Effects of polyamines, polyamine analogs, and inhibitors of protein synthesis on spermidine-spermine N-1-acetyltransferase gene expression
Effects of polyamines, polyamine analogs, and inhibitors of protein synthesis on spermidine-spermine N-1-acetyltransferase gene expression
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DOI：
10.1021/bi9612273
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发表时间：
1996-11-12
期刊：
影响因子：
2.9
通讯作者：
Porter, CW
中科院分区：
文献类型：
--
作者：
FogelPetrovic, M;Vujcic, S;Porter, CW
关键的多胺分解代谢酶亚精胺-精胺N-1-乙酰转移酶(SSAT)是已知的为数不多的被天然多胺诱导的基因之一。某些多胺类似物明显夸大了这种反应，因此为研究潜在的调节机制提供了有用的工具，如图所示，最有效地诱导SSAT活性的类似物N-1，N-11-二乙基去甲精胺(DENSPM)使Malme-3M人类黑色素瘤细胞中的SSAT mRNA最大增加20倍，免疫可检测的SSAT蛋白增加300倍。相比之下，天然多胺精胺的效果要差得多，SSAT的mRNA增加了3倍，蛋白质增加了7倍，尤其是精胺和类似物在基因转录和mRNA稳定方面的差异被证明是由于不同的影响。虽然类似的DENSPM被认为是最有效的SSAT活性和mRNA的诱导剂，但我们现在报道，蛋白质合成的抑制剂能够将SSAT mRNA增加到几乎类似的水平。抑制剂诱导的SSAT基因表达增加涉及基因转录和mRNA稳定；这表明，在基础条件下，SSAT基因的表达被一种或多种不稳定的蛋白质抑制。蛋白质合成抑制剂仅在阻止蛋白质合成的浓度下诱导SSAT mRNA，而DENSPM则在不阻止蛋白质合成的浓度下诱导SSAT mRNA。蛋白抑制剂与DENSPM或精胺联合使用可增加SSAT mRNA的表达。综上所述，这些发现提示在SSAT基因的调控中有两条独立但可能汇聚的途径，一条是由多胺及其类似物介导的，另一条是由SSAT基因转录和/或mRNA稳定的不稳定抑制因子介导的。除了其明显的调控重要性，由蛋白质合成抑制剂诱导SSAT mRNA是研究这一有趣基因转录后调控的一个潜在有用的系统。
The key polyamine catabolizing enzyme spermidine-spermine N-1-acetyltransferase (SSAT) is among the few genes known to be inducible by the natural polyamines. Certain polyamine analogs markedly exaggerate this response and thus provide useful tools for studying the underlying regulatory mechanisms, As shown here, the analog which most potently induces SSAT activity, N-1,N-11-diethylnorspermine (DENSPM), increases SSAT mRNA in MALME-3M human melanoma cells to a maximum of >20-fold and immunodetectable SSAT protein to >300-fold. By comparison, the natural polyamine spermine is far less effective, increasing SSAT mRNA by similar to 3-fold and protein by similar to 7-fold, In particular, the difference in mRNA accumulation by spermine and the analog was shown to be due to differential effects on both gene transcription and mRNA stabilization. Although the analog DENSPM has been regarded as the most potent inducer of SSAT activity and mRNA, we now report that inhibitors of protein synthesis are capable of increasing SSAT mRNA to nearly comparable levels. Inhibitor-induced accumulation in SSAT mRNA was shown to involve increased gene transcription and mRNA stabilization; This suggests that, under basal conditions, SSAT gene expression is suppressed by a labile protein (or proteins). While induction of SSAT mRNA by inhibitors of protein synthesis only occurred at concentrations which blocked protein synthesis, that by DENSPM took place at concentrations which did not. The combination of either protein inhibitor with DENSPM or spermine produced an additive increase in SSAT mRNA. Taken together, these findings suggest the involvement of two separate but possibly converging pathways in the regulation of SSAT mRNA, one mediated by polyamines and their analogs and the other mediated by a labile repressor of SSAT gene transcription and/or mRNA stabilization. In addition to its apparent regulatory importance, induction of SSAT mRNA by inhibitors of protein synthesis represents a potentially useful system for studying the posttranscriptional regulation of this interesting gene.