Subcellular regulation of VCP/p97 during differentiation and retrodifferentiation. A. The successful separation of the different U937 cell populations into subcellular compartments was controlled by GAPDH for the cytosol, clathrin for the membrane-fraction and nucleoporin62 (nup62) for the nucleus, respectively. B. Cytosol, membranes and nuclei of undifferentiated U937 control cells (U937), differentiated populations (3d until 18d) and retrodifferentiated U937 cells (Retro), respectively, were separated by SDS-PAGE, and VCP/p97 expression levels as well as the tyrosine phosphorylation patterns were examined by Western blot analysis. The Coomassie stain of the different fractions was used as a loading control. Densitometric analysis and normalization to the appropriate Coomassie stain was performed using the ImageJ software (NIH, Bethesda, MD, USA).