Induction of mouse metallothionein-I mRNA by bacterial endotoxin is independent of metals and glucocorticoid hormones.

Abstract

Induction of metallothionein-I (MT-I) mRNA by bacterial endotoxin (LPS) was examined. A single injection of LPS induced MT-I mRNA accumulation in both liver and kidney comparable to that induced by heavy metals. Maximal message levels were achieved 6 hr after LPS administration, prior to any increase in either hepatic or renal Zn or Cu. Experiments in which LPS was administered to transgenic mice harboring recombinant genes made by fusing the MT-I gene promoter to the herpes simplex virus thymidine kinase structural gene revealed that the response to LPS is independent of glucocorticoid hormones. These experiments begin to define the region of the MT-I gene promoter required for the LPS response.It has been well documented that the synthesis of metallothionein (MT) is regulated by both heavy metals, such as Cd and Zn, and glucocorticoid hormones (1-4). We have shown both in vivo and in cultured cells that the regulation of the mouse MT-I gene occurs primarily at the level of gene transcription for both classes of inducers (5-7). Definition of the region(s) of the MT-I gene promoter necessary for regulation by heavy metals has been approached by fusing deleted variants of the MT-I gene promoter to easily assayable genes, such as the herpes simplex virus (HSV) thymidine kinase (TK) gene, and analyzing metal regulation after the fused genes were introduced into either tissue culture cells or mouse eggs (8,9). These studies indicate that the region of the mouse MT-I promoter necessary for metal regulation maps within 90 nucleotides 5' of the normal MT-I transcription initiation site. Similar analysis of the region important for glucocorticoid regulation has not been possible because the mouse MT-I promoter is not responsive to glucocorticoids when transferred to other cells (9-11).In Like MT, some acute-phase proteins are regulated by elevated glucocorticoid levels resulting from stresses such as surgical trauma, pain, apprehension, and exposure to heat and cold (14-17). However, for MTs the response to inflammatory agents does not appear to be glucocorticoid-mediated because it has been recently shown that the injection of turpentine induced comparable amounts of hepatic MT in adrenalectomized and control rats (18). This suggests that there may be several mechanisms regulating MT synthesis that are operative during different types of stress and implies that perhaps a third class of regulatory molecule can affect MT-I gene transcription. Here we present several lines of evidence that rule out metal or glucocorticoid involvement in the response to the potent inflammatory agent LPS and thus support the notion that a third class of molecules may mediate MT-I gene expression during stress. MATERIALS AND METHODSMT-I mRNA Accumulation Time Course. Male SwissWebster mice, 14-17 g, were injected subcutaneously with ZnSO4 (5 mg/kg) or intraperitoneally with LPS (3 mg/kg; Difco; lipopolysaccharide W, Salmonella typhosa 0901). Tissues were removed and MT-I mRNA levels were measured in total nucleic acid samples as desc...

Metallothionein RNA levels in HL‐60 cells Effect of cadmium, differentiation, and protein kinase C activation

“…MT gene expression is predominantly regulated at the level of transcription [5][6][7][8][9]. Though the mechanism of regulation is poorly understood, rapid induction occurs upon exposure to metals [5] and, in mammalian cells, to various circulating factors such as glucocorticoid hormones [6], ainterferon [7], and interleukin-1 and other mediators of the inflammatory response [8,9].…”

“…Though the mechanism of regulation is poorly understood, rapid induction occurs upon exposure to metals [5] and, in mammalian cells, to various circulating factors such as glucocorticoid hormones [6], ainterferon [7], and interleukin-1 and other mediators of the inflammatory response [8,9]. It has been suggested that a common pathway for MT induction involves protein kinase C (PKC) activation since MT levels increase in serum-starved cells after treatment with growth factors and TPA, agents which function in part through PKC activation [10,11].…”

Altered Organ Growth and Zinc and Copper Distribution in Endotoxin-Treated Neonatal Mice

“…Induction of MT synthesis protects macrophages against endotoxin-induced cell killing (I 1). A distinct 5' regulatory site uniquely responsive to endotoxin modulates MT-I gene transcription in mouse liver and kidney (12).…”

Rat metallothionein-1 structural gene and three pseudogenes, one of which contains 5'-regulatory sequences.

“…The proposed functional roles of metallothioneins include: protection against heavy metal ion intoxication by cadmium or mercury (49); biological response to stress (51,64), and regulation of zinc and copper during development (3,5,52,59). The existence of numerous independent induction responses to different agents regulating MT gene expression suggests a complex role for the regulatory recognition sequences in these genes (16,22,30,43). The sequencing of members of a family of MT genes allowed us both to explore in detail the evolutionary relationship among these genes and to compare the regions of sequence involved in regulating MT gene expression.…”

“…Metallothioneins are usually isolated as two major isoforms, designated MT-1 and MT-2. The metallothionein (MT) genes are inducible by metal ions (4,17), glucocorticoid hormones (19,20,36,37), stress (51), bacterial endotoxin (16), iodoacetate (18), and interferon (22). Human MT-1 and MT-2 genes show differential expression with metal ion and hormone inducers (57).…”