Kim P S, Kim K R, Arvan P
Division of Endocrinology, Beth Israel Hospital, Boston, Massachusetts 02215.
Am J Physiol. 1993 Sep;265(3 Pt 1):C704-11. doi: 10.1152/ajpcell.1993.265.3.C704.
In the endoplasmic reticulum (ER) of cultured porcine thyrocytes, newly synthesized thyroglobulin (Tg, the precursor in thyroid hormone synthesis) initially forms protein aggregates, which are dissolved into monomers and then assembled to dimers, before intracellular transport and secretion. However, studies suggest that in different physiological states and in different cells, folding efficiency in the ER may vary; with this in mind we have set out to further characterize the phenomenon of nascent Tg aggregation. In primary cultured thyrocytes, fresh thyroid follicular tissue (of porcine and rat origin), and the FRTL-5 cell line, nascent Tg appears transiently aggregated with mispaired, interchain disulfide linkages. Using a cell lysis procedure that maximally inhibits proteolysis as well as artifactual disulfide formation, Tg aggregates of M(r) > or = 2,000,000 can be stably isolated by gel filtration. Furthermore, stimulation with thyrotropin and other hormones that enhance Tg production may alter but does not eliminate formation of these aggregates. We conclude that transient disulfide-linked aggregation occurs normally during Tg folding in the ER of thyroid epithelial cells.
在培养的猪甲状腺细胞的内质网（ER）中，新合成的甲状腺球蛋白（Tg，甲状腺激素合成的前体）最初形成蛋白质聚集体，这些聚集体在细胞内运输和分泌之前先溶解为单体，然后组装成二聚体。然而，研究表明，在不同的生理状态和不同的细胞中，内质网中的折叠效率可能会有所不同；考虑到这一点，我们着手进一步表征新生Tg聚集现象。在原代培养的甲状腺细胞、新鲜的甲状腺滤泡组织（猪和大鼠来源）以及FRTL-5细胞系中，新生Tg会短暂聚集，形成错配的链间二硫键。使用一种能最大程度抑制蛋白水解以及人为二硫键形成的细胞裂解程序，通过凝胶过滤可稳定分离出分子量大于或等于2,000,000的Tg聚集体。此外，用促甲状腺激素和其他能增强Tg产生的激素刺激可能会改变但不会消除这些聚集体的形成。我们得出结论，在甲状腺上皮细胞内质网中，Tg折叠过程中正常会发生短暂的二硫键连接聚集。
