HEK293 cells were transfected with HA-tagged spinophilin, V5-tagged SAPAP3, and Myc-tagged mGluR5. A. Transfected lysates were immunoprecipitated with HA or Myc antibodies and immunoblotted with spinophilin, SAPAP3, and mGluR5 antibodies. B. Overexpression of mGluR5 significantly increased the amount of SAPAP3 in spinophilin immunoprecipitates. C. Overexpression of spinophilin had no significant effect on the association of SAPAP3 with mGluR5. D. SAPAP3 overexpression significantly enhanced the association of spinophilin with mGluR5. E. Schema of SAPAP3/mGluR5-dependent bridging of spinophilin. ** p<0.01, *** p <0.001.