LIGAND REQUIREMENTS OF ERBB-2 TO CAUSE CELL TRANSFORMATION

gpl 85 erbB-2受体样分子在体内被酪氨酸磷酸化 在造血、乳腺上皮和成纤维细胞系中。这 这一现象可以用三种假设来解释：（1）配体的产生 所有这些细胞系;（2）组织培养物中存在配体 （3）gp 185 erbB-2是组成型活性的。这些假设 研究erbB-2的磷酸化状态， 确定的培养基和转化和生化活性的一个 具有erbB-2的胞外结构域和erbB-2的胞外结构域的嵌合分子， 表皮生长因子受体（erbB-2）胞内区 EC/EGFR IC）。这种嵌合分子是通过利用 在erbB-2和EGFR cDNA中产生的独特限制性位点， 岗位这种分子被证明是无法区分的， 亲本erbB-2通过其结合一组单克隆抗体的能力来评估。 针对蛋白质天然构型产生的抗体。 此外，它可以在体内被生物化学和生物学刺激 被这些单克隆抗体所感染增加其磷酸酪氨酸 内容和传递促有丝分裂信号。然而，这种分子 在转染试验中没有显示转化活性，并且没有酪氨酸 当在NIH/3 T3细胞中以一定水平表达时， 与其母体分子相当。因此，erbB-2分子似乎 具有组成型激酶和生物活性。使用 下调剂，以实现转化的逆转， 基于这些数据，表型似乎是合理的可能性。

The gpl85 erbB-2 receptor-like molecule is tyrosine phosphorylated in vivo in hematopoietic, mammary epithelial and fibroblast cell lines. This phenomenon can be explained by three hypotheses: (1) a ligand is produced by all of these cell lines; (2) a ligand is present in the tissue culture medium: and (3) the gpl85 erbB-2 is constitutively active. These hypotheses were tested studying the phosphorylation status of erbB-2 in a chemically defined medium and the transforming and biochemical activities of a chimeric molecule bearing the extracellular domain of erbB-2 and the intracellular domain of the epidermal growth factor receptor (erbB-2 EC/EGFR IC). This chimeric molecule was engineered by taking advantage of unique restriction sites generated in erbB-2 and EGFR cDNAs at homologous positions. This molecule was shown to be indistinguishable from the parental erbB-2 as assessed by its ability to bind a panel of monoclonal antibodies raised against the protein in its native configuration. Furthermore, it could be biochemically and biologically stimulated in vivo by some of these monoclonal antibodies. increasing its phosphotyrosine content and delivering a mitogenic signal. Nevertheless, this molecule showed no transforming activity in a transfection assay and no tyrosine phosphorylation in vivo when expressed in NIH/3T3 cells at levels comparable to its parental molecules. The erbB-2 molecule, therefore, seems to be endowed with constitutive kinase and biological activities. The use of down-regulating agents in order to achieve reversion of the transformed phenotype seems a rational possibility on the basis of these data.