Large Scale Co-Isolation of Vimentin and Nuclear Lamins from Ehrlich Ascites Tumor Cells Cultured in Vitro

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Abstract
Ehrlich ascites tumor (EAT) cells propagated in mass suspension culture were used as a starting material for the simultaneous isolation and purification of large quantities of the intermediate filament protein vimentin and the nuclear lamins A/C and B. Triton cytoskeletons, obtained by repeated washing of cells witb a low ionic strength buffer containing Triton X-100 and 4 mM Mg2±, were extracted with 6 M urea at low salt concentration and in the presence of EDTA. Separation of solubilized proteins from unfolded chromatin (DNA) was accomplished by recondensation of the chromatin (DNA) in the presence of Mg2± before centrifugation. To achieve separation of vimentin from nuclear lamins, the urea extract was subjected to DEAE-Sepharose CL-6B chromatography. Single-stranded DNA-cellulose chromatography was employed for the final purification of vimentin and for the separation of lamin B from lamins A/C. Further purification of lamin B was carried out by CM-Sepharose CL-6B chromatography and of lamins A/C by chromatography on hydroxyl-apatite. All chromatographies were performed in the presence of 6 M urea .500 g of pelleted EAT cells yielded approximately 700 mg of vimentin, 225 mg of lamins A/C and 21 mg of lamin B. 2D-polyacryl-amide gel electrophoresis revealed great microheterogeneity of lamins A/C, which to a high extent was due to phosphorylation, whereas lamin B was much less heterogeneous. In the absence of urea and at low salt concentration, lamins A/C required pH 5 to stay in solution whereas lamin B required pH 7.5. Increasing the salt concentration to 150 or 250 mM NaCl resulted in the formation of paracrystais from a urea-free mixture of lamins A/C and B. Although the lamins could not be assembled into Intermediate filaments under a variety of ionic conditions, the preparations obtained will be useful for further biochemical characterization of these nuclear proteins.