Peles E, Ben-Levy R, Tzahar E, Liu N, Wen D, Yarden Y
Department of Chemical Immunology, Weizmann Institute of Science, Rehovot, Israel.
EMBO J. 1993 Mar;12(3):961-71. doi: 10.1002/j.1460-2075.1993.tb05737.x.
The Neu/HER-2 receptor tyrosine kinase is overexpressed in some types of human adenocarcinomas, including tumors of the breast and the ovary. A 44 kDa glycoprotein that elevates tyrosine phosphorylation of Neu has been isolated and named Neu differentiation factor (NDF), or heregulin. Here we show that NDF affects tyrosine phosphorylation of Neu in human tumor cells of breast, colon and neuronal origin, but not in ovarian cells that overexpress the receptor. By using monoclonal antibodies (mAbs) to Neu, we found that the ovarian receptor is immunologically and biochemically similar to the mammary p185neu. Nevertheless, unlike breast-derived Neu, the ovarian protein did not display covalent cross-linking to radiolabeled NDF, and was devoid of ligand-induced association with phosphatidylinositol 3'-kinase. Direct binding analysis showed that NDF binds with high affinity (Kd approximately 10(-9) M) to mammary cells, but its weak association with ovarian cells is probably mediated by heparin-like molecules. Similar to the endogenous receptor, the ectopically overexpressed Neu of mammary cells, but not of ovarian and fibroblastic cells, exhibited elevated levels of NDF-induced phosphorylation and covalent cross-linking of the radiolabeled factor. Taken together, our results imply that NDF binding to cells requires both Neu and an additional cellular component, whose identity is still unknown, but its tissue distribution is more restricted than the expression of the neu gene.
Neu/HER-2受体酪氨酸激酶在某些类型的人类腺癌中过度表达，包括乳腺癌和卵巢癌。一种能提高Neu酪氨酸磷酸化水平的44 kDa糖蛋白已被分离出来，并被命名为Neu分化因子（NDF），即这里所说的调节素。我们在此表明，NDF会影响源自乳腺、结肠和神经元的人类肿瘤细胞中Neu的酪氨酸磷酸化，但对过度表达该受体的卵巢细胞没有影响。通过使用针对Neu的单克隆抗体（mAb），我们发现卵巢受体在免疫和生化方面与乳腺的p185neu相似。然而，与源自乳腺的Neu不同，卵巢蛋白不会与放射性标记的NDF发生共价交联，也不会因配体诱导而与磷脂酰肌醇3'-激酶结合。直接结合分析表明，NDF与乳腺细胞具有高亲和力结合（解离常数Kd约为10^(-9) M），但其与卵巢细胞的弱结合可能是由类肝素分子介导的。与内源性受体相似，乳腺细胞中异位过度表达的Neu（而非卵巢细胞和成纤维细胞中的Neu）在NDF诱导下，放射性标记因子的磷酸化和共价交联水平有所升高。综上所述，我们的结果表明，NDF与细胞的结合既需要Neu，也需要另一种仍未知的细胞成分，其组织分布比neu基因的表达更具局限性。
