Olayioye M A, Beuvink I, Horsch K, Daly J M, Hynes N E
Friedrich Miescher Institute, P.O. Box 2543, CH-4002 Basel, Switzerland.
J Biol Chem. 1999 Jun 11;274(24):17209-18. doi: 10.1074/jbc.274.24.17209.
Epidermal growth factor (EGF) binding to its receptor, ErbB1, triggers various signal transduction pathways, one of which leads to the activation of signal transducer and activator of transcription (Stat) factors. The mechanism underlying ErbB1-induced Stat activation and whether Stats are downstream targets of other ErbB receptors have not been explored. In this report we show that ErbB2, ErbB3, and ErbB4 do not potentiate Stat5 phosphorylation by EGF. However, neu differentiation factor-induced heterodimers of ErbB2 and ErbB4 activated Stat5. In A431 cells, Stat1, Stat3, and Stat5, were constitutively complexed with ErbB1 and rapidly phosphorylated on tyrosine in response to EGF. Neither mutation of the conserved tyrosine residue (Tyr694) nor inactivation of the Stat5a SH2 domain disrupted this association. However, an intact SH2 domain was necessary for EGF-induced Stat5a phosphorylation. In contrast to prolactin, which induced only Tyr694 phosphorylation of Stat5a, EGF promoted phosphorylation on Tyr694 and additional tyrosine residue(s). Janus kinases (Jaks) were also constitutively associated with ErbB receptors and were phosphorylated in response to EGF-related ligands. However, we provide evidence that EGF- and neu differentiation factor-induced Stat activation are dependent on Src but not Jak kinases. Upon EGF stimulation, c-Src was rapidly recruited to Stat/ErbB receptor complexes. Pharmacological Src kinase inhibitors and a dominant negative c-Src ablated both Stat and Jak tyrosine phosphorylation. However, dominant negative Jaks did not affect EGF-induced Stat phosphorylation. Taken together, the experiments establish two independent roles for Src kinases: (i) key molecules in ErbB receptor-mediated Stat signaling and (ii) potential upstream regulators of Jak kinases.
表皮生长因子（EGF）与其受体ErbB1结合后，会触发多种信号转导途径，其中一条途径会导致信号转导和转录激活因子（Stat）的激活。ErbB1诱导Stat激活的机制以及Stat是否为其他ErbB受体的下游靶点尚未得到研究。在本报告中，我们表明ErbB2、ErbB3和ErbB4不会增强EGF诱导的Stat5磷酸化。然而，神经分化因子诱导的ErbB2和ErbB4异二聚体可激活Stat5。在A431细胞中，Stat1、Stat3和Stat5与ErbB1组成性结合，并在EGF刺激下迅速发生酪氨酸磷酸化。保守酪氨酸残基（Tyr694）的突变或Stat5a SH2结构域的失活均不会破坏这种结合。然而，完整的SH2结构域对于EGF诱导的Stat5a磷酸化是必需的。与仅诱导Stat5a Tyr694磷酸化的催乳素不同，EGF可促进Tyr694和其他酪氨酸残基的磷酸化。Janus激酶（Jaks）也与ErbB受体组成性结合，并在EGF相关配体刺激下发生磷酸化。然而，我们提供的证据表明，EGF和神经分化因子诱导的Stat激活依赖于Src激酶而非Jak激酶。在EGF刺激下，c-Src迅速被招募到Stat/ErbB受体复合物中。药理学Src激酶抑制剂和显性负性c-Src可消除Stat和Jak的酪氨酸磷酸化。然而，显性负性Jaks并不影响EGF诱导的Stat磷酸化。综上所述，这些实验确立了Src激酶的两个独立作用：（i）ErbB受体介导的Stat信号传导中的关键分子；（ii）Jak激酶的潜在上游调节因子。
