SHH pathway activation is required for CXCR4 signaling in medulloblastoma. A, CXCL12-induced changes in cAMP levels were measured by ELISA in SmoA1 tumor cells pretreated (12 hours) with cyclopamine (10 µmol/L, gray triangles), its inactive isomer tomatidine (10 µmol/L, lighter gray circles), or vehicle control (HPBCD, black squares) and normalized to t = 0 values (*, P < 0.001 for the difference between the cyclopamine and vehicle/tomatidine conditions by 2-way ANOVA, n = 3). B, cyclopamine pretreatment did not affect PACAP-activated cAMP induction (n = 3). C, CXCL12 (1 µg/mL, 10 minutes) induced significant Gαi activation (GTP loading) without changing total Gαi or CXCR4 levels in whole-cell lysates. Cyclopamine (10 µmol/L) pretreatment blocked CXCL12 effects. D, the mean # SEM (n = 3) for CXCL12 activation of Gαi (*, P < 0.001) and cyclopamine blockade of this effect (#, P < 0.001). IB, immunoblotting; IP, immunoprecipitation.