Cellular factors mediate cadmium-dependent actin depolymerization.
Cadmium exposure produces depolymerization of the actin cytoskeleton in several cultured cell lines, and we have previously shown that in renal mesangial cells this effect is caused by picomolar concentrations of cytosolic Cd2+. The present study was undertaken to explore further the basis of this action of Cd2+. Skeletal muscle actin was labeled with pyrene and rates of polymerization and depolymerization were followed in vitro by changes in fluorescence. Concentrations of 100 microM or higher Cd2+ increased the rate of polymerization while lower concentrations stabilized actin filaments. Because this is in contrast to the observation that Cd2+ favors depolymerization in cultured mesangial cells, we examined the role of cellular factors in modifying the actions of Cd2+ on the polymerization/depolymerization equilibrium. Inclusion in the in vitro polymerization assay of cytosol from mesangial cells pre-treated with 5 microM CdCl2 caused a decrease in the rate of polymerization and an increase in the rate of depolymerization, relative to cytosol from control cells. EGTA normalized these rates, indicating involvement of Ca2+-dependent factors. Likewise, cytoskeleton from Cd2+-treated cells caused a Ca2+-dependent decrease in actin polymerization. Ligand blotting with [125I]actin revealed loss of binding of a 93-kDa protein from the cytosol and an increase in binding of a 49-kDa protein in the cytoskeletal fraction upon treatment of mesangial cells with Cd2+. Based on their electrophoretic mobility and Ca2+ dependence of actin binding these are tentatively identified as members of the gelsolin and severin families, respectively. Thus, Cd2+ may exert its effect on the mesangial cell cytoskeleton by altering the levels or actin-binding activity of actin-associated proteins.
Wang
Z
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Department of Clinical Biochemistry, University of Toronto, Canada.
Templeton
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DM
D000199:Actins / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002021:Buffers; D002104:Cadmium / Q000633:toxicity*; D019256:Cadmium Chloride; D002118:Calcium / Q000378:metabolism; D002458:Cell Fractionation; D002478:Cells, Cultured; D002712:Chlorides / Q000633:toxicity; D004591:Electrophoresis, Polyacrylamide Gel; D005453:Fluorescence; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D008970:Molecular Weight; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017830:Octoxynol / Q000737:chemistry; D011108:Polymers; D011817:Rabbits; D013054:Spectrophotometry, Atomic
D000199:Actins; D002021:Buffers; D002712:Chlorides; D007457:Iodine Radioisotopes; D011108:Polymers; D002104:Cadmium; D017830:Octoxynol; D019256:Cadmium Chloride; D002118:Calcium