Internalization and half-life of membrane-bound macrophage colony-stimulating factor

The binding of recombinant human macrophage colony-stimulating factor (M-CS F) soluble receptor (rh-M-CSF-sR) to membrane-bound macrophage colony stimu lating factor (m-M-CSF) and the internalization and recycling of rh-M-CSF-s R/m-M-CSF complexes mediated by m-M-CSF were studied with a model of J6-1 c ell line. The results indicated that m-M-CSF bound rh-M-CSF-sR with high af finity (k(d) = 1.78 x 10(-12) mol/L) and mediated a temperature- and energy -dependent internalization of rh-M-CSF-sR, and that internalized rh-M-CSF-s R could return to ii-to cell surface in an m-M-CSF-bound state, suggesting that m-M-CSF may have a capability to mediate the internalization and recyc ling of rh-M-CSF-sR/m-M-CSF complexes. In addition, the half-lives of cell- associated M-CSF and its receptor of stimulated normal human cord blood mon onuclear cells (CBMCs) and 4 leukemic cell lines were measured by indirect immunofluorescence and flow cytometry. The results showed that the half-liv es of the various kinds of WI-CSF isoforms and M-CSF-R in 4 leukemic cells, except those of membrane-bound M-CSF receptor (M-CSF-mR) of K562 and HL-60 cells, were longer than those of corresponding M-CSF isoform and its recep tor in stimulated normal human CBMCs, suggesting that there is a slow degra dation rate of cell-associated M-CSF and its receptor in leukemic cells.