Differential post‐transcriptional control of ornithine decarboxylase and spermidine‐spermine N¹‐acetyltransferase by polyamines

Abstract

Ornithine decarboxylase (ODC) and spermidine/ spermine NLacetyltransferase (SSAT) are short-lived polyamine enzymes with rate-limiting roles in controlling polyamine biosynthesis and catabolism, respectively. We have found that treatment of MALME-3M human melanoma cells for 6 h with 10 ~tglml cycloheximide (CHX) increases ODC and SSAT mRNA 6-9-fold. When cells containing CHX-induced SSAT mRNA were washed and post-incubated for an additional 6 h in drug free media, enzyme activity increased only 2-fold above that in untreated ceils despite the > 6-fold increase in accumulated mRNA. Inclusion of 10 ~VI spermine or spermidine in the postincubation medium increased SSAT activity ,~ 7-fold without further elevating SSAT mRNA levels. This indicates posttranscriptional regulation which, due to the similarity between polyamine-mediated increases in SSAT activity and available mRNA, probably occurs at the level of mRNA translation. In contrast to the SSAT response, polyamines markedly reduced ODC activity (but not mRNA) to one sixth that in cells not exposed to polyamines. The findings illustrate how via posttranscriptional mechanisms, shifts in intracellular polyamine pools can simultaneously and differentially regulate polyamine biosynthesis and catabolism. It is hypothesized that these posttranscriptional responses enable cells to rapidly and sensitively control intracellular spermidine and spermine pools.

Activated Polyamine Catabolism Depletes Acetyl-CoA Pools and Suppresses Prostate Tumor Growth in TRAMP Mice

“…As shown in Table II, SSAT activity in the prostate tissue was elevated ϳ20-fold in both the SSAT and TRAMP/SSAT mice compared with wildtype and TRAMP mice. The more modest 2-3-fold enhancement of SSAT activity in the liver despite a 20-fold increase SSAT mRNA (38,39) would seem to reflect tissue-specific translational control of this gene (38,39). Increases in SSAT activity were accompanied by a profound (i.e.…”

“…SSAT expression in the prostates and livers from SSAT transgenic mice. Total RNA was isolated from the prostates and livers of littermates obtained from the TRAMP ϫ SSAT cross and subjected to Northern blot analysis and enzyme activity assay (33,39). Note the presence of a 3-kb heteronuclear SSAT RNA and a 1.7-kb mature SSAT mRNA.…”

Loss of inhibitor of apoptosis proteins as a determinant of polyamine analog-induced apoptosis in human melanoma cells

“…Total RNA was isolated using the RNeasy minikit (Qiagen, Valencia, CA, USA) and Northern blot analysis of survivin mRNA from untreated and 10 mm DENSPM-treated cells was conducted as reported previously (Fogel-Petrovic et al, 1996). Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) cDNA (Clontech Laboratories, Inc., Palo Alto, CA, USA) was used to evaluate loading.…”

Disrupted Spermine Homeostasis: A Novel Mechanism in Polyglutamine-Mediated Aggregation and Cell Death

“…SSAT mRNA and protein expression are tightly regulated by intracellular polyamine levels and are part of a feedback system controlling cytosolic spermine concentrations (Porter et al, 1990). Thus, SSAT mRNA increases with increased cytosolic spermine concentration (Shappell et al, 1993;Fogel-Petrovic et al, 1996;Shantz and Pegg, 1999;Suppola et al, 2001). No significant differences were observed in the basal level of SSAT mRNA between polyQ19-YFP and polyQ57-YFP CAD cells.…”

“…8). Despite disruption of synthetic pathways, changes in intracellular spermine levels are difficult to observe because of multilevel homeostatic mechanisms controlling spermine concentrations (Porter et al, 1990;Halmekyto et al, 1991;Fogel-Petrovic et al, 1996;Hayashi et al, 1996;Pietila et al, 1997;Morrison et al, 1998;Kepka-Lenhart et al, 2000;Suppola et al, 2001). SSAT, the enzyme that catalyzes the back-conversion of spermine to N-acetyl forms, is tightly regulated by intracellular spermine.…”