Regulation of iron homeostasis by the p53-ISCU pathway.

Yuki Funauchi,Yataro Daigo,Paulisally Hau Yi Lo,Koichi Matsuda,Chizu Tanikawa,Jinichi Mori,Atsushi Takano,Atsushi Okawa,Yusuke Nakamura,Yohei Miyagi

doi:10.1038/srep16497

Abstract

Accumulation of iron in tissues increases the risk of cancer, but iron regulatory mechanisms in cancer tissues are largely unknown. Here, we report that p53 regulates iron metabolism through the transcriptional regulation of ISCU (iron-sulfur cluster assembly enzyme), which encodes a scaffold protein that plays a critical role in Fe-S cluster biogenesis. p53 activation induced ISCU expression through binding to an intronic p53-binding site. Knockdown of ISCU enhanced the binding of iron regulatory protein 1 (IRP1), a cytosolic Fe-S protein, to an iron-responsive element in the 5′ UTR of ferritin heavy polypeptide 1 (FTH1) mRNA and subsequently reduced the translation of FTH1, a major iron storage protein. In addition, in response to DNA damage, p53 induced FTH1 and suppressed transferrin receptor, which regulates iron entry into cells. HCT116 p53+/+ cells were resistant to iron accumulation, but HCT116 p53−/− cells accumulated intracellular iron after DNA damage. Moreover, excess dietary iron caused significant elevation of serum iron levels in p53−/− mice. ISCU expression was decreased in the majority of human liver cancer tissues, and its reduced expression was significantly associated with p53 mutation. Our finding revealed a novel role of the p53-ISCU pathway in the maintenance of iron homeostasis in hepatocellular carcinogenesis.

Highlights

To identify novel p53 target genes, we conducted a cDNA microarray analysis using mRNAs isolated from p53-mutant U373MG glioblastoma cells that were infected with adenovirus designed to express wild-type p53 (Ad-p53) or LacZ (Ad-LacZ)[6]
Competition with non-labelled iron regulatory elements (IRE) probe and IRP1 knockdown markedly reduced the intensity of the shifted band (Supplementary Fig S3a–c), indicating the specificity of IRP1-IRE interaction. These results suggested that the p53-ISCU pathway positively modulated ferritin heavy polypeptide 1 (FTH1) protein levels through the IRP1-IRE regulatory system
These findings indicated that the p53-ISCU pathway regulated transferrin receptor (TFRC) expression by inhibiting IRP1 binding to the IRE in the 3′ untranslated region (UTR) of TFRC

Summary

Results

Identification of ISCU as a p53-inducible gene. To identify novel p53 target genes, we conducted a cDNA microarray analysis using mRNAs isolated from p53-mutant U373MG glioblastoma cells that were infected with adenovirus designed to express wild-type p53 (Ad-p53) or LacZ (Ad-LacZ)[6]. Similar to the result with FTH1, IRE-protein complex formation was increased in cells treated with siISCU (Supplementary Fig. S4c) These findings indicated that the p53-ISCU pathway regulated TFRC expression by inhibiting IRP1 binding to the IRE in the 3′ UTR of TFRC. ISCU depletion increased intracellular iron levels in ADR-treated HCT116 cells (Supplementary Fig. S5a). These findings suggested that the p53-ISCU pathway plays an important role in the regulation of iron homeostasis. Tfrc expression was significantly decreased in p53+/+ mice (Supplementary Fig. S6b,c) These findings suggested that p53 regulated iron regulatory proteins in vivo.

Discussion

Author Contributions

Additional Information