Siegel P M, Muller W J
Institute for Molecular Biology and Biotechnology, McMaster University, Hamilton, ON, Canada.
Proc Natl Acad Sci U S A. 1996 Aug 20;93(17):8878-83. doi: 10.1073/pnas.93.17.8878.
Overexpression of the Neu/ErbB-2 receptor tyrosine kinase has been implicated in the genesis of human breast cancer. Indeed, expression of either activated or wild-type neu in the mammary epithelium of transgenic mice results in the induction of mammary tumors. Previously, we have shown that many of the mammary tumors arising in transgenic mice expressing wild-type neu occur through somatic activating mutations within the neu transgene itself. Here we demonstrate that these mutations promote dimerization of the Neu receptor through the formation of disulfide bonds, resulting in its constitutive activation. To explore the role of conserved cysteine residues within the region deleted in these altered Neu proteins, we examined the transforming potential of a series of Neu receptors in which the individual cysteine residues were mutated. These analyses indicated that mutation of certain cysteine residues resulted in the oncogenic activation of Neu. The increased transforming activity displayed by the altered receptors correlated with constitutive dimerization that occurred in a disulfide bond-dependent manner. We further demonstrate that addition of 2-mercaptoethanol to the culture medium interfered with the specific transforming activity of the mutant Neu receptors. These observations suggest that oncogenic activation of Neu results from constitutive disulfide bond-dependent dimerization.
Neu/ErbB-2受体酪氨酸激酶的过表达与人类乳腺癌的发生有关。事实上，在转基因小鼠的乳腺上皮中表达活化型或野生型neu都会导致乳腺肿瘤的诱发。此前，我们已经表明，在表达野生型neu的转基因小鼠中出现的许多乳腺肿瘤是通过neu转基因自身的体细胞激活突变产生的。在这里，我们证明这些突变通过二硫键的形成促进Neu受体的二聚化，从而导致其组成性激活。为了探究在这些改变的Neu蛋白中缺失区域内保守半胱氨酸残基的作用，我们检测了一系列单个半胱氨酸残基发生突变的Neu受体的转化潜能。这些分析表明，某些半胱氨酸残基的突变导致了Neu的致癌激活。改变后的受体所表现出的增强的转化活性与以二硫键依赖方式发生的组成性二聚化相关。我们进一步证明，向培养基中添加2-巯基乙醇会干扰突变型Neu受体的特异性转化活性。这些观察结果表明，Neu的致癌激活是由组成性二硫键依赖的二聚化引起的。
