REGULATION OF METALLOTHIONEIN GENE-EXPRESSION - STUDIES IN TRANSFECTED PRIMARY CULTURES OF CHICK-EMBRYO LIVER-CELLS

To study the regulation of expression of the metallothionein gene in n ormal liver cells, we transfected chick embryo liver cells in primary cultures with constructs containing luciferase or chloramphenicol acet yl transferase (as reporter genes) under the control of differing leng ths of the 5'-promoter region of the chick metallothionein gene (conta ining 30, 122, 190, or 623 base pairs upstream of the transcriptional start site). We controlled for efficiency of transfection by co-transf ections with a plasmid containing a bacterial beta-galactosidase gene under the control of the SV 40 promoter and enhancer. Treatment of the transfected cells with transition metallic ions (cadmium, cobalt, and zinc) or sodium arsenite produced increases in activities of lucifera se or chloramphenicol acetyl transferase, relative to beta-galactosida se, and this activity mapped to the first 122 base pairs of the promot er. Although heme has recently been reported to induce the endogenous metallothionein gene in chick embryo liver cells, 10-50 mu M heme did not increase reporter gene activities in transfected cells. Neverthele ss, the heme-dependent induction of endogenous heme oxygenase-1 in the se cells was normal. We conclude that the heme-dependent induction of the liver metallothionein gene depends upon DNA region(s) outside the regulatory region of the chick metallothionein gene studied here and t hat elements within the first 122 base pairs of the metallothionein pr omoter are sufficient to confer responsiveness to transition metals or sodium arsenite.