Fig. 4. Cytoplasmic VPARP-rods and their relation to MVP expression levels. (A) Anti-VPARP staining of untransfected SW1573 (a) and HeLa (b) cells showed a normal VPARP distribution, including the VPARP-rods. Background staining was absent as revealed by the staining of SW1573 cells with an isotype antibody (c). Bar, 10 µm. (B) The left-hand graph depicts the average length of the VPARP-rods in untransfected SW1573 cells, in its vault-overexpressing drug-resistant derivative SW1573/2R120 and in the SW1573/MVP-GFP transfectant. The numbers in the bars indicate the number of VPARP-rods measured. The data were analyzed by the Student's t-test. The P-value was in all cases below 0.05, indicating statistically significant differences. The right-hand graph shows the quantification of the MVP (black bars) and VPARP (gray bars) levels as determined by immunoblotting (see inlay; lane 1, SW1573/MVP-GFP; lane 2, SW1573/2R120; and lane 3, SW1573, with equal amounts of total protein loaded). The levels of VPARP and MVP in the SW1573 cells are arbitrarily set at 1 and corrected for loading using the ß-tubulin signal as a reference. Note that the two protein bands visible in the MVP panel in lane 1 represent the endogenous MVP and the MVP-GFP fusion product.

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