MEF2D-fusion (M-fusion) genes are newly discovered recurrent gene abnormalities that are detected in approximately 5 % of acute lymphoblastic leukemia (ALL) cases. Their introduction to cells has been reported to transform cell lines or increase the colony formation of bone marrow cells, suggesting their survival-supporting ability, which prompted us to examine M-fusion-targeting drugs. To identify compounds that reduce the protein expression level of MEF2D, we developed a high-throughput screening system using 293T cells stably expressing a fusion protein of MEF2D and luciferase, in which the protein expression level of MEF2D was easily measured by a luciferase assay. We screened 3766 compounds with known pharmaceutical activities using this system and selected staurosporine as a potential inducer of the proteolysis of MEF2D. Staurosporine induced the proteolysis of M-fusion proteins in M-fusion (+) ALL cell lines. Proteolysis was inhibited by caspase inhibitors, not proteasome inhibitors, suggesting caspase dependency. Consistent with this result, the growth inhibitory effects of staurosporine were stronger in M-fusion (+) ALL cell lines than in negative cell lines, and caspase inhibitors blocked apoptosis induced by staurosporine. We identified the cleavage site of MEF2D-HNRNPUL1 by caspases and confirmed that its caspase cleavage-resistant mutant was resistant to staurosporine-induced proteolysis. Based on these results, we investigated another Food and Drug Administration-approved caspase activator, venetoclax, and found that it exerted similar effects to staurosporine, namely, the proteolysis of M-fusion proteins and strong growth inhibitory effects in M-fusion (+) ALL cell lines. The present study provides novel insights into drug screening strategies and the clinical indications of venetoclax.
Keywords: 3-Methyladenine (PubChem CID: 135398661); Acute lymphoblastic leukemia; Bafilomycin A1 (PubChem CID: 6436223); Bax channel blocker (PubChem CID: 2729027); Bortezomib (PubChem CID: 387447); Cycloheximide (PubChem CID: 6197); Cytarabine (PubChem CID: 6253); Drug discovery; Drug repositioning; Epoxomicin (PubChem CID: 11226684); High throughput screening; K252a (PubChem CID: 3035817); MEF2D; MG-132 (PubChem CID: 462382); MG-262 (PubChem CID: 490002); Staurosporine; Staurosporine (PubChem CID: 44259); Venetoclax (PubChem CID: 49846579); Vincristine (PubChem CID: 5978); Z-VAD-FMK (PubChem CID: 5497174).
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