Membrane Orientation and Subcellular Localization of Transmembrane Protein 106B (TMEM106B), a Major Risk Factor for Frontotemporal Lobar Degeneration
Membrane Orientation and Subcellular Localization of Transmembrane Protein 106B (TMEM106B), a Major Risk Factor for Frontotemporal Lobar Degeneration
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DOI：
10.1074/jbc.m112.365098
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发表时间：
2012-06-01
影响因子：
4.8
通讯作者：
Haass, Christian
中科院分区：
文献类型：
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作者：
Lang, Christina M.;Fellerer, Katrin;Haass, Christian
TMEM 106 B在全基因组关联研究中被确定为额颞叶变性（FTLD）与TAR DNA结合蛋白（TDP）-43病理学的主要风险因素。TMEM 106 B单核苷酸多态性与FTLD-TDP风险的最显著相关性在颗粒蛋白前体（GRN）突变患者中观察到。随后的研究表明TMEM 106 B表达与患者血清中的GRN水平之间呈负相关。然而，在本研究中，这没有得到证实，因为我们未能检测到在异源细胞中敲低或外源表达TMEM 106 B后GRN水平的显著改变。为了了解TMEM 106 B在健康和疾病中的功能，我们研究了这种完全未知的蛋白质的膜取向和亚细胞定位。通过差异膜提取和潜在的N-糖基化位点的顺序突变，我们确定TMEM 106 B为具有高度糖基化的管腔结构域的2型膜整合蛋白。糖基化是将TMEM 106 B转运到内质网以外的晚期细胞区室所部分需要的。内源性以及过表达的TMEM 106 B定位于晚期内体和溶酶体。有趣的是，液泡H+-ATP酶的抑制显著增加了TMEM 106 B的水平，这一发现可能提供了与GRN的意想不到的生化联系，因为这种蛋白质在相同条件下也强烈增加。我们的研究结果为理解TMEM 106 B在FTLD（一种无法治愈的神经退行性疾病）中的病理作用提供了生物化学和细胞生物学基础。
TMEM106B was identified as a major risk factor in a genome-wide association study for frontotemporal lobar degeneration (FTLD) with TAR DNA-binding protein (TDP)-43 pathology. The most significant association of TMEM106B single nucleotide polymorphisms with risk of FTLD-TDP was observed in patients with progranulin (GRN) mutations. Subsequent studies suggested an inverse correlation between TMEM106B expression and GRN levels in patient serum. However, in this study, this was not confirmed as we failed to detect a significant alteration of GRN levels upon knockdown or exogenous expression of TMEM106B in heterologous cells. To provide a basis for understanding TMEM106B function in health and disease, we investigated the membrane orientation and subcellular localization of this completely uncharacterized protein. By differential membrane extraction and sequential mutagenesis of potential N-glycosylation sites, we identified TMEM106B as a type 2 integral membrane protein with a highly glycosylated luminal domain. Glycosylation is partially required for the transport of TMEM106B beyond the endoplasmic reticulum to late cellular compartments. Endogenous as well as overexpressed TMEM106B localizes to late endosomes and lysosomes. Interestingly, the inhibition of vacuolar H+-ATPases significantly increased the levels of TMEM106B, a finding that may provide an unexpected biochemical link to GRN, because this protein is also strongly increased under the same conditions. Our findings provide a biochemical and cell biological basis for the understanding of the pathological role of TMEM106B in FTLD, an incurable neurodegenerative disorder.