SCF^Fbl12 Increases p21^Waf1/Cip1 Expression Level through Atypical Ubiquitin Chain Synthesis

Abstract

The cyclin-dependent kinase (CDK) inhibitor p21 is an unstructured protein regulated by multiple turnover pathways. p21 abundance is tightly regulated, and its defect causes tumor development. However, the mechanisms that underlie the control of p21 level are not fully understood. Here, we report a novel mechanism by which a component of the SCF ubiquitin ligase, Fbl12, augments p21 via the formation of atypical ubiquitin chains. We found that Fbl12 binds and ubiquitinates p21. Unexpectedly, Fbl12 increases the expression level of p21 by enhancing the mixed-type ubiquitination, including not only K48-but also K63-linked ubiquitin chains, followed by promotion of binding between p21 and CDK2. We also found that proteasome activator PA28␥ attenuates p21 ubiquitination by interacting with Fbl12. In addition, UV irradiation induces a dissociation of p21 from Fbl12 and decreases K63-linked ubiquitination, leading to p21 degradation. These data suggest that Fbl12 is a key factor that maintains adequate intracellular concentration of p21 under normal conditions. Our finding may provide a novel possibility that p21's fate is governed by diverse ubiquitin chains.

Probing protein ubiquitination in live cells

“…We used these ubiquitin probes to analyze the ubiquitination of PAF15 (mono-Ub) 38, 39 , DNMT3A (K63-Ub) 46 , p21 (K48- and K63-Ub) 47, 48 , Cyclin B1 (K11-Ub) 49 , p53 (K48-Ub) 50 and H2A (mono-and K63-Ub) 51, 52 (Fig. 3C, Extended Data Fig.…”

E2 ubiquitin-conjugating enzyme UBE2L6 promotes Senecavirus A proliferation by stabilizing the viral RNA polymerase

“…Previous reports also have identified UBE2L3 as catalyzing the conjugation of p27Kip1 to heterogeneous ubiquitin chains and protecting them from degradation [ 54 ]. RNF4 forms K11/K33 ubiquitin chain conjugates of β-catenin that inhibit degradation [ 55 ], and SCFFbl12 forms K48/K63 ubiquitin chains inhibiting degradation of p21 Cip1/Waf1 [ 56 ]. Here we found that UBE2L6 inhibits the degradation of SVA 3D by catalyzing the K48/K63 mixed chains.…”

USP15 Deubiquitinates TUT1 Associated with RNA Metabolism and Maintains Cerebellar Homeostasis

“…Usp15 was amplified from the cDNA clone from the Kazusa DNA Research Institute and inserted into pcDNA3-Flag and pcDNA3-Myc vectors. The pCAGEN-His-Ub (wild-type and mutants) construct was described previously (57).…”