Nuclear forms of parathyroid hormone-related peptide are translated from non-AUG start sites downstream from the initiator methionine
Nuclear forms of parathyroid hormone-related peptide are translated from non-AUG start sites downstream from the initiator methionine
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DOI：
10.1210/en.142.2.694
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发表时间：
2001-02-01
期刊：
影响因子：
4.8
通讯作者：
Karaplis, AC
中科院分区：
文献类型：
--
作者：
Nguyen, MTA;He, B;Karaplis, AC
PTH相关肽（PTHrP）通常是一种分泌性蛋白质，通过细胞核/核仁水平的内分泌作用发挥其至少部分生物学功能。为了深入了解这种肽进入细胞质用于随后的核输入的机制，我们表征了其核形式。在转染的COS-1细胞中，产生了三种核PTHrP物质，它们大于成熟形式的蛋白质，但小于prepro-PTHrP，并且包括肽的氨基和羧基末端区域。这表明，核PTHrP蛋白包含部分的前原肽，并可能产生从交替启动翻译在下游的非AUG密码子内的信号sequence.Transient表达的PTHrP的形式，其中一个独特的起始ATG突变为一个noninitiator ATC密码子，和另一个包含一个工程化的N-连接的糖基化位点，产生肽的大小与核PTHrP蛋白。这些被低效地靶向ER，绕过ER转运，并且仅定位于核仁。使用针对PTHrP的前区的多克隆抗血清，核PTHrP种类显示具有前肽序列。因此，我们的数据认为，核PTHrP形式导致翻译开始在交替，内部密码子。这可能构成哺乳动物蛋白质中下游非AUG密码子处的翻译起始的第一个实例。
PTH-related peptide (PTHrP), normally a secreted protein, exerts at least part of its biological functions via intracrine actions at the level of the cell nucleus/nucleolus. To gain insight into the mechanism whereby this peptide accesses the cytosol for subsequent nuclear import, we characterized its nuclear forms. In transfected COS-1 cells, three nuclear PTHrP species were produced, which were larger than the mature form of the protein but smaller than prepro-PTHrP and comprised both the amino- and carboxyl-terminal regions of the peptide. This suggested that nuclear PTHrP proteins contain part of the prepropeptide and Likely arise from alternate initiation of translation at downstream non-AUG codons within the signal sequence.Transient expression of two PTHrP forms, one in which the unique initiator ATG was mutated to a noninitiator ATC codon, and another encompassing an engineered N-linked glycosylation site, generated peptides of size comparable to nuclear PTHrP proteins. These were inefficiently targeted to the ER, bypassed ER transit, and exclusively localized to nucleoli. Using a polyclonal antiserum against the proregion of PTHrP, nuclear PTHrP species were shown to harbor the propeptide sequence. Hence, our data argue that nuclear PTHrP forms result from translation initiated at alternate, internal codons. This may constitute the first example of translation initiation at downstream non-AUG codons in a mammalian protein.