Osherov N, Gazit A, Gilon C, Levitzki A
Department of Biological Chemistry, Hebrew University of Jerusalem, Israel.
J Biol Chem. 1993 May 25;268(15):11134-42.
The HER2 (neu/erb-B2) proto-oncogene codes for a transmembrane receptor with tyrosine kinase activity and with high homology to the EGF receptor (HER1). The high incidence of HER2 overexpression in breast and ovary carcinomas prompted us to synthesize protein tyrosine kinase inhibitors (tyrphostins) which selectively inhibit the HER2 kinase activity. Two groups of tyrphostins were developed: one highly selective in inhibiting HER1 as opposed to HER2, the other highly selective in inhibiting HER2. Both the HER1 and the HER2 selective blockers were competitive with ATP binding. This suggests that even though the kinase domains of the respective receptors show an 80% degree of homology it is possible to design small molecules capable of discriminating between them. These results also show that the two kinases differ in their ATP binding sites. Mitogenic signaling induced by EGF in NIH3T3 cells overexpressing either HER1 or HER1-2 (possessing the HER2 kinase domain) was blocked identically by the agents that discriminate between the two in vitro. This paradox was further explored and elucidated. We propose that high intracellular ATP levels prevent inhibitor binding to the receptor. The antiproliferative action of the two distinct selective tyrphostins observed may result from the inhibition of a downstream element, presumably a tyrosine kinase, which mediates mitogenic signaling.
HER2（neu/erb - B2）原癌基因编码一种具有酪氨酸激酶活性且与表皮生长因子受体（HER1）高度同源的跨膜受体。HER2在乳腺癌和卵巢癌中高表达，促使我们合成选择性抑制HER2激酶活性的蛋白酪氨酸激酶抑制剂（ tyrphostins）。我们开发了两组tyrphostins：一组对HER1的抑制作用高度选择性，而对HER2的抑制作用较弱；另一组对HER2的抑制作用高度选择性。HER1和HER2选择性阻滞剂均与ATP结合具有竞争性。这表明，尽管各自受体的激酶结构域显示出80%的同源性，但仍有可能设计出能够区分它们的小分子。这些结果还表明，这两种激酶的ATP结合位点不同。在过表达HER1或HER1 - 2（具有HER2激酶结构域）的NIH3T3细胞中，由表皮生长因子诱导的促有丝分裂信号传导，在体外能区分这两者的试剂作用下被同样地阻断。我们对这一矛盾现象进行了进一步的探索和阐释。我们认为，细胞内高ATP水平会阻止抑制剂与受体结合。观察到的两种不同选择性tyrphostins的抗增殖作用可能是由于抑制了一个下游元件，推测是一种介导促有丝分裂信号传导的酪氨酸激酶。
