Synergistic effects of hepatocyte growth factor on human cord blood CD34(+) progenitor cells are the result of c-met receptor expression

Hepatocyte growth factor (HGF) is a pleiotropic grow;th factor which, in addition to its mitogenic potency for primary hepatocytes, also has a role in the regulation of cell motility, cell growth and morphogenesis, In the present study, we show that c-met, the high-affinity receptor for HGF, is expressed on human cord blood (CB) CD34(+) progenitor cells and CD34(+)Thy-1(+) Lin(-) (lin(-)) cells, We have investigated the capacity of HGF to synergize with other growth factors to induce colony formation by CB CD34(+) progenitor cells, CD34(+) cells were cultured in semisolid medium containing serum with increasing concentrations of GM-CSF, G-CSF, macrophage colony-stimulating factor (M-CSF), stem cell factor (SCF), interleukin 3 (IL-3) and IL-11 alone or in combination with HGF, HGF acted as a potent synergist and enhanced, up to fourfold, colony formation induced by GM-CSF, G-CSF or M-CSF. HGF in combination with SCF, IL-3 or IL-11 did not induce proliferation of colony forming units-granulocyte macrophage (CFU-GM) above control levels, In serum-deprived cultures, HGF was only detectably synergistic with IL-11, and all other culture combinations showed no proliferation, To determine whether the stimulatory effect of IL-11 and the synergistic effect of HGF in the absence of serum could be attributed to the effect of these two cytokines on stem cells, IL-ll-stimulated and unstimulated lin(-) cells were analyzed for expression of c-met, CD34(+)Thy-1(+)Lin(-) cells were positive for c-met, both in the presence and absence of IL-II stimulation, and Northern analysis indicated that c-met RNA expression was upregulated in response to IL-11 compared to unstimulated controls, These results provide strong evidence for upregulation of the HGF receptor on primitive hematopoietic cells by IL-II, and for the synergistic role of HCF in colony formation by hematopoietic stem cells.