The N‐terminal X‐X‐Pro sequence of the HIV‐1 Tat protein is important for the inhibition of dipeptidyl peptidase IV (DP IV/CD26) and the suppression of mitogen‐induced proliferation of human T cells

Abstract

Recent data in the literature suggest that the HIV-1 Tat(I-86) protein exhibits immunosuppressive effects. Moreover, Tat was found to interact with dipeptidyl peptidase IV (DP IV), which is identical to the T cell activation marker CD26. Here we show that the N-terminal amino acid sequence of Tat is essential for the inhibition of DP IV-catalyzed IL-2(1-12) degradation. Nterminal modification of Tat with rhodamine prevented inhibition of enzymatic activity of DP IV as well as suppression of DNA synthesis of mitogen-stimulated human T cells. Moreover, natural peptides containing the X-X-Pro N-terminal motif of Tat also inhibited DP IV activity. These data suggest the existence of endogenous immunomodulatory oligopeptides which influence immune cell proliferation and differentiation via DP IV a~ does HIV-1 Tat.

Crystal Structures of HIV-1 Tat-derived Nonapeptides Tat-(1–9) and Trp2-Tat-(1–9) Bound to the Active Site of Dipeptidyl-peptidase IV (CD26)

“…The hydrophobic side chain would likely replace the Tat-(1-9) methionine side chain in the S1 pocket of DPPIV. This view is supported by a kinetic study showing that the peptides FAPAG, FHPKR, and IKPEA have an inhibitory potential comparable to peptides featuring an N-terminal Met (17). Peptides with Ala, Gly, or Thr in the N-terminal position lacked the ability to inhibit DPPIV and indicated that an N-terminal hydrophobic residue is a prerequisite for a peptide to act as a DPPIV inhibitor.…”

“…6 are also well defined in the electron density, but only poor density is observed for the side chains because they do not form contacts to DPPIV. These side chains were consequently placed with the most likely conformation determined by NMR spectroscopy of peptide Trp 2 -Tat-(1-9) in aqueous solution, which indicated that the main chain conformation of this nonapeptide is determined by Pro 3 (17,34,35). It is notable that the conformation of Trp 2 -Tat-(1-9) in the NMR study is comparable to that found here for the N-terminal 6 residues of Trp 2 -Tat-(1-9).…”

Implications of DPP4 modification of proteins that regulate stem/progenitor and more mature cell types

“…Proteins with proline, hydroxylproline, or N-methylglycine in the third position are thought to prevent cleavage by DPP4. 43 This highlights the complexity of potential DPP4 cleavage kinetics, which may differ in vitro and in vivo, and further highlights the necessity of testing the individual DPP4 cleavage potential of each protein of interest.…”

Anergic T cells exert antigen-independent inhibition of cell-cell interactions via chemokine metabolism

“…The CD26 ectopeptidase inhibitor 12 13 ), antimouse CD26 (H194-112; BD Biosciences), antimouse CD3 (2C11; BD Biosciences), and antimouse CD28 (MCA1363; Serotec). The human chemokine CXCL-12 (stromal-derived factor-1␣ [SDF-1␣]) was purchased from Pepro Tech (Peterborough, United Kingdom).…”

“…To exclude the possibility that CD26 signaling modified other intrinsic properties of anergic T cells, the naturally occurring peptide YY peptide containing the X-X-Pro N-terminal motif known to inhibit DPPIV enzymatic activity was also employed 12 to treat anergic T cells prior to injection (30 nM for 30 minutes at room temperature). The following day, PKH26-labeled C6 T cells (5-7 ϫ 10 6 ) were injected intraperitoneally.…”