Schönauer Ria, Jin Wenjun, Ertel Anastasia, Nemitz-Kliemchen Melanie, Panitz Nydia, Hantmann Elena, Seidel Anna, Braun Daniela A, Shril Shirlee, Hansen Matthias, Shahzad Khurrum, Sandford Richard, Saunier Sophie, Benmerah Alexandre, Bergmann Carsten, Hildebrandt Friedhelm, Halbritter Jan
Division of Nephrology, University Hospital Leipzig Medical Center, Leipzig, Germany.
Department of Medicine, Division of Nephrology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA.
Kidney Int. 2020 Oct;98(4):958-969. doi: 10.1016/j.kint.2020.05.027. Epub 2020 Jun 4.
Biallelic mutations in MAPKBP1 were recently associated with late-onset cilia-independent nephronophthisis. MAPKBP1 was found at mitotic spindle poles but could not be detected at primary cilia or centrosomes. Here, by identification and characterization of novel MAPKBP1 variants, we aimed at further investigating its role in health and disease. Genetic analysis was done by exome sequencing, homozygosity mapping, and a targeted kidney gene panel while coimmunoprecipitation was used to explore wild-type and mutant protein-protein interactions. Expression of MAPKBP1 in non-ciliated HeLa and ciliated inner medullary collecting duct cells enabled co-localization studies by fluorescence microscopy. By next generation sequencing, we identified two novel homozygous MAPKBP1 splice-site variants in patients with nephronophthisis-related chronic kidney disease. Splice-site analyses revealed truncation of C-terminal coiled-coil domains and patient-derived deletion constructs lost their ability to homodimerize and heterodimerize with paralogous WDR62. While wild-type MAPKBP1 exhibited centrosomal, basal body, and microtubule association, mutant proteins lost the latter and showed reduced recruitment to cell cycle dependent centriolar structures. Wild-type and mutant proteins had no reciprocal influence upon co-expression excluding dominant negative effects. Thus, MAPKBP1 appears to be a novel microtubule-binding protein with cell cycle dependent centriolar localization. Truncation of its coiled-coil domain is enough to abrogate its dimerization and results in severely disturbed intracellular localizations. Delineating the impact of impaired dimerization on cell cycle regulation and intracellular kidney signaling may provide new insights into common mechanisms of kidney degeneration. Thus, due to milder clinical presentation, MAPKBP1-associated nephronophthisis should be considered in adult patients with otherwise unexplained chronic kidney disease.
MAPKBP1的双等位基因突变最近被发现与迟发性非纤毛相关性肾痨有关。在有丝分裂纺锤体极发现了MAPKBP1，但在初级纤毛或中心体中未检测到。在此，通过鉴定和表征新型MAPKBP1变体，我们旨在进一步研究其在健康和疾病中的作用。通过外显子组测序、纯合性定位和靶向肾脏基因检测进行基因分析，同时使用免疫共沉淀来探索野生型和突变型蛋白-蛋白相互作用。MAPKBP1在非纤毛的HeLa细胞和有纤毛的髓质内集合管细胞中的表达使得能够通过荧光显微镜进行共定位研究。通过下一代测序，我们在患有肾痨相关慢性肾脏病的患者中鉴定出两个新型纯合MAPKBP1剪接位点变体。剪接位点分析显示C末端卷曲螺旋结构域被截断，患者来源的缺失构建体失去了与同源WDR62同源二聚化和异源二聚化的能力。虽然野生型MAPKBP1表现出与中心体、基体和微管的关联，但突变蛋白失去了后者，并且显示出对细胞周期依赖性中心粒结构的募集减少。野生型和突变型蛋白在共表达时没有相互影响，排除了显性负效应。因此，MAPKBP1似乎是一种新型的微管结合蛋白，具有细胞周期依赖性中心粒定位。其卷曲螺旋结构域的截断足以消除其二聚化，并导致细胞内定位严重紊乱。描绘二聚化受损对细胞周期调控和细胞内肾脏信号传导的影响可能为肾脏退化的常见机制提供新的见解。因此，由于临床表现较轻，在患有其他不明原因慢性肾脏病的成年患者中应考虑MAPKBP1相关的肾痨。
