SPRED proteins do not inhibit the kinase activity of DYRK1A. A, HEK293 cells were transfected with the indicated plasmids (FLAG-SPRED1/2, HA-DYRK1A, and myc-Raf1) or a control pXJ40 vector. 24 h post-transfection cell lysates were subjected to immunoprecipitation (IP) using anti-FLAG. The immunoprecipitates were separated on SDS-PAGE and immunoblotted with the antibodies indicated on the left. Whole cell lysates (WCL) were immunoblotted (IB) to verify equal protein expression levels in all the samples tested. B, HEK293 cells were transfected with the indicated plasmids (FLAG-SPRED2, HA-WT-DYRK1A or HA-KD-DYRK1A, and myc-Raf1). Lysates obtained using the above setup were treated with alkaline phosphatase or BSA as a control and resolved by SDS-PAGE as mentioned in A.