Liu X, Hwang H, Cao L, Buckland M, Cunningham A, Chen J, Chien K R, Graham R M, Zhou M
Victor Chang Cardiac Research Institute, St. Vincent's Hospital, Darlinghurst, New South Wales 2010, Australia.
Proc Natl Acad Sci U S A. 1998 Oct 27;95(22):13024-9. doi: 10.1073/pnas.95.22.13024.
Neuregulins are a multi-isoform family of growth factors that activate members of the erbB family of receptor tyrosine kinases. The membrane-anchored isoforms contain the receptor-activating ligand in their extracellular domain, a single membrane-spanning region, and a long cytoplasmic tail. To evaluate the potential biological role of the intracellular domain of the membrane-anchored neuregulin isoforms, we used a domain-specific gene disruption approach to produce a mouse line in which only the region of the neuregulin gene encoding almost the entire intracellular domain was disrupted. Consistent with previous reports in which all neuregulin isoforms were disrupted, the resulting homozygous neuregulin mutants died at E10.5 of circulatory failure and displayed defects in neural and cardiac development. To further understand these in vivo observations, we evaluated a similarly truncated neuregulin construct after transient expression in COS-7 cells. This cytoplasmic tail-deleted mutant, unlike wild-type neuregulin isoforms, was resistant to proteolytic release of its extracellular-domain ligand, a process required for erbB receptor activation. Thus, proteolytic processing of the membrane-bound neuregulin isoforms involved in cranial ganglia and heart embryogenesis is likely developmentally regulated and is critically controlled by their intracellular domain. This observation indicates that erbB receptor activation by membrane-bound neuregulins most likely involves a unique temporally and spatially regulated "inside-out" signaling process that is critical for processing and release of the extracellular-domain ligand.
神经调节蛋白是一类多异构体的生长因子家族，可激活受体酪氨酸激酶erbB家族的成员。膜锚定异构体在其细胞外结构域中含有受体激活配体、一个单一的跨膜区域和一个长的细胞质尾巴。为了评估膜锚定神经调节蛋白异构体细胞内结构域的潜在生物学作用，我们采用了一种结构域特异性基因破坏方法来培育一个小鼠品系，其中神经调节蛋白基因中仅编码几乎整个细胞内结构域的区域被破坏。与之前所有神经调节蛋白异构体均被破坏的报道一致，产生的纯合神经调节蛋白突变体在胚胎第10.5天死于循环衰竭，并在神经和心脏发育方面表现出缺陷。为了进一步理解这些体内观察结果，我们在COS-7细胞中瞬时表达后评估了一个类似截短的神经调节蛋白构建体。与野生型神经调节蛋白异构体不同，这个缺失细胞质尾巴的突变体对其细胞外结构域配体的蛋白水解释放具有抗性，而这一过程是erbB受体激活所必需的。因此，参与颅神经节和心脏胚胎发生的膜结合神经调节蛋白异构体的蛋白水解加工可能受到发育调控，并且由它们的细胞内结构域严格控制。这一观察结果表明，膜结合神经调节蛋白对erbB受体的激活很可能涉及一个独特的、在时间和空间上受到调控的“由内向外”信号传导过程，这一过程对于细胞外结构域配体的加工和释放至关重要。
