Runx1 isoforms have various protein stability and susceptibility to proteasome-mediated degradation. (A-B) Protein stability of Runx1 isoforms. 293T cells were transfected with indicated construct. Forty-eight hours later, cells were treated with 100 ng/mL CHX for indicated time. α-Tubulin served as a loading control. (A) Representative western blotting result of 3 independent experiments. (B) Quantification of the results in panel A. Intensities at 0 h were set to 100%. Mean ± SD of 2 independent experiments is shown. (C-D) Inhibition of proteasome-mediated degradation pathway. 293T cells were transfected with the indicated construct. Forty-eight hours later, cells were treated with 10 µM MG132 for 24 hours. α-Tubulin served as a loading control. (C) Representative western blotting result of 3 independent experiments is shown. (D) Quantification of the results in panel C. Runx1 signals were normalized to those of tubulin, and vehicle (DMSO)–treated signals were set to 1. Mean ± SD of 3 independent experiments is shown. (E) Western blot of phosphorylation of “S303”. Replicate membranes were probed with anti-Runx1 and anti-phospho S303 antibodies, respectively. (F) Quantification of panel E. Mean ± SD of 3 independent experiments is shown.