FIG. 4.

Induction of plakoglobin by fusion proteins in AML. (a) Comparison of plakoglobin mRNA regulation by fusion proteins in microarray experiments and in real-time RT-PCR analyses in the different U937 cell lines. Expression levels of the U937-vector control cell line were set at 1. (b) Plakoglobin protein expression in fusion protein-expressing U937 cells by Western blot analysis. (c) Western blot analysis of plakoglobin expression in tetracycline-inducible U937-AML1-ETO cells and other myeloid cell lines. (d) Control U937 cells, U937-AML1-ETO, or U937-PML-RARα cells were zinc induced for 24 h before cycloheximide was added to block protein synthesis. Cells were harvested at the indicated time points and analyzed for plakoglobin and β-catenin protein levels. (e) NB4 leukemia cells carry an endogenous t(15;17). These cells but not the resistant NB4-R2 cells differentiate towards granulocytes upon exposure to ATRA. Western blot analysis indicated that plakoglobin protein levels were decreased by ATRA in responsive NB4 cells but not in ATRA-resistant NB4-R2 cells. (f) Expression levels of plakoglobin in bone marrow samples at the time of diagnosis in 62 patients with AML. Plakoglobin expression was significantly higher in fusion protein-positive patients than in others (P = 0.04).