For immunoblotting, total cell or pre-IP extracts were lysed in sample buffer containing SDS and protease and phosphatase inhibitors. Proteins were resolved on a SDS polyacrylamide gel, transferred to a polyvinylidene difluoride (PVDF) membrane, hybridized with a primary antibody, reacted with the horseradish peroxidase-conjugated secondary antibody, and visualized using chemiluminescent substrate (Thermo Scientific).