Btk:ER-induced calcium mobilization is dependent on PLCγ2. A, expression of Btk:ER in parental and PLCγ2-deficient DT40 cells. WT Btk:ER was transfected into parental and PLCγ2-deficient cells and stable clones selected that expressed equal levels of Btk:ER. Whole cell lysates were immunoblotted with antiserum specific for Btk. B, Btk:ER-induced calcium mobilization is dependent on PLCγ2. Calcium mobilization in parental and PLCγ2-deficient cells expressing Btk:ER was measured as described in the legend for Fig 2C. Ionomycin (250 ng/ml) was used as a positive control.