Transient overexpression of PU.1 induces differentiation toward the monocytic lineage in AML1-ETO⁺ Kasumi-1 cells.

(A) PU.1 induces differentiation in t(8;21)⁺ Kasumi-1 cells. Kasumi-1 cells were transiently transfected with PU.1 (pGsam-PU.1-ires-NGFR) or the empty vector (pGsam-ires-NGFR) and morphologic changes were observed on day 5 (original magnification, × 63). Arrows indicate the differentiating cells. (B) PU.1 overexpression in Kasumi-1 cells. Western blot shows PU.1 expression and β-tubulin in transfected Kasumi-1 cells after day 5. (C) PU.1 induces CD11b expression in Kasumi-1 cells. FACS analysis was performed for the cell surface expression of CD11b in Kasumi-1 cells transfected with empty vector or PU.1. (D) PU.1 induces CD14 expression in Kasumi-1 cells. In the same experiment FACS analysis was performed for the cell surface expression of CD14 in Kasumi-1 cells transfected with empty vector or PU.1. (E) Kasumi-1 cell number decreases in PU.1-transfected cells. The transfected cells described in the legend to Panel D were counted by trypan blue staining on days 1, 2, 3, 4, and 5 after transfection. (F) Model of AML1-ETO blocking PU.1 function. Model is of AML1-ETO interacting with PU.1 and displacing its coactivator c-Jun. This down-regulation of the PU.1 transcriptional activity by AML1-ETO results in down-regulation of PU.1 target genes important for myeloid differentiation.