Activation of metallothioneins and alpha-crystallin/sHSPs in human lens epithelial cells by specific metals and the metal content of aging clear human lenses.
OBJECTIVE
To identify those metallothionein and alpha-crystallin/small heat-shock genes induced by toxic metals in human lens cells and to evaluate the levels of these metals between young and aged human lenses.


METHODS
Human SRA01/04 and primary human lens epithelial cells were cultured and exposed to Cd(2+), Cu(2+), and Zn(2+). The levels of lens metallothioneins (Ig, If, Ih, Ie, and IIa) and alpha-crystallin/small heat-shock (alphaA-crystallin, alphaB-crystallin, and HSP27) genes were analyzed by semiquantitative and quantitative competitive RT-PCR. The content of aluminum, cadmium, calcium, chromium, copper, iron, lead, magnesium, manganese, nickel, potassium, sodium, and zinc in young (mean, 32.8 years), middle-aged (mean, 52.3 years), and old (mean, 70.5 years) human lenses was analyzed by inductively coupled plasma-emission spectroscopy.


RESULTS
Lens metallothioneins (Ig, If, Ih, Ie, and IIa) and alpha-crystallin/small heat-shock genes (alphaA-crystallin, alphaB-crystallin, and HSP27) were differentially induced by specific metals in SRA01/04 human lens epithelial cells. Cd(2+) and Zn(2+), but not Cu(2+), induced the metallothioneins, whereas Cd(2+) and Cu(2+), but not Zn(2+), induced alphaB-crystallin and HSP27. alphaA-crystallin was induced by Cu(2+) only. Similar responses of the metallothionein IIa gene were detected in identically treated primary human lens epithelial cells. Cd(2+) and Zn(2+) induced metallothionein IIa to five times higher levels than metallothionein Ig. Of 13 different metals, only iron was altered, exhibiting an 81% decrease in old versus young lenses.


CONCLUSIONS
Induction of metallothioneins and alpha-crystallin/small heat shock proteins by different metals indicates the presence of metal-specific lens regulatory pathways that are likely to be involved in protection against metal-associated stresses.
Hawse
John R
JR
Department of Biology, West Virginia University, Morgantown, West Virginia 26506, USA.
Cumming
Jonathan R
JR
Oppermann
Brian
B
Sheets
Nancy L
NL
Reddy
Venkat N
VN
Kantorow
Marc
M
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D002104:Cadmium / Q000494:pharmacology; D002478:Cells, Cultured; D003300:Copper / Q000494:pharmacology; D004847:Epithelial Cells / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D008668:Metallothionein / Q000096:biosynthesis* / Q000235:genetics; D008670:Metals / Q000032:analysis / Q000494:pharmacology*; D008875:Middle Aged; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015032:Zinc / Q000494:pharmacology; D038201:alpha-Crystallins / Q000096:biosynthesis* / Q000235:genetics
D006360:Heat-Shock Proteins; D008670:Metals; D038201:alpha-Crystallins; D002104:Cadmium; D003300:Copper; D008668:Metallothionein; D015032:Zinc