Clewes Oliver, Fahey Mark S, Tyler Sue J, Watson Judy J, Seok Heon, Catania Caterina, Cho Kwangwook, Dawbarn David, Allen Shelley J
Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol, UK.
J Neurochem. 2008 Nov;107(4):1124-35. doi: 10.1111/j.1471-4159.2008.05698.x. Epub 2008 Sep 21.
Nerve growth factor (NGF) promotes cell survival via binding to the tyrosine kinase receptor A (TrkA). Its precursor, proNGF, binds to p75(NTR) and sortilin receptors to initiate apoptosis. Current disagreement exists over whether proNGF acts neurotrophically following binding to TrkA. As in Alzheimer's disease the levels of proNGF increase and TrkA decrease, it is important to clarify the properties of proNGF. Here, wild-type and cleavage-resistant mutated forms (M) of proNGF were engineered and their binding characteristics determined. M-proNGF and NGF bound to p75(NTR) with similar affinities, whilst M-proNGF had a lower affinity than NGF for TrkA. M-proNGF behaved neurotrophically, albeit less effectively than NGF. M-proNGF addition resulted in phosphorylation of TrkA and ERK1/2, and in PC12 cells elicited neurite outgrowth and supported cell survival. Conversely, M-proNGF addition to cultured cortical neurons initiated caspase 3 cleavage. Importantly, these biological effects were shown to be mediated by unprocessed M-proNGF. Surprisingly, binding of the pro region alone to TrkA, at a site other than that of NGF, caused TrkA and ERK1/2 phosphorylation. Our data show that M-proNGF stimulates TrkA to a lesser degree than NGF, suggesting that in Alzheimer brain the increased proNGF : NGF and p75(NTR) : TrkA ratios may permit apoptotic effects to predominate over neurotrophic effects.
神经生长因子（NGF）通过与酪氨酸激酶受体A（TrkA）结合来促进细胞存活。其前体，前体神经生长因子（proNGF），与p75神经营养因子受体（p75(NTR)）和sortilin受体结合以启动细胞凋亡。目前对于proNGF与TrkA结合后是否具有神经营养作用存在分歧。由于在阿尔茨海默病中proNGF水平升高而TrkA水平降低，因此阐明proNGF的特性很重要。在此，构建了proNGF的野生型和抗切割突变形式（M），并确定了它们的结合特性。M-proNGF和NGF以相似的亲和力与p75(NTR)结合，而M-proNGF与TrkA的亲和力低于NGF。M-proNGF具有神经营养作用，尽管其效果不如NGF。添加M-proNGF导致TrkA和ERK1/2磷酸化，并在PC12细胞中引发神经突生长并支持细胞存活。相反，向培养的皮质神经元中添加M-proNGF会引发半胱天冬酶3的切割。重要的是，这些生物学效应被证明是由未加工的M-proNGF介导的。令人惊讶的是，pro区域单独与TrkA在NGF结合位点以外的位点结合会导致TrkA和ERK1/2磷酸化。我们的数据表明，M-proNGF对TrkA的刺激程度低于NGF，这表明在阿尔茨海默病大脑中，proNGF:NGF和p75(NTR):TrkA的比例增加可能使凋亡效应比神经营养效应占主导地位。
