PDF(Pubmed)
Abstract：
Upregulated signal flow through RAS and the mitogen-associated protein kinase (MAPK) cascade is the unifying mechanistic theme of the RASopathies, a family of disorders affecting development and growth. Pathogenic variants in more than 20 genes have been causally linked to RASopathies, the majority having a dominant role in promoting enhanced signaling. Here, we report that SPRED2 loss of function is causally linked to a recessive phenotype evocative of Noonan syndrome. Homozygosity for three different variants-c.187C>T (p.Arg63∗), c.299T>C (p.Leu100Pro), and c.1142_1143delTT (p.Leu381Hisfs∗95)-were identified in four subjects from three families. All variants severely affected protein stability, causing accelerated degradation, and variably perturbed SPRED2 functional behavior. When overexpressed in cells, all variants were unable to negatively modulate EGF-promoted RAF1, MEK, and ERK phosphorylation, and time-course experiments in primary fibroblasts (p.Leu100Pro and p.Leu381Hisfs∗95) documented an increased and prolonged activation of the MAPK cascade in response to EGF stimulation. Morpholino-mediated knockdown of spred2a and spred2b in zebrafish induced defects in convergence and extension cell movements indicating upregulated RAS-MAPK signaling, which were rescued by expressing wild-type SPRED2 but not the SPRED2Leu381Hisfs∗95 protein. The clinical phenotype of the four affected individuals included developmental delay, intellectual disability, cardiac defects, short stature, skeletal anomalies, and a typical facial gestalt as major features, without the occurrence of the distinctive skin signs characterizing Legius syndrome. These features, in part, characterize the phenotype of Spred2-/- mice. Our findings identify the second recessive form of Noonan syndrome and document pleiotropic consequences of SPRED2 loss of function in development.
摘要：
通过RAS和丝裂原相关蛋白激酶（MAPK）级联的信号流上调是RASopathies的统一机制主题，影响发育和生长的疾病家族。超过20个基因的致病变异与放射病有因果关系，大多数在促进增强的信号传导中起主导作用。这里,我们报告SPRED2功能丧失与Noonan综合征的隐性表型有因果关系.三种不同变体的纯合性-c.187C>T（p。Arg63*),c.299T>C（p。Leu100Pro)，和c.1142_1143delTT（p。Leu381Hisfs*95）-在来自三个家庭的四个受试者中确定。所有变体严重影响蛋白质稳定性，导致加速降解，和可变扰动的SPRED2功能行为。当在细胞中过表达时，所有变体都不能负调节EGF促进的RAF1，MEK，和ERK磷酸化，和原代成纤维细胞的时程实验（p。Leu100Pro和p.Leu381Hisfs*95）记录了对EGF刺激的MAPK级联激活增加和延长。在斑马鱼中，吗啉代介导的spred2a和spred2b的敲低诱导了会聚和延伸细胞运动的缺陷，表明RAS-MAPK信号传导上调，通过表达野生型SPRED2而不是SPRED2Leu381Hisfs*95蛋白来拯救它们。四个受影响的个体的临床表型包括发育迟缓，智力残疾,心脏缺陷,身材矮小,骨骼异常,和典型的面部完形作为主要特征，没有明显的皮肤征象的出现，特点是Legius综合征。这些特点,在某种程度上,表征Spred2-/-小鼠的表型。我们的发现确定了Noonan综合征的第二种隐性形式，并记录了SPRED2在发育中功能丧失的多效性后果。
