Valius M, Kazlauskas A
National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Cell. 1993 Apr 23;73(2):321-34. doi: 10.1016/0092-8674(93)90232-f.
Upon ligand-induced tyrosine phosphorylation, the platelet-derived growth factor (PDGF) receptor (PDGFR) beta subunit associates with PLC-gamma 1, RasGAP, P13K, and a 64 kd protein. To determine the relative role of each of these associated proteins in PDGFR signaling, we constructed a PDGFR mutant (F5) unable to bind any of them and a panel of "add-back" mutants that could bind only one of the receptor-associated proteins. F5 PDGFR failed to activate PLC-gamma 1, P13K, or Ras and was unable to trigger DNA synthesis. Permitting association of F5 PDGFR with either PLC-gamma 1 or P13K restored Ras activation and a mitogenic response. Surprisingly, even though binding of the 64 kd protein almost fully restored Ras activation, it did not rescue the receptor's ability to trigger DNA synthesis. Thus Ras activation is insufficient to trigger PDGF-dependent DNA synthesis, and PLC-gamma 1 and P13K are independent downstream mediators of PDGF's mitogenic signal.
在配体诱导的酪氨酸磷酸化作用下，血小板衍生生长因子（PDGF）受体（PDGFR）的β亚基与磷脂酶C-γ1（PLC-γ1）、RasGAP、磷脂酰肌醇-3激酶（PI3K）以及一种64千道尔顿的蛋白质相结合。为了确定这些相关蛋白各自在PDGFR信号传导中的相对作用，我们构建了一个无法与它们中的任何一个结合的PDGFR突变体（F5）以及一组只能与一种受体相关蛋白结合的“回补”突变体。F5 PDGFR无法激活PLC-γ1、PI3K或Ras，并且无法触发DNA合成。使F5 PDGFR与PLC-γ1或PI3K缔合可恢复Ras激活及促有丝分裂反应。令人惊讶的是，尽管64千道尔顿蛋白质的结合几乎完全恢复了Ras激活，但它并未挽救受体触发DNA合成的能力。因此，Ras激活不足以触发PDGF依赖性DNA合成，并且PLC-γ1和PI3K是PDGF促有丝分裂信号的独立下游介质。
