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

The CXC chemokine stromal cell-derived factor(SDF)-1 is produced constituti vely 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 corece ptor 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 th at B lymphocytes, NK cells and, to a lesser extent, T lymphocytes inactivat e 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 Leu(5)-Ser(6) bond yielding SDF-1(6-6 7). Processing was observed with intact cells, cell membrane preparations a nd soluble cathepsin G obtained by extraction of the membranes with Triton X-100. Cathepsin G is released by neutrophils and monocytes and binds on th e surface of lymphocytes by an apparently saturable process. Analysis of th e 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 sourc e, and was abrogated by inhibitors of serine proteases and chymostatin. Dip rotin 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-regulatin g SDF-1 activity.