Colony-stimulating factor-1 (CSF-1) plays a central role in the survival, proliferation, differentiation, and function of monocytes and macrophages. CSF-1 is synthesized as both a soluble and a membrane-spanning growth factor. The membrane-spanning isoform is biologically active, but it can also be proteolytically cleaved to generate a soluble growth factor. A recent study revealed that the TNF-α-converting enzyme is involved in this activity, and, moreover, that membrane-spanning CSF-1 undergoes internalization. These findings may have important implications for the posttranslational regulation and the functions of cell-surface CSF-1.
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