Sd. Fu et al., Distinct functions of two isoforms of a homeobox gene, BP1 and DLX7, in the regulation of the beta-globin gene, GENE, 278(1-2), 2001, pp. 131-139
Homeotic proteins are transcription factors that regulate the expression of
multiple genes involved in development and differentiation. We previously
isolated a cDNA encoding such a protein from the human leukemia cell line K
562, termed Beta Protein 1 (BP1), which is involved in negative regulation
of the human beta -globin gene. Sequence comparison revealed that BP1 is a
member of the distal-less (DLX) family of homeobox genes and that it shares
its homeodomain and 3' sequences with another DLX cDNA, DLX7. BP1 and DLX7
exhibit unique 5' regions, diverging at nucleotide 565 of BP1. We mapped t
his new distal-less family member BP1 to chromosome 17q21-22 by FISH and PC
R, which is the same locus to which DLX7 has been mapped. These results str
ongly suggest that BP1 and DLX7 are isoforms (derived from the same gene).
Since our previous data demonstrated that BP1 and DLX7 are frequently co-ex
pressed, we determined whether DLX7 is also involved in the negative regula
tion of the beta -globin gene. Mobility shift assays demonstrated that both
BP1 and DLX7 proteins, synthesized in vitro, bind to the same BP1 binding
site. However, using transient assays, we showed that although BP1 represse
s activity of a reporter gene through either of two silencer DNA sequences
upstream of the beta -globin gene, DLX7 did not show repressor activity aga
inst the beta -globin promoter. Further characterization of these apparent
isoforms is of significance since they are jointly expressed in acute myelo
id leukemia and in many leukemia cell lines. (C) 2001 Elsevier Science B.V.
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