Zinc mesoporphyrin induces rapid and marked degradation of the transcription factor Bach1 and up-regulates HO-1.
Heme oxygenase 1 (HO-1) is the first and rate-controlling enzyme in heme degradation. Bach1 is a mammalian transcriptional repressor of HO-1. To understand how zinc mesoporphyrin (ZnMP) induces the expression of HO-1, we investigated the effects of ZnMP on Bach1 mRNA and protein levels in human hepatoma Huh-7 cells by quantitative RT-PCR and Western blots. We found that ZnMP markedly up-regulated HO-1 mRNA and protein levels, and rapidly and significantly decreased Bach1 protein levels by increasing degradation of Bach1 protein [half life (t(1/2)) from 19 h to 45 min], whereas ZnMP did not influence Bach1 mRNA levels. The proteasome inhibitors, epoxomicin and MG132, significantly inhibited degradation of Bach1 by ZnMP in a dose-dependent fashion, indicating that the degradation of Bach1 by ZnMP is proteasome-dependent. Purified Bach1 C-terminal fragment bound heme, but there was no evidence for binding of ZnMP to the heme-binding region of Bach1. In conclusion, ZnMP produces profound post-transcriptional down-regulation of Bach1 protein levels and transcriptional up-regulation of HO-1. Our results indicate that ZnMP up-regulates HO-1 gene expression by markedly increasing Bach1 protein degradation in a proteasome-dependent manner.
Hou
Weihong
W
The Liver-Biliary-Pancreatic Center, Carolinas Medical Center, Charlotte, NC 28232-2861, USA.
Shan
Ying
Y
Zheng
Jianyu
J
Lambrecht
Richard W
RW
Donohue
Susan E
SE
Bonkovsky
Herbert L
HL
D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D051856:Fanconi Anemia Complementation Group Proteins / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006418:Heme / Q000378:metabolism; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008665:Metalloporphyrins / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015854:Up-Regulation
C102108:BACH1 protein, human; D050976:Basic-Leucine Zipper Transcription Factors; D051856:Fanconi Anemia Complementation Group Proteins; D007976:Leupeptins; D008665:Metalloporphyrins; D009842:Oligopeptides; D012333:RNA, Messenger; D011994:Recombinant Proteins; D006418:Heme; C058069:zinc mesoporphyrin; D051547:Heme Oxygenase-1; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; C078846:epoxomicin