Properties and regulation of human spermidine/spermine N1-acetyltransferase stably expressed in Chinese hamster ovary cells.
Spermidine/spermine N1-acetyltransferase (SSAT) appears to be the rate-limiting enzyme of polyamine catabolism, yet studies of its regulation have been limited by the low amounts of SSAT in uninduced cells. A system for studying SSAT was established by stably transfecting Chinese hamster ovary cells with a construct where SSAT cDNA was under control of the cytomegalovirus promoter. Thirteen of 44 clones expressed significantly increased SSAT activity (650-1900 compared with 24 pmol/min/mg protein in control cells). SSAT activity was directly proportional to SSAT protein, which turned over very rapidly (t(1)/(2) of 29 min) and was degraded through the ubiquitin/proteasomal pathway. The increased SSAT activity caused perturbations in polyamine homeostasis and led to a reduction in the rate of growth under clonal conditions. N1,N12-bis(ethyl)spermine greatly increased SSAT activity in controls and SSAT transfected clones (to about 10 and 60 nmol/min/mg protein, respectively). N1, N12-Bis(ethyl)spermine caused an increase in the SSAT half-life and a slight increase in SSAT mRNA, but these changes were insufficient to account for the increase in SSAT protein suggesting that translational regulation of SSAT must also occur.
McCloskey
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DE
Department of Cellular and Molecular Physiology, The Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
Coleman
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CS
Pegg
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D000123:Acetyltransferases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004789:Enzyme Activation; D004795:Enzyme Stability; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D000099228:Diamine N-Acetyltransferase
D000123:Acetyltransferases; D000099228:Diamine N-Acetyltransferase