C/EBP slows the proliferation of 32D cl3 myeloblasts that cannot differentiate due to the expression of bcr-abl^p210 and of Ba/F3 lymphoid cells. (A) Total cellular proteins were prepared from 32D cl3 cells (32D), from a cell line known to express bcr-abl^p210 (K562), from a pool of 32D cl3 cells transduced with a control retrovirus (32D-Neo), and from a pool of 32D cl3 cells transduced with a retrovirus expressing bcr-abl^p210 and G418 resistance (32D-bcr/abl). These extracts were then subjected to Western blotting with a c-abl antisera (left panel). The locations of c-abl and bcr-abl^p210 are indicated. A G418-resistant subclone was derived the 32D-bcr/abl pool by limiting dilution and was shown to express a similar level of bcr-abl^p210 (not shown). This line was then transduced with the pBabePuro-C/EBPWT-ER retroviral vector. A subclone resistant to G418 and puromycin was selected. A total cellular protein extract derived from this line was subjected to Western blotting for C/EBP (right panel). (B) Total cellular RNAs were prepared from 32D-Neo and 32D-bcr/abl cells in IL-3 or after 0, 1, 2, 3, or 4 days in G-CSF. RNA samples were also prepared from 32D-bcr/abl cells cultured in G-CSF for 6, 8, or 10 days. These RNAs were then subjected to Northern blotting for MPO, GCSFR, and 18S RNAs. (C) 32D-bcr/abl, 32D-bcr/abl-WT-ER, Ba/F3(G), and Ba/F3(G)-WTER cells in IL-3 were cultured in the absence or presence of estradiol. Ba/F3(G) cells are a derivative of Ba/F3 cells which express the G-CSFR. Ba/F3(G)-WTER cells express C/EBPWT-ER in addition. Cell counts were enumerated daily with a hemocytometer and Trypan Blue Dye. Results shown are the mean of three determinations. SEs were less than 10% of each mean.