Ubiquitin-Conjugating Enzyme UBE2D2 Is Responsible for FBXW2 (F-Box and WD Repeat Domain Containing 2)-Mediated Human GCM1 (Glial Cell Missing Homolog 1) Ubiquitination and Degradation

Glial cell missing homolog 1 (GCM1) is an important transcription factor regulating placental cell fusion. Recently, we have demonstrated that GCM1 is a labile protein and that the F-box protein FBXW2 (F-box and WD repeat domain containing 2) mediates GCM1 ubiquitination for proteasomal degradation. Multiple factors are involved in the ubiquitin-proteasome degradation system. Therefore, in order to better understand the mechanism regulating GCM1 stability, we further isolated and characterized the E2 ubiquitin-conjugating enzyme responsible for FBXW2-mediated ubiquitination of GCM1 in this study. We prepared and screened a variety of E2 proteins in an in vitro ubiquitination assay system for GCM1 and found that UBE2D2 is required for the SCFFBXW2 E3 ligase in regulation of GCM1 ubiquitination. We also demonstrated that the enzyme activity of UBE2D2 is required for GCMa ubiquitination and for association with the SCFFBXW2 complex. Moreover, knocking down UBE2D2 expression by RNA interference not only suppressed FBXW2-mediated GCM1 ubiquitination, but also prolonged the half-life of GCM1 in vivo. Our results suggest that UBE2D2 is a functional E2 protein which, together with FBXW2, regulates GCM1 stability in the placenta.