Levels of available HOXB4 protein determine the magnitude of HOXB4-induced proliferation responses. (A) Western blot analyses of HOXB4 levels in HOXB4(WT)- or HOXB4(W→G)-transduced primary BM cells. (B) Accumulation of HOXB4(WT) and HOXB4(W→G) proteins in nuclear compartments of the transduced BaF3 cells. N indicates nuclear extracts; and Cy, cytoplasmic fraction. (C) Pulse-chase analysis of HOXB4(WT) and HOXB4(W→G) proteins. (D) HOX protein levels in HOXB4(WT) and HOXB4(W→G)-transduced BM cells sorted in subpopulations expressing high (filled symbols) or low (open symbols) levels of GFP. c-Jun levels are shown as a loading control. (E) IL-3–induced proliferation responses of populations shown in panel D. (F) Expansion of total nucleated cells over a 7-day period in cultures initiated with populations of cells sorted as described for panel D. Results represent mean values ± SD of a representative experiment (n = 2) performed in duplicate. (G) Representative assay showing preferential expansion of HOXB4^highLy5.1⁺ cells in liquid cultures initiated with a 1:5 mixture of HOXB4^highLy5.1⁺ and HOXB4^lowLy5.2⁺ BM cells.