RESUMO
The acute phase response is characterized by positive and negative regulation of many liver proteins including GSTs (glutathione S-transferases) and albumin. The expression of albumin and some GSTs are dependent on HNF1 (hepatic nuclear factor 1). Interleukin 6 plus dexamethasone induce a nuclear protein (IL6DEX-NP) in rat hepatocytes in vitro that binds to a promoter element adjacent to the HNF1 site of rGSTA2 and decreases its expression. We determined how HNF1 and IL6DEX-NP regulate rGSTA2 and albumin expression in rats during the acute phase response after LPS (lipopolysaccharide) treatment. Expression of rGSTA2 and albumin mRNA decreased 3 h after LPS treatment and remained low for 48 h. Transcription rates showed a similar pattern but albumin transcription was less affected. HNF1 and IL6DEX-NP binding to the rGSTA2 promoter was present in control livers but was absent at 3 and 6 h after LPS. By 12 h, HNF1 and IL6DEX-NP binding to the rGSTA2 promoter reappeared and increased to above normal at 48 h. The patterns of HNF1 and IL6DEX-NP binding to the albumin promoter were similar. Affinity of IL6DEX-NP for the albumin promoter was less than that for the rGSTA2 promoter and changes in the transcription rates were consistent with the difference. Early decreases in rGSTA2 and albumin during the acute phase response are due to decreased binding of HNF1. Later persistent decreases in transcriptional rate of rGSTA2 and to a lesser extent albumin are due to increased IL6DEX-NP binding. IL6DEX-NP appears to be an important negative regulator of gene expression in vitro and in vivo.
Assuntos
Reação de Fase Aguda/enzimologia , Reação de Fase Aguda/metabolismo , Albuminas/biossíntese , Proteínas de Ligação a DNA , Dexametasona/imunologia , Glutationa Transferase/biossíntese , Interleucina-6/fisiologia , Fígado/enzimologia , Proteínas Nucleares/fisiologia , Fatores de Transcrição/fisiologia , Reação de Fase Aguda/genética , Reação de Fase Aguda/fisiopatologia , Albuminas/genética , Animais , Sítios de Ligação/genética , Glutationa Transferase/genética , Fator 1 Nuclear de Hepatócito , Fator 1-alfa Nuclear de Hepatócito , Fator 1-beta Nuclear de Hepatócito , Hepatócitos/química , Lipopolissacarídeos/farmacologia , Fígado/fisiopatologia , Masculino , Proteínas Nucleares/metabolismo , Regiões Promotoras Genéticas/genética , Ligação Proteica/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Fatores de Transcrição/metabolismo , Transcrição Gênica/efeitos dos fármacosRESUMO
A decrease in concentration of some liver proteins, including the detoxification enzyme glutathione S-transferase A2 (rGSTA2), occurs during the acute-phase response. Interleukin 6 (IL-6) with dexamethasone (DEX) decreases transcription of rGSTA2 in rat hepatocytes. The promoter region that mediates suppression of rGSTA2 was localized to 150 bp. These 150 bp were divided and used for electrophoretic mobility-shift assays. Induction of a protein that specifically bound to an oligonucleotide from this region required new protein synthesis and IL-6 with DEX in the culture media. The protein bound to part of the hepatocyte nuclear factor 1 (HNF1) site but was different from and did not displace HNF1. A core sequence, TGATT, was required for binding. The protein also bound to an HNF1 site in the albumin promoter. We hypothesize that IL-6 along with DEX induced a novel protein that decreased transcription of rGSTA2 and possibly albumin by interfering with the transactivating function of HNF1. The protein may be an important negative regulator of transcription during the acute-phase response.