Differential detergent fractionation of isolated hepatocytes: Biochemical, immunochemical and two‐dimensional gel electrophoresis characterization of cytoskeletal and noncytoskeletal compartments

Abstract

Two‐dimensional (2‐D) gel electrophoresis is often used in toxicologic and metabolic studies to assess treatment‐ or stage‐specific changes in protein synthesis, degradation or posttranslational modification. When combined with cell fractionation studies the detectability of low abundance proteins is enhanced, and changes in subcellular distribution of proteins can also be monitored. Detergent fractionation is a simpler alternative to differential pelleting, which partitions cellular constituents into functionally distinct populations while preserving cytoskeletal integrity. We defined and characterized a differential detergent fractionation (DDF) protocol to enable protein dynamics in cytoskeletal and noncytoskeletal compartments of isolated hepatocytes to be monitored simultaneously. Rat hepatocytes were maintained in suspension culture and fractionated by sequential extraction with detergentcontaining buffers (digitonin/EDTA, Triton/EDTA, Tween/deoxycholate). DDF reproducibly yielded four electrophoretically distinct fractions enriched in cytosolic, membrane‐organelle, nuclear membrane and cytoskeletal‐matrix markers, respectively. Immunoblotting with over 20 different antibodies corroborated the selectivity of fractionation and was used to characterize the distribution profiles of cytoskeletal (actin, tubulins, cytokeratins, vinculin, myosin, desmoplakins, fodrin, nuclear lamins) and noncytoskeletal proteins (heat‐shock 70 proteins, glutathione‐S‐transferase, calpains, carbamoyl phosphate synthetase, etc.), as well as to identify spots in 2‐D gels. Detergent buffers were compatible with equilibrium or nonequilibrium 2‐D gel electrophoretic analysis. Extensive 2‐D maps of acidic and basic proteins in each fraction were generated along with a tabular listing of M_r and pI. Thus, DDF reproducibly partitions hepatocytic proteins into functionally distinct cytoskeletal and noncytoskeletal compartments that are readily analyzed by 2‐D gel electrophoresis. DDF is simple, applicable to use with other cell types or culture systems and is especially useful when biomaterial is limited (i.e., clinical studies).