Research Center C-873, University of Medicine and Dentistry of New Jersey, New Jersey Dental School, Newark, NJ 07103, USA.
Int J Biol Sci. 2006 Aug 30;2(4):216-26. doi: 10.7150/ijbs.2.216.
Our studies on homeostatic restitution of cellular and subcellular membranes showed that vesicular intracellular transport is engaged in systematic and coordinated replacement of lipids and proteins in the membranes of the secretory, non-dividing epithelial cells (Slomiany et al., J. Physiol. Pharmacol. 2004; 55: 837-860). In this report, we present evidence on the homeostatic restitution of lipids in the biomembranes that constitute nuclear envelopes. We investigated nuclear membranes lipid synthesis by employing purified intact nuclei (IN), the outer nuclear membrane (ONM), the inner nuclear membrane (INM) and the cell cytosol (CC). In contrast to Endoplasmic Reticulum (ER) which in the presence of CC generates new biomembrane that forms ER vesicles transporting ER products to Golgi, the IN, ONM and INM are not producing transport vesicles. Instead, the newly synthesized lipids remain in the nuclear membranes. The membranes (INM, ONM) of IN incubated with CC become enriched with newly synthesized phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylinositol phosphates (PIPs) and phosphatidic acid (PA). The incubation of separated ONM and INM with CC also enriched the membranes with IN specific lipids identified above. Moreover, the incubation of IN or its membranes with CC afforded retention of numerous CC proteins on the nuclear membrane. Here, we concentrated on 30kDa CC protein that displayed affinity to nuclear membrane PIP2. The 30kDa CC protein bound to PIP2 of IN, INM, and ONM. With IN, initially the PIP2-30kDa CC protein complex was detected on ONM, after 30-120 min of incubation, was found on INM and in nuclear contents. At the same time when the 30 kDa protein was released from INM and found in nuclear contents, the PIP2 of INM and ONM became undetectable, while the lipid extract from the membrane displaced from IN contained labeled PI only. Since ONM is an uninterrupted continuum of ER and INM, we speculate that the synthesis of the lipids in the ER, in the region adjacent to nucleus, is defining nuclear outer and inner biomembrane composition, is responsible for transport of the cytosolic protein into the nucleus and, replenishment of ER membrane used for vesicular transport.
我们的研究表明，细胞和亚细胞膜的内稳性恢复中涉及到囊泡细胞内运输，它参与了分泌型非分裂上皮细胞（Slomiany 等人，《生理药理学杂志》，2004 年；55：837-860）的膜中脂质和蛋白质的系统性和协调性替换。在本报告中，我们提供了关于构成核膜的生物膜中脂质内稳性恢复的证据。我们通过使用纯化的完整核（IN）、外核膜（ONM）、内核膜（INM）和细胞质（CC）来研究核膜脂质的合成。与内质网（ER）不同，ER 在 CC 的存在下生成新的生物膜，该膜形成 ER 囊泡，将 ER 产物运输到高尔基体，而 IN、ONM 和 INM 并不产生运输囊泡。相反，新合成的脂质保留在核膜中。与 CC 孵育的 IN 的膜（INM、ONM）富含新合成的磷脂酰胆碱（PC）、磷脂酰肌醇（PI）、磷酸肌醇磷酸（PIPs）和磷脂酸（PA）。与 CC 孵育的分离的 ONM 和 INM 也使上述 IN 特异性脂质在膜中富集。此外，CC 蛋白在核膜上的保留。在这里，我们集中研究了与核膜 PIP2 具有亲和力的 30kDa CC 蛋白。该 30kDa CC 蛋白与 IN、INM 和 ONM 的 PIP2 结合。与 IN 一起，最初在 ONM 上检测到 PIP2-30kDa CC 蛋白复合物，孵育 30-120 分钟后，在 INM 和核内容物中发现。同时，当 30kDa 蛋白从 INM 中释放并在核内容物中发现时，INM 和 ONM 的 PIP2 变得不可检测，而从 IN 中置换的膜的脂质提取物仅含有标记的 PI。由于 ONM 是 ER 和 INM 的连续体，我们推测 ER 中脂质的合成，在靠近细胞核的区域，决定了核外和核内生物膜的组成，负责将细胞质蛋白运入细胞核，并补充用于囊泡运输的 ER 膜。
