Role of Polyamines in the Control of Cell Proliferation and Differentiation

7 – Polyamine Metabolism

Publisher Summary This chapter investigates the links between polyamines and tumors. It is particularly interesting to modify the culture conditions to clarify the influence of the environmental milieu on the activities of the polyamine biosynthetic enzymes by enhancing or decreasing the levels of these enzymes to see the role of polyamines in the cell growth process. To this purpose, several studies have been carried out with rat hepatoma cells growing in culture. Studies of the effects of growth conditions on ornithine decarboxylase (ODC) activity presents evidence that dilution of high-density hepatoma cell cultures with fresh medium results in a very large and transient increase in enzyme activity. Furthermore, among the factors affecting the growth conditions of the cultured cells, the addition of fresh medium or serum to the culture has been demonstrated to be one of the most important for a variety of other cell lines. In spite of the decades of research, most of the role of polyamines in eliciting the peculiar neoplastic behavior and in permitting invasive neoplastic growth remains unclear.

Polyamines in mammalian tumors. Part I.

Cystathionine gamma-synthase, the first committed enzyme of methionine biosynthesis in higher plants, is encoded by the CGS1 gene in Arabidopsis thaliana. We have shown previously that the stability of the CGS1 mRNA is negatively regulated in response to methionine application [Chiba, Y., Ishikawa, M., Kijima, F., Tyson, R. H., Kim, J., Yamamoto, A., Nambara, E., Leustek, T., Wallsgrove, R. M. & Naito, S. (1999) Science 286, 1371-1374]. To determine whether methionine itself is the effector of the CGS1 exon 1-mediated posttranscriptional regulation, we carried out transfection experiments. The results suggested that, rather than methionine, S-adenosyl-L-methionine (AdoMet), or one of its metabolites, acts as the effector of this regulation. To further identify the actual effector, we exploited the wheat germ in vitro translation system. The effects of various metabolites and analogs of AdoMet were tested by using RNA carrying a CGS1 exon 1-reporter fusion. These tests identified AdoMet as the effector of this regulation. S-adenosyl-L-ethionine, an analog of AdoMet, also had effector activity. A. thaliana mto1 mutants, which are deficient in this regulation, showed a much reduced response to AdoMet in vitro, with a leaky allele showing a less reduced response. RNA translated in vitro in the presence of AdoMet contained a 5'-truncated RNA species, similar to the one that we previously suggested was an in vivo degradation intermediate of CGS1 mRNA. Together, the results show that the basic reactions of CGS1 exon 1-mediated posttranscriptional regulation occur in the wheat germ in vitro translation system, and that AdoMet acts as the effector.

S-adenosyl-l-methionine is an effector in the posttranscriptional autoregulation of the cystathionine γ-synthase gene in Arabidopsis

Biological transmethylation reactions and polyamine biosynthesis share the substrate S-adenosyl-l-methionine.Under normal conditions, decarboxylated S-adenosyl-l-methionine, the aminopropyl donor for polyamine biosynthesis, does not accumulate because of its rapid utilization in spermidine and spermine synthesis. Alteration of polyamine synthesis by DL-αdifluoromethylornithine, an enzyme-activated irreversible inhibitor of l-ornithine decarboxylase, leads to a striking accumulation of decarboxylated S-adenosyl-l-methionine in rat hepatoma cclls cultured in vitro and in rat ventral prostate. This increase is due both to lack of putrescine and spermidine for the aminopropyltransferase reactions and to the elevation of S-adenosyl-l-methionine decarboxylase activity. The biological implications of accumulation of decarboxylated S-adenosyl-l-methionine are discussed with regard to the regulation of S-adenosyl-l-methionine decarboxylase activity and to the antiproliferative effects of dl-α-difluoromethylornithine.

https://febs.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1432-1033.1982.tb06559.x

Accumulation of decarboxylated S-adenosyl-L-methionine in mammalian cells as a consequence of the inhibition of putrescine biosynthesis.

Decarboxylated S-adenosyl-L-methionine and its nine analogs have been prepared by a modified method of Jamieson including alkylation of the appropriate aminoalkyl-adenosyl thioether with alkyl iodides in a mixture of formic and acetic acids in the presence of silver perchlorate. The use of silver perchlorate allowed various combinations of the thioether and the alkyl iodide, and prompted the reaction. The sulfonium compounds were obtained as a white hygroscopic powder in 99% ethanol after purification by silica gel column chromatography with a solvent system of butanol-acetic acid-water (1 : 1 : 1). The chemical and physical data of the sulfonium compounds supported a general structure containing 2 mol of sulfuric acid and 0.5 mol of ethanol. The nuclear magnetic resonance data showed the existence of sulfonium diastereoisomers.

Yoko Nakazawa

Papers

Improved Synthesis of Decarboxylated S-Adenosylmethionine and Related Sulfonium Compounds

Action of decarboxylated S-adenosylmethionine analogs in the spermidine-synthesizing system from rat prostate

Improved synthesis of decarboxylated s-adenosylmethionine and related sulfonium compounds