Huang Huan, Starodub Olga, McIntosh Avery, Kier Ann B, Schroeder Friedhelm
Department of Pathobiology, Texas A&M University, College Station, Texas 77843-4466, USA.
J Biol Chem. 2002 Aug 9;277(32):29139-51. doi: 10.1074/jbc.M202923200. Epub 2002 May 22.
Although unesterified long chain fatty acids interact with peroxisome proliferator-activated receptors to initiate transcription within the nucleus, almost nothing is known regarding factors regulating long chain fatty acid distribution to the nucleus of living cells. The possibility that the liver fatty acid-binding protein (L-FABP) may function in this role was addressed in transfected L-cell fibroblasts overexpressing L-FABP using a series of fluorescent fatty acids differing in chain length and unsaturation. After 30 min of incubation, oxidation of BODIPY-, NBD-, and cis-parinaric acids was undetectable in L-cells. Likewise, L-cells very poorly esterified these fluorescent fatty acids in the following order: 0% BODIPY-C5, NBD-C6 (short chain length) < 0-3% NBD-C18, BODIPY-C16, cis-parinaric acid (long chain length) < 11% BODIPY-C12 (medium chain length). Real time confocal and multiphoton laser scanning microscopy (CLSM and MPLSM) showed that these fluorescent fatty acids were generally taken up in the following order: long chain (BODIPY-C16, NBD-C18) > medium chain (BODIPY-C12) short chain (BODIPY-C5, NBD-C6). The fluorescent fatty acids were imaged in the nucleus, primarily associated with the nuclear envelope, at levels about 2-3-fold lower than outside the nucleus. CLSM and MPLSM showed that L-FABP expression enhanced by 2-4-fold the initial rate and/or average maximal uptake of the long and medium chain but not the short chain fluorescent fatty acids in living cells. Furthermore, L-FABP expression increased the targeting of long and medium but not short chain fluorescent fatty acids to the nucleus by 2.9-4.4-fold and increased the proportion (i.e. nuclear:cytoplasm ratio) of medium and long chain but not short chain fatty acids by 2-3.6-fold. In summary, these results showed for the first time the presence of unesterified fatty acids in the nucleus of living cells and demonstrated that expression of a fatty acid-binding protein, L-FABP, specifically enhanced uptake and intracellular targeting of long and medium chain fatty acids to the nucleus.
尽管未酯化的长链脂肪酸与过氧化物酶体增殖物激活受体相互作用以启动细胞核内的转录，但对于调节长链脂肪酸向活细胞细胞核分布的因素却几乎一无所知。利用一系列链长和不饱和度不同的荧光脂肪酸，在过表达肝脏脂肪酸结合蛋白（L-FABP）的转染L细胞成纤维细胞中探讨了L-FABP可能发挥这一作用的可能性。孵育30分钟后，在L细胞中未检测到BODIPY、NBD和顺式紫黄质酸的氧化。同样，L细胞对这些荧光脂肪酸的酯化能力很差，顺序如下：0%BODIPY-C5、NBD-C6（短链长度）<0-3%NBD-C18、BODIPY-C16、顺式紫黄质酸（长链长度）<11%BODIPY-C12（中链长度）。实时共聚焦和多光子激光扫描显微镜（CLSM和MPLSM）显示，这些荧光脂肪酸的摄取顺序一般为：长链（BODIPY-C16、NBD-C18）>中链（BODIPY-C12）>短链（BODIPY-C5、NBD-C6）。荧光脂肪酸在细胞核中成像，主要与核膜相关，其水平比细胞核外低约2-3倍。CLSM和MPLSM显示，L-FABP的表达使活细胞中长链和中链荧光脂肪酸的初始速率和/或平均最大摄取量提高了2-4倍，但对短链荧光脂肪酸没有影响。此外，L-FABP的表达使长链和中链荧光脂肪酸向细胞核的靶向作用提高了2.9-4.4倍，并使中链和长链脂肪酸（而非短链脂肪酸）的比例（即核：细胞质比率）提高了2-3.6倍。总之，这些结果首次表明活细胞的细胞核中存在未酯化脂肪酸，并证明脂肪酸结合蛋白L-FABP的表达特异性增强了长链和中链脂肪酸向细胞核的摄取及细胞内靶向作用。
