Smurf1 targets Securin for ubiquitin-dependent degradation and regulates the metaphase-to-anaphase transition.

The HECT E3 ligase Smurf1 (Smad ubiquitination regulatory factor 1) plays a critical role in several important biological pathways by targeting many proteins for ubiquitination and degradation, such as Smad1/5, MEKK2 and RhoA. However, the function of Smurf1 in metaphase-to-anaphase transition remains unclear. Here, we show that Smurf1 interacts with and targets Securin, an inhibitor of sister-chromatid separation, for poly-ubiquitination and proteasomal degradation. Further results demonstrate that Securin is a physiological substrate of Smurf1 in MEF cells. Knockdown of Smurf1 results in sister-chromatid separation inhibition and delay of anaphase onset. This study provides the first evidence that Smurf1 functions as a novel regulator for the metaphase-to-anaphase transition.