Küch Eva-Maria, Vellaramkalayil Regina, Zhang Ingrid, Lehnen Daniela, Brügger Britta, Sreemmel Wolfgang, Ehehalt Robert, Poppelreuther Margarete, Füllekrug Joachim
Biochim Biophys Acta. 2014 Feb;1841(2):227-39. doi: 10.1016/j.bbalip.2013.10.018.
The acyl-CoA synthetase 4 (ACSL4) has been implicated in carcinogenesis and neuronal development. Acyl-CoA synthetases are essential enzymes of lipid metabolism, and ACSL4 is distinguished by its preference for arachidonic acid. Two human ACSL4 isoforms arising from differential splicing were analyzed by ectopic expression in COS cells. We found that the ACSL4_v1 variant localized to the inner side of the plasma membrane including microvilli, and was also present in the cytosol. ACSL4_v2 contains an additional N-terminal hydrophobic region; this isoform was located at the endoplasmic reticulum and on lipid droplets. A third isoform was designed de novo by appending a mitochondrial targeting signal. All three ACSL4 variants showed the same specific enzyme activity. Overexpression of the isoenzymes increased cellular uptake of arachidonate to the same degree, indicating that the metabolic trapping of fatty acids is independent of the subcellular localization. Remarkably, phospholipid metabolism was changed by ACSL4 expression. Labeling with arachidonate showed that the amount of newly synthesized phosphatidylinositol was increased by all three ACSL4 isoenzymes but not by ACSL1. This was dependent on the expression level and the localization of the ACSL4 isoform. We conclude that in our model system exogenous fatty acids are channeled preferentially towards phosphatidylinositol by ACSL4 overexpression. The differential localization of the endogenous isoenzymes may provide compartment specific precursors of this anionic phospholipid important for many signaling processes.
酰基辅酶A合成酶4（ACSL4）与癌症发生和神经元发育有关。酰基辅酶A合成酶是脂质代谢的关键酶，而ACSL4以其对花生四烯酸的偏好而著称。通过在COS细胞中异位表达，分析了由可变剪接产生的两种人类ACSL4异构体。我们发现ACSL4_v1变体定位于包括微绒毛在内的质膜内侧，也存在于细胞质中。ACSL4_v2包含一个额外的N端疏水区域；这种异构体位于内质网和脂滴上。通过附加线粒体靶向信号从头设计了第三种异构体。所有三种ACSL4变体都表现出相同的比酶活性。同工酶的过表达使花生四烯酸的细胞摄取增加到相同程度，表明脂肪酸的代谢捕获与亚细胞定位无关。值得注意的是，ACSL4的表达改变了磷脂代谢。用花生四烯酸标记表明，所有三种ACSL4同工酶都增加了新合成的磷脂酰肌醇的量，但ACSL1没有。这取决于ACSL4异构体的表达水平和定位。我们得出结论，在我们的模型系统中，外源性脂肪酸通过ACSL4的过表达优先导向磷脂酰肌醇。内源性同工酶的差异定位可能为这种对许多信号传导过程重要的阴离子磷脂提供特定区域的前体。
