Choudhuri S, McKim J M, Klaassen C D
Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City 66160-7417.
Toxicol Appl Pharmacol. 1993 Mar;119(1):1-10. doi: 10.1006/taap.1993.1037.
Expression of the metallothionein I (MT-I) gene was studied in liver and brain of control mice and rats, as well as following administration of Cd and lipopolysaccharide (LPS). Time-course studies revealed that MT mRNA reached a maximum in liver of both mice and rats 6 hr following treatment with Cd or LPS. MT mRNA from control and Cd- and LPS-treated rat brains could not be detected by Northern-blot analysis of total RNA, but Northern analysis with poly(A)-enriched RNA revealed that induction of MT mRNA in rat brain does occur with both Cd and LPS treatment. In contrast, mouse brain MT mRNA was easily detected by Northern-blot analysis of total RNA. It was also clear from Northern-blot analyses of both mouse and rat brain that LPS induced more MT mRNA than did Cd. Quantitation of MT mRNA by solution hybridization revealed that Cd and LPS induced similar amounts of MT mRNA in livers of mice (about 0.64 fmol/micrograms total RNA by Cd and 0.68 by LPS) and rats (about 0.23 fmol/micrograms total RNA by Cd and 0.21 by LPS). Therefore, both inducers increased MT mRNA about threefold more in mouse liver than in rat liver. In mouse and rat brain, LPS induced about twice as much MT mRNA as did Cd (about 0.08 fmol/micrograms total RNA by Cd and 0.16 by LPS in mice and about 0.006 fmol/micrograms total RNA by Cd and 0.008 by LPS in rats). However, the actual amount of MT mRNA induced in rat brain by either inducer was minimal compared to that in mouse brain. In fact, Cd induced 13 times more MT mRNA in mouse brain than in rat brain, and LPS induced about 20 times more MT mRNA in mouse brain than in rat brain. Cd distribution to liver was similar in both mice and rats, but the Cd concentration in mouse brain was about 60% more than that in rat brain. Distribution of LPS was also similar in mouse and rat livers, as well as in mouse and rat brains. Therefore, there exists a difference in the expression of MT gene in both liver and brain of mice and rats, the expression in mice being higher than that in rats. These findings suggest that such differential expression of the MT gene cannot be entirely accounted for by the difference in the tissue distribution of inducers. Other tissue-specific and species-specific factors controlling MT gene expression appear to be involved.
研究了对照小鼠和大鼠肝脏及大脑中金属硫蛋白I（MT-I）基因的表达情况，以及镉（Cd）和脂多糖（LPS）给药后的表达情况。时间进程研究表明，在用Cd或LPS处理6小时后，小鼠和大鼠肝脏中的MT mRNA均达到最大值。通过对总RNA进行Northern印迹分析，未检测到对照、Cd处理和LPS处理的大鼠大脑中的MT mRNA，但对富含多聚腺苷酸（poly(A)）的RNA进行Northern分析表明，Cd和LPS处理均能诱导大鼠大脑中MT mRNA的表达。相比之下，通过对总RNA进行Northern印迹分析很容易检测到小鼠大脑中的MT mRNA。从小鼠和大鼠大脑的Northern印迹分析中也可以清楚地看出，LPS诱导的MT mRNA比Cd诱导的更多。通过溶液杂交对MT mRNA进行定量分析表明，Cd和LPS在小鼠肝脏（Cd诱导约0.64 fmol/μg总RNA，LPS诱导约0.68 fmol/μg总RNA）和大鼠肝脏（Cd诱导约0.23 fmol/μg总RNA，LPS诱导约0.21 fmol/μg总RNA）中诱导的MT mRNA量相似。因此，两种诱导剂在小鼠肝脏中诱导的MT mRNA比在大鼠肝脏中多约三倍。在小鼠和大鼠大脑中，LPS诱导的MT mRNA是Cd诱导的约两倍（小鼠中Cd诱导约0.08 fmol/μg总RNA，LPS诱导约0.16 fmol/μg总RNA；大鼠中Cd诱导约0.006 fmol/μg总RNA，LPS诱导约0.008 fmol/μg总RNA）。然而，与小鼠大脑相比，两种诱导剂在大鼠大脑中诱导的MT mRNA实际量极少。事实上，Cd在小鼠大脑中诱导的MT mRNA比在大鼠大脑中多13倍，LPS在小鼠大脑中诱导的MT mRNA比在大鼠大脑中多约20倍。Cd在小鼠和大鼠肝脏中的分布相似，但小鼠大脑中的Cd浓度比大鼠大脑中的高约60%。LPS在小鼠和大鼠肝脏以及小鼠和大鼠大脑中的分布也相似。因此，小鼠和大鼠肝脏及大脑中MT基因的表达存在差异，小鼠中的表达高于大鼠。这些发现表明，MT基因的这种差异表达不能完全由诱导剂在组织分布上的差异来解释。似乎还涉及其他控制MT基因表达的组织特异性和物种特异性因素。
