細胞増殖因子ポリアミンの輸送機構

抄録

The polyamine content in cells is regulated by both polyamine biosynthesis and its transport. We recently obtained and characterized three clones of polyamine transport genes (pPT104, pPT79 and pPT71) in Escherichia coli. The system encoded by pPT104 was the spermidine-preferential uptake system and that encoded by pPT79 the putrescine-specific uptake system. Furthermore, these two systems were ABC (ATP binding cassette) transporters consisting of four kinds of proteins : pPT104 clone encoded PotA, -B, -C, and -D proteins and pPT79 clone encoded PotF, -G, -H, and -I proteins. PotD and -F proteins were periplasmic substrate binding proteins and PotA and -G proteins membrane associated proteins having the nucleotide binding site. PotB and -C proteins, and PotH and -I proteins were transmembrane proteins probably forming channels for spermidine and putrescine, respectively. Their amino acid sequences in the corresponding proteins were similar to each other. The functions of PotA and -D proteins in the spermidine-preferential uptake system encoded by pPT104 clone were studied in detail through a combined biochemical and genetic approach. In contrast, the putrescine transport system encoded by pPT71 consisted of one membrane protein (PotE protein) having twelve transmembrane segments, and was active in both the uptake and excretion of putrescine. The uptake was dependent on the membrane potential, and the excretion was due to the exchange reaction between putrescine and ornithine. In mouse mammary carcinoma FM3A cells, it was shown that the antizyme, which negatively regulates the amount of ornithine decarboxylase, also negatively regulates the activity of polyamine transport.