Nomura F, Noda M
First Department of Medicine, Chiba University School of Medicine, Japan.
Hepatology. 1993 Oct;18(4):870-3. doi: 10.1002/hep.1840180419.
ADP ribosylation is considered one of the important covalent modifications of cellular proteins catalyzed by ADP ribosyltransferase, which transfers ADP ribose moiety of NAD to an acceptor protein. Because a growing body of evidence has suggested significant biological roles for mono-ADP ribosylations in transmembrane signal transduction and other cell metabolism, how alcohol intake alters them is of interest. Cholera toxin and pertussis toxin have been widely used as probes to investigate the roles of GTP-binding proteins (G-proteins) in the transduction of hormonal and sensory signals. We first tested effects of long-term alcohol intake on these toxin-catalyzed ADP ribosylations of G-proteins in rat liver plasma membranes. Treatment of rat liver plasma membrane with [32P]NAD and thiol-preactivated cholera toxin resulted in the labeling of a 44-kD band, most likely an alpha-subunit of the stimulatory GTP-binding protein, the extent of which was much greater in alcohol-fed rats than in pair-fed controls. Analogous experiments with pertussis toxin also demonstrated enhancement of toxin-catalyzed ADP ribosylation of the inhibitory GTP-binding protein after long-term alcohol intake. More interesting was that long-term alcohol intake remarkably stimulated endogenous mono-ADP ribosylation of a 58-kD protein in a GTP-dependent manner. In vitro, ethanol (50 mmol/L) or a single load of ethanol (3 gm/kg) did not stimulate the reaction. Thus long-term alcohol intake stimulated both toxin-catalyzed and endogenous mono-ADP ribosylations of proteins in rat liver plasma membranes. Pursuit of alcohol interaction with mono-ADP ribosylation may provide an interesting approach to the study of alcohol's effects on the liver.
ADP核糖基化被认为是由ADP核糖基转移酶催化的细胞蛋白质重要共价修饰之一，该酶将NAD的ADP核糖部分转移到受体蛋白上。由于越来越多的证据表明单ADP核糖基化在跨膜信号转导和其他细胞代谢中具有重要生物学作用，因此酒精摄入如何改变这些过程备受关注。霍乱毒素和百日咳毒素已被广泛用作探针，以研究GTP结合蛋白（G蛋白）在激素和感觉信号转导中的作用。我们首先测试了长期酒精摄入对大鼠肝细胞膜中这些毒素催化的G蛋白ADP核糖基化的影响。用[32P]NAD和硫醇预激活的霍乱毒素处理大鼠肝细胞膜，导致一条44-kD条带被标记，最有可能是刺激性GTP结合蛋白的α亚基，在酒精喂养的大鼠中其标记程度比配对喂养的对照组大得多。用百日咳毒素进行的类似实验也表明，长期酒精摄入后，毒素催化的抑制性GTP结合蛋白的ADP核糖基化增强。更有趣的是，长期酒精摄入以GTP依赖的方式显著刺激了一种58-kD蛋白的内源性单ADP核糖基化。在体外，乙醇（50 mmol/L）或单次给予乙醇（3 gm/kg）并未刺激该反应。因此，长期酒精摄入刺激了大鼠肝细胞膜中蛋白质的毒素催化和内源性单ADP核糖基化。探索酒精与单ADP核糖基化的相互作用可能为研究酒精对肝脏的影响提供一个有趣的途径。
