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FOG is a multitype zinc finger protein that is essential for megakaryopoiesis, binds to the amino-terminal finger of GATA-1, and modulates the transcription of GATA-1 target genes. Presently investigated are effects of FOG and GATA-1 on the transcription of the megakaryocytic integrin gene,αIIb. In GATA-1-deficient FDCER cells (in the presence of endogenous FOG), ectopically expressed GATA-1 activated transcription 3–10-fold both from αIIbtemplates and the endogenous αIIbgene. The increased expression of FOG increased reporter construct transcription 30-fold overall. Unexpectedly, αIIbgene transcription also was stimulated efficiently upon the ectopic expression in of FOG per se. This occurred in the absence of any detectable expression of GATA-1 and was observed in multiple independent sublines for both the endogenousαIIbgene and transfected constructs yet proved to depend largely upon conserved GATA elements 457 and 55 base pairs upstream from the transcriptional start site. In 293 cells, FOG plus GATA-1 but not FOG alone only moderately stimulatedαIIbtranscription, and no direct interactions of FOG with the αIIbpromoter were detectable. Thus, FOG acts in concert with GATA-1 to stimulateαIIbexpression but also can act via a GATA-1-independent route, which is proposed to involve additional hematopoietic-restricted cofactors (possibly GATA-2).

The zinc finger protein GATA-1 functions in a concentration-dependent fashion to activate the transcription of erythroid and megakaryocytic genes. Less is understood, however, regarding factors that regulate the GATA-1gene. Presently elements within intron 1 are shown to markedly affect its erythroid-restricted transcription. Within a full-length 6.8-kilobaseGATA-1gene construct (G6.8-Luc) the deletion of a central subdomain of intron 1 inhibited transcription ≥10-fold in transiently transfected erythroid SKT6 cells, and likewise inhibited high-level transcription in erythroid FDCW2ER-GATA1 cells. In parental myeloid FDCER cells, however, low-level transcription was largely unaffected by intron 1 deletions. Within intron 1, repeated GATA and Ap1 consensus elements in a central region are described which when linked directly to reporter cassettes promote transcription in erythroid SKT6 and FDCER-GATA1 cells at high rates. Moreover, GATA-1 activated transcription from this subdomain in 293 cells, and in SKT6 cells this subdomain footprinted in vivo. For stably integrated GFP reporter constructs in erythroid SKT6 cells, corroborating results were obtained. Deletion of intronic GATA and Ap1 motifs abrogated the activity of G6.8-pEGFP; activity was decreased by 43 and 56%, respectively, by the deletion of either motif; and the above 1800-base pair region of intron 1 per sewas transcribed at rates uniformly greater than G6.8-pEGFP. Also described is the differential utilization of exons 1a and 1b among primary erythromegakaryocytic and myeloid cells.