Human GM3 synthase:: A new mRNA variant encodes an NH2-terminal extended form of the protein
Human GM3 synthase:: A new mRNA variant encodes an NH2-terminal extended form of the protein
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DOI：
10.1016/j.bbaexp.2006.07.001
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发表时间：
2006-07-01
期刊：
影响因子：
--
通讯作者：
Colombo, Irma
中科院分区：
文献类型：
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作者：
Berselli, Patrizia;Zava, Stefania;Colombo, Irma
到目前为止，所有人类GM（3）合酶mRNA变异体都预测了一种362个氨基酸的蛋白质，其底物活性高度限于乳糖神经酰胺。在这份报告中，我们描述了一个新的GM 3合酶转录含有一个额外的翻译起始密码子，位于上游和框内，到目前为止被认为是独特的翻译起始位点在人类GM 3合酶基因的鉴定。体外表达研究表明，新的转录本产生更长形式的人GM 3合酶，其有效地易位到微粒体腔中并糖基化。此外，稳定的cDNA转染到哺乳动物细胞中引起GM 3合酶活性的三倍增加，与更广泛的底物特异性相关。尽管这种转录本最初在人胎盘中被鉴定，但RT-PCR分析证实了在未分化的HL 60细胞中也有相同的mRNA表达，但在单核细胞谱系中没有。总之，这些结果是第一次证明存在一种新的人GM 3合酶亚型，它可能在HL 60细胞分化过程中发挥重要作用。还讨论了GM 3合酶的两种异构体的存在的功能相关性。(c)2006 Elsevier B. V.保留所有权利。
All human GM(3) synthase mRNA variants until now identified predict a protein of 362 amino acids having substrate activity highly restricted to lactosylceramide. In this report we describe the identification of a new GM3 synthase transcript containing an additional translation start codon, located upstream and in-frame with that up to now considered unique translation initiation site in the human GM3 synthase gene. In vitro expression studies showed that the new transcript produces a longer form of human GM3 synthase, that is efficiently translocated into the microsomal lumen and glycosylated. Moreover, stable cDNA transfection into mammalian cells gives rise to a threefold increase of GM3 synthase activity, associated to a broader substrate specificity. Although this transcript has been initially identified in the human placenta, RT-PCR analyses verified the expression of an identical mRNA also in undifferentiated HL60 cells, but not in the monocytic lineage. Altogether, these results are the first demonstration of the existence of a new isoform of human GM3 synthase, which could play an important role during HL60 cell differentiation. The functional relevance of the existence of two isoforms of GM3 synthase is also discussed. (c) 2006 Elsevier B.V. All rights reserved.