Figure 9.

Induction of the aggregation of endogenous K18 by mutant K8. (A) Aggregation induced by expression of K8ΔN. HepG2 cells were transfected with plasmids encoding Myc epitope-tagged full-length K8 (K8FL; left), K8ΔN (middle), or K8ΔC (right). The cells were then subjected to staining with antibodies to Myc (red) and Hoechst 33258 (blue). Bar, 10 μm. (B) Quantitative analysis of aggregate formation in cells expressing K8FL, K8ΔN, or K8ΔC. The percentage of cells containing aggregates among those expressing the recombinant K8 proteins was determined for the experiment shown in A. Data are means ± SD of values from triplicate cultures. (C) Induction of aggregation of endogenous K18 by expression of K8ΔN. HeLa cells were transfected with a plasmid encoding HA-tagged K8ΔN. The cells were then subjected to double staining with antibodies to HA (red; left) and to K18 (green; middle). Expression of K8ΔN at high levels (arrowheads) induced marked perinuclear aggregation of endogenous K18, whereas low levels of K8ΔN expression (arrows) did not affect the fibrous array of the endogenous protein. The superimposed images (merge) on the right, also showing Hoechst 33258 staining (blue), reveal that HA-K8ΔN colocalized with endogenous K18. Bar, 20 μm.