Ulrich E, Duwel A, Kauffmann-Zeh A, Gilbert C, Lyon D, Rudkin B, Evan G, Martin-Zanca D
Imperial Cancer Research Fund Laboratories, London, UK.
Oncogene. 1998 Feb 19;16(7):825-32. doi: 10.1038/sj.onc.1201842.
Survival signalling by ligand-activated tyrosine kinase receptors plays a crucial role in maintaining the balance between cell viability and apoptosis in multicellular organisms. To identify receptor domains and pathways involved in survival signalling, the nerve growth factor receptor TrkA was expressed in Rat-1/MycER fibroblasts. We demonstrate that wt-TrkA receptor delays c-Myc-, U.V.- and Cycloheximide-induced apoptosis and activates targets such as the mitogen-activated protein kinase (MAPK) Erk2 and the serine/threonine kinase Akt/PKB, both of which have been implicated in survival signalling. TrkA mutated within its SHC binding site (Y490F) delays c-Myc-induced apoptosis without activating endogenous Akt/PKB. In contrast, the TrkA Y490F mutant receptor does not delay U.V.-induced apoptosis whilst TrkA mutated at its PLC-gamma binding site (Y785F) is capable of protecting from apoptosis induced by c-Myc or U.V. treatment. The double mutant TrkA YY490/785FF fails to block either of these two apoptotic stimuli. While P13-kinase inhibitors LY294002 and Wortmannin completely block survival signalling following U.V. treatment, neither drug affects the ability of TrkA to block c-Myc-induced apoptosis. We show that the Akt/PKB pathway is essential for NGF stimulated TrkA survival signalling in the case of U.V.-induced apoptosis, but that apoptosis induced by c-Myc is also blocked by a novel, Akt/PKB-independent, pathway. These observations suggest that TrkA can activate different survival signalling pathways, which can interfere with specific apoptotic pathways.
配体激活的酪氨酸激酶受体介导的生存信号在多细胞生物体中维持细胞活力与凋亡之间的平衡起着关键作用。为了确定参与生存信号的受体结构域和信号通路，将神经生长因子受体TrkA在Rat-1/MycER成纤维细胞中表达。我们证明野生型TrkA受体可延迟c-Myc、紫外线和环己酰亚胺诱导的凋亡，并激活诸如丝裂原活化蛋白激酶（MAPK）Erk2和丝氨酸/苏氨酸激酶Akt/PKB等靶点，这两者均与生存信号有关。在其SHC结合位点发生突变的TrkA（Y490F）可延迟c-Myc诱导的凋亡，但不激活内源性Akt/PKB。相反，TrkA Y490F突变体受体不能延迟紫外线诱导的凋亡，而在其PLC-γ结合位点发生突变的TrkA（Y785F）能够保护细胞免受c-Myc或紫外线处理诱导的凋亡。双突变体TrkA YY490/785FF无法阻断这两种凋亡刺激中的任何一种。虽然PI3-激酶抑制剂LY294002和渥曼青霉素在紫外线处理后完全阻断生存信号，但这两种药物均不影响TrkA阻断c-Myc诱导的凋亡的能力。我们表明，在紫外线诱导的凋亡情况下，Akt/PKB信号通路对于NGF刺激的TrkA生存信号至关重要，但c-Myc诱导的凋亡也可被一条新的、不依赖Akt/PKB的信号通路阻断。这些观察结果表明，TrkA可激活不同的生存信号通路，这些通路可干扰特定的凋亡通路。
