Functional screen of genes on chromosome 7q that contribute to the pathogenesis of myelodysplastic syndrome (MDS) / acute myeloid leukemia (AML) and to the response to hypomethylating agents
Final Report Abstract
The immunomodulatory drug (IMiD) lenalidomide is a highly effective and specific treatment for multiple myeloma and myelodysplastic syndrome with del(5q). Lenalidomide and its analogues thalidomide and pomalidomide have additional pleiotropic effects including teratogenicity, inhibition of TNF release in monocytes5 and stimulation of IL-2 release by T cells.6 For a long time, the molecular mechanism of this class of drugs remained elusive. In 2010 it has been shown that thalidomide binds the CRBN-DDB1-CUL4A- ROC1 (CRBN-CRL4) E3 ubiquitin ligase and that this interaction is responsible for thalidomide-induced teratogenicity. E3 ligases are enzymes that attach ubiquitin chains to their substrates what generally results in their proteasomal degradation. We hypothesized that altered ubiquitination of substrates of the CRBN-CRL4 E3 ligase is responsible for the effects of lenalidomide and its analogues. In order to identify such substrates we applied SILAC (stable isotope labeling by amino acids in cell culture)-based quantitative mass spectrometry studies to globally assess changes in ubiquitination and proteome levels in a multiple myeloma cell line. These analysis and subsequent validation experiments revealed that lenalidomide and other IMiDs activate the CRBN- CRL4 E3 ligase to specifically ubiquitinate two members of the Ikaros transcription factor family, IKZF1 (Ikaros) and IKZF3 (Aiolos), resulting in their proteasomal degradation. Inactivation of IKZF1 and IKZF3 selectively inhibits growth of multiple myeloma while overexpression of IKZF3 mutants that do not bind to CRBN confers resistance to lenalidomide. Lenalidomide-induced degradation of IKZF1 and IKZF3 is also responsible for increased IL-2 release from T cells. In aggregate, our study revealed the mechanism of lenalidomide in multiple myeloma and T cells. Furthermore, selective ubiquitination and degradation of specific targets provides a novel mechanism of therapeutic activity for proteins that are otherwise considered “undruggable”.
Publications
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Biology of MDS. Chapter in the Education Book of the 17th Meeting of the European Hematology Association, Amsterdam 2012
Krönke J, Ebert BL
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Lenalidomide Causes Selective Degradation of IKZF1 and IKZF3 in Multiple Myeloma Cells. Science. 2014 Jan 17;343(6168):301-5
Krönke J, Udeshi N, Narla A, Grauman P, Hurst SN, McConkey M, Svinkina T, Heckl D, Comer E, Li X, Ciarlo C, Hartman E, Munshi N, Schenone M, Schreiber SL, Carr SA, Ebert BL
