Abstract
Hematopoiesis is regulated by an interacting network of cells, cell surface proteins, and cytokines/chemokines. CD26 is a cell surface peptidase (Dipeptidylpeptidase IV) that cleaves the N-terminal dipeptide from various substrates, such as selected members of the chemokine family, at a penultimate proline or alanine residue. CD26 is expressed by hematopoietic stem (HSCs) and progenitor (HPCs) cells, as well as a number of other immature and mature cell types. By truncating the chemokine stromal derived factor-1 (SDF-1/CXCL12), CD26 has been implicated in modulation of chemotaxis, homing and mobilization of HSCs/HPCs. Inhibition of CD26 by small peptides such as Diprotin A, or deletion of CD26 (e.g. cells from CD26 −/− mice or siRNA induced decreases in CD26) manifests in enhanced chemotaxis of HSCs/HPCs to SDF-1/CXCL12, and enhanced homing/engraftment of HSCs in mice. We hypothesized that inhibition of CD26 would manifest in enhanced activities of other functions of SDF-1/CXCL12. Moreover, since CD26 truncates other chemokines, we reasoned that inhibition of CD26 would enhance hematopoietic activities of these other chemokines. SDF-1/CXCL12 enhances survival/anti-apoptosis of HSCs/HPCs. We now report that pretreating mouse bone marrow cells (BMCs) with Diprotin A, whether or not the cells were washed prior to plating, or use of CD26 −/− mouse BMCs in a delayed addition of growth factor setting resulted in enhanced survival of HPCs at concentrations of SDF-1/CXCL12 at least 100-fold less than that which would normally manifest survival enhancing activities. We also assessed the influence of CD26 inhibition or deletion on the myelosuppressive effects of chemokines with known inhibitory activity and those that had not previously shown this activity. Suppression/deletion of CD26 on mouse BMCs greatly enhanced the activity of myelosuppressive chemokines such as is MIP-1α/CCL3 and GCP-2/CXCL6, such that these chemokines demonstrated inhibition of colony formation by multi-cytokine stimulated CFU-GM, BFU-E, and CFU-GEMM, at concentrations of these chemokines at least 100-fold less than that possible without inhibition/deletion of CD26. However, CD26 inhibition/deletion did not change the activity of non-myelosuppressive chemokines such as MIP-1β/CCL4, RANTES/CCL5, or SDF-1/CXCL12 into suppressive molecules. Since survival of HPCs is related to the cell cycle status of HPCs, such that slow or non-cycling HPCs are less sensitive to stresses leading to apoptosis, the enhanced activity of SDF-1/CXCL12 and the myelosuppressive chemokines (which are specifically inhibitory to HPCs in S-phase of the cell cycle) may act as coordinating separate signals to protect HPCs from stress-induced apoptosis. These results demonstrate that CD26 plays a modulating role on different hematopoietic activities mediated by chemokines, and this role for CD26 should be taken into account when describing models of chemokine effects on hematopoiesis, and attempts at modifying these effects.
Compartmentalization within the nucleus: discovery of a novel subnuclear region.