Ubiquitin pathway inhibitors blocked menin inhibitor-induced reduction of menin protein, but not mRNA. MV4;11 and THP-1 cell lines were treated for 8 hours with 3 μM MI-503 and E1 inhibitor PYR-41, followed by analysis of menin protein levels with Western blotting (A). MV4;11 and THP-1 cell lines were treated for 8 or 24 hours with 10 μM proteasome inhibitor MG132 and 0-3 μM MI-503 followed by analysis of protein levels by Western blotting, and mRNA levels by qRT-PCR. (B, D) Typical Western blot of menin and c-Myc expression in MV4;11 and THP-1 cell lines with indicated treatments. (C, E) MEN1 mRNA level was detected by qRT-PCR in MV4;11 and THP-1 cell lines.