Activation of cytochrome P450IA1 gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin in wild-type and high-activity variant mouse hepatoma cells.
We analyzed the function of a DNA domain located upstream of the cytochrome P450IA1 gene in wild-type (Hepa 1c1c7) mouse hepatoma cells and in high-activity variant (HAV) cells that overtranscribe the gene in response to the inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Transfection experiments indicated that both wild-type and HAV DNA confer responsiveness to TCDD upon the bacterial chloramphenicol acetyltransferase (CAT) gene. However, the level of CAT activity was four- to fivefold higher when the hybrid genes were expressed in the HAV cells. These findings imply that an alteration in a trans-acting function confers the HAV phenotype. Studies of mRNA accumulation imply that TCDD acts by enhancing the rate of mRNA initiation rather than by removing a block in mRNA elongation. We found that both wild-type and HAV cells used the same transcriptional promoter as that described previously for the cytochrome P450IA1 gene in C57BL/6 mouse liver. Both cell types exhibited superinduction of cytochrome P450IA1 gene expression in response to TCDD plus cycloheximide.
Hirst
M A
MA
Department of Pharmacology, Stanford University School of Medicine, California 94305.
Jones
K W
KW
Whitlock
J P
JP
D000818:Animals; D002461:Cell Line, Transformed; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004147:Dioxins / Q000494:pharmacology*; D005784:Gene Amplification; D005786:Gene Expression Regulation; D008114:Liver Neoplasms, Experimental / Q000032:analysis*; D051379:Mice; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D014158:Transcription, Genetic; D014162:Transfection
D004147:Dioxins; D000072317:Polychlorinated Dibenzodioxins; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; D015500:Chloramphenicol O-Acetyltransferase