GATA2 is a transcription factor indispensable for development and maintenance of hematopoietic stem cells. Hematopoietic stem cells in G0 phase express GATA2 (Suzuki N, PNAS 103: 2202 2006), but proliferating hematopoietic progenitor cells, as well as proliferating cells in several other tissues, also express this factor. Gata2 knockout experiments indicate that GATA2 regulates cell proliferation; however, precise mechanisms have not been elucidated. Previously, we found oscillatory expressions of GATA2 during the cell cycle. In G1/S and G2/M phases, Cdk4 and Cdk2, forming complexes with several cyclins, phosphorylate GATA2 and induce GATA2 degradation (

Koga S, Blood 109: 4200, 2007
). In this study, we demonstrate the bidirectional control between GATA2 and Cyclin/Cdk systems. To identify GATA2 target genes regulating cell proliferation, we searched for conserved GATA factor-binding sequences in evolutionarily conserved regions (ECRs, http://ecrbrowser.dcode.org), and found conserved GATA sequences in ECRs in intron 3 and intron 4 of the CyclinD2 (Ccnd2) gene, and in intron 3 and 3′UTR of the CyclinE1 (Ccne1) gene. In ChIP experiments using synchronized Ba/F3 and P815 cells, GATA2 binding to these regions was high in late G1 phase, and then rapidly declined in early S phase. One hour treatment using a Cdk1/2 inhibitor, roscovitine, cancelled this regression in early S phase, implicating Cdk2 as a negative regulator of GATA2 binding to target genes. Significant GATA2 binding to Ccnd2 and Ccne1 genes was also detected in embryonic day 13.5 fetal liver cells. Exogenous GATA2 expression augmented transcriptional activity of these binding regions in luciferase assay. Induction of GATA2 siRNA repressed Ccnd2 and Ccne1 mRNA expression. Furthermore, Ccnd2 and Ccne1 mRNA expression, as well as Gata2 mRNA expression, was significantly reduced in placental and aortic regions of embryonic day 10.0 conceptihar boring insertions of green fluorescent protein cDNA at translation start sites of bothGata2 alleles (
Minegishi N, Blood 102: 896, 2003
). These results indicate that Ccnd2 andCcne1 genes are direct targets of GATA2. GATA2 binds to Ccnd2 and Ccne1 genes and activates their transcription in the G1 phase of proliferating cells. In G1/S transition, Cdk2activity, probably enhanced by CyclinE1 expression, attenuate GATA2 binding to Ccnd2and Ccne1 genes. In this fashion, bidirectional control of GATA2 and G1 cyclins may contribute to the transient expression of CyclinD2 and CyclinE1 in G1 phase, and to the acceleration of S-phase entry. In addition, it appears plausible that lack of Cdk activities causes differences in GATA2 functions in hematopoietic stem cells in G0 phase.

Topics:
cyclins, gata2 gene, transcription factor, rna, messenger, cdk2 protein, human, cdc2 protein kinase, complex, cyclin-dependent kinase 4, dna, complementary, luciferases

Disclosures: No relevant conflicts of interest to declare.

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2008, The American Society of Hematology
2008
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