Stoops Janelle, Byrd Samantha, Hasegawa Haruki
Department of Therapeutic Discovery, Amgen Inc., Seattle, WA 98119, USA.
Biochim Biophys Acta. 2012 Oct;1823(10):1643-57. doi: 10.1016/j.bbamcr.2012.06.015. Epub 2012 Jun 20.
Russell bodies are intracellular aggregates of immunoglobulins. Although the mechanism of Russell body biogenesis has been extensively studied by using truncated mutant heavy chains, the importance of the variable domain sequences in this process and in immunoglobulin biosynthesis remains largely unknown. Using a panel of structurally and functionally normal human immunoglobulin Gs, we show that individual immunoglobulin G clones possess distinctive Russell body inducing propensities that can surface differently under normal and abnormal cellular conditions. Russell body inducing predisposition unique to each immunoglobulin G clone was corroborated by the intrinsic physicochemical properties encoded in the heavy chain variable domain/light chain variable domain sequence combinations that define each immunoglobulin G clone. While the sequence based intrinsic factors predispose certain immunoglobulin G clones to be more prone to induce Russell bodies, extrinsic factors such as stressful cell culture conditions also play roles in unmasking Russell body propensity from immunoglobulin G clones that are normally refractory to developing Russell bodies. By taking advantage of heterologous expression systems, we dissected the roles of individual subunit chains in Russell body formation and examined the effect of non-cognate subunit chain pair co-expression on Russell body forming propensity. The results suggest that the properties embedded in the variable domain of individual light chain clones and their compatibility with the partnering heavy chain variable domain sequences underscore the efficiency of immunoglobulin G biosynthesis, the threshold for Russell body induction, and the level of immunoglobulin G secretion. We propose that an interplay between the unique properties encoded in variable domain sequences and the state of protein homeostasis determines whether an immunoglobulin G expressing cell will develop the Russell body phenotype in a dynamic cellular setting.
拉塞尔小体是免疫球蛋白的细胞内聚集体。尽管通过使用截短的突变重链对拉塞尔小体生物发生机制进行了广泛研究，但可变区序列在此过程以及免疫球蛋白生物合成中的重要性在很大程度上仍不清楚。我们使用一组结构和功能正常的人免疫球蛋白G，发现单个免疫球蛋白G克隆具有独特的诱导拉塞尔小体的倾向，在正常和异常细胞条件下可能表现不同。每个免疫球蛋白G克隆独特的诱导拉塞尔小体的倾向通过重链可变区/轻链可变区序列组合中编码的内在物理化学性质得到证实，这些序列组合定义了每个免疫球蛋白G克隆。虽然基于序列的内在因素使某些免疫球蛋白G克隆更容易诱导形成拉塞尔小体，但诸如应激细胞培养条件等外在因素在揭示通常不易形成拉塞尔小体的免疫球蛋白G克隆的拉塞尔小体形成倾向方面也发挥作用。通过利用异源表达系统，我们剖析了各个亚基链在拉塞尔小体形成中的作用，并研究了非同源亚基链对共表达对拉塞尔小体形成倾向的影响。结果表明，单个轻链克隆可变区中所包含的特性及其与配对重链可变区序列的兼容性强调了免疫球蛋白G生物合成的效率、拉塞尔小体诱导的阈值以及免疫球蛋白G的分泌水平。我们提出，可变区序列中编码的独特特性与蛋白质稳态状态之间的相互作用决定了表达免疫球蛋白G的细胞在动态细胞环境中是否会呈现拉塞尔小体表型。
