Identification of novel functional regions important for the activity of HOXB7 in mammalian cells

Members of the HOX family of homeobox transcription factors play a role in pattern formation in diverse developmental systems. The clearly documented role of HOX genes in the proliferation and differentiation of primary hemat opoietic cells and cell lines provides a convenient system to pursue a bioc hemical analysis of HOX gene function in mammalian cells. To explore the ro le of HOXB7 in myeloid hematopoiesis, a number of mutations and deletions i n the gene were constructed that targeted sequences with known functions or in regions that had not been examined previously. The wild-type and mutant B7 constructs were introduced into the murine myelomonocytic cell line, 32 D, and assayed for their effects on G-CSF-induced myeloid differentiation. Wild-type HOXB7 inhibited the differentiation of 32D cells, whereas mutatio ns in the Pbx-binding pentapeptide motif or the DNA-binding homeodomain, as well as internal deletions of the N-terminal unique region, blocked this e ffect. Interestingly, mutations eliminating two target sites for casein kin ase II, the glutamate-rich C terminus, or the first 14 amino acids of IIOXB 7, led to enhanced 32D differentiation. A model proposing a role for these regions of HOXB7 is presented. The Journal of Immunology, 2001.