PKA-mediated activation of ERK1/2 underlies adenosine-ADORA2B-mediated erythrocyte SphK1 activation in SCD Tg mice and SCD patients. SphK1 activity, membrane bound total, and phosphorylated SphK1 in primary erythrocytes from (A,C) SCD transgenic mice and (B,D) SCD patients after treatment with N (10 μM NECA), N+M (10 μM NECA + 10 μM MRS1754), N+H (10 μM NECA + 10 μM H89), N+P (10 μM NECA + 20 μM PD98059), F (10 μM Forskolin), and F+P (10 μM Forskolin+ 20 μM PD98059) for 30 minutes. Values shown represent the mean ± SEM (n = 3 for SCD patients and n = 5 for normal human subjects; n = 3 for SCD transgenic mice and n = 4 for WT mice). *P < .05 N or F vs control; **P < .05 N+M, N+H, N+P vs N; ***P < .05 F+P vs F. (E) Working model: hypoxia or tissue damage leads to increased plasma adenosine which signals through ADORA2B and subsequent PKA and ERK1/2 pathways to activate SphK1 and produce more S1P in erythrocyte.