Cloning and Characterization of a Human Polyamine Oxidase That is Inducible by Polyamine Analogue Exposure

Mammalian polyamine catabolism is under the control of two enzymes, spermidine/spermine N1-acetyltransferase and the flavin adenine dinucleotide-dependent polyamine oxidase (PAO). In this study, the cloning and initial characterization of human PAO is reported. A 1894-bp cDNA with an open reading frame of 1668-bp codes for a protein of 555 amino acids. In vitro transcription/translation of this cDNA clone produces the expected M(r) 61,900 protein with PAO activity. The PAO activity of this clone is inhibited by MDL 72,527, a specific inhibitor of mammalian PAO. However, neither pargyline, a specific monoamine oxidase inhibitor, nor semicarbazide, a specific diamine oxidase inhibitor, inhibits the PAO activity of this clone. PAO has been referred to as being constitutively expressed. However, 24-h exposure of a non-small cell lung carcinoma cell line, NCI H157, to 10 microM of N1,N"-bis(ethyl)norspermine results in approximately 5-fold induction of PAO mRNA and a >3-fold induction of PAO activity. These results demonstrate that in at least one cell type, PAO is up-regulated in response to polyamine analogue exposure. The PAO clone described here should provide a useful tool, which will facilitate the dissection of the role of polyamine catabolism in normal growth and in response to the antitumor polyamine analogues.