Yamaguchi Tomohiro, Omatsu Naoto, Morimoto Emi, Nakashima Hiromi, Ueno Kanki, Tanaka Tamotsu, Satouchi Kiyoshi, Hirose Fumiko, Osumi Takashi
Graduate School of Life Science, University of Hyogo, 3-2-1, Koto, Kamigori, Hyogo 678-1297, Japan.
J Lipid Res. 2007 May;48(5):1078-89. doi: 10.1194/jlr.M600493-JLR200. Epub 2007 Feb 17.
A lipid droplet (LD)-associated protein, perilipin, is a critical regulator of lipolysis in adipocytes. We previously showed that Comparative Gene Identification-58 (CGI-58), a product of the causal gene of Chanarin-Dorfman syndrome, interacts with perilipin on LDs. In this study, we investigated the function of CGI-58 using RNA interference. Notably, CGI-58 knockdown caused an abnormal accumulation of LDs in both 3T3-L1 preadipocytes and Hepa1 hepatoma cells. CGI-58 knockdown did not influence the differentiation of 3T3-L1 adipocytes but reduced the activity of both basal and cAMP-dependent protein kinase-stimulated lipolysis. In vitro studies showed that CGI-58 itself does not have lipase/esterase activity, but it enhanced the activity of adipose triglyceride lipase. Upon lipolytic stimulation, endogenous CGI-58 was rapidly dispersed from LDs into the cytosol along with small particulate structures. This shift in localization depends on the phosphorylation of perilipin, because phosphorylated perilipin lost the ability to bind CGI-58. During lipolytic activation, LDs in adipocytes vesiculate into micro-LDs. Using coherent anti-Stokes Raman scattering microscopy, we pursued the formation of micro-LDs in single cells, which seemed to occur in cytoplasmic regions distant from the large central LDs. CGI-58 is not required for this process. Thus, CGI-58 facilitates lipolysis in cooperation with perilipin and other factors, including lipases.
脂滴（LD）相关蛋白围脂滴蛋白是脂肪细胞中脂解作用的关键调节因子。我们之前发现，钱纳林 - 多夫曼综合征致病基因的产物比较基因识别-58（CGI-58）可与脂滴上的围脂滴蛋白相互作用。在本研究中，我们利用RNA干扰技术研究了CGI-58的功能。值得注意的是，敲低CGI-58会导致3T3-L1前脂肪细胞和Hepa1肝癌细胞中脂滴异常积累。敲低CGI-58并不影响3T3-L1脂肪细胞的分化，但会降低基础和cAMP依赖性蛋白激酶刺激的脂解活性。体外研究表明，CGI-58本身不具有脂肪酶/酯酶活性，但它能增强脂肪甘油三酯脂肪酶的活性。在脂解刺激下，内源性CGI-58会与小颗粒结构一起迅速从脂滴分散到细胞质中。这种定位变化取决于围脂滴蛋白的磷酸化，因为磷酸化的围脂滴蛋白失去了结合CGI-58的能力。在脂解激活过程中，脂肪细胞中的脂滴会形成微脂滴。利用相干反斯托克斯拉曼散射显微镜，我们追踪了单细胞中微脂滴形成的过程，这似乎发生在远离中央大脂滴的细胞质区域。这一过程不需要CGI-58参与。因此，CGI-58与围脂滴蛋白及其他包括脂肪酶在内的因子协同促进脂解作用。
