Identification of a mechanism by which lens epithelial cells limit accumulation of overexpressed ferritin H-chain.
The primary cultures of canine lens epithelial cells were transiently transfected with cDNAs for dog ferritin H- or L-chains in order to study differential expression of these chains. By using chain-specific antibodies, we determined that at 48 h after transfection overexpression of L-chain was much higher (9-fold over control) than that of H-chain (1.7-fold). We discovered that differentially transfected cells secrete overexpressed chains as homopolymeric ferritin into the media. Forty-eight hours after transfection accumulation of H-ferritin in the media was much higher (3-fold) than that of L-ferritin. This resulted in lowering of the concentration of H-chain in the cytosol. Co-transfection of cells with both H- and L-chain cDNAs increased the intracellular levels of H-chain and eliminated secretion of H-ferritin to the media. We concluded that lens epithelial cells differentially regulate concentration of both ferritin chains in the cytosol. The overexpressed L-chain accumulated in the cytosol as predominantly homopolymeric L-ferritin. This is in contrast to H-chain, which is removed to the media unless there is an L-chain available to form heteropolymeric ferritin. These data indicate that the inability of cells to more strictly control cytosolic levels of L-chain may augment its accumulation in lenses of humans with hereditary hyperferritinemia cataract syndrome, which is caused by overexpression of L-chain due to mutation in the regulatory element in the untranslated region of the mRNA of the chain.
Goralska
Malgorzata
M
Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, North Carolina 27606, USA. margaret_goralska@ncsu.edu
Holley
Benjamin L
BL
McGahan
M Christine
MC
D000818:Animals; D001052:Apoferritins; D015153:Blotting, Western; D002386:Cataract / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004285:Dogs; D004591:Electrophoresis, Polyacrylamide Gel; D004847:Epithelial Cells / Q000378:metabolism*; D015785:Eye Diseases, Hereditary / Q000378:metabolism; D005293:Ferritins / Q000096:biosynthesis* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D019189:Iron Metabolism Disorders; D007908:Lens, Crystalline / Q000378:metabolism*; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D018076:DNA, Complementary; D010455:Peptides; D012333:RNA, Messenger; D011994:Recombinant Proteins; D005293:Ferritins; D001052:Apoferritins