Figure 5.

Ultrastructural localization of cytokeratins in control, caspase-3, and caspase-7–transfected MCF-7 cells after treatment with TRAIL. (A) The cytoplasm of a cell transfected with caspase-3, and exposed to TRAIL for 6 h, is largely devoid of labeling for K18, but the label is concentrated over large (asterisks) and small spheroidal inclusions. Remnants of the dense, fibrillar component (black arrowheads) are evident alongside the enlarged granular component (curved black arrow) of the nucleolus. The inset is a threefold magnification of the area outlined. (B) In a nontransfected cell, exposed to TRAIL for 6 h, K18 is localized in sheaves (double white arrows) present throughout the cytoplasm. The inset shows the diffuse distribution of cytokeratin 18–labeled intermediate filaments in control cells. (C) The cytoplasm of a cell transfected with caspase-7, and exposed to TRAIL for 6 h, contains a large spheroidal cytoplasmic inclusion (asterisk), together with two smaller inclusions (curved white arrows) which are labeled with 10 nm immunogold after incubation with the M30 antibody, which is specific to the cleaved form of K18. The rest of the cell, including a remnant of the nucleolar dense fibrillar component (black arrowhead) is devoid of label. The inset is a threefold magnification of the area outlined. (D) The cytoplasm of a cell transfected with caspase-7 and exposed to TRAIL for 6 h. Labeling by both the M30 antibody (10 nm immunogold) and the 3055 antibody, which is specific to the phosphorylated form of this cytokeratin (5 nm immunogold), is evident over a large spheroidal inclusion (asterisk). The inset is a threefold magnification of the area outlined. Bars, 1 μm.