FKBP2 and plasmacytoma: Consistently, trypan blue exclusion assay showed that FKBP13 knockdown resulted in increased cell death in J558 plasmacytoma cells (Figure 3C), which correlated to upregulation of apoptotic markers, such as Annexin V positivity, caspase-3 cleavage, and PARP1/2 expression (Figures 3D,E).