GATA-2/estrogen receptor chimera regulates cytokine-dependent growth of hematopoietic cells through accumulation of p21^WAF1 and p27^Kip1 proteins

GATA-2 is considered to be essential for the development, maintenance, and function of hematopoietic stem cells (HSCs). However, it was also reported that GATA-2 inhibits the growth of HSCs. To examine the role of GATA-2 in the growth of hematopoietic cells, we introduced an estradiol-inducible form of GATA-2 (GATA-2/estrogen receptor [ER]) into interleukin 3 (IL-3)-dependent cell lines, Ba/F3, 32D, and FDC-P1. Estradiol-induced GATA-2 suppressed c-myc mRNA expression and inhibited IL-3-dependent growth in these clones. As for this mechanism, GATA-2 was found to inhibit ubiquitin/proteasome-dependent degradation of p21^WAF1 and p27^KIp1 and to induce their accumulation by repressing the expression of Skp2 and Cul1, both of which are components of the ubiquitin ligase for p21^WAF1 and p27^Kip1. Overexpression of c-myc restored the expression of Skp2 and Cull mRNA, reduced the amounts of p21^WAF1 and p27^Kip1 proteins, and canceled GATA-2-induced growth suppression, suggesting that down-regulation of c-myc expression may be primarily responsible for GATA-2-induced growth suppression. Next, we transduced retrovirus containing GATA-2/ER into murine bone marrow mononuclear cells (MNCs) and stem/progenitor (Sca-1⁺Lin^-) cells. GATA-2/ER suppressed cytokine-dependent growth of MNCs and Sca-1⁺Lin^- cells by about 70%, which was also accompanied by the reduced expression of c-myc, Skp2, and Cul1 mRNA and the accumulation of p21^WAF1 and p27^Kip1 proteins. In addition, the amount of GATA-2 protein was found to decline in hematopoietic stem/progenitor cells that were promoted to enter cell cycle by the stimulation with cytokines. These results suggest that GATA-2 may regulate expression levels of p21^WAF1 and p27^Kip1, thereby contributing to the quiescence of hematopoietic stem/progenitor cells.