A case report of spontaneous mutation (C33>U) in the iron-responsive element of L-ferritin causing hyperferritinemia-cataract syndrome.
The hereditary hyperferritinemia cataract syndrome (HHCS) is an autosomal dominant disorder characterized by juvenile-onset cataracts and elevated serum ferritin levels. It is caused by mutation in the iron response element (IRE) within the 5'UTR of L-ferritin gene. The mutation results in a loss of post-transcriptional negative feedback exerted by the interaction between iron regulatory proteins 1, 2 (IRP1 and IRP2) and IRE, which leads to uncontrolled expression of L-ferritin. In this paper, we describe the molecular pathogenesis of non-hereditary hyperferritinemia cataract syndrome (non-H-HCS) in a patient with typical HHCS ocular lens morphology and high ferritin levels without obvious family history. Initial sequencing of the full-length L-ferritin cloned from genomic DNA demonstrated a mutation (C33>T) in the IRE of the affected patient but not in her unaffected family members. The mutation (C/T heterozygote) was also detected in cDNA derived from her blood mononuclear cells. Structure-prediction-modeling indicates that this mutation would significantly alter the secondary structure of the IRE, resulting in a loss of the interaction between IRP and IRE. By using IRP1/IRP2-human IgG1 Fc fusion proteins, we established a novel in vitro report system (modified ELISA) to verify impaired IRE/IRP binding. Both the C33>U and A40G mutations (the first identified mutation for HHCS) showed a dramatically decreased binding to IRP1/IRP2 protein, compared to the normal IRE RNA. Surprisingly, a decrease in L-ferritin mRNA levels was observed in the affected patient compared to controls suggesting a mechanism of transcriptional negative feedback by high intracellular L-ferritin protein levels not described heretofore. Taken together, spontaneous mutation in the IRE of L-ferritin may cause non-H-HCS by the same mechanism as HHCS. In addition, under abnormal circumstances, the protein level of L-ferritin may be principally controlled by post-transcriptional regulation rather than the transcriptional regulation. The successful establishment of an ELISA report system provides an alternative method to evaluate precisely the interaction between protein and RNA.
Cao
Wei
W
Cell Biology Laboratory, Department of Biochemistry, University College Cork, Cork, Ireland. caowei_111@yahoo.com.cn
McMahon
Mary
M
Wang
Bo
B
O'Connor
Rosemary
R
Clarkson
Michael
M
D002386:Cataract / Q000235:genetics*; D002460:Cell Line; D004252:DNA Mutational Analysis; D015536:Down-Regulation; D025461:Feedback, Physiological; D005260:Female; D005293:Ferritins / Q000097:blood* / Q000235:genetics* / Q000378:metabolism; D006579:Heterozygote; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000235:genetics; D007074:Immunoglobulin G / Q000235:genetics; D007501:Iron / Q000378:metabolism*; D035941:Iron Regulatory Protein 1 / Q000235:genetics / Q000378:metabolism; D035942:Iron Regulatory Protein 2 / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D008958:Models, Molecular; D010375:Pedigree; D017354:Point Mutation; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020218:Response Elements / Q000235:genetics*; D013577:Syndrome
D007141:Immunoglobulin Fc Fragments; D007074:Immunoglobulin G; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D005293:Ferritins; D007501:Iron; D035941:Iron Regulatory Protein 1; D035942:Iron Regulatory Protein 2