Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya 467-8603, Japan.
Nucleic Acids Res. 2024 Aug 27;52(15):9193-9209. doi: 10.1093/nar/gkae497.
Stress induces global stabilization of the mRNA poly(A) tail (PAT) and the assembly of untranslated poly(A)-tailed mRNA into mRNPs that accumulate in stress granules (SGs). While the mechanism behind stress-induced global PAT stabilization has recently emerged, the biological significance of PAT stabilization under stress remains elusive. Here, we demonstrate that stress-induced PAT stabilization is a prerequisite for SG formation. Perturbations in PAT length impact SG formation; PAT shortening, achieved by overexpressing mRNA deadenylases, inhibits SG formation, whereas PAT lengthening, achieved by overexpressing their dominant negative mutants or downregulating deadenylases, promotes it. PABPC1, which specifically binds to the PAT, is crucial for SG formation. Complementation analyses reveal that the PABC/MLLE domain of PABPC1, responsible for binding PAM2 motif-containing proteins, plays a key role. Among them, ataxin-2 is a known SG component. A dominant-negative approach reveals that the PAM2 motif of ataxin-2 is essential for SG formation. Notably, ataxin-2 increases stress sensitivity, lowering the threshold for SG formation, probably by promoting the aggregation of PABPC1-bound mRNA. The C-terminal region is responsible for the self-aggregation of ataxin-2. These findings underscore the critical roles of mRNA PAT, PABPC1 and ataxin-2 in SG formation and provide mechanistic insights into this process.
压力诱导 mRNA 多聚腺苷酸尾（PAT）的整体稳定，并将未翻译的多聚腺苷酸化 mRNA 组装成应激颗粒（SGs）。虽然最近出现了压力诱导的整体 PAT 稳定的机制，但压力下 PAT 稳定的生物学意义仍不清楚。在这里，我们证明压力诱导的 PAT 稳定是 SG 形成的前提。PAT 长度的干扰会影响 SG 的形成；通过过表达 mRNA 脱腺苷酶缩短 PAT，会抑制 SG 的形成，而通过过表达其显性负突变体或下调脱腺苷酶来延长 PAT，则会促进 SG 的形成。特异性结合 PAT 的 PABPC1 对于 SG 的形成至关重要。互补分析表明，PABPC1 的 PABC/MLLE 结构域负责结合含有 PAM2 基序的蛋白质，在其中发挥关键作用。其中，ataxin-2 是已知的 SG 成分。一种显性负突变的方法表明，ataxin-2 的 PAM2 基序对于 SG 的形成是必不可少的。值得注意的是，ataxin-2 增加了压力敏感性，降低了 SG 形成的阈值，可能是通过促进 PABPC1 结合的 mRNA 的聚集来实现的。C 端区域负责 ataxin-2 的自身聚集。这些发现强调了 mRNA PAT、PABPC1 和 ataxin-2 在 SG 形成中的关键作用，并为这一过程提供了机制上的见解。
