Role of interleukin 6 and corticosteroids in the regulation of expression of glutathione S-transferases in primary cultures of rat hepatocytes.
The effect of recombinant interleukin 6 (rIL-6) on the transcript levels of rat glutathione S-transferase (GST) genes rGSTA2, rGSTP1, rGSTM1 and rGSTM2 was examined in primary cultures of rat hepatocytes. rIL-6 had little effect on the increase in expression of rGSTP1 that occurs in cultured hepatocytes. Dexamethasone (DEX), in contrast, prevented the expression of rGSTP1 by hepatocytes, and rIL-6 in combination with DEX had no additional effect. Neither rIL-6 nor DEX alone had a significant effect on the transcript levels of rGSTA2, rGSTM1 and rGSTM2 in cultured hepatocytes. However, when both were present (15 ng/ml rIL-6 and 10(-7) M DEX) the transcript levels of rGSTA2, rGSTM1 and rGSTM2 decreased significantly (P < 0.05) after 48 h in culture. If the rIL-6 was removed from the cultures after 24 h, the levels of transcripts recovered and were the same at 48 h as cells cultured without rIL-6 for the entire period. Dose-response relationships of rIL-6 with 10(-7) M DEX were determined for transcripts of each GST isoenzyme and the IC50 values were between 1.5 and 7.5 ng/ml. Declines in transcript levels of rGSTA2 were observed with rIL-6 plus 10(-8) or 10(-7) M DEX but not with rIL-6 plus 10(-9), 10(-6), or 10(-5) M DEX. To determine if the cytokine and glucocorticoid effects were mediated by sequences in the 5'-flanking sequence of rGSTA2, a plasmid construct containing a 1.6 kb fragment of the 5'-flanking sequence of the rGSTA2 gene and the chloramphenicol acetyltransferase (CAT) reporter gene was used to transfect rat hepatocytes in primary culture. The addition of rIL-6 and DEX to the culture medium caused a significant (P < 0.05) decrease in CAT activity after 48 h in culture. If rIL-6 was removed after 24 h in culture, CAT activity after an additional 24 h in culture was greater than the CAT activity in cells cultured for 48 h without rIL-6. Therefore cytokines and glucocorticoids may be important physiological regulators of GST expression.
Voss
S H
SH
Emory University School of Medicine, Division of Digestive Diseases, Atlanta, GA 30322, USA.
Park
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Y
Kwon
S O
SO
Whalen
R
R
Boyer
T D
TD
D000818:Animals; D015500:Chloramphenicol O-Acetyltransferase; D003907:Dexamethasone / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D005982:Glutathione Transferase / Q000096:biosynthesis* / Q000145:classification / Q000235:genetics; D015850:Interleukin-6 / Q000494:pharmacology*; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000096:biosynthesis; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D015850:Interleukin-6; D012333:RNA, Messenger; D011994:Recombinant Proteins; D003907:Dexamethasone; D015500:Chloramphenicol O-Acetyltransferase; D005982:Glutathione Transferase