Glucose elevates ornithine decarboxylase expression in vero cells

Abstract

The addition of Earle's balanced salt solution (EBSS) of amino acids that are transported by a Na+-dependent cotransport system was not required by Vero cells for ornithine decarboxylase (ODC:EC 4.1.1.17) amplification. Vero cell ODC activity was elevated tenfold above basal levels when confluent cells were incubated for 5 hr in EBSS alone. ODC activity increased as a function of the incubation time in EBSS and was not elevated above basal enzyme levels when cells were incubated in EBSS minus glucose. ODC expression increased as a function of the glucose concentration in EBSS, with 20 mM glucose producing a 90-fold increase in ODC activity. ODC expression is more responsive to glucose in high-density quiescent cultures than in low-density growing cultures. Enhanced ODC expression by glucose depended on Na+ and K+ concentrations. The specific activity of ODC was also elevated above basal levels when mannose or fructose replaced glucose in EBSS. The addition of alanine or asparagine to EBSS enhanced ODC activity above levels obtained with EBSS containing standard (5.5 mM) glucose concentrations. In the absence of glucose, alanine was more effective than asparagine in enhancing ODC expression. These results suggest that the transport of amino acids is not an absolute requirement for Vero cell ODC expression and that ODC expression is linked to changes in cellular energetics and/or ion fluxes.

N-ω-chloroacetyl-l-ornithine, a new competitive inhibitor of ornithine decarboxylase, induces selective growth inhibition and cytotoxicity on human cancer cells versus normal cells

“…We selected the non-tumorigenic Vero lineage as control cell line 53,54 . Administration of NCAO resulted in decreased cell viability and increased growth inhibition in a dose-and time-dependent manner, according to the trypan blue assay.…”

Sodium-dependent co-transported analogues of glucose stimulate ornithine decarboxylase mRNA expression in LLC-PK1 cells

“…Frozen cell suspensions were thawed and cell homogenates were prepared as previously described [9]. A sample (0.6 ml) of cell supematant was added to 0.35 ml of ODC buffer and preincubated for 10 min at 37°C in a shaking water bath.…”

“…The assay was stopped after 60 min by addition of 0.5 ml of citric acid. Released 14CO2 was trapped in Hyamine hydroxide, and radioactivity was determined as previously described [9].…”

“…It has been recognized for a number of years that the addition of amino acids to tissue-culture media increases the specific activity of ornithine decarboxylase (ODC) [1,2], a key enzyme in the regulation of polyamine biosynthesis (for review of this system see [3]). It is now well established that Na+-dependent cotransported amino acids, but not amino acids that are transported by passive carrier-mediated systems, enhance ODC expression in a wide variety of different types of cultured cells, including neuroblastoma [4,5], Chinese-hamster ovary [6], rat glioma [7], rat hepatocytes [8], monkey kidney [9] and pig kidney [10]. In the absence of Na+-dependent co-transported amino acids, glucagon [8] and nerve growth factor or epidermal growth factor [51 were reported to be incapable of inducing ODC in their respective target cells.…”

“…balanced salts solution (EBSS) in the absence of any amino acids [9]. In the same study it was shown that the ability of glucose to increase Vero-cell ODC activity is dependent on the extracellular concentration of Na+, suggesting that this ion could have a role in regulating the activity of this enzyme.…”