A Molecular Mechanism Underlying Genotype-Specific Intrahepatic Cholestasis Resulting From MYO5B Mutations
A Molecular Mechanism Underlying Genotype-Specific Intrahepatic Cholestasis Resulting From MYO5B Mutations
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MYO5B 突变导致的基因型特异性肝内胆汁淤积的分子机制
DOI：
10.1002/hep.31002
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发表时间：
2020-04-23
期刊：
影响因子：
13.5
通讯作者：
Ijzendoorn, Sven C. D. van
中科院分区：
文献类型：
--
作者：
Overeem, Arend W.;Li, Qinghong;Ijzendoorn, Sven C. D. van
背景与目的进行性家族性肝内胆汁淤积症(PFIC)6与编码肌球蛋白VB(myosin VB，myoVb)的MYO5B基因的错义而非双等位基因无义或移码突变有关。这种基因型-表型相关性以及MYO5B突变导致PFIC的机制尚不清楚。本研究的目的是确定myoVb的缺失或患者特异性的myoVb突变体的表达是否与胆小管蛋白定位缺陷有关，如果是，通过何种机制。方法和结果我们证明了胆汁淤积症相关的myoVb蛋白中600位氨基酸的Proline被替换为亮氨酸(P660L)导致胆小管蛋白在囊泡中的细胞内积聚。值得注意的是，MYO5B在体外和体内的敲除没有引起小管定位缺陷。相反，只包含尾部结构域的myoVb突变体的表达与Myo5b-P660L突变的影响相同。利用额外的myoVb和rab11a突变体，我们证明了运动域缺陷的myoVb抑制了专门的心尖循环内小体的形成，并且它对小管蛋白定位的干扰作用依赖于它与活性的rab11a的相互作用，并且发生在反高尔基网络/循环内小体界面上。结论我们的结果揭示了MYO5B运动域突变导致小管蛋白在肝细胞中错误定位的机制，这出人意料地不涉及myoVb功能丧失，但正如我们所提出的那样，它介导了一种毒性获得功能。这些结果解释了为什么影响运动域的双等位基因MYO5B突变而不是那些消除myoVb表达的双等位基因突变与PFIC6相关。
Background and Aims Progressive familial intrahepatic cholestasis (PFIC) 6 has been associated with missense but not biallelic nonsense or frameshift mutations in MYO5B, encoding the motor protein myosin Vb (myoVb). This genotype-phenotype correlation and the mechanism through which MYO5B mutations give rise to PFIC are not understood. The aim of this study was to determine whether the loss of myoVb or expression of patient-specific myoVb mutants can be causally related to defects in canalicular protein localization and, if so, through which mechanism.Approach and Results We demonstrate that the cholestasis-associated substitution of the proline at amino acid position 600 in the myoVb protein to a leucine (P660L) caused the intracellular accumulation of bile canalicular proteins in vesicular compartments. Remarkably, the knockout of MYO5B in vitro and in vivo produced no canalicular localization defects. In contrast, the expression of myoVb mutants consisting of only the tail domain phenocopied the effects of the Myo5b-P660L mutation. Using additional myoVb and rab11a mutants, we demonstrate that motor domain-deficient myoVb inhibited the formation of specialized apical recycling endosomes and that its disrupting effect on the localization of canalicular proteins was dependent on its interaction with active rab11a and occurred at the trans-Golgi Network/recycling endosome interface.Conclusions Our results reveal a mechanism through which MYO5B motor domain mutations can cause the mislocalization of canalicular proteins in hepatocytes which, unexpectedly, does not involve myoVb loss-of-function but, as we propose, a rab11a-mediated gain-of-toxic function. The results explain why biallelic MYO5B mutations that affect the motor domain but not those that eliminate myoVb expression are associated with PFIC6.