Audhya Anjon, Emr Scott D
Department of Cellular and Molecular Medicine, University of California, San Diego, School of Medicine, La Jolla, CA 92093-0668, USA.
EMBO J. 2003 Aug 15;22(16):4223-36. doi: 10.1093/emboj/cdg397.
The essential phospholipid PI4,5P(2) is generated by a well conserved PI4P 5-kinase, Mss4, in yeast. Balanced production and turnover of PI4,5P(2) is important for normal organization of the actin cytoskeleton and cell viability. Previous studies have shown that multiple PI phosphatases can regulate PI4,5P(2) levels. We report a new, unexpected regulatory mechanism for PI4,5P(2) homeostasis, directed by nuclear-cytoplasmic shuttling of the lipid kinase. We show that Mss4 is a phosphoprotein, which contains a functional nuclear localization signal (NLS) and can shuttle between the cytoplasm and the nucleus. Temperature-conditional mss4 cells that accumulate Mss4 protein in the nucleus exhibit reduced levels of PI4,5P(2), depolarization of the actin cytoskeleton and a block in Mss4 phosphorylation, suggesting an essential role for phosphorylated Mss4 at the plasma membrane. Through the isolation of gene dosage-dependent suppressors of mss4 mutants, we identified Bcp1, a protein enriched in the nucleus, which is required for Mss4 nuclear export and is related to the mammalian BRCA2-interacting protein BCCIP. Together, these studies suggest a new mechanism for lipid kinase regulation through regulated nuclear-cytoplasmic shuttling.
必需磷脂PI4,5P(2)由酵母中一种保守性良好的PI4P 5-激酶Mss4生成。PI4,5P(2)的平衡生成与周转对于肌动蛋白细胞骨架的正常组织和细胞活力至关重要。先前的研究表明，多种PI磷酸酶可调节PI4,5P(2)水平。我们报告了一种由脂质激酶的核质穿梭指导的、全新的、意想不到的PI4,5P(2)稳态调节机制。我们发现Mss4是一种磷蛋白，含有功能性核定位信号（NLS），可在细胞质和细胞核之间穿梭。在细胞核中积累Mss4蛋白的温度条件性mss4细胞表现出PI4,5P(2)水平降低、肌动蛋白细胞骨架去极化以及Mss4磷酸化受阻，这表明磷酸化的Mss4在质膜上具有重要作用。通过分离mss4突变体的基因剂量依赖性抑制子，我们鉴定出Bcp1，一种在细胞核中富集的蛋白，它是Mss4核输出所必需的，并且与哺乳动物BRCA2相互作用蛋白BCCIP相关。这些研究共同揭示了一种通过调节核质穿梭来调节脂质激酶的新机制。
