HEK293 cells were transfected with SAPAP3 and mGluR5 and/or spinophilin in the absence or presence of PPlα. A. HA immunoprecipitates and/or lysates were immunoblotted with spinophilin, SAPAP3 and Myc antibodies. B. Overexpression of PP1 significantly decreased SAPAP3 association with spinophilin. C. HA immunoprecipitates and/or lysates were immunoblotted with spinophilin, mGluR5, and Myc antibodies. D. Overexpression of PP1 decreased mGluR association with spinophilin. E. WT or F451A (FA) mutant spinophilin were transfected with SAPAP3 and mGluR5. Mutant spinophilin did not bind endogenous PP1, but had no effect on the association of spinophilin with SAPAP3 (F) or mGluR5 (G). **P<0.01, ****P<0.0001.