Insoluble α-globin accumulates after proteasome inhibition in β-thalassemic erythroid cells. (A) Coomassie-stained triton acetic acid urea gel showing α-globin precipitates in Th3/+ erythrocyte membranes. The marker lane M shows purified α and β-globins. (B) Th3/+ reticulocytes were pulse labeled with ³⁵S-methionine and ³⁵S-cysteine and chased with unlabeled amino acids for the indicated periods of time with or without proteasome inhibitors. Radiolabeled soluble and insoluble globins were isolated from equal numbers of cells, fractionated by triton acetic acid urea gel electrophoresis, and visualized by autoradiography. (C) Quantification of autoradiographs from panel B; n = 3 mice/group. *P < .05 versus DMSO. (D) α-globin Western blots of soluble and insoluble fractions from mouse fetal liver erythroid cultures (48 hours differentiation) of wild-type, Th3/+, and Th3/Th3 erythroblasts. (E) α-globin Western blots of soluble and insoluble fractions from mouse fetal liver erythroid cultures (72 hours of differentiation) treated with vehicle or MG132 (1 or 10μM) for 12 hours.