Departments of Cell and Developmental Biology, Division of Pediatric Cardiology, Department of Pediatrics and Communicable Diseases, and Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109, USA.
Proc Natl Acad Sci U S A. 2012 Oct 23;109(43):17472-7. doi: 10.1073/pnas.1203106109. Epub 2012 Oct 9.
Mutations that cause defects in levels of the signaling lipid phosphatidylinositol 3,5-bisphosphate [PI(3,5)P(2)] lead to profound neurodegeneration in mice. Moreover, mutations in human FIG4 predicted to lower PI(3,5)P(2) levels underlie Charcot-Marie-Tooth type 4J neuropathy and are present in selected cases of amyotrophic lateral sclerosis. In yeast and mammals, PI(3,5)P(2) is generated by a protein complex that includes the lipid kinase Fab1/Pikfyve, the scaffolding protein Vac14, and the lipid phosphatase Fig4. Fibroblasts cultured from Vac14(-/-) and Fig4(-/-) mouse mutants have a 50% reduction in the levels of PI(3,5)P(2), suggesting that there may be PIKfyve-independent pathways that generate this lipid. Here, we characterize a Pikfyve gene-trap mouse (Pikfyve(β-geo/β-geo)), a hypomorph with ~10% of the normal level of Pikfyve protein. shRNA silencing of the residual Pikfyve transcript in fibroblasts demonstrated that Pikfyve is required to generate all of the PI(3,5)P(2) pool. Surprisingly, Pikfyve also is responsible for nearly all of the phosphatidylinositol-5-phosphate (PI5P) pool. We show that PI5P is generated directly from PI(3,5)P(2), likely via 3'-phosphatase activity. Analysis of tissues from the Pikfyve(β-geo/β-geo) mouse mutants reveals that Pikfyve is critical in neural tissues, heart, lung, kidney, thymus, and spleen. Thus, PI(3,5)P(2) and PI5P have major roles in multiple organs. Understanding the regulation of these lipids may provide insights into therapies for multiple diseases.
导致信号脂质磷脂酰肌醇 3,5-二磷酸 [PI(3,5)P(2)] 水平缺陷的突变会导致小鼠发生严重的神经退行性变。此外，预测降低 PI(3,5)P(2)水平的人类 FIG4 突变是 Charcot-Marie-Tooth 型 4J 神经病的基础，并且存在于选定的肌萎缩侧索硬化病例中。在酵母和哺乳动物中，PI(3,5)P(2)是由包括脂质激酶 Fab1/Pikfyve、支架蛋白 Vac14 和脂质磷酸酶 Fig4 的蛋白质复合物产生的。从 Vac14(-/-)和 Fig4(-/-)小鼠突变体培养的成纤维细胞中，PI(3,5)P(2)的水平降低了 50%，这表明可能存在不依赖于 PIKfyve 的途径来产生这种脂质。在这里，我们描述了一种 Pikfyve 基因捕获小鼠（Pikfyve(β-geo/β-geo)），这是一种 Pikfyve 蛋白水平正常的约 10%的低功能突变体。在成纤维细胞中沉默残留的 Pikfyve 转录本表明，Pikfyve 是产生所有 PI(3,5)P(2)池所必需的。令人惊讶的是，Pikfyve 也负责几乎所有的磷脂酰肌醇-5-磷酸（PI5P）池。我们表明 PI5P 直接从 PI(3,5)P(2)产生，可能通过 3'-磷酸酶活性。对 Pikfyve(β-geo/β-geo)小鼠突变体组织的分析表明，Pikfyve 在神经组织、心脏、肺、肾、胸腺和脾脏中至关重要。因此，PI(3,5)P(2)和 PI5P 在多个器官中具有重要作用。了解这些脂质的调节可能为多种疾病的治疗提供新的思路。
