R516fs and E235K mutations exhibit reduced protein stability and shortened half-lives compared with wild-type (WT) menin. A, Western blot analysis of MEFΔMen1 whole-cell extracts following overexpression of wild-type menin in the presence of the protein synthesis inhibitor cycloheximide (CHX, 10 μmol/L) alone or pretreated with the proteosome inhibitor MG132 (10 μmol/L). B, Normalized FLAG band signal intensity plotted as a function of time in the presence of CHX with and without MG132 pretreatment. Overexpression of the R516fs (C–D), E235K(E, F), and A541T (G, H) menin proteins with normalized FLAG band signal intensity plotted as a function of time in the presence of CHX alone or in combination with MG132 pretreatment. n = 3 experimental replicates, mean ± SEM. *, P < 0.05; ***, P < 0.01; ****, P < 0.0001 by two-way ANOVA.