The colony-stimulating factor, CSF-1, stimulates cultured quiescent murine bone marrow-derived macrophages (BMM) to enter DNA synthesis with a lag phase of 10-12 h. The binding, dissociation, internalization, and degradation of 125I-CSF-1 by BMM during the lag phase were investigated. Quiescent BMM express ~ 5 x 104 cell surface receptor sites/cell but contain additional cryptic sites (~ 105/cell) that can appear at the cell surface within 10 min at 37°C. Studies of the binding reaction at both 2° C (K(d) ≤ 2 x 10-13 M) and 37°C (K(d) ~ 4 x 10-10 M) are consistent with the existence of a single class of cell surface sites. The disappearance of cell surface 125I-CSF-1 following a 2-37°C temperature shift results from two, competitive, first order processes, internalization and dissociation. Internalization (t 1/2 = 1.6 min) is 6 times more frequent than dissociation (t 1/2 = 9.6 min). Following internalization, 10-15% of the intracellular CSF-1 is rapidly degraded whereas the remaining 85-90% is slowly degraded by a chloroquin-sensitive first order process (t 1/2 > 3.5 h). These findings were confirmed and extended by studies of the uptake of 125I-CSF-1 at 37°C. Following addition of 125I-CSF-1, cell surface receptors are rapidly down-regulated (t 1/2 ~ 7 min) and their replacement does not commence until 20-60% of pre-existing surface receptor sites have disappeared. Despite receptor replacement, initially from the cryptic pool and later by de novo synthesis and/or receptor recycling (4 molecules/cell/s at steady state), the number of receptors at the cell surface remains low. The process results in the intracellular accumulation of large amounts of 125I-CSF-1 (> 105 molecules/cell) by BMM. Thus, whereas the kinetics of association, dissociation, and internalization of CSF-1 with BMM and peritoneal exudate macrophages are similar, BMM, which exhibit a higher proliferative response, degrade growth factor 12 times more slowly.
|Original language||English (US)|
|Number of pages||9|
|Journal||Journal of Biological Chemistry|
|State||Published - 1986|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology