C. Effect of USP44 and USP7 coexpression on FOXP3 ubiquitination. HEK293T cells were transfected with plasmids encoding MYC-FOXP3, either FLAG-USP44 or FLAG-USP7 or both, His-ubiquitin. Cells were treated with 20 μM MG132 for 4 hrs before being harvested, lysed, and incubated on Ni-NTA beads to pull down ubiquitinated FOXP3, which was visualized by immunoblotting using antibodies specific for MYC. 