Differential nuclear localization and kinase activity of alternative ErbB4 intracellular domains
Differential nuclear localization and kinase activity of alternative ErbB4 intracellular domains
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DOI：
10.1038/sj.onc.1210501
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发表时间：
2007-10-18
期刊：
影响因子：
8
通讯作者：
Elenius, K.
中科院分区：
文献类型：
--
作者：
Sundvall, M.;Peri, L.;Elenius, K.
ErbB 4受体酪氨酸激酶的可裂解同种型释放可溶性胞内结构域（ICD），其可易位至细胞核并调节信号传导。然而，ErbB 4基因被选择性剪接，产生具有不同胞质尾的CYT-1和CYT-2同种型。在这里，我们讨论了CYT 4（ICD 1）或CYT-2（ICD 2）类型的两种替代ErbB 4 ICD在向细胞核的信号传导方面是否不同。共聚焦显微镜和提取的核细胞组分表明，显着更多的ICD 2易位到细胞核相比，ICD 1。与源自全长ErbB 4亚型的膜锚定80 kDa片段不同，这两种ICD在代谢稳定性或遍在化方面没有差异。然而，ICD 2在酪氨酸残基处磷酸化的程度更高，并且表现出比ICDI更大的体外激酶活性。突变ICD 2激酶结构域内的ATP结合位点（ICD 2 K751 R）可阻断其酪氨酸磷酸化并显著减少其核转位。当在全长ErbB 4的背景下表达时，ICD 2在促进STAT 5靶基因β-酪蛋白的转录激活方面也比ICD 1更有效。这些发现表明，ErbB 4的两种替代ICD在其核积累方面不同，并且该机制涉及差异激酶活性，但不涉及泛素调节的ICD稳定性。
Cleavable isoforms of the ErbB4 receptor tyrosine kinase release a soluble intracellular domain (ICD) that may translocate to the nucleus and regulate signaling. However, ErbB4 gene is alternatively spliced generating CYT-1 and CYT-2 isoforms with different cytoplasmic tails. Here, we addressed whether the two alternative ErbB4 ICDs of either CYT4 (ICD1) or CYT-2 (ICD2) type differ in signaling to the nucleus. Confocal microscopy and extraction of nuclear cell fractions indicated that significantly more ICD2 translocated to the nuclei when compared to ICD1. Unlike the membrane-anchored 80 kDa fragments derived from full-length ErbB4 isoforms, the two ICDs did not differ from each other in metabolic stability or ubiquitylation. However, ICD2 was phosphorylated at tyrosine residues to a higher extent and demonstrated greater in vitro kinase activity than ICDI. Mutating the ATP-binding site within ICD2 kinase domain (ICD2 K751R) blocked its tyrosine phosphorylation and significantly reduced its nuclear translocation. When expressed in the context of full-length ErbB4, ICD2 was also more efficient than ICD1 in promoting transcriptional activation of the STAT5 target gene beta-casein. These findings indicate that the two alternative ICDs of ErbB4 differ in their nuclear accumulation, and that the mechanism involves differential kinase activity but not ubiquitin-regulated ICD stability.