The Cbl protooncoprotein stimulates CSF-1 receptor multiubiquitination andendocytosis, and attenuates macrophage proliferation

Colony-stimulating factor-1 (CSF-1) activation of the CSF-1 receptor (CSF-1 R) causes Cbl protooncoprotein tyrosine phosphorylation, Cbl-CSF-1R associa tion and their simultaneous multiubiquitination at the plasma membrane. The CSF-1R is then rapidly internalized and degraded, whereas Cbl is deubiquit inated in the cytoplasm without being degraded. We have used primary macrop hages from gene-targeted mice to study the role of Cbl, Cbl(-/-) macrophage s form denser colonies and, at limiting CSF-1 concentrations, proliferate f aster than Cbl(+/+) macrophages. Their CSF-1Rs fail to exhibit multiubiquit ination and a second wave of tyrosine phosphorylation previously suggested to be involved in preparation of the CSF-1-CSF-1R complex for endocytosis. Consistent with this result, Cbl(-/-) macrophage cell surface CSF-1-CSF-1R complexes are internalized more slowly, yet are still lysosomally degraded, and the CSF-1 utilization by Cbl(-/-) macrophages is reduced similar to 2- fold. Thus, attenuation of proliferation by Cbl is associated with its posi tive regulation of the coordinated multiubiquitination and endocytosis of t he activated CSF-1R, and a reduction in the time that the CSF-1R signals fr om the cell surface. The results provide a paradigm for studies of the mech anisms underlying Cbl attenuation of proliferative responses induced by lig ation of receptor tyrosine kinases.