Department of Cell and Developmental Biology, Oregon Health and Sciences University, School of Medicine, Portland, OR 97239-3098, USA.
Department of Neurobiology and Anatomy and Internal Medicine, Division of Hematology and Hematologic Malignancies, University of Utah, School of Medicine, Salt Lake City, UT 94132, USA.
Development. 2014 Aug;141(15):3062-71. doi: 10.1242/dev.110130. Epub 2014 Jul 3.
ProBMP4 is generated as a latent precursor that is sequentially cleaved at two sites within the prodomain to generate an active ligand. An initial cleavage occurs adjacent to the ligand domain, which generates a non-covalently associated prodomain/ligand complex that is subsequently dissociated by cleavage at an upstream site. An outstanding question is whether the two sites need to be cleaved sequentially and in the correct order to achieve proper control of BMP4 signaling during development. In the current studies, we demonstrate that mice carrying a knock-in point mutation that causes simultaneous rather than sequential cleavage of both prodomain sites show loss of BMP4 function and die during mid-embryogenesis. Levels of mature BMP4 are severely reduced in mutants, although levels of precursor and cleaved prodomain are unchanged compared with wild type. Our biochemical analysis supports a model in which the transient prodomain/ligand complex that forms during sequential cleavage plays an essential role in prodomain-mediated stabilization of the mature ligand until it can acquire protection from degradation by other means. By contrast, simultaneous cleavage causes premature release of the ligand from the prodomain, leading to destabilization of the ligand and loss of signaling in vivo.
ProBMP4 作为一个潜在的前体被生成，该前体在原结构域内的两个位点处被顺序切割，以生成一个活性配体。最初的切割发生在配体结构域附近，生成一个非共价结合的原结构域/配体复合物，随后通过在上游位点的切割而解离。一个悬而未决的问题是，两个位点是否需要按正确的顺序进行顺序切割，以在发育过程中对 BMP4 信号进行适当的控制。在当前的研究中，我们证明，携带导致两个原结构域位点同时而不是顺序切割的点突变的小鼠表现出 BMP4 功能丧失，并在胚胎中期死亡。突变体中成熟的 BMP4 水平严重降低，尽管与野生型相比，前体和切割的原结构域水平没有变化。我们的生化分析支持这样一种模型，即形成于顺序切割过程中的瞬时原结构域/配体复合物在原结构域介导的成熟配体稳定中发挥着重要作用，直到配体可以通过其他方式获得免受降解的保护。相比之下，同时切割导致配体从原结构域中过早释放，导致配体失稳并在体内失去信号。
