Cell Surface Colony-Stimulating Factor 1 Can Be Cleaved by TNF-α Converting Enzyme or Endocytosed in a Clathrin-Dependent Manner

Abstract

CSF-1 is a hemopoietic growth factor, which plays an essential role in macrophage and osteoclast development. Alternative splice variants of CSF-1 are synthesized as soluble or membrane-anchored molecules, although membrane CSF-1 (mCSF-1) can be cleaved from the cell membrane to become soluble CSF-1. The activities involved in this proteolytic processing, also referred to as ectodomain shedding, remain poorly characterized. In the present study, we examined the properties of the mCSF-1 sheddase in cell-based assays. Shedding of mCSF-1 was up-regulated by phorbol ester treatment and was inhibited by the metalloprotease inhibitors GM6001 and tissue inhibitor of metalloproteases 3. Moreover, the stimulated shedding of mCSF-1 was abrogated in fibroblasts lacking the TNF-alpha converting enzyme (TACE, also known as a disintegrin and metalloprotease 17) and was rescued by expression of wild-type TACE in these cells, strongly suggesting that the stimulated shedding is TACE dependent. Additionally, we observed that mCSF-1 is predominantly localized to intracellular membrane compartments and is efficiently internalized in a clathrin-dependent manner. These results indicate that the local availability of mCSF-1 is actively regulated by ectodomain shedding and endocytosis. This mechanism may have important implications for the development and survival of monocyte lineage cells.

Global Characterization of Protein Secretion from Human Macrophages Following Non-canonical Caspase-4/5 Inflammasome Activation

“…MMP14 and ADAM10 are known to convert transmembrane molecules into a soluble form through a proteolytic process called ectodomain shedding, and they also share common substrates (35,36). In addition, it has also been shown that a close relative and functionally similar protease to ADAM10, ADAM17 (37), can induce proteolytic processing and shedding of macrophage colony-stimulating factor (M-CSF) (38). M-CSF is a cytokine that promotes the release of proinflammatory chemokines and has an important role in innate immunity and in inflammatory processes.…”

A Brief History of Tumor Necrosis Factor α – converting Enzyme: An Overview of Ectodomain Shedding

“…However, there are several cytokines (such as the cell surface isoform of colony stimulating factor-1) that are active in both their membrane-bound form and their soluble form. 44,45 Some receptors, including vascular growth factor receptor 2 and c-Kit, are also subjected to ectodomain shedding, 46,47 and in theory, the cleavage of these receptors results in the down-regulation of the availability of these receptors and, consequently, signaling through these receptors. In contrast, the interleukin 6 receptor, which has also been shown to be released by TACE, acts as a functional soluble receptor via binding to interleukin 6 and gp130.…”

Regulation of Receptor Tyrosine Kinase Ligand Processing

“…Some members of the PDGF ( platelet-derived growth factor) receptor subfamily are regulated by ligand shedding, including cKit/SCFR , FLT3/Flk2 ), and CSF1R/Ems (Horiuchi et al 2007b). These RTK pathways play important immune roles including regulating haematopoiesis (cKit and FLT3) (Ashman 1999;Naoe and Kiyoi 2004) or macrophage and osteoclast development (CSF1R) (Cecchini et al 1997).…”