The Functional Redundancy of Neddylation E2s and E3s in Modulating the Fitness of Regulatory T Cells

Neddylation is necessary for activation of Cullin-RING ligases (CRLs), which degrade various immune regulatory proteins. Our recent study showed that while depletion of neddylation E2–E3 pair Ube2f-Sag in regulatory T (T(reg)) cells had no obvious phenotype, the same depletion of either Ube2m or Rbx1 caused inflammation disorders with different severity. Whether these E2s or E3s compensate each other in functional regulations of T(reg) cells is, however, previously unknown. In this report, we generated Foxp3(Cre);Ube2m(fl/fl);Ube2f(fl/fl) or Foxp3(Cre);Rbx1(fl/fl);Sag(fl/fl) double-null mice by simultaneous deletion of both neddylation E2s or E3s in T(reg) cells, respectively. Remarkably, Ube2m&Ube2f double-null mice developed much severe autoimmune phenotypes than did Ube2m-null mice, indicating that Ube2m markedly compensates Ube2f in T(reg) cells. The minor worsened autoimmune phenotypes seen at the very early stage in Rbx1&Sag double-null than Rbx1-null mice is likely due to already severe phenotypes of the later, indicating a minor compensation of Rbx1 for Sag. The RNA profiling-based analyses revealed that up- and down-regulations of few signaling pathways in T(reg) cells are associated with the severity of autoimmune phenotypes. Finally, severer inflammation phenotypes seen in mice with double E3-null than with double E2-null T(reg) cells indicate a neddylation-independent mechanism of 2 E3s, also known to serve as the RING component of CRLs in regulation of T(reg) cell fitness.