Expression of hereditary hemochromatosis C282Y HFE protein in HEK293 cells activates specific endoplasmic reticulum stress responses.
BACKGROUND
Hereditary Hemochromatosis (HH) is a genetic disease associated with iron overload, in which individuals homozygous for the mutant C282Y HFE associated allele are at risk for the development of a range of disorders particularly liver disease. Conformational diseases are a class of disorders associated with the expression of misfolded protein. HFE C282Y is a mutant protein that does not fold correctly and consequently is retained in the Endoplasmic Reticulum (ER). In this context, we sought to identify ER stress signals associated with mutant C282Y HFE protein expression, which may have a role in the molecular pathogenesis of HH.


RESULTS
Vector constructs of Wild type HFE and Mutant C282Y HFE were made and transfected into HEK293 cell lines. We have shown that expression of C282Y HFE protein triggers both an unfolded protein response (UPR), as revealed by the increased GRP78, ATF6 and CHOP expression, and an ER overload response (EOR), as indicated by NF-kappaB activation. Furthermore, C282Y HFE protein induced apoptotic responses associated with activation of ER stress. Inhibition studies demonstrated that tauroursodeoxycholic acid, an endogenous bile acid, downregulates these events. Finally, we found that the co-existence of both C282Y HFE and Z alpha 1-antitrypsin protein (the protein associated with the liver disease of Z alpha 1-antitrypsin deficiency) expression on ER stress responses acted as potential disease modifiers with respect to each other.


CONCLUSIONS
Our novel observations suggest that both the ER overload response (EOR) and the unfolded protein response (UPR) are activated by mutant C282Y HFE protein.
Lawless
Matthew W
MW
Hepatology Research Division and Department of Clinical Medicine, Institute of Molecular Medicine, Trinity Centre for Health Sciences, Trinity College Dublin, St, James Hospital, Dublin, Ireland. mlawles@tcd.ie
Mankan
Arun K
AK
White
Mary
M
O'Dwyer
Michael J
MJ
Norris
Suzanne
S
D051702:Activating Transcription Factor 6 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D005786:Gene Expression Regulation; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics*; D008954:Models, Biological; D020641:Polymorphism, Single Nucleotide; D017510:Protein Folding; D021381:Protein Transport; D015398:Signal Transduction; D013655:Taurochenodeoxycholic Acid / Q000494:pharmacology; D051742:Transcription Factor CHOP / Q000378:metabolism; D014162:Transfection; D000515:alpha 1-Antitrypsin / Q000235:genetics
C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; C111835:CCL2 protein, human; D018932:Chemokine CCL2; C497249:DDIT3 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C103673:HFE protein, human; C000717247:HSPA5 protein, human; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I; D016209:Interleukin-8; D008565:Membrane Proteins; D000515:alpha 1-Antitrypsin; D051742:Transcription Factor CHOP; D013655:Taurochenodeoxycholic Acid; C031655:ursodoxicoltaurine