Identification of a GATA-overlapping sequence within the enhancer of the murine GPIIb promoter that induces transcriptional deregulation in human K562 cells

Characterization of human glycoprotein VI gene 5' regulatory and promoter regions

OBJECTIVE

Platelet glycoprotein VI is a collagen receptor belonging to the immunoglobulin-like protein family that is essential for platelet interactions with collagen and is exclusively expressed in the megakaryocytic lineage. The objective of this study was to characterize the human glycoprotein VI gene (GP6) 5' regulatory and promoter regions.

METHODS AND RESULTS

We first used 5' RACE to establish experimentally that the major transcription start site lies 28 bp upstream from the start codon. We next subcloned the 5' regulatory region of GP6 into pGL3-basic [pGL3(-1576)] and used deletion mutagenesis to identify important regulatory regions, comparing the activity of transiently expressed promoter-luciferase constructs in Dami and HeLa cells. We found that megakaryocyte lineage-specific transcription is largely controlled within the segment -191/-39. By site-directed mutagenesis, we confirmed that a GATA-1 site at -176 and an Ets-1 site at -45 play important roles in the regulation of GP6 transcriptional activity.

CONCLUSIONS

We have determined that the GP6 sequence -191 to -39 represents the core promoter and that transcription is driven largely by GATA-1 (-176) and c-Ets-1 (-45) sites within this segment.

Enforced expression of the GATA-3 transcription factor affects cell fate decisions in hematopoiesis

OBJECTIVE

Three GATA family transcription factors are involved in various aspects of hematopoiesis. Their lineage-restricted expression correlates well with their function in selective lineage commitment and differentiation. We focused on the role of GATA-3 to determine whether an intrinsic variation among different GATA proteins, in addition to the distinct expression pattern, determines lineage specification.

MATERIALS AND METHODS

Using a retroviral vector, we introduced the GATA-3 gene into primary murine hematopoietic stem cells (HSC) and examined their development in in vitro suspension culture and colony-forming assays as well as in vivo competitive repopulation studies.

RESULTS

Although GATA-3 expression normally is restricted to lymphoid precursor and committed T cells, overexpression of GATA-3 in HSC results in cessation of cell expansion followed by selective induction of megakaryocytic and erythroid differentiation and inhibition of myeloid and lymphoid precursor development in liquid suspension culture and in vitro colony-forming assays. Competitive repopulation studies show that transplanted GATA-3-expressing HSC/progenitor cells give one wave of erythrocyte development but fail to expand in the bone marrow or to reconstitute other lineages.

CONCLUSIONS

The selective megakaryocytic/erythroid differentiation in HSC with enforced GATA-3 expression suggests a functional redundancy among GATA proteins and indicates that the specific lineage fate determination by individual GATA proteins is largely regulated at the level of expression in a lineage and developmental-stage restricted fashion, whereas the identity of the GATA factor may not be as important.