Requirement for SHP-2 in PECAM-1—mediated cell survival. DT40 cells and an SHP-2^- variant of DT40 expressing the indicated levels of PECAM-1 (A) were induced to undergo programmed cell death by addition of 25 nM staurosporine. Twelve hours later, the cells were lysed and caspase levels determined as in Figures 1 and 4. ITIM-less PECAM-1 (B, far right) fails to prevent Bax-mediated cell death in DT40 cells, similar to the results shown for HEK 293 cells (Figure 4). In the absence of SHP-2 (lower panels), wild-type PECAM-1, even at slightly higher expression levels, fails to protect DT40 cells from apoptosis. Data shown in panel B represent the mean ± the standard deviation of triplicate determinations. All of the bands were derived from a single gel to which equal protein levels were loaded.