Up-regulation of G-CSFR by AML1-MTG8 and down-regulation by AML1b in L-G infectants.

(A) Schematic representation of AML1b protein, AML1-MTG8 protein, and deletion mutants of AML1-MTG8 proteins, D538 and D487. Runt indicates the runt homology region; PST, proline, serine, threonine-rich region; NHR, nervy homology region; Zn, zinc finger motifs. Note that AML1-MTG8 retains the runt homology region and most of the MTG8 protein. (B) Expression of AML1b and AML1-MTG8 protein in L-G cells detected by Western blot analyses. Proteins from the L-G infectants with viruses encoding AML1b and AML1 MTG8 or with a control virus were analyzed by immunodetection using anti-HA antibody. The positions of AML1 and AML1-MTG8 are indicated by arrows. (C) Ligand binding assay for G-CSFR activity of L-G infectants. The activity was measured as described in “Materials and methods.” (D) Northern blot analyses showing the expression of G-CSFR mRNA. Total RNAs (5 μg of RNA) were prepared from L-G infectants cultured with IL-3, blotted, and hybridized with³²P-labeled mouse G-CSFR cDNA and human G3PDH cDNA. (E) Northern blot analyses showing the expression of G-CSFR mRNA in deletion mutants of AML1-MTG8. Total RNAs were prepared from L-G infectants cultured with IL-3, blotted, and hybridized with³²P-labeled mouse G-CSFR cDNA and human G3PDH.