Departments of Animal Sciences and Applied Biological Chemistry, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
Biochem Biophys Res Commun. 2010 Apr 9;394(3):697-702. doi: 10.1016/j.bbrc.2010.03.054. Epub 2010 Mar 11.
The insulin receptor substrate (IRS) proteins are major substrates of both insulin receptor and insulin-like growth factor (IGF)-I receptor tyrosine kinases. Previously, we reported that IRS-3 is localized to both cytosol and nucleus, and possesses transcriptional activity. In the present study, we identified Bcl-3 as a novel binding protein to IRS-3. Bcl-3 is a nuclear protein, which forms a complex with the homodimer of p50 NF-kappaB, leading to enhancement of transcription through p50 NF-kappaB. We found that Bcl-3 interacts with the pleckstrin homology domain and the phosphotyrosine binding domain of IRS-3, and that IRS-3 interacts with the ankyrin repeat domain of Bcl-3. In addition, IRS-3 augmented the binding activity of p50 to the NF-kappaB DNA binding site, as well as the tumor necrosis factor (TNF)-alpha-induced transcriptional activity of NF-kappaB. Lastly, IRS-3 enhanced NF-kappaB-dependent anti-apoptotic gene induction and consequently inhibited TNF-alpha-induced cell death. This series of results proposes a novel function for IRS-3 as a transcriptional regulator in TNF-alpha signaling, distinct from its function as a substrate of insulin/IGF receptor kinases.
胰岛素受体底物（IRS）蛋白是胰岛素受体和胰岛素样生长因子（IGF）-I 受体酪氨酸激酶的主要底物。先前，我们报道 IRS-3 定位于细胞质和细胞核，并具有转录活性。在本研究中，我们鉴定出 Bcl-3 是 IRS-3 的一种新的结合蛋白。Bcl-3 是一种核蛋白，与 p50 NF-κB 的同源二聚体形成复合物，通过 p50 NF-κB 增强转录。我们发现 Bcl-3 与 IRS-3 的pleckstrin 同源结构域和磷酸酪氨酸结合结构域相互作用，而 IRS-3 与 Bcl-3 的锚蛋白重复结构域相互作用。此外，IRS-3 增强了 p50 与 NF-κB DNA 结合位点的结合活性，以及 TNF-α诱导的 NF-κB 的转录活性。最后，IRS-3 增强了 NF-κB 依赖性抗凋亡基因的诱导，从而抑制了 TNF-α诱导的细胞死亡。这一系列结果提出了 IRS-3 在 TNF-α信号转导中作为转录调节剂的新功能，与作为胰岛素/IGF 受体激酶底物的功能不同。
