The Ubiquitin Conjugating Enzyme Ubch10 Competes With Ubch3 For Binding To The Scf Complex, A Ubiquitin Ligase Involved In Cell Cycle Progression

Ubiquitylation, which regulates most biological pathways, occurs through an enzymatic cascade involving a ubiquitin (ub) activating enzyme (E1), a ub conjugating enzyme (E2) and a ub ligase (E3). UbcH3 is the E2 that interacts with SCF (Skp1/Cul1/F‐box protein) complex and ubiquitylates many proteins (p27kip1, p21Cip1, cyclin E) that regulate the G1/S transition. Previously we demonstrated that UbcH3 interferes with UbcH10 functions, an E2 involved in the cell cycle regulation, at the G2/M transition, by competing for Anaphase‐promoting complex (APC). In this work, we aim to determine the effects of UbcH10 on the function of UbcH3. We showed by in vitro degradation assays that addition of UbcH10 inhibited UbcH3‐catalyzed degradation of a typical SCF substrate, p27kip1, while it had no effect on the degradation of a non SCF substrate, such as á‐lactalbumin. The competition for the binding to the SCF was confirmed by GST pull‐down assays using GST‐Roc1, the RING subunit of SCF that normally interacts with UbcH3. The results showed that UbcH10 was able to interact with Roc1 and decreased UbcH3/Roc1 interaction. These data suggest that a balance between UbcH3 and UbcH10 levels are critical for controlling the cell cycle progression and thus highlight a novel mechanism for regulating the progress through the cell cycle.