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

Abstract

We have previously shown that the clinically relevant polyamine analog N 1 ,N 11 -diethylnorspermine (DENSPM) causes rapid apoptosis in human melanoma SK-MEL-28 cells via a series of events that include mitochondrial release of cytochrome c and activation of the caspase cascade. Upstream to these events, DENSPM downregulates polyamine biosynthesis and potently upregulates polyamine catabolism at the level of spermidine/spermine N 1 -acetyltransferase (SSAT). In searching for downstream effectors that either contribute to or abrogate the apoptotic response, we observed that DENSPM treatment of SK-MEL-28 cells for 30 h led to cytosolic release of Smac/Diablo, a mitochondrial protein known to bind and inhibit the function of inhibitor of apoptosis proteins (IAPs). Subsequently, we found that DENSPM markedly lowered survivin and ML-IAP protein (but not XIAP) levels by 18 h via an apparently Smac/Diablo-independent pathway. Proteasome inhibitors fully prevented survivin and ML-IAP protein loss as well as apoptosis, suggesting that the proteasome-mediated degradation of survivin and ML-IAP is causally linked to the cellular outcome. We also observed that structural analogs of DENSPM which differentially induced SSAT and apoptosis lowered survivin and ML-IAP levels in a manner that correlated with enzyme activity. The linkage between IAPs and SSAT was more directly established by the finding that selective prevention of SSAT induction by small interfering RNA prevented survivin and ML-IAP loss as well as apoptosis during DENSPM treatment. Among the melanoma cell lines (SK-MEL-28, MALME-3M, A375 and LOX), survivin degradation correlated temporally with the onset of DENSPM induced apoptosis or growth inhibition. By contrast, ML-IAP degradation occurred only during rapid apoptosis seen in SK-MEL-28 cells. These data suggest a sequence of events whereby DENSPM induction of SSAT leads to loss of IAP proteins and a more fulminate apoptotic response. The findings implicate survivin and ML-IAP as important determinants of polyamine analog drug action in melanoma cells.

Metabolic and Antiproliferative Consequences of Activated Polyamine Catabolism in LNCaP Prostate Carcinoma Cells

“…Thus, the seemingly modest 20-fold increase in SSAT activity seen here in LNCaP cells resulted in exceedingly high levels of intracellular and extracellular acetylated polyamines, which undoubtedly had a profound impact on the metabolic equilibrium of polyamines. We also note that enzyme induction is also associated with polyamine species such as DiAcSpm that are rarely seen in cells unless SSAT is overexpressed (31) or analogue-induced (29).…”

“…As more direct evidence for this relationship, McCloskey et al (28) showed that DENSPM-resistant Chinese hamster ovary cells are unable to induce SSAT. Recently, Chen et al (29,30) reported that small interference RNA interference with DENSPM induction of SSAT prevented polyamine pool depletion while blocking analogue-induced apoptosis in human melanoma cells.…”

Modulation of pro- and anti-apoptotic factors in human melanoma cells exposed to histone deacetylase inhibitors

“…Recently, an analogue of polyamine was demonstrated to cause rapid apoptosis in human melanoma SK-Mel28 cells degrading survivin. 34 Accordingly, the attenuation of survivin expression was demonstrated to make human melanomas more suscep- Table 2. Effect of VPA on VPA-sensible and -resistant human melanoma cell lines.…”

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

“…Correlations between SSAT induction and growth inhibition have been repeatedly suggested by early work in a variety of tumor types (14,16,17). Recently that relationship was more precisely defined by the finding that SSAT-targeted small interfering RNA minimizes analogue-mediated enzyme induction and at the same time prevents polyamine pool depletion and apoptosis (18,19).…”