PTK7 expression increases resistance to apoptosis in an anthracycline-induced cytotoxicity assay. (A-B) Annexin V staining was measured by flow cytometry after exposure of Baf3 (A) and TF1 (B) cells to anthracyclines (concentrations of doxorubicin are indicated in panels A and B). Expression of PTK7 was associated with a decreased frequency of annexin V-positive cells in both models. (C-D) Apoptosis was also evaluated by measuring executive caspase activity (caspases 3 and 7, luminometric assay). PTK7 expression was associated with a decreased induction of caspase activity in both models. (E) Same as in Figure 4B, except that TF1 cells and primary AML samples were sensitized to apoptosis (24-hour incubation, doxorubicin 2.5μM) and that recombinant proteins (PTK7-Fc and Nectin4-Fc) were added to compete with this effect. Percentage of surviving cells was measured as in Figure 5A. Student t test was used for statistics; all P values < .05.