Role of CD26/DPP IV in chemokine processing and HIV infection

Dominique Schols and Paul Proost. Rega Institute for Medical Research, K.U. Leuven, B-3000 Leuven (Belgium).

Background: In order to infect a target cell, the HIV envelope glycoprotein gp120 has to interact with both the cellular receptor CD4 and an HIV-co-receptor, i.e. the CC or CXC chemokine receptor CCR5 or CXCR4. Blocking these co-receptors by specific ligands protects the cell from viral infection and thus can reduce viral transmission and pathogenesis. Material and Methods: Purification and characterization of several natural chemokine variants were performed and their antiviral activity in different cell-types evaluated. Natural chemokines were isolated through a 4-step concentration and purification procedure comprising adsorption to silicic acid, heparin-sepharose chromatography, cation exchange chromatography, and reverse-phase HPLC. In addition, the role of CD26/dipeptidyl-peptidase IV (CD26/DPP IV) in the processing of the CC chemokines RANTES and MIP-1a and the CXC chemokine SDF-1 were studied in detail. Results: The natural CC-chemokine RANTES(3-68), missing the two NH₂-terminal residues, has been isolated from leukocytes. The highly specific amino peptidase CD26/DPP IV, present in blood in soluble and also membrane-bound form, was shown to be responsible for this NH₂-terminal truncation of RANTES. This processing of RANTES clearly enhanced its anti-HIV-1 activity. Also SDF-1 was NH₂-terminally cleaved to SDF-1 (3-68) by CD26/DPP IV, but SDF-1(3-68) lost both lymphocyte chemotactic and CXCR4-signaling properties. However, SDF-1 (3-68) still desensitised the SDF-1(1-68)-induced Ca²⁺ response. In contrast to CD26/DPP IV-processed RANTES(3-68), SDF-1(3-68) had diminished potency to inhibit HIV-1 infection. For MIP-1a, 2 isoforms (LD78a and LD78ß) have been reported, but mainly the biological activities and receptor binding properties of LD78a have been investigated. The LD78 ß isoform was shown to efficiently chemoattract lymphocytes and monocytes through CCR5 interaction. This chemokine, purified from stimulated leukocytes, inhibited HIV-1 infection in CCR5-transfected cells, PBMCs and purified monocytes at low concentrations (e.g. LD78a showed no activity at 100 ng/ml, whereas LD78b at 100 ng/ml completely blocked viral replication). Furthermore, after cleavage of the NH₂-terminal Ala-Pro dipeptide by CD26, LD78ß(3 - 70) became the most potent anti-HIV chemokine described so far. Conclusion: This research will make it feasible to develop specific chemokine analogs that potently block HIV entry.