Um Moonkyoung, Lodish Harvey F
Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02142, USA.
J Biol Chem. 2006 Mar 3;281(9):5648-56. doi: 10.1074/jbc.M510943200. Epub 2006 Jan 4.
The hematopoietic cytokine erythropoietin (Epo) prevents neuronal death during ischemic events in the brain and in neurodegenerative diseases, presumably through its antiapoptotic effects. To explore the role of different signaling pathways in Epo-mediated antiapoptotic effects in differentiated human neuroblastoma SH-SY5Y cells, we employed a prolactin receptor (PrlR)/erythropoietin receptor (EpoR) chimera system, in which binding of prolactin (Prl) to the extracellular domain activates EpoR signaling in the cytosol. On induction of apoptosis by staurosporine, Prl supports survival of the SH-SY5Y cells expressing the wild-type PrlR/EpoR chimera. In these cells Prl treatment strongly activates the STAT5, AKT, and MAPK signaling pathways and induces weak activation of the p65 NF-kappaB factor. Selective mutation of the eight tyrosine residues of the EpoR cytoplasmic domain results in impaired or absent activation of either STAT5 (mutation of Tyr(343)) or AKT (mutation of Tyr(479)) or both (mutation of all eight tyrosine residues). Most interestingly, Prl treatment does not prevent apoptosis in cells expressing mutant PrlR/EpoR chimeras in which either the STAT5 or the AKT signaling pathways are not activated. In contrast, ERK 1/2 is fully activated by all mutant PrlR/EpoR chimeras, comparable with the level seen with the wild-type PrlR/EpoR chimera, implying that activation of the MAPK signaling pathway per se is not sufficient for antiapoptotic activity. Therefore, the antiapoptotic effects of Epo in neuronal cells require the combinatorial activation of multiple signaling pathways, including STAT5, AKT, and potentially MAPK as well, in a manner similar to that observed in hematopoietic cells.
造血细胞因子促红细胞生成素（Epo）可预防脑缺血事件及神经退行性疾病中的神经元死亡，推测这是通过其抗凋亡作用实现的。为了探究不同信号通路在Epo介导的分化人神经母细胞瘤SH-SY5Y细胞抗凋亡作用中的作用，我们采用了催乳素受体（PrlR）/促红细胞生成素受体（EpoR）嵌合体系统，其中催乳素（Prl）与细胞外结构域的结合可激活胞质中的EpoR信号。用星形孢菌素诱导凋亡时，Prl可支持表达野生型PrlR/EpoR嵌合体的SH-SY5Y细胞存活。在这些细胞中，Prl处理可强烈激活STAT5、AKT和MAPK信号通路，并诱导p65 NF-κB因子的弱激活。EpoR胞质结构域八个酪氨酸残基的选择性突变导致STAT5（Tyr(343)突变）或AKT（Tyr(479)突变）或两者（所有八个酪氨酸残基突变）的激活受损或缺失。最有趣的是，Prl处理不能预防表达突变型PrlR/EpoR嵌合体的细胞凋亡，其中STAT5或AKT信号通路未被激活。相反，所有突变型PrlR/EpoR嵌合体均可使ERK 1/2完全激活，与野生型PrlR/EpoR嵌合体的激活水平相当，这意味着MAPK信号通路的激活本身不足以产生抗凋亡活性。因此，Epo在神经元细胞中的抗凋亡作用需要多种信号通路的联合激活，包括STAT5、AKT以及可能的MAPK，其方式与造血细胞中观察到的类似。
