Figure 4. CSN6-mediated p57 downregulation is Skp2-dependent. (A) Skp2 deficiency diminished CSN6’s capability to reduce steady-state expression of p57. Indicated WT and Skp2−/− MEF cells after transfection with indicated plasmids were immunoblotted with indicated antibodies. (B) Skp2-mediated p57 ubiquitination requires the presence of CSN6. 293T cells were transfected with the indicated plasmids. The proteasome inhibitor MG132 was added 6 h prior to cell harvesting. The amount of ubiquitinated p57 was analyzed by immunoprecipitation (IP) with anti-Flag followed by immunoblotting (IB) with anti-Ubi. TCE, total cell extracts.