Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi 221005, India.
Department of Zoology, Banaras Hindu University, Varanasi 221005, India.
Eur J Cell Biol. 2023 Jun;102(2):151300. doi: 10.1016/j.ejcb.2023.151300. Epub 2023 Feb 24.
A-kinase anchoring protein (AKAP) comprises a family of scaffold proteins, which decides the subcellular localisation of a combination of signalling molecules. Spoonbill (Spoon) is a putative A-kinase anchoring protein in Drosophila. We have earlier reported that Spoon suppresses ribonuclear foci formed by trinucleotide repeat expanded transcripts associated with Spinocerebellar Ataxia 8 neurodegeneration in Drosophila. However, the role of Spoonbill in cellular signalling was unexplored. In this report, we have unravelled a novel function of Spoon protein in the regulation of the apoptotic pathway. The Drosophila TNFα homolog, Eiger, induces apoptosis via activation of the JNK pathway. We have shown here that Spoonbill is a positive regulator of the Eiger-induced JNK signalling. Further genetic interaction studies show that the spoon interacts with components of the JNK pathway, TGF-β activated kinase 1 (Tak1 - JNKKK), hemipterous (hep - JNKK) and basket (bsk - JNK). Interestingly, Spoonbill alone can also induce ectopic activation of the JNK pathway in a context-specific manner. To understand the molecular mechanism underlying Spoonbill-mediated modulation of the JNK pathway, the interaction between Spoon and Drosophila JNK was assessed. basket encodes the only known JNK in Drosophila. This serine/threonine-protein kinase phosphorylates Jra/Kay, which transcriptionally regulate downstream targets like Matrix metalloproteinase 1 (Mmp1), puckered (puc), and proapoptotic genes hid, reaper and grim. Interestingly, we found that Spoonbill colocalises and co-immunoprecipitates with the Basket protein in the developing photoreceptor neurons. Hence, we propose that Spoon plays a vital role in JNK-induced apoptosis. Furthermore, stress-induced JNK activation underlying Parkinson's Disease was also examined. In the Parkinson's Drosophila model of neurodegeneration, depletion of Spoonbill leads to a partial reduction of JNK pathway activation, along with improvement in adult motor activity. These observations suggest that the putative scaffold protein Spoonbill is a functional and physical interacting partner of the Drosophila JNK protein, Basket. Spoon protein is localised on the outer mitochondrial membrane (OMM), which may perhaps provide a suitable subcellular niche for activation of Drosophila Basket protein by its kinases which induce apoptosis.
A-激酶锚定蛋白（AKAP）由一组支架蛋白组成，决定了信号分子组合的亚细胞定位。勺状（Spoon）是果蝇中一种假定的 A-激酶锚定蛋白。我们之前曾报道过，Spoon 抑制与脊髓小脑共济失调 8 神经退行性变相关的三核苷酸重复扩展转录物形成的核糖核蛋白焦点。然而，Spoonbill 在细胞信号转导中的作用尚未得到探索。在本报告中，我们揭示了 Spoon 蛋白在调节细胞凋亡途径中的新功能。果蝇 TNFα 同源物 Eiger 通过激活 JNK 途径诱导细胞凋亡。我们在这里表明，Spoonbill 是 Eiger 诱导的 JNK 信号的正调节剂。进一步的遗传相互作用研究表明，勺状与 JNK 途径的成分相互作用，包括 TGF-β 激活激酶 1（Tak1-JNKKK）、半翅目（hep-JNKK）和篮子（bsk-JNK）。有趣的是，Spoonbill 本身也可以在特定情况下诱导 JNK 途径的异位激活。为了了解 Spoonbill 介导的 JNK 途径调节的分子机制，评估了 Spoon 和果蝇 JNK 之间的相互作用。basket 编码果蝇中唯一已知的 JNK。这种丝氨酸/苏氨酸蛋白激酶磷酸化 Jra/Kay，转录调节下游靶标，如基质金属蛋白酶 1（Mmp1）、puckered（puc）和促凋亡基因 hid、reaper 和 grim。有趣的是，我们发现 Spoonbill 在发育中的光感受器神经元中与 Basket 蛋白共定位和共免疫沉淀。因此，我们提出 Spoon 在 JNK 诱导的细胞凋亡中起关键作用。此外，还检查了帕金森病的应激诱导 JNK 激活。在帕金森病果蝇神经退行性变模型中，Spoonbill 的耗竭导致 JNK 途径激活部分减少，同时成年运动活动改善。这些观察结果表明，假定的支架蛋白 Spoonbill 是果蝇 JNK 蛋白 Basket 的功能性和物理相互作用伙伴。Spoon 蛋白定位于外线粒体膜（OMM）上，这可能为其激酶诱导的果蝇 Basket 蛋白的激活提供了合适的亚细胞龛位，从而诱导细胞凋亡。
