Rapid inactivation of stromal cell-derived factor-1 by cathepsin G associated with lymphocytes

Abstract

The CXC chemokine stromal cell‐derived factor (SDF)‐1 is produced constitutively in different tissues. It is the only known ligand for CXCR4, which is widely expressed in leukocytes and in some tissue cells, and acts as coreceptor for X4 HIV strains. Because of the general interest in the mechanisms that regulate the activity of constitutively expressed chemokines, we have studied the inactivation of SDF‐1 in cells that bear CXCR4. Here we show that B lymphocytes, NK cells and, to a lesser extent, T lymphocytes inactivate SDF‐1 by N‐terminal processing. Inactivation is due to cathepsin G which is associated with the membrane of lymphocytes and rapidly cleaves off five N‐terminal residues by acting on the Leu5‐Ser6 bond yielding SDF‐1(6–67). Processing was observed with intact cells, cell membrane preparations and soluble cathepsin G obtained by extraction of the membranes with Triton X‐100. Cathepsin G is released by neutrophils and monocytes and binds on the surface of lymphocytes by an apparently saturable process. Analysis of the product obtained, the time course and the sensitivity to inhibitors shows that cathepsin G is the only protease involved. Conversion of SDF‐1 to SDF‐1(6–67) was complete within minutes to 1–2 h depending on the enzyme source, and was abrogated by inhibitors of serine proteases and chymostatin. Diprotin A, an inhibitor of dipeptidyl peptidase IV, was without effect. Owing to its availability on the surface of SDF‐1‐responsive cells and its rapid effect, cathepsin G is likely to play a significant role in down‐regulating SDF‐1 activity.

Altered SDF-1/CXCR4 axis in patients with primary myelofibrosis and in the Gata1low mouse model of the disease

“…Since production of SDF-1 in the marrow of Gata1 low mice is not higher than normal (Figure 1), entrapment of SDF-1 within the increased number of mutant megakaryocytes reduces the amount of SDF-1 available for other cells in the marrow. Furthermore, since SDF-1 is very sensitive to protease degradation [27][28][29][30] and both the full length and its proteolytic products 58 are recognized by immunostaining, it is possible that the high levels of SDF-1 observed in the marrow both of Gata1 low mice and PV patients represent proteolytically cleaved SDF-1. In summary, it is possible that, in spite of high levels of SDF-1 immunostaining, the marrow of the animal model and of the PMF patients is deprived of functional SDF-1 because of increased SDF-1 uptake by the high numbers of defective megakaryocytes and presence of inactive degradation products of SDF-1 bound to the extracellular matrix.…”

“…In fact, under steady-state conditions, the levels of soluble SDF-1 present in the blood of younger animals are low. SDF-1 is very sensitive to protease degradation [27][28][29][30] .…”

Proteolytic Activation of Alternative CCR1 Ligands in Inflammation

“…Not surprisingly, proteolytic removal of N-terminal residues has also been shown to inactivate CC and CXC chemokines (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38). In many cases, these truncated chemokines were still able to bind their receptors and, as a result, functioned as antagonists in chemotaxis assays in vitro (27, 30 -34, 36) and exhibited antiinflammatory properties in vivo (27,32).…”

Neutrophil-derived MMP-9 mediates synergistic mobilization of hematopoietic stem and progenitor cells by the combination of G-CSF and the chemokines GROβ/CXCL2 and GROβT /CXCL2Δ4

“…34 Accumulation of NE and CG within marrow 35,36 and degradation of SDF-1␣ by NE, altering SDF-1␣ gradients, 37 have been shown to be associated with G-CSF mobilization. Because we routinely observe elevated plasma MMP-9 levels in mice mobilized by the GRO␤ chemokines and MMP-9, NE, and CG can degrade SDF-1␣, 37,45,46 it is possible that either or both of these mechanisms could be relevant to mobilization by GRO␤ or GRO␤ T , alone or in combination with G-CSF. We quantitated MMP-9, NE, and CG enzyme activities and SDF-1␣ and SCF protein in plasma and marrow extravascular fluid, to evaluate molecular mechanisms associated with mobilization by GRO␤ T , G-CSF, and, in particular, the combination of G-CSF plus GRO␤ ( Figure 1).…”

“…12,[80][81][82] A correlation between reduction in marrow SDF-1␣ by NE and PBSC mobilization by G-CSF was reported, suggesting that altered blood/marrow SDF-1 gradients might be responsible. 37 This attractive potential mechanism is supported by the fact that SDF-1␣ can be processed and inactivated by NE, 37 CG, 46 and MMP-9. 45 However, we observed no effect of GRO␤ or GRO␤ T on plasma or marrow SDF-1, making it unlikely that it plays a role in GRO␤ mobilization.…”