Immunomodulatory agents lenalidomide and pomalidomide co-stimulate T cells by inducing degradation of T cell repressors Ikaros and Aiolos via modulation of the E3 ubiquitin ligase complex CRL4(CRBN.).
Bottom Line: We confirm that Aiolos and Ikaros are transcriptional repressors of interleukin-2 expression.The findings link lenalidomide- or pomalidomide-induced degradation of these transcriptional suppressors to well documented T cell activation.In conclusion, we present a molecular model in which drug binding to cereblon results in the interaction of Ikaros and Aiolos to CRL4(CRBN) , leading to their ubiquitination, subsequent proteasomal degradation and T cell activation.
Affiliation: Celgene Corporation, Summit, NJ, USA.Show MeSH
Mentions: CRL4CRBN is an E3 ubiquitin ligase complex known to modify target substrates with ubiquitin. Therefore, because lenalidomide- or pomalidomide-mediated degradation of Aiolos and Ikaros requires the proteosome (Fig 2B), we investigated whether lysine ubiquitination was required for drug-mediated Aiolos degradation. To prevent ubiquitination of Aiolos, a Flag-tagged mutant IKZF3 (Flag-MT-IKZF3), in which all 30 lysine residues were conservatively substituted with arginines, was constructed. Jurkat cells were transfected with either a Flag-tagged WT IKZF3, Flag-MT-IKZF3, or an empty vector control. Cells were treated with lenalidomide or pomalidomide for 24 h and extracts were analysed by Western blot for Aiolos. Drug treatment caused degradation of endogenous Aiolos and recombinant Flag-WT-Aiolos, but not of Flag-MT-Aiolos, consistent with a mechanism of degradation that involves drug-induced lysine ubiquitination (Fig 4A).