Ulatowski L M, Lam M, Vanderburg G, Stallcup M R, Distelhorst C W
Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106.
J Biol Chem. 1993 Apr 5;268(10):7482-8.
We have found that synthesis of the 78-kDa glucose-regulated protein, GRP78, was increased following glucocorticoid treatment of S49 and W7MG1 mouse lymphoma cell lines. These lines synthesized a 74-kDa mouse mammary tumor virus envelope glycoprotein precursor, Pr74, both constitutively and in response to glucocorticoid treatment. In these cell lines, nascent Pr74 was not processed normally but was retained within the endoplasmic reticulum where it was bound stably by GRP78. GRP78 synthesis was not increased following glucocorticoid treatment of the W7.2 mouse lymphoma cell line, which does not synthesize Pr74, suggesting that the increase in GRP78 synthesis following glucocorticoid treatment of S49 and W7MG1 cells was secondary to the glucocorticoid-induced increase in Pr74 synthesis. Consistent with this hypothesis, the glucocorticoid-induced increase in Pr74 synthesis preceded the increase in GRP78 synthesis. Also, there was a direct correlation between the level of GRP78 synthesis and the level of Pr74 synthesis among multiple subclones of the W7-ENV/N line. This line was derived from the W7.2 line by retroviral mediated transfer of a constitutively expressed sequence encoding a defective form of Pr74 that was bound stably by GRP78 within the endoplasmic reticulum. An elevation in the steady state level of GRP78 mRNA was not detected either in glucocorticoid-treated S49 cells and W7MG1 cells or in subclones of the W7-ENV/N line that have an increased level of GRP78 synthesis. Therefore, it appears that the binding of Pr74 to GRP78 induces an increase in GRP78 synthesis that is regulated at a translational level, rather than at a transcriptional level.
我们发现，用糖皮质激素处理S49和W7MG1小鼠淋巴瘤细胞系后，78 kDa葡萄糖调节蛋白（GRP78）的合成增加。这些细胞系组成性地以及在对糖皮质激素处理作出反应时，都会合成一种74 kDa小鼠乳腺肿瘤病毒包膜糖蛋白前体Pr74。在这些细胞系中，新生的Pr74不能正常加工，而是保留在内质网中，并在那里被GRP78稳定结合。用糖皮质激素处理不合成Pr74的W7.2小鼠淋巴瘤细胞系后，GRP78的合成没有增加，这表明用糖皮质激素处理S49和W7MG1细胞后GRP78合成的增加是糖皮质激素诱导的Pr74合成增加的继发结果。与这一假设一致的是，糖皮质激素诱导的Pr74合成增加先于GRP78合成的增加。此外，在W7-ENV/N系的多个亚克隆中，GRP78合成水平与Pr74合成水平之间存在直接相关性。该细胞系是通过逆转录病毒介导转移一个组成性表达的序列而从W7.2细胞系衍生而来，该序列编码一种有缺陷形式的Pr74，它在内质网中被GRP78稳定结合。无论是在经糖皮质激素处理的S49细胞和W7MG1细胞中，还是在GRP78合成水平增加的W7-ENV/N系亚克隆中，均未检测到GRP78 mRNA稳态水平的升高。因此，似乎Pr74与GRP78的结合诱导了GRP78合成的增加，这种增加是在翻译水平而非转录水平上受到调节。
