Samanta A, LeVea C M, Dougall W C, Qian X, Greene M I
Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia 19104.
Proc Natl Acad Sci U S A. 1994 Mar 1;91(5):1711-5. doi: 10.1073/pnas.91.5.1711.
The neu protooncogene (also known as c-erbB2, NGL, and HER2) encodes a 185-kDa transmembrane glycoprotein with intrinsic tyrosine kinase activity that resembles the receptor for epidermal growth factor. The p185 gene and protein were originally identified in the brain and are thought to play a critical role in neurogenesis. Aberrant c-erbB2 protein overexpression also occurs in several human adenocarcinomas. A ligand for p185, neu-activating factor (NAF), specifically binds to neu receptor and increases the p185c-neu tyrosine phosphorylation in vitro and in vivo in a dose-dependent manner. We now show that NAF specifically binds to purified p185 expressed in baculovirus. Direct binding analysis showed that NAF binds with high affinity (Kd = 1.3 nM). We have investigated changes in the structure and association state of baculovirus-produced neu holoreceptor that are induced by ligand binding. In this study, we used sucrose gradients to show that purified p185c-neu exists mainly in the monomeric form at low concentrations, whereas at higher concentrations p185c-neu exists as dimers or multimers. At low concentrations, but in the presence of ligand, p185c-neu sediments as a dimeric or multimeric form. Monomer-oligomer interconversion is absolutely ligand dependent at low receptor concentrations. The high molecular weight form of the receptor is enzymatically more active, as a consequence of ligand-driven activation of the receptor kinase. Oncogenic p185neu receptors sediment predominantly as high molecular weight forms and have constitutively active kinases.
神经原癌基因（也称为c-erbB2、NGL和HER2）编码一种185 kDa的跨膜糖蛋白，具有内在酪氨酸激酶活性，类似于表皮生长因子受体。p185基因和蛋白最初在大脑中被鉴定出来，被认为在神经发生中起关键作用。异常的c-erbB2蛋白过表达也发生在几种人类腺癌中。p185的配体，神经激活因子（NAF），特异性结合神经受体，并在体外和体内以剂量依赖的方式增加p185c-neu酪氨酸磷酸化。我们现在表明，NAF特异性结合杆状病毒中表达的纯化p185。直接结合分析表明，NAF以高亲和力结合（Kd = 1.3 nM）。我们研究了配体结合诱导的杆状病毒产生的神经全受体的结构和缔合状态变化。在本研究中，我们使用蔗糖梯度表明，纯化的p185c-neu在低浓度下主要以单体形式存在，而在较高浓度下p185c-neu以二聚体或多聚体形式存在。在低浓度下，但在配体存在的情况下，p185c-neu以二聚体或多聚体形式沉降。在低受体浓度下，单体-寡聚体相互转化绝对依赖于配体。受体的高分子量形式在酶促作用下更具活性，这是配体驱动受体激酶激活的结果。致癌性p185neu受体主要以高分子量形式沉降，并具有组成型活性激酶。
