Cell-cycle–dependent oscillation of GATA2 expression in hematopoietic cells

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Abstract
In vitro manipulation of hematopoietic stem cells (HSCs) is a key issue in both transplantation therapy and regenerative medicine, and thus new methods are required to achieve HSC expansion with self-renewal. GATA2 is a transcription factor controlling pool size of HSCs. Of interest, continuous overexpression of GATA2 does not induce HSC proliferation. In this report, we demonstrate that GATA2 expression, in leukemic and normal hematopoietic cells, oscillates during the cell cycle, such that expression is high in S phase but low in G1/S and M phase. GATA2 binding to target Bcl-X gene also oscillates in accordance with GATA2 expression. Using a green fluorescent protein (GFP)–GATA2 fusion protein, we demonstrate cell-cycle–specific activity of proteasome-dependent degradation of GATA2. Immunoprecipitation/immunoblotting analysis demonstrated phosphorylation of GATA2 at cyclin-dependent kinase (Cdk)–consensus motifs, S/T0P+1, and interaction of GATA2 with Cdk2/cyclin A2–, Cdk2/cyclin A2–, and Cdk4/cyclin D1–phosphorylated GATA2 in vitro. Mutants in phosphorylation motifs exhibited altered expression profiles of GFP-GATA2 domain fusion proteins. These results indicate that GATA2 phosphorylation by Cdk/cyclin systems is responsible for the cell-cycle–dependent regulation of GATA2 expression, and suggest the possibility that a cell-cycle–specific “on-off” response of GATA2 expression may control hematopoietic-cell proliferation and survival.