ERK signaling mediates resistance to immunomodulatory drugs in the bone marrow microenvironment (CRISPR Screen)

Immunomodulatory drugs (IMiDs) have markedly improved patient outcome in multiple myeloma (MM); however, resistance to IMiDs commonly underlies relapse of disease. Here we identify and validate that TNF receptor associated factor protein family TRAF2 KD/KO in MM cells mediates IMiDs resistance via activation of non-canonical NF-kB and MEK-ERK signaling. Within MM bone marrow (BM) stromal cell supernatants, TNF-a induces proteasomal degradation of TRAF2, non-canonical NF-kB, and downstream ERK signaling in MM cells, whereas IL-6 directly triggers ERK activation. RNA sequencing of MM patient samples shows nearly universal ERK pathway activation at relapse on lenalidomide maintenance therapy, confirming its clinical relevance. Combination MEK inhibitor treatment restores IMiDs sensitivity of TRAF2 KO cells both in vitro and in vivo using an inducible TRAF2 KD MM xenograft model. Our studies provide the framework for clinical trials of MEK inhibitors to overcome IMiDs resistance in the BM microenvironment and improve patient outcome in MM. Overall design: Genome-wide CRISPR/cas9 screening in MM1S cells for Pomalidomide resistance