Lymphoid-specific expression of the Id3 gene in hematopoietic cells. Selective antagonism of E2A basic helix-loop-helix protein associated with Id3-induced differentiation of erythroleukemia cells.

Accumulating evidence implicates functions of the Id family of helix-loop-helix proteins in the regulation of cell growth and differentiation in metazoa. Within the mammalian hematopoietic organ, expression of the Id3 gene is restricted to the lymphoid cell compartment. We show here that in non-lymphoid hematopoietic cells, repression of transcription is correlated with hypermethylation of sequences in the vicinity of the upstream regulatory region of the Id3 gene, suggestive of a strict developmental control of expression of this gene in lymphoid versus non-lymphoid hematopoietic cells. Enforced ectopic expression of Id3 in K562 erythroid progenitor cells promotes erythroid differentiation and is correlated with a quantitative/qualitative shift in the profile of interacting TAL1 and E protein heterodimers that bind to a consensus E box sequence in in vitro band shift assays, consistent with selective targeting of E2A E protein(s) by Id3 and suggesting a possible mechanism involving TAL1-mediated differentiation. By using a Gal 4-VP16 two-hybrid competition assay and an E box-dependent reporter assay, we demonstrate directly that the E2A protein E47 preferentially associates with Id3 in vivo. These observations provide a paradigm for understanding how overlapping but distinct specificities of individual Id proteins may constitute a developmentally regulated program underlying cell determination in diverse lineages.