Endotoxin induction of murine metallothionein gene expression

Bacterial endotoxin-lipopolysaccharide (LPS) rapidly induced hepatic metallothionein (MT) mRNA levels in the LPS-sensitive CD-1 strain of mice. This LPS effect was severely attenuated in the LPS-resistant C3H/HeJ strain of mice, but could be mimicked by injection of human recombinant interleukin-1 alpha (IL-1 alpha) or human recombinant tumor necrosis factor (TNF-alpha). In the CD-1 strain, LPS induction of MT gene expression occurred in each of 10 organs examined (liver, kidney, pancreas, intestine, lung, heart, brain, ovary, uterus, and spleen). Solution hybridization with probes specific for MT-I or MT-II mRNA established that these genes were co-induced in each of the organs and that the liver and kidney contained the highest absolute levels of these mRNAs, whereas in the intestine and spleen they were 10-20-fold lower. LPS and cytokine induction of hepatic MT gene expression occurred in hypophysectomized mice, which suggests a lack of significant involvement of glucocorticoids. Several recombinant cytokines (TNF-alpha, IL-1 alpha, IL-1 beta, IL-6, interferon-gamma (IFN-gamma), as well as poly(rI.rC) were effective inducers of hepatic MT-I and MT-II genes. As an attempt to determine which of these cytokines may mediate LPS effects on MT gene expression in vivo, CD-1 mice were injected with LPS or various cytokines, and RNA from liver, ovary, and uterus was extracted at various times postinjection and analyzed by Northern blotting using probes specific for IL-1 alpha, IL-1 beta, TNF-alpha, IL-6, and MT mRNA. In each organ examined, LPS, IL-1 alpha, or IL-1 beta injection caused a rapid, coordinate, transient increase in the levels of each of the cytokine mRNAs which peaked by 1 h and declined to low levels by 4 h. In contrast, levels of MT mRNA did not reach a peak until 4-6 h postinjection. TNF-alpha had minimal effects on expression of cytokine and MT genes in organs other than liver. IL-6 had no effect on hepatic cytokine mRNA levels, and induced MT mRNA only in the liver which suggests a direct effect of IL-6 on hepatic MT gene expression. These data suggest that the acute effects of LPS on MT gene expression may include complex paracrine interactions between a variety of cytokines and the cells expressing MT genes in each organ, and tissue-specific cytokine effects on the MT genes.