Background/Purpose: The role of Cullin-Ring ubiquitin ligase (CRL) activity in regulating T cell function is largely unexplored. Thus, we sought to determine if cullin neddylation and CRL activity regulates signaling initiated through the T-cell receptor (TCR) complex to modulate T cell activation and effector functions.

Methods: To determine if TCR complex signaling affects CRL activity, we treated T cells in vitro, with a specific neddylation inhibitor (MLN4924), a drug currently undergoing clinical trials for several maligancies, that prevents CRL activation in combination with CD3 activation and measured IL-2 production. We then assessed CRL activity during TCR complex signaling by examining the neddylation status of the cullin subunit of the CRL. In addition, we knocked down the cullin subunit of the CRLs in T cell lines and examined T cell function. Further we treated arthritis prone mice that have a TCR signaling defect with MLN4924 in vivo to assess the impact of CRL inactivation on T cell activation and effector function.

Results: Treating T cells with MLN4924 lowers the threshold for TCR signaling, as evidenced by enhanced IL-2 production and regulatory T cell (Treg) development upon suboptimal TCR stimulation. Moreover, MLN4924 treatment of the arthritis-prone SKG mouse, arrests arthritis progression and decreases the numbers of IL-17 producing T cell effectors in vivo. We found that strong TCR complex signaling results in cullin deneddylation, which renders the CRL inactive. After knocking down cullins in T cell lines, we found that IL-2 production is increased compared to the parental cell line, but some individual cullin knockdowns do not achieve the same enhancement of IL-2 production as MLN4924 treatment, suggesting that multiple CRLs contribute to regulating TCR complex signaling and IL-2 production.

Conclusion: Thus, we propose that strong TCR complex signaling normally triggers cullin deneddylation to shut off CRL activity and the otherwise tonic ubiquitination and degradation of proteins essential for TCR complex signaling and IL-2 production. Ongoing studies are elucidating the specific CRL targets that contribute to the phenotype seen.

Significance: These findings represent the first step in understanding the interplay between neddylation, CRL-mediated ubiquitination and TCR complex signaling. Expanding our knowledge of how CRLs neddylation regulates TCR complex signaling and T cell function will create opportunities for developing drugs to modulate T cell function to treat immune-mediated diseases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/activated-cullin-ring-ubiquitin-ligases-crls-dampen-t-cell-signaling-and-inactivation-of-crls-arrests-the-progression-of-inflammatory-arthritis/