E3 Ligase Rbx1 Orchestrates Thymus Development and Fate Determination of αβ-γδ T Cells.

T lymphocytes consist of αβ and γδ T cells, which mature and differentiate from the same progenitor cells in the thymus. Cullin-RING ligases (CRLs), the largest family of ubiquitin ligases, require neddylation on the scaffold protein Cullins for their ligase activity. The role of neddylation-CRL system in thymus development and fate determination of αβ/γδ T cells remains elusive. Here, we generated conditional knockout mouse models with thymus individual deletion of Ube2m or Ube2f, 2 neddylation E2-conjugating enzymes, and Rbx1 or Sag, 2 dual neddylation and ubiquitylation E3 ligases. We found that only Rbx1, but not Ube2m/Ube2f, nor Sag, plays an essential role in thymus development and fate determination of αβ/γδ T cells. Specifically, Rbx1 loss causes shrinkage of the thymus, delayed T cell development, increased γδ T cells in the thymus, increased the ratio of immature Gzma (+) γδ T cells, and decreased the ratio of the proliferative subpopulation. Some of these phenotypes were moderately rescued by simultaneous Bim deletion. Mechanistically, Rbx1 loss alters the Akt, NF-κB, and metabolic pathways in progenitor γδ T cells/DN3a cells. Finally, Rbx1 loss altered the γδ T1/T17 cell population in the thymus, suggesting that Rbx1 controls the fate of γδ T cells.