F HEK293T cells transfected with Strep-tagged empty vector or MARCH2 with GST-tagged NEMO and each different HA-tagged ubiquitin mutants (indicated lysine (K) only, other lysines (K) mutated to arginines (R) were treated with MG132 (10 μM) for 6 h before harvest. Lysates were subjected to pull down with GST beads, followed by immunoblotting with an anti-HA antibody. Whole cell lysates were determined by immunoblotting with the indicated antibodies. 