The proapoptotic activity of S1PR2 is mediated by Gα13. (A-I) The 3 indicated DLBCL cell lines were transfected with plasmids encoding either wild-type or mutant S1PR2, or Gα12, or Gα13. Cell viability and apoptosis were assessed after 48 hours by CellTiter Blue assay (A,D,G), Annexin V staining (B,E,H), and cleaved caspase-3 staining (C,F,I). Data are represented as means + SEM of at least 3 independent experiments. Note that roughly equal expression of the 4 constructs was verified using FLAG-tagged versions of the proteins (data not shown). (J-K) Viability and apoptosis of SU-DHL6 cells that inducibly express S1PR2 72 hours posttransfection with the indicated siRNAs; transfected cells were additionally exposed to doxycycline for the last 48 hours of the experiment where indicated. Cell viability was assessed using CellTiter Blue assay (J); apoptosis was assessed by Annexin V staining (K). Data represent means +SEM of 3 independent experiments. *P < .05, **P < .01, and ***P < .001 (2-tailed Students t test). (L) Expression levels of Gα12 and Gα13 during B-cell development, as determined using publicly available data from Genomicscape.²⁴  Ctr, control; n.s., not significant.