Carboxypeptidase M Expressed by Human Bone Marrow Cells Cleaves the C-terminal Lysine of SDF-1: Another Player in Hematopoietic Stem/Progenitor Cell Mobilization?

¹ Research and Development, Canadian Blood Services, Edmonton, Alberta, Canada
² Research and Development, Canadian Blood Services, Edmonton, Alberta, Canada; Department of Medicine, University of Alberta, Edmonton, Alberta, Canada
³ Laboratory of Medical Biochemistry, Department of Pharmaceutical Sciences, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium

^* To whom correspondence should be addressed. E-mail: anna.janowska{at}blood.ca.

	Abstract

Carboxypeptidase M (CPM) is a membrane-bound zinc-dependent protease that cleaves C-terminal basic residues such as arginine or lysine from peptides/proteins. We examined whether CPM is expressed by hematopoietic and stromal cells and could degrade stromal cell-derived factor (SDF)-1, a potent chemoattractant for hematopoietic stem/progenitor cells (HSPC). We found that (i) CPM transcript is expressed by bone marrow (BM) and mobilized peripheral blood (mPB) CD34⁺ cells, myeloid, erythroid and megakaryocytic cell progenitors, mononuclear cells (MNC), polymorphonuclear cells (PMN) and stromal cells including mesenchymal stem cells; and that (ii) granulocyte-colony stimulating factor (G-CSF) significantly increases its expression at the gene and protein levels in MNC and PMN. Moreover, we found that recombinant CPM cleaves full-length SDF-1 (1-68) rapidly, removing the C-terminal lysine and yielding des-lys SDF-1 (1-67). We demonstrated that such CPM treatment of SDF-1 reduced the in vitro chemotaxis of HSPC, which, however, was preserved when the CPM was exposed to the carboxypeptidase inhibitor DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid. Thus we present evidence that CPM is expressed by cells occurring in the BM microenvironment and that the mobilizing agent G-CSF strongly upregulates it in MNC and PMN. We suggest that cleavage of the C-terminal lysine residue of SDF-1 by CPM leads to attenuated chemotactic responses and could facilitate G-CSF-induced mobilization of HSPC from BM to PB.