Osherov N, Levitzki A
Department of Biological Chemistry, Alexander Silberman Institute of Life Science, Hebrew University of Jerusalem, Israel.
Eur J Biochem. 1994 Nov 1;225(3):1047-53. doi: 10.1111/j.1432-1033.1994.1047b.x.
The precise role of src-type kinases as signal transducers has been under intensive investigation but only in a few instances has their role been revealed in any detail. Thus, src, fyn and yes are activated upon stimulation by platelet-derived growth factor or colony-stimulating factor in cells expressing high levels of these receptors. Activation of src-family kinases by other receptor tyrosine kinases such as the epidermal-growth-factor (EGF) receptor has not been directly demonstrated. In this report, we demonstrate EGF-dependent activation of src-family tyrosine kinases in NIH3T3 cells overexpressing the human EGF receptor. Activation is rapid (< 1 min) and persistent (up to 16 h). Furthermore, we show a correlation between the level of EGF receptor expressed and the degree of src-family kinase activation. We show that src-family kinase activity is also activated by addition of EGF to PC12 cells, which endogenously express relatively high levels of EGF receptor. Most strikingly, we show that A431 cells, which endogenously express very high levels of EGF receptor, show 10-fold elevated src-family kinase activity as compared to DHER14 cells, and that this activity is constitutive. This activity is completely blocked by AG1478, a specific inhibitor of the EGF-receptor tyrosine kinase activity, pointing to a direct link between overexpression of the EGF receptor and enhanced src-family kinase activity. Our findings suggest that EGF-dependent src-family kinase activity is detectable only when the levels of EGF receptor reach a specific level. Additionally, high levels of EGF receptor, as in A431 cells, may contribute to the elevated activation of src-family kinases. Sustained src-family kinase activation, similar to that seen in v-src-transformed cells, may play a role in tumorogenesis and tumor maintenance.
src 型激酶作为信号转导分子的确切作用一直受到深入研究，但仅在少数情况下其作用才得到详细揭示。因此，在表达高水平这些受体的细胞中，src、fyn 和 yes 在血小板衍生生长因子或集落刺激因子刺激下被激活。其他受体酪氨酸激酶，如表皮生长因子（EGF）受体，对 src 家族激酶的激活尚未得到直接证实。在本报告中，我们证明了在过表达人 EGF 受体的 NIH3T3 细胞中，src 家族酪氨酸激酶的 EGF 依赖性激活。激活迅速（<1 分钟）且持续（长达 16 小时）。此外，我们显示了 EGF 受体表达水平与 src 家族激酶激活程度之间的相关性。我们还表明，向内源性表达相对高水平 EGF 受体的 PC12 细胞中添加 EGF 也能激活 src 家族激酶活性。最引人注目的是，我们发现内源性表达非常高水平 EGF 受体的 A431 细胞，与 DHER14 细胞相比，src 家族激酶活性升高了 10 倍，且这种活性是组成性的。这种活性被 EGF 受体酪氨酸激酶活性的特异性抑制剂 AG1478 完全阻断，这表明 EGF 受体过表达与 src 家族激酶活性增强之间存在直接联系。我们的研究结果表明，只有当 EGF 受体水平达到特定水平时，才能检测到 EGF 依赖性 src 家族激酶活性。此外，如在 A431 细胞中那样的高水平 EGF 受体，可能有助于 src 家族激酶的激活增强。与 v-src 转化细胞中所见类似的持续 src 家族激酶激活，可能在肿瘤发生和肿瘤维持中起作用。
