FLT-3 JMD deletions produce prosurvival signals. (A) Spontaneous apoptosis was measured in cells expressing the different constructs. After growing in rm IL-3 overnight, the cells were deprived of cytokines and cultured for 48 hours. Apoptosis was then measured by staining with annexin V, followed by flow cytometry. The flow plots from the assay are shown in supplemental Figure 4. (B) Signaling in cells expressing the 4 identified JMD deletions was measured by phospho-western analysis of whole-cell lysates. For comparison, lysates from cells expressing FLT-3/ITD and the parental cell line grown in the absence of rm IL-3 for 4 hours are included.