Efflux of polyamines from human lymphocytes and from L 1210 cells

Modified responses to PGE2 in polyamine biosynthesis by T lymphocytes of gastric- and conjunctiva basal cell-carcinoma patients

The response to Prostaglandin (PG) E2 of T cells from gastric carcinoma (GC)- and conjunctiva-basal cell carcinoma (conjunctiva-BCC)-bearing patients has been studied in relation to polyamine metabolism. Polyamines are crucial co-factors in cell growth as well as differentiation and many works report that lymphocyte spermine (SP), spermidine (SPD) and putrescine (PUT) levels may be related to tumor proliferation. The present work aims to detect the basal and PGE2 induced concentrations of these polyamines and cAMP, ornithine decarboxylase (ODC), spermine N1-acetyltransferase (SAT) activities of T lymphocytes drawn from patients suffering from GC and conjunctiva-BCC since many carcinomas are characterized by high levels of PGE2. Data obtained from lymphocytes of neoplastic subjects were compared with those derived from PGE2-treated control lymphocytes. Results highlight a very significant increase of all the polyamine metabolites in PGE2-treated T cells from neoplastic patients in respect to the untreated and PGE2-treated control lymphocytes. Therefore, it is conceivable that the PGE2 content increase, often occurring during the epithelial tumour development, may contribute, through enhancement of polyamine metabolism, to tumor progression.

JAR human placental choriocarcinoma cells actively synthesize, take up and release polyamines

Uptake of polyamines has been investigated extensively in many cells, but not in placenta, where the polyamine-polyamine oxidase system is supposed to have an immunoregulatory function in pregnancy. Due to the importance of the transfer in this tissue, we have started this study. JAR human placental choriocarcinoma cells in monolayer at confluency were used as a model for measuring the key enzymes of polyamine synthesis and interconversion, rate of uptake and efflux, and the polyamine content. Polyamines were taken up by JAR cells and released by an independent mechanism. Ornithine decarboxylase and spermidine acetyltransferase activities and the rate of transport in and out of the cell were much higher than in other cells, such as L1210 cells. However the systems used for uptake and release appear in many respects to be similar to those observed in L1210 cells, but different from others. The uptake appears to be regulated by an inhibitory protein. Moreover, protein kinase C appears to be involved in the process. The efflux also is regulated as in L1210 cells, through control of H+ and Ca2+ concentration. In conclusion, this study shows that, in JAR cells, ornithine decarboxylase and spermidine acetyltransferase activities were much higher than in other cells, and so was the rate of transport in and out of the cells. As a result, a much higher polyamine content was observed.

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.

A kinetic characterization of putrescine and spermidine uptake and export in human erythrocytes

Using human erythrocytes as a model system for the study of mammalian polyamine transport, detailed kinetic parameters regarding the uptake and export of putrescine and spermidine were determined. The putrescine uptake data indicated a multi-component uptake system comprised of a low-capacity saturable component and a non-saturable component. The saturable putrescine uptake component demonstrated a calculated Km of 21.0 microM and a V(max) of only 6.52 x 10(-13) M/s. The non-saturable linear putrescine uptake rate was defined by a significant pH dependence, a lack of uptake inhibition by related polyamines, and a permeability pi of 3.19 x 10(-8) s-1. These findings suggested that non-saturable putrescine uptake involved a process of simple diffusion. Spermidine uptake exhibited Michaelis-Menten kinetics with a Km and Vmax of 12.5 microM and 1.36 x 10(-12) M/s, respectively. Spermidine uptake did not demonstrate pH dependence and was not significantly inhibited by any of the tested polyamines. The Arrhenius plot of spermidine uptake was determined to be biphasic with calculated activation energies of spermidine uptake of 135.2 kJ/mol for 19-21 degrees C and 59.3 kJ/mol for 21-35 degrees C. These data suggest the possibility of multiple spermidine uptake processes which are not mediated by simple diffusion across the cell membrane. The putrescine export process demonstrated both saturable and non-saturable components. The calculated Km, V(max) and pi for putrescine export were 33.8 microM, 1.19 x 10(-11) M/s and 2.81 x 10(-7) s-1, respectively. The spermidine export process was non-saturable up to intracellular spermidine concentrations of 4 microM. At similar intracellular and extracellular concentrations of putrescine and spermidine, however, export processes displayed rates which were an order of magnitude greater than their respective uptake rates. This finding supports the possible presence of mediated putrescine and spermidine export processes different than simple diffusion.

Characterization of putrescine and cadaverine export in mammalian cells. A pharmacological approach

We characterized the mechanism(s) involved in the efflux of putrescine/cadaverine from cultured mammalian cells using various pharmacological agents. Verapamil and quinine inhibited putrescine and cadaverine export in monocytic-leukemic RAW 264 and H35 hepatoma cells in a concentration-dependent manner with an IC50 in the micromolar range. Verapamil, which inhibits L-type calcium channels, inhibited putrescine export, regardless of whether calcium was present in the extracellular medium or not. Furthermore, the export of putrescine in the absence of verapamil did not appear to depend upon extracellular calcium. Neither intracellular calcium, external sodium, changes in intracellular pH nor phosphorylation affected the levels of putrescine export independently from changes in intracellular putrescine levels. The data suggest that verapamil and quinine inhibit putrescine/cadaverine efflux from the cell by binding directly to an integral membrane protein.

Characterization of a COS cell line deficient in polyamine transport

In the present study, we describe the isolation and characterization of a COS cell line deficient in polyamine uptake that may provide an important tool for the molecular cloning of polyamine transporter(s). The cells were selected by isolation for resistance against the cytotoxic agent, methylglyoxal bis(guanylhydrazone) (MGBG), which is entering the cells using the same transport system as the polyamines. The isolated cell line was capable of growing in the presence of 100 microM MGBG, which totally inhibited the growth of the wild-type cells. The transport of putrescine and spermidine was markedly decreased in the COS-MGBGr cells. The decrease in putrescine transport was mainly a result of a 14-fold decrease in Vmax, whereas the reduced spermidine uptake was due to a 3-4-fold decrease in Vmax as well as 12-fold increase in Km, indicating the existence of at least two separate transport systems. No major difference in polyamine content was seen between the parental and the COS-MGBGr cells when grown without MGBG. In the presence of MGBG, both cell lines exhibited an increase in putrescine content. Treatment with MGBG also resulted in a decrease in spermidine and spermine contents in the wild-type cells. In the COS-MGBGr cells, on the other hand, there were no statistically significant effects on the spermidine and spermine contents by MGBG treatment. In the wild-type cells, depletion of polyamines, e.g., by treatment with the ornithine decarboxylase inhibitor 2-difluoromethylornithine (DFMO), stimulated the uptake of polyamines (3-7-fold), whereas in the COS-MGBGr cells the effect of DFMO treatment on polyamine transport was only minor. In contrast to the growth-medium of the wild-type cells, large amounts of polyamines accumulated in the medium of the COS-MGBGr cells, presumably indicating that COS cells normally excrete polyamines and then salvage them using the polyamine transport system.