, they strengthen the view that the proper regulation of polyamine metabolism plays an important role in the keratinocyte maturation.

Molecular mechanisms of the chemopreventive effects of resveratrol and its analogs in colorectal cancer: key role of polyamines?

Resveratrol (3,4',5-trihydroxy-trans-stilbene), a phytoalexin found in grape skins, peanuts, and red wine, has been reported to exhibit a wide range of biological and pharmacological properties. It has been speculated that dietary resveratrol may act as an antioxidant, promote nitric oxide production, inhibit platelet aggregation, and increase high-density lipoprotein cholesterol and thereby serve as a cardioprotective agent (the so-called "French paradox"). Recently, it was demonstrated that resveratrol can function as a cancer chemopreventive agent, and there has been a great deal of experimental effort directed toward defining this effect. It has been shown that resveratrol and some of its analogues interfere with signal transduction pathways. Thus the activities of various protein kinases are inhibited, the expression of nuclear proto-oncogenes declines, and the activity of ornithine decarboxylase (ODC) is reduced. ODC, which catalyzes the rate-limiting step in the biosynthesis of polyamines, is closely linked with cellular proliferation and carcinogenesis. This review summarizes the recent advances that have provided new insights into the molecular mechanisms underlying the promising properties of resveratrol focusing on the key role of the polyamine metabolism in colorectal cancer cells.

Effect of insulin on cephalexin uptake and transepithelial transport in the human intestinal cell line Caco-2

We investigated whether cephalexin transport in Caco-2 cells is regulated by insulin. After the insulin pretreatment, cephalexin uptake, and transport as well as PEPT1 mRNA and protein expression in the cells were measured. Cephalexin uptake was significantly increased by the insulin pretreatment. Insulin significantly increased cephalexin saturable uptake, but had no significant effect on the non-saturable one. PEPT1 protein expression on the apical membrane, but not PEPT1 mRNA expression, was increased by the insulin pretreatment. The enhancement of cephalexin uptake by the insulin pretreatment was inhibited by genistein, a tyrosine kinase inhibitor, and colchicine, an agent that disrupts protein translocation. Apical-to-basolateral transport of cephalexin has increased by the insulin pretreatment at the apical side and long-term insulin pretreatment at the basolateral side. It is considered that insulin mainly binds to its receptor on the apical and basolateral membranes, thereby promoting PEPT1 translocation from the intracellular pool to the apical membrane surface; consequently, PEPT1 protein expression on the apical membrane is increased.

Anticancer therapeutic potential of soy isoflavone, genistein

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.

Polyamines interact with DNA as molecular aggregates

New compounds, named nuclear aggregates of polyamines, having a molecular mass of 8000, 4800 and < 1000 Da, were found in the nuclear extracts of several replicating cells. Their molecular structure is based on the formation of ionic bonds between polyamine ammonium and phosphate groups. The production of the 4800 Da compound, resulting from the aggregation of five or more < 1000 Da units, was increased in Caco-2 cells treated with the mitogen gastrin. Dissolving single polyamines in phosphate buffer resulted in the in vitro aggregation of polyamines with the formation of compounds with molecular masses identical to those of natural aggregates. After the interaction of the 4800 Da molecular aggregate with the genomic DNA at 37 degrees C, both the absorbance of DNA in phosphate buffer and the DNA mobility in agarose gel increased greatly. Furthermore, these compounds were able to protect the genomic DNA from digestion by DNase I, a phosphodiesterasic endonuclease. Our data indicate that the nuclear aggregate of polyamines interacts with DNA phosphate groups and influence, more efficaciously than single polyamines, both the conformation and the protection of the DNA.

Insufficiently charged isosteric analogue of spermine: interaction with polyamine uptake, and effect on Caco-2 cell growth

We characterised a novel, charge-insufficient isosteric analogue of spermine, 11-[(amino)oxy]-4,9-diaza-1-aminoundecane (AOSPM). This analogue was synthesised by displacing aminopropyl group by aminooxyethyl group, the latter having pK(a) of about 5. Charge deficiency of the AOSPM molecule was fixed at a definite atom, while pK(a) of the rest nitrogen was similar to the parent polyamine. AOSPM competed with putrescine, spermidine and spermine for the uptake into the cell, and was accumulated in the cells in high amounts when exogenous polyamine synthesis was impaired. It was not recognised by the cells as growth-promoting polyamine, since it was unable to restore growth arrest due to polyamine deprivation. Like natural spermine, this polyamine analogue prevented oxidative DNA damage. AOSPM could be used not only as a tool to study polyamine homeostasis in the cell, but may have distinct applications either as radiation protector, a stable and non-toxic inhibitor of polyamine uptake or, as an appropriate vector, to enhance the uptake of impermeable compounds into the cell.

Nonsteroidal anti-inflammatory drugs stimulate spermidine/spermine acetyltransferase and deplete polyamine content in colon cancer cells

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colonic tumourigenesis and have an established usefulness in cancer prevention. Because polyamines are essential for neoplastic cell growth, the aim of this study was to evaluate the effect of NSAIDs (indomethacin, a nonselective COX-1 and COX-2 inhibitor) on polyamine metabolism in colon cancer cells.

METHODS

Both cell counting and thymidine incorporation into cellular DNA were used to assess colon cancer cell growth. Activities of polyamine-metabolising enzymes, polyamine content (HPLC) and ODC and c-myc protein expression (Western blot) were measured in colon cancer cells treated with indomethacin during logarithmic phase of proliferation.

RESULTS

Indomethacin impaired growth of human colon cancer cells (Caco-2 and HCT-116). As a result, ornithine decarboxylase activity and c-myc protein expression were decreased. Treatment with indomethacin induced intracellular oxidant formation in colon cancer cells significantly increased the spermidine/spermine-acetyltrasferase activity (SSAT) and enhanced polyamine acetylation and efflux from colon cancer cells. Impairment of cell growth by indomethacin could not be reversed by exogenous polyamines.

CONCLUSION

Taken together, our results suggest that NSAIDs affect polyamine metabolism in colon cancer cells by inducing SSAT activity, and that polyamine depletion in NSAID-treated colon cancer cells is mainly due to enhanced polyamine acetylation and irreversible depletion of intracellular polyamine pools.

Polyamines in the gut lumen: bioavailability and biodistribution

Polyamines arrive in the gut lumen mainly with food. Shortly after a meal, the majority of luminal polyamines disappear from the duodenal and jejunal lumen, by a mechanism of passive diffusion. The majority of luminal polyamines are degraded in the gut before reaching systemic circulation. Hence, there is broad evidence that luminal polyamines are indeed absorbed, distributed throughout the body, and utilized for cellular growth in remote organs and tissues. In addition, luminal polyamines are crucially involved in normal, adaptive and neoplastic growth of the gut per se, and are taken up by normal and neoplastic epithelial cells of the gut mucosa by a tightly regulated and presumably active transport process. Uptake of polyamines into intestinal and colonic epithelial cells is the highest during cell proliferation, and is stimulated by mitogens and peptide growth factors. Understanding the mechanisms of polyamine uptake in neoplastic cells of the gut, as well as the "biodistribution/bioavailability" of luminal polyamines in man, may provide clinically relevant information that can be used in inhibiting cancer cell growth by deprivation of intracellular polyamine pools.

Permeability characteristics of polyamines across intestinal epithelium using the Caco-2 monolayer system: comparison between transepithelial flux and mitogen-stimulated uptake into epithelial cells

The polyamines putrescine, spermidine, and spermine are present in foods in high amounts, and are used for cell growth throughout the body. Surprisingly little is known about the mechanisms of polyamine absorption in the gut. To elucidate the mechanisms, transepithelial transport of polyamines was studied in human enterocytelike Caco-2 cells, grown on permeable filter supports. Transport of all three polyamines across Caco-2 cell monolayers was linear; intraepithelial accumulation of polyamines was higher in confluent than in differentiated Caco-2 cells, but still negligible in comparison with the overall transport across the monolayers. Epidermal growth factor (EGF) enhanced polyamine accumulation in Caco-2 cells four-fold, and basolateral uptake was higher than apical uptake if the cells were stimulated to grow. The amounts of polyamines taken up by the cells were nevertheless negligible in comparison with the net polyamine flux across the monolayers. Basolateral excretion of polyamines was in the picomolar range, whereas their transepithelial transport, occurring presumably by passive diffusion through the paracellular pathway, contributed hundreds of micromoles of polyamines to the basolateral chamber. We conclude that transepithelial transport of polyamines occurs by passive diffusion, and that it is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.

Transepithelial transport of putrescine across monolayers of the human intestinal epithelial cell line, Caco-2

AIM: To study the transepithelial transport characteristics of the polyamine putrescine in human intestinal Caco-2 cell monolayers to elucidate the mechanisms of the putrescine intestinal absorption.

METHODS: The transepithelial transport and the cellular accumulation of putrescine was measured using Caco-2 cell monolayers grown on permeable filters.

RESULTS: Transepithelial transport of putrescine in physiological concentrations ( > 0.5 mM) from the apical to basolateral side was linear. Intracellular accumulation of putrescine was higher in confluent than in fully differentiated Caco-2 cells, but still negligible (less than 0.5%) of the overall transport across the monolayers in apical to basolateral direction.EGF enhanced putrescine accumulation in Caco-2 cells by four fold, as well as putrescine conversion to spermidine and spermine by enhancing the activity of S adenosylmethionine decarboxylase. However, EGF did not have any significant influence on putrescine flux across the Caco- 2 cell monolayers. Excretion of putrescine from Caco-2 cells into the basolateral medium did not exceed 50 picomoles, while putrescine passive flux from the apical to the basolateral chamber, contributed hundreds of micromoles polyamines to the basolateral chamber.

CONCLUSION: Transepithelial transport of putrescine across Caco-2 cell monolayers occurs in passive diffusion, and is not influenced when epithelial cells are stimulated to proliferate by a potent mitogen such as EGF.

Glycine supply to human enterocytes mediated by high-affinity basolateral GLYT1

BACKGROUND & AIMS

Intestinal glycine transport is involved in nutrient absorption and enterocyte homeostasis, particularly for glutathione synthesis. The primary aim of this study was to characterize the mechanism of postabsorptive (basolateral) glycine acquisition by the enterocyte.

METHODS

Assimilation of [(14)C]glycine was studied in human enterocytic Caco-2 cells, and expression of the glycine transporter GLYT1 was examined in Caco-2 cells and human intestine by reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. The regulation of glycine transport in Caco-2 cells by phorbol-ester-induced protein kinase C activation was investigated.

RESULTS

Basolateral glycine uptake into Caco-2 cells is predominantly Na(+) and Cl(-) dependent and is 4-fold greater than apical uptake. The dominant Na(+)- and Cl(-)-dependent mechanism was characterized by a restricted inhibition profile, selectively sensitive to sarcosine, with an apparent Michaelis constant of 40-80 micromol/L, indicating system GLY. Consistent with these functional data, molecular techniques detected expression of GLYT1 messenger RNA and protein in the human intestine and Caco-2 cells. Protein kinase C activation reduced maximum velocity for GLYT1-mediated glycine uptake without effect on the Michaelis constant. The reduction in functional activity was independent of a measured protein kinase C-induced decrease in GLYT1 messenger RNA levels.

CONCLUSIONS

Enterocytes express GLYT1 along the length of the crypt-villus axis, where it mediates high-affinity basolateral glycine uptake.

Hydroxylamine-containing inhibitors of polyamine biosynthesis and impairment of colon cancer cell growth

Polyamine synthesis (by the action of ornithine decarboxylase [ODC] and S-adenosylmethionine decarboxylase [SAMDC]) and polyamine content are high in colon cancer. In addition, colonic lumen is rich in polyamines synthesised by colonic microflora; for this reason, polyamine depletion in colon cancer may be a logical approach to impair growth of colon cancer cells. We evaluated highly specific and reportedly non-toxic hydroxylamine-containing inhibitors of ODC (1-aminooxy-3-aminopropane, APA) and SAMDC (S-(5'-deoxy-5'-adenosyl)-methylthioethyl-hydroxylamine, AMA) in human colon cancer cells (Caco-2 and HT-29) in culture. APA depleted ODC activity within 24 hr, more rapidly than did difluoromethylornithine. APA and AMA in combination (100 microM each) reduced ODC and SAMDC activities to undetectable levels within 24 hr and intracellular polyamines to 8-23% of control. The resulting growth arrest could be reversed only by twice as much spermidine as is physiologically present in the colonic lumen. In concentrations sufficient to deplete growth, APA and AMA were not toxic. Simultaneous treatment with APA, AMA, and 5-fluorouracil reduced colon cancer cell survival more potently than treatment with 5-fluorouracil alone. The hydroxylamine-containing ODC and SAMDC inhibitors APA and AMA are potent inhibitors of colon cancer cell proliferation and might be therapeutically promising in colon cancer.

EGF-stimulated polyamine accumulation in the colon carcinoma cell line, Caco-2

BACKGROUND

Polyamines (putrescine, spermidine and spermine) are ubiquitous molecules indispensable for cell proliferation. In the intestinal lumen they are present in high amounts. Polyamine accumulation in proliferating cells of the intestinal mucosa is high, and it occurs both by enhanced synthesis and by increased uptake from the lumen.

AIMS

To study mitogen-induced polyamine accumulation in the gut, we treated proliferating Caco-2 cells with epidermal growth factor (EGF) and measured the activity of ornithine decarboxylase (ODC) and putrescine uptake. Furthermore, we investigated whether EGF-induced changes in the apical membrane could be responsible for the effect of EGF on polyamine uptake in Caco-2 cells.

METHODS

Putrescine uptake, ODC activity and intracellular polyamine content were evaluated in the presence of 100 ng/ml EGF. To study the mechanisms of EGF-stimulated polyamine uptake, apical membrane vesicles were isolated, and putrescine uptake into the vesicles measured. Possible enrichment in brush border membrane cytoskeleton proteins (ezrin and villin) was assessed by Western blot.

RESULTS

Treatment with EGF induced an increase in ODC activity, which occurred within the first minutes of treatment and reached peak values after 3 h. In contrast, an increase in putrescine uptake was more sustained, with peak levels at 12 h. Both synthesis and uptake contributed to an over 60% increase in intracellular putrescine and spermidine after EGF treatment. There were no detectable changes in apical membrane cytoskeleton (as concluded by the absence of ezrin and villin enrichment in EGF-treated Caco-2 cells). However, in apical membrane vesicles isolated from EGF-pretreated cells, putrescine uptake was enhanced twofold.

CONCLUSIONS

EGF stimulates both synthesis and uptake of polyamines in Caco-2 cells. Enhanced synthesis seems to ensure rapid supply with polyamines in the earliest stages of growth, while the uptake is responsible for the maintenance of high polyamine intracellular levels during late growth phases. EGF-stimulated polyamine uptake is apparently not a consequence of structural changes in the apical membrane, but is likely to occur by a distinct EGF-induced alteration of the polyamine transporter itself.

Polyamine uptake across the basolateral membrane of the enterocyte is mediated by a high-affinity carrier: a study using isolated basolateral membrane vesicles

BACKGROUND/AIMS

Polyamine uptake from the circulation plays an important role in the maintenance of the intracellular polyamine content during extensive proliferation in intestinal mucosal cells.

METHODS

Isolated basolateral membrane vesicles of the rabbit enterocyte were used to characterize polyamine transport across the basolateral side of the intestinal epithelium. Incorporation of spermidine and spermine into the basolateral membrane was rapid, although 30-60% of polyamines were initially bound to the basolateral membrane. In order to avoid the influence of binding on the actual uptake into the vesicles, polyamine incorporation was measured at 37 and 4 degrees C, and kinetic parameters were calculated from the difference in polyamine incorporation rates at these temperatures.

RESULTS

Uptake kinetics was saturable, with Km values of 13.34 and 12.35 micromol/l and Vmax of 159 and 105 pmol/mg protein/ min for spermidine and spermine, respectively. It was also temperature dependent, with Q10 values (calculated between uptake velocities at 37 and 25 degrees C) of 2.56 for spermidine and 1.90 for spermine. At physiological pH, polyamine uptake was at its highest. Since at this pH polyamines are fully charged, charge might be essential for polyamines to be taken up across the basolateral membrane. Polyamine uptake was inhibited by di-, tri- and tetracations, and there was no evidence for sodium cotransport. Transport of putrescine was not inhibited by spermine and spermidine, although spermidine inhibited spermine uptake in a competitive manner, with Ki of 127 micromol/l.

CONCLUSION

These results imply that a saturable high-affinity transport system for polyamine does exist at the basolateral side of the enterocyte. Such a transport system may be responsible for the active transport of polyamine into rapidly proliferating enterocytes.

Interaction of putrescine with nuclear oligopeptides in the enterocyte-like Caco-2 cells

Intestinal cells are able both to synthesize and take up putrescine, the main compound of the metabolic polyamine pathway. Polyamine binding to nuclear macromolecules is thougth to modulate DNA synthesis and transcription. Our aim was to study the fate of putrescine when taken up from the medium in the enterocyte-like Caco-2 cells and to analyze its binding to nuclear proteins. After having incubated the cells with 14C-putrescine (0.8 microM), during cell replication and differentiation, the nuclei were separated by sequential centrifugations in a sucrose gradient. About 20% of the putrescine taken up by Caco-2 cells resulted in the nuclei in both proliferating and differentiated cells. The binding of polyamines to nuclear proteins was studied on nuclear extracts, separated by both alkaline polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) and gel permeation chromatography (GPC). No radioactivity was found in nuclear protein extracts when using the SDS-PAGE method. Conversely, in replicating cells, GPC showed that the greatest amount of radioactivity was present in the nuclear peaks corresponding to oligopeptides with a molecular weight of 4,800-8,000 daltons. High-performance liquid chromatography analysis showed the presence of putrescine and spermidine in the 8, 000-dalton protein peak, whereas in the 4,800-dalton peak spermine was found in addition to putrescine. The radioactive count in the HPLC separated polyamines showed that a small percentage of the radioactivity present in the 8,000 and 4,800-dalton GPC peaks was linked to spermine and spermidine, suggesting an interconversion of the supplemented putrescine. Conversely, in differentiated cells, the nuclear oligopeptides did not reveal any radioactivity or any polyamines, suggesting that the binding of polyamines to nuclear oligopeptides is exclusively concerned with replicating cells.

Low-dose deoxycholic acid stimulates putrescine uptake in colon cancer cells (Caco-2)

Deoxycholic acid (DCA) has long been implicated as tumour-promoting agent in the colon. Polyamines are necessary for cell proliferation, they are accumulated in high amounts in colon cancer cells, and their concentrations in the colonic lumen can reach millimolar levels. The aim of this study was to investigate the effects of physiological DCA concentrations on proliferation and polyamine content in human colon cancer cells (Caco-2) in culture. Over an initial 48 h in culture, DCA stimulated Caco-2 cell proliferation rate three-fold, reaching a maximum with 20 microM DCA. DCA-induced increases in ornithine decarboxylase (ODC) activity corresponded to peak proliferation rates, occurring only during the initial 48 h of cell proliferation. Treatment with low-dose DCA resulted in a two-fold increase in putrescine uptake, first noted after 2 days in culture, but persisting until the cells became confluent (day 5). Both basal and DCA-stimulated putrescine uptake in Caco-2 cells were saturable. Kinetic analysis of the uptake data showed that DCA-stimulated putrescine uptake was due to an increase in the capacity of the putative putrescine transporter, without changes in its affinity, therefore implying an increased number of putrescine transporters in the cell membrane, without change in their structure.

Amphiregulin acts as an autocrine growth factor in two human polarizing colon cancer lines that exhibit domain selective EGF receptor mitogenesis

Colonic enterocytes, like many epithelial cells in vivo, are polarized with functionally distinct apical and basolateral membrane domains. The aims of this study were to characterize the endogenous epidermal growth factor (EGF)-like ligands expressed in two polarizing colon cancer cell lines, HCA-7 Colony 29 (HCA-7) and Caco-2, and to examine the effects of cell polarity on EGF receptor-mediated mitogenesis. HCA-7 and Caco-2 cells were grown on plastic, or as a polarized monolayer on Transwell filters. Cell proliferation was measured by 3H-thymidine incorporation and EGF receptor (EGFR) binding was assessed by Scatchard analysis. EGFR ligand expression was determined by Northern blot analysis, reverse transcription polymerase chain reaction, metabolic labelling and confocal microscopy. We found that amphiregulin (AR) was the most abundant EGFR ligand expressed in HCA-7 and Caco-2 cells. AR was localized to the basolateral surface and detected in basolateral-conditioned medium. Basolateral administration of neutralizing AR antibodies significantly reduced basal DNA replication. A single class of high-affinity EGFRs was detected in the basolateral compartment, whereas the apical compartment of polarized cells, and cells cultured on plastic, displayed two classes of receptor affinity. Basolateral administration of transforming growth factor alpha (TGF-alpha) or an EGFR neutralizing antibody also resulted in a dose-dependent stimulation or attenuation, respectively, of DNA replication. However, no mitogenic response was observed when these agents were added to the apical compartment or to confluent cells cultured on plastic. We conclude that amphiregulin acts as an autocrine growth factor in HCA-7 and Caco-2 cells, and EGFR ligand-induced proliferation is influenced by cellular polarity.

Hormonal regulation of oligopeptide transporter pept-1 in a human intestinal cell line

The intestinal oligopeptide transporter (cloned as Pept-1) has major roles in protein nutrition and drug therapy. A key unstudied question is whether expression of Pept-1 is hormonally regulated. In this experiment, we investigated whether insulin has such a role. We used a human intestinal cell monolayer (Caco-2) as the in vitro model of human small intestine and glycylglutamine (Gly-Gln) as the model substrate for Pept-1. Results showed that addition of insulin at a physiological concentration (5 nM) to incubation medium greatly stimulates Gly-Gln uptake by Caco-2 cells. This stimulation was blocked when genistein, an inhibitor of tyrosine kinase, was added to incubation medium. Studies of the mechanism of insulin stimulation showed the following. 1) Stimulation occurred promptly (30-60 min) after exposure to insulin. 2) There was no significant change in the Michaelis-Menten constant of Gly-Gln transport, but there was a nearly twofold increase in its maximal velocity. 3) Insulin effect persisted even when Golgi apparatus, which is involved in trafficking of newly synthesized Pept-1, was dismantled. 4) However, there was complete elimination of insulin effect by disruption of microtubules involved in trafficking of preformed Pept-1. 5) Finally, with insulin treatment, there was no change in Pept-1 gene expression, but the amount of Pept-1 protein in the apical membrane was increased. In conclusion, the results show that insulin, when it binds to its receptor, stimulates Gly-Gln uptake by Caco-2 cells by increasing the membrane population of Pept-1. The mechanism appears to be increased translocation of this transporter from a preformed cytoplasmic pool.

Antizyme-dependent and -independent mechanisms are responsible for increased spermidine transport in amino acid-restricted human cancer cells

Amino acid deprivation can inhibit tumour cell proliferation. Since polyamines are required for cell growth, we hypothesised that their regulatory pathways can respond to amino acid restriction. We report here that exposure of human colon adenocarcinoma Caco-2 cells to a medium restricted for a single amino acid, but not for D-glucose, activates spermidine transport. The increase was rapid and seemed transient with a maximum 4-6 hr after amino acid removal. Kinetics showed that the maximal velocity of transport was solely increased in L-methionine- or L-leucine-deprived cells, indicating increased number of transporters. The intracellular level of complex of ornithine decarboxylase (ODC) with antizyme, a negative regulator of polyamine transport, was decreased by 16-29% in amino acid-deprived cells. However, exposure to limited amounts of amino acid increased transport without altering the ODC-antizyme complex level. We propose that antizyme-independent mechanisms, sensitive to the amino acid concentration, also participate to the control of spermidine transport.

Post-translational modifications of eukaryotic initiation factor-5A (eIF-5A) as a new target for anti-cancer therapy

Eukaryotic translation initiation factor 5A (eIF-5A) is the only cell protein that contains the unusual basic amino acid hypusine [N epsilon-(4-amino-2-hydroxybutyl)lysine]. Hypusine is formed by the transfer of the butylamine portion from spermidine to the epsilon-amino group of a specific lysine residue of eIF-5A precursor and the subsequent hydroxylation at carbon 2 of the incoming 4-aminobutyl moiety. Agents that reduce cell hypusine levels inhibit the growth of mammalian cells. These observations suggest that hypusine is crucial for proliferation and transformation of eukaryotic cells. Here we have studied whether the inhibition of hypusine synthesis can potentiate the anti-cancer activity of the anti-tumour agents interferon-alpha (IFN alpha) and cytosine arabinoside (ara-C). We have found that IFN alpha increased epidermal growth factor receptor (EGF-R) expression, but reduced S phase and proliferative marker expression in human epidermoid KB cells and that this effect was antagonised by epidermal growth factor (EGF). Growth inhibition induced by IFN alpha was paralleled by decreased hypusine synthesis and, when EGF counteracted anti-proliferative effects, a reconstitution of hypusine levels was recorded. We also studied the effects of IFN alpha on the cytotoxicity of the recombinant toxin TP40 which inhibits elongation factor 2, another step of protein synthesis, through EGF-R binding and internalisation; IFN alpha induced an about 27-fold increase of TP40 cytotoxicity in KB cells. Ara-C, another antineoplastic agent commonly used in haematologic malignancies, induced both apoptosis and iron depletion in human acute myeloid leukaemic cells. The combination of ara-C and of the iron chelator desferioxamine, a strong inhibitor of hypusine synthesis, had a synergistic activity on apoptosis in these cells. The data strongly suggest that the post-translational modifications of eIF-5A could be a suitable target for the potentiation of the activity of anti-cancer agents.

Synergistic induction of ornithine decarboxylase by asparagine and gut peptides in intestinal crypt cells

The objective of this study was to determine whether the amino acid asparagine stimulated the activity of ornithine decarboxylase (ODC) synergistically with epidermal growth factor (EGF) or gastrin in IEC-6 cells, a line of normal rat small intestinal crypt cells. Cells were grown in DMEM containing 5% dialyzed fetal bovine serum, and serum was deprived for 24 h before experiments. Exposure to EGF or gastrin alone increased ODC activity 4.5- to 6-fold. Asparagine alone increased the enzyme activity 10- to 13-fold in IEC-6 cells. Simultaneous addition of asparagine and EGF or gastrin, however, increased ODC activity more than 40-fold. In contrast, there was no synergistic induction of ODC activity when gastrin and EGF were added together. Increased ODC activity in cells treated with asparagine and EGF or gastrin was associated with an increase in ODC mRNA and protein levels. The rate of transcription of the ODC gene was significantly increased by exposure to EGF or gastrin. Asparagine alone had little or no effect on the rate of transcription of the ODC gene. When given together with EGF or gastrin, asparagine also had no additional effect on the transcription rate of the ODC gene. The half-life of mRNA for ODC in unstimulated IEC-6 cells was approximately 30 min and increased to more than 2 h in cells exposed to asparagine, although neither gastrin nor EGF prolonged the stability of ODC mRNA. The half-life of mRNA for ODC after combined addition of asparagine and EGF or gastrin was extended to approximately 2 h, similar to asparagine alone. Combined addition of asparagine and EGF or gastrin also significantly increased DNA synthesis compared with cells exposed to each of the three agents alone. In conclusion, 1) simultaneous addition of asparagine and EGF or gastrin increases ODC activity in a synergistic manner and 2) asparagine increases ODC mRNA levels through completely distinct mechanisms from EGF or gastrin. EGF or gastrin specifically stimulates transcription of the ODC gene, whereas asparagine affects a posttranscriptional process.

Premature stimulation of rat sucrase-isomaltase (SI) by exogenous insulin and the analog B-Asp10 is regulated by a receptor-mediated signal triggering SI gene transcription

The mechanism(s) by which insulin enhance prematurely the activity of brush border membrane (BBM) hydrolases in rat immature intestine is unknown. Therefore, we have compared the responses of four BBM enzymes [sucrase-isomaltase (SI), maltase, lactase-phloridzine hydrolase (LPH), and aminopeptidase] with exogenous insulin, the analog B-Asp10, IGF-I, and antireceptor MAb [insulin-receptor (IR) MAb] given to preweaning pups. Low doses of insulin caused a precocious induction of SI and of SI mRNA and stimulated maltase activity without effect on LPH nor on aminopeptidase activities. IGF-I given at the same dose as that of insulin had no detectable effect on these enzymes. Administration to sucklings of IR MAb prevented the effect of endogenous insulin by inhibiting the expression of SI and maltase without effect on LPH activity. B-Asp10, an insulin analogue that exhibits in vitro a 3.5-fold increase in receptor affinity with sustained signaling of the receptor tyrosine kinase, caused an overexpression of SI by 3.5-fold and of maltase by 1.5-fold compared with equivalent doses of normal insulin. The premature increases in SI activity, SI mRNA, and maltase activity in response to insulin were dose-dependent and were associated with dose-dependent increases in intracellular spermine and spermidine concentrations. In conclusion, these data suggest that the premature induction of SI by insulin is mediated by a dose-dependent signal initiated by binding of the hormone to its intestinal receptor, which after transduction into the cell indirectly triggers the transcription of the SI gene, possibly by changes in intracellular polyamine concentrations.

Polyamine deficiency alters EGF receptor distribution and signaling effectiveness in IEC-6 cells

Cell growth and migration are essential processes for the differentiation, maintenance, and repair of the intestinal epithelium. Epidermal growth factor (EGF) is an important factor in the reorganization of the cytoskeleton required for both processes. Because we had previously found significant changes in the cytoskeleton during polyamine deficiency, it was of interest to know whether those changes could prevent EGF from stimulating growth and migration. Polyamine biosynthesis in IEC-6 cells was interrupted by treatment with alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase, the primary rate-limiting enzyme of polyamine biosynthesis. DFMO halted cell proliferation and inhibited cell migration, and neither function could be normally stimulated by EGF. Immunocytochemistry of the transferrin receptor (used as a marker for the endocytic pathway) revealed an abnormal distribution of the EGF receptor (EGFR) 10 min after binding EGF. Polyamine deficiency depleted the cells of interior microfilaments, thickened the actin cortex, and prevented the prompt association of EGF-bound EGFR with actin. EGF-stimulated 170-kDa protein tyrosine phosphorylation and the kinase activity of purified membrane EGFR were reduced by 50%. Immunoprecipated EGFR protein concentration, however, was not reduced by polyamine deficiency. All of these changes could be prevented by supplementation with putrescine. Cytoskeletal disruption, reduced EGFR phosphorylation and kinase activity, aberrant intracellular EGFR distribution, and delayed association with actin filaments suggest a partial explanation for the dependence of epithelial cell growth and migration on polyamines.

Polyamines in goat's colostrum and milk

The concentration and secretion of putrescine (PTR), spermidine (SPD), and spermine (SPM) was examined in colostrum and milk of 60 dairy goats (Polish White and German Brown) during 90 days of lactation. It has been found that milk polyamine pattern is related to breed, age, offspring number, lactation period, milking time, and individual goat-to-goat variations. The mean level of PTR and SPD was significantly higher, whereas SPM level was significantly lower in German Brown than Polish White goats. These differences were maintained during whole observation period (90 days after parturition). Elder goats, bearing two and three kids, secreted colostrum with a higher concentration of PTR and a lower concentration of SPD than young goats having one kid. There was a highly significant positive relationship between the age or litter total weight and PTR concentration in colostrum of Polish White goats. In contrast to PTR, the SPD level was negatively correlated with the age or litter total weight. The daily secretion of PTR, SPD, and SPM progressively increased from the 1st to 90th day of lactation. It was dependent on the increase of milk secretion rate, which could be illustrated by the highly significant correlation between daily milk yield and secretion of SPD in milk of German Brown and Polish White goats. The concentration of SPD in milk sampled in the evening was usually higher than in that from morning milking, however, significant only in the case of German Brown goats. In general, goat's colostrum and milk are rich in polyamines, which the total concentration is the highest when compared to milk of other mammals examined so far (e.g., human, rat, sow, and cow).

Interferon alpha2 recombinant and epidermal growth factor modulate proliferation and hypusine synthesis in human epidermoid cancer KB cells

We previously found that interferon alpha2 recombinant (IFNalpha) increases the expression of epidermal growth factor receptor (EGF-R) in the human epidermoid cancer KB cell line. Here we report the effects of IFNalpha and epidermal growth factor (EGF) on KB cell cycle kinetics. IFNalpha (1000 i.u./ml) for 48 h decreased the S-phase fraction and diminished the expression of Ki67 and proliferating cell nuclear antigen on KB cells. Incubation of IFNalpha-treated KB cells with 10 nM EGF for 12 h reversed these effects. We then studied several biochemical markers of cell proliferation. Ornithine decarboxylase activity was decreased to about one-tenth by IFNalpha and partly restored by EGF. Hypusine is contained only in eukaryotic initiation factor 5A and its levels are correlated with cell proliferation. IFNalpha decreased hypusine synthesis by 75%; exposure of cells to EGF for 12 h restored hypusine synthesis almost completely. We also studied the effects of IFNalpha on the cytotoxicity of the recombinant toxin TP40, which inhibits elongation factor 2 through EGF-R binding and internalization. IFNalpha greatly enhanced the TP40-induced inhibition of protein synthesis in KB cells. In conclusion, IFNalpha, which affects protein synthesis machinery and increases EGF-R expression, enhances the tumoricidal activity of TP40 and hence could be useful in the setting of anti-cancer therapy.

Polyamine transport in mammalian cells. An update

The uptake and release of the natural polyamines putrescine, spermidine and spermine by mammalian cells are integral parts of the systems that regulate the intracellular concentrations of these biogenic amines according to needs. Although a general feature of all tissues, polyamine uptake into intestinal mucosa cells is perhaps the most obvious polyamine transport pathway of physiological and pathophysiological importance. Mutant cell lines lacking the ability to take up polyamines from the environment are capable of releasing polyamines. This indicates that uptake and release are functions of two different transport systems. The isolation of a transporter gene from a mammalian cell line is still lacking. Overaccumulation of polyamines is controlled by release and by a feedback regulation system that involves de novo synthesis of antizyme, a well known protein that also regulates the activity of ornithine decarboxylase. Recent work has demonstrated that Ca(2+)-signalling pathways are also involved. Although there is consensus about the importance of polyamine uptake inhibitors in the treatment of neoplastic disorders, a practically useful uptake inhibitor is still missing. However, the attempts to target tumours, and to increase the selectivity of cytotoxic agents by combining them with the polyamine structure, are promising. New, less toxic and more selective anticancer drugs can be expected from this approach.