Crystallography & Molecular Biology Division, Saha Institute of Nuclear Physics, Kolkata, India.
Homi Bhabha National Institute, Mumbai, India.
Mol Biol Rep. 2023 Apr;50(4):3451-3458. doi: 10.1007/s11033-023-08289-5. Epub 2023 Feb 9.
δ-tubulin - a member of tubulin superfamily, is found in a subset of eukaryotes including human where it has a role in centriole maturation. The mutation in the gene results in a disorganized microtubule triplet arrangement leading to formation of defective centriole. Since centriole maturation is a periodic event, it will be interesting to see if δ-tubulin is also regulated in a cell cycle dependent manner.
In this regard we show that the abundance of δ-tubulin mRNA remains unchanged throughout the cell cycle. However, the protein level varies periodically with a significantly higher expression in S-phase, implying regulation at the level of translation. Sequence analysis establishes the presence of a 90-base long conserved region, including a consensus motif of nine residues in the 5´-untranslated region (5´-UTR) of δ-tubulin transcript. The deletion analysis of the conserved region using luciferase reporter assay system confirms its strong inhibitory effect on translation. Interestingly, microtubule associated protein 4 (MAP4) is found to interact specifically with the 90-base long conserved region in the 5´-UTR and possibly responsible, at least partially, for the translation inhibitory activity of the UTR. Remarkably, MAP4 interacts with δ-tubulin in a periodic manner at protein level also.
The results reported here show that δ-tubulin protein expression is regulated at posttranscriptional level and strongly suggest the role of MAP4 in modulation of both abundance and function of δ-tubulin.
δ-微管蛋白是微管蛋白超家族的成员，存在于包括人类在内的一部分真核生物中，在中心体成熟中发挥作用。该基因的突变导致微管三联体排列紊乱，导致中心体缺陷的形成。由于中心体成熟是一个周期性事件，因此观察δ-微管蛋白是否也以细胞周期依赖的方式进行调节将是很有趣的。
在这方面，我们表明δ-微管蛋白 mRNA 的丰度在整个细胞周期中保持不变。然而，蛋白质水平周期性变化，S 期表达水平显著升高，暗示翻译水平的调节。序列分析确定了一个 90 个碱基长的保守区的存在，包括δ-微管蛋白转录物 5'非翻译区（5'UTR）中 9 个残基的共识基序。使用荧光素酶报告基因检测系统对保守区进行缺失分析，证实其对翻译具有强烈的抑制作用。有趣的是，微管相关蛋白 4（MAP4）被发现与 5'UTR 中 90 个碱基长的保守区特异性相互作用，并可能至少部分负责 UTR 的翻译抑制活性。值得注意的是，MAP4 还以周期性方式在蛋白质水平上与 δ-微管蛋白相互作用。
这里报道的结果表明，δ-微管蛋白蛋白表达在转录后水平受到调节，并强烈提示 MAP4 在调节 δ-微管蛋白的丰度和功能方面的作用。
