The level of substrate ornithine can alter polyamine‐dependent DNA synthesis following phorbolester stimulation of cultured hepatoma cells

Abstract

Although the precise intracellular function(s) of the polyamines remain incompletely defined, a myraid of evidence now shows that the polyamines must accumulate or be maintained at a specific intracellular concentration in order for all mammalian cells to grow or divide. The initial step in polyamine biosynthesis normally involves the decarboxylation of ornithine by the enzyme ornithine decarboxylase (ODCase E.C. 4.1.1.17) to yield putrescine. Increases in the steady-state level of intracellular ornithine have been reported to markedly alter the accumulation of the polyamines following stimulation of Reuber H35 Hepatoma cells with 12-O-tetradecanoylphorbol-beta-acetate (TPA) in the presence of serum (Wu and Byus: (Biochem. Biophys. Acta 804:89-99, 1984); Wu et al.: (Cancer Res. 41:3384-3391, 1981). We wished to determine whether or not incubation of H35 hepatoma cells with exogenous ornithine would result in a stimulation of DNA synthesis following treatment with the mitogens TPA and insulin. For these studies, H35 cells were maintained under serum-free conditions for 2-3 days in order to obtain synchronous cultures suitable for analysis of the level of DNA synthesis. Cultures treated in this manner were highly viable, maintained similar growth rates, and possessed the equivalent levels of intracellular ornithine and polyamines as the serum-containing cultures. Arginine levels, however, were approximately twofold higher following culture under serum-restricted conditions for 3 days. The addition of exogenous ornithine (0.5 mM) was accompanied by a 4-5-fold increase in intracellular steady-state ornithine levels and by a 6-8-fold increase in the presence of TPA and ornithine. In a manner identical to the serum-containing cultures (Wu and Byus (1984] the addition of TPA and exogenous ornithine to the serum-free cells caused a dose-dependent increase in intracellular putrescine (up to 5-fold) and a concomitant decrease in ODC activity in comparison to stimulation with TPA alone. The addition of TPA led to a 3-5-fold increase in the incorporation of tritiated thymidine into DNA. In the presence of exogenous ornithine, TPA-induced DNA synthesis was further stimulated more than twofold in a dose-dependent manner. Insulin (10(-10)-10(-8) M) proved to be more efficacious as a mitogen in the H35 cells and led to greater stimulation of DNA synthesis than TPA. Insulin alone also resulted in a higher steady-state level of ornithine and putrescine in comparison with TPA alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of <i>L</i>-Ornithine on Metabolic Processes of the Urea Cycle in Human Keratinocytes

“…A similar result was described by Byus and Wu [19] . They investigated human hepatoma cells (H35) and showed a promotion of proliferation by incubation with 0.5 m M L -ornithine.…”

Urea cycle enzymes through the development of pacu (Piaractus mesopotamicus): the role of ornithine carbamoyl transferase

“…In the period between hatching and the first feeding, there is a decrease of polyamines. The ornithine concentration can be sufficient to supply polyamine synthesis during the development, since the maintenance of the cell polyamine concentration for growing, proliferation (Pilz et al 1990) and DNA synthesis is dependent on it and is altered by the concentration of its precursor, ornithine (Byus and Wu 1991). The ODC gene is housekeeping, and the putrescine production is regulated by polyamine levels in the ODC translation (Matsufuji et al 1996, Saito et al 2000.…”

Alteration of the microRNA-122 regulatory network in rat models of hepatotoxicity

“…Besides, many validated target genes of miRNA-122 are involved in cell proliferation (Tsai et al, 2009). Particularly, CAT-1 is responsible for the transport of the cationic amino acids, and this intake stimulates DNA synthesis for cell replication (Byus and Wu, 1991). Cyclin G1, on the other hand, modulates the G2/M transition of the cell cycle, and experimental evidences obtained in cancer cell lines and tumor xenograft have shown that suppression of Cyclin G1 reduces cell proliferation and induces apoptosis, which leads to the inhibition of tumor growth (Chen et al, 1997;Gordon et al, 2000).…”