Abstract
AbstractPrimitive, proliferating hematopoietic progenitors (defined as cytokine low-responding primitive progenitors; CLRPP), isolated from human CD34+ cells, expressed endoglin (CD105) and produced transforming growth factor-β1 (TGF-β1). Culture of CLRPP in serum-free conditions with anti-TGF-β1 monoclonal antibody produced a substantial decrease in bcl-2 protein/RNA levels and a significant reduction of cloning and long-term culture-initiating cell (LTC-IC) activities. GATA-1 and PU.1 RNA levels were significantly up-regulated in anti-TGF-β1–treated CLRPP, which generated an increased number of cells expressing CD15/CD11b/glycophorin-A. The described effects of TGF-β1 neutralization were observed in the absence of any relevant effect on cell cycle; number of cell divisions; p53, c-myc, and p21 RNA levels; bcl-xL and bax protein levels; and c-myc/p16/p21/p107/Rb cell cycle–related protein levels. A relevant increase in p27 protein levels was observed in anti-TGF-β1–treated CLRPP, suggesting a role for p27 in the regulation of the hematopoietic potential. The present study on human progenitors and previously reported data on TGF-β1 knockout mice suggest that, at the autocrine level, the cell cycle inhibitor TGF-β1 plays an important role in regulating the survival and differentiation of primitive proliferating hematopoietic progenitors by cell cycle–independent mechanisms.
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