Regulation of the receptor specificity and function of the chemokine RANTES (regulated on activation, normal T cell expressed and secreted) by dipeptidyl peptidase IV (CD26)-mediated cleavage

Enhancement of human immunodeficiency virus type 1 infection by the CC-chemokine RANTES is independent of the mechanism of virus-cell fusion

We have studied the effects of CC-chemokines on human immunodeficiency virus type 1 (HIV-1) infection, focusing on the infectivity enhancement caused by RANTES. High RANTES concentrations increase the infectivity of HIV-1 isolates that use CXC-chemokine receptor 4 for entry. However, RANTES can have a similar enhancing effect on macrophagetropic viruses that enter via CC-chemokine receptor 5 (CCR5), despite binding to the same receptor as the virus. Furthermore, RANTES enhances the infectivity of HIV-1 pseudotyped with the envelope glycoprotein of murine leukemia virus or vesicular stomatitis virus, showing that the mechanism of enhancement is independent of the route of virus-cell fusion. The enhancing effects of RANTES are not mediated via CCR5 or other known chemokine receptors and are not mimicked by MIP-1alpha or MIP-1beta. The N-terminally modified derivative aminooxypentane RANTES (AOP-RANTES) efficiently inhibits HIV-1 infection via CCR5 but otherwise mimics RANTES by enhancing viral infectivity. There are two mechanisms of enhancement: one apparent when target cells are pretreated with RANTES (or AOP-RANTES) for several hours, and the other apparent when RANTES (or AOP-RANTES) is added during virus-cell absorption. We believe that the first mechanism is related to cellular activation by RANTES, whereas the second is an increase in virion attachment to target cells.

Secretion of human meprin from intestinal epithelial cells depends on differential expression of the alpha and beta subunits

Human meprin (N-benzoyl-l-tyrosyl-p-aminobenzoic acid hydrolase, EC 3.4.24.18), an astacin-type metalloprotease, is expressed by intestinal epithelial cells as a dimeric protein complex of alpha and beta subunits. In transfected cells, intracellular proteolytic removal of the membrane anchor from the alpha subunit results in its secretion, while the beta subunit and alpha/beta heterodimers are retained at the cell membrane. We investigated the consequence of differential intracellular processing of alpha and beta subunits in the human small and large intestine using subunit-specific immunohistochemistry, in situ hybridization and biosynthetic studies in organ culture. In the ileum, both subunits localize to the brush-border membrane of villus enterocytes. In contrast, the beta subunit is not expressed in the colon, which leads to the secretion of the alpha subunit. We conclude that differential expression of meprin alpha and beta subunits is a unique means of targeting the proteolytic activity of the alpha subunit either to the brush-border membrane in the ileum or to the lumen in the colon, suggesting dual functions of cell-associated and luminal meprin. Meprin alpha and beta subunits are also coexpressed in distinct lamina propria leukocytes, suggesting an additional role for this protease in leukocyte function in the intestinal mucosa.

CD26-processed RANTES(3-68), but not intact RANTES, has potent anti-HIV-1 activity

The natural CC-chemokine RANTES(3-68), missing two NH2-terminal residues, has been isolated from leukocytes and tumor cells. The highly specific aminopeptidase dipeptidyl peptidase IV (DPP IV), also called CD26, was shown to be responsible for this NH2-terminal truncation of RANTES. Here it is reported that CD26/DPP IV treatment of RANTES enhances its anti-HIV-1 activity. RANTES(3-68) inhibited infection of PBMC by M-tropic HIV-1 strains ten-fold more efficiently than intact RANTES. This difference in antiviral potency between intact and truncated RANTES was even more pronounced (at least 25-fold) in CCR5-transfected cell lines. In HOS.CD4.CCR5 transfected cells, RANTES(1-68) had virtually no anti-HIV-1 activity (IC50 > 130 nM), whereas RANTES(3-68) was a potent inhibitor of HIV-1 replication (1C50: 5.5 nM). The anti-HIV-1 activity of RANTES(1-68) in the different cell types correlated with the expression of CD26. Moreover, the addition of soluble CD26 together with RANTES(1-68) significantly enhanced the antiviral activity of RANTES in HOS.CD4.CCR5 cells (IC50: 13 nM). These observations point to an important role of CD26-mediated processing of RANTES in inhibiting the replication of CCR5-binding HIV strains in HIV-infected persons and in preventing the development of AIDS.

Functional comparison of two human monocyte chemotactic protein-2 isoforms, role of the amino-terminal pyroglutamic acid and processing by CD26/dipeptidyl peptidase IV

Human Monocyte Chemotactic Protein (MCP)-2 has originally been isolated from stimulated osteosarcoma cells as a chemokine coproduced with MCP-1 and MCP-3. Here, a 5'-end extended MCP-2 cDNA was cloned from a human testis cDNA library. It encoded a 76 residue MCP-2 protein, but differed from the reported bone marrow-derived MCP-2 cDNA sequence in codon 46, which coded for a Lys instead of a Gln. This MCP-2Lys46 variant, caused by a single nucleotide polymorphism (SNP), was biologically compared with MCP-2Gln46. The coding regions were subcloned into the bacterial expression vector pHEN1, and after transformation of Escherichia coli, the two MCP-2 protein variants were recovered from the periplasm. The recombinant proteins were purified to homogeneity by heparin-Sepharose affinity chromatography and reversed-phase HPLC. Edman degradation revealed a Gln residue at the NH2 terminus instead of a pGlu. To evaluate the influence of the cyclization, this Gln was chemically converted into pGlu in both MCP-2 variants. The conversion was confirmed by electrospray mass spectrometry. rMCP-2Gln46 and rMCP-2Lys46 and the NH2-terminal cyclic counterparts were tested on monocytic cells in calcium mobilization and chemotaxis assays. No significant difference in biological activity was observed between the rMCP-2Gln46 and rMCP-2Lys46 isoforms. However, for both MCP-2 variants the NH2-terminal pyroglutamate was shown to be essential for chemotaxis, but not for calcium mobilization. NH2-terminal truncation of rMCP-2Lys46 by the serine protease CD26/dipeptidyl peptidase IV (CD26/DPP IV) resulted in the cleavage of the NH2-terminal Gln-Pro dipeptide, whereas synthetic MCP-2 with an amino-terminal pGlu remained unaffected. CD26/DPP IV-clipped rMCP-2Lys46(3-76) was almost completely inactive in both chemotaxis and signaling assays. These observations indicate that the NH2-terminal pGlu in MCP-2 is necessary for chemotactic activity but also that it protects the protein against degradation by CD26/DPP IV.

Cytokine regulation of human immunodeficiency virus type 1 entry and replication in human monocytes/macrophages through modulation of CCR5 expression

Human macrophages express chemokine receptors that act as coreceptors for human immunodeficiency virus type 1 (HIV-1) and are major targets for HIV-1 infection in vivo. The effects of cytokines on HIV-1 infection of macrophages and on the expression of CCR5, the principal coreceptor for macrophage-tropic viruses, have now been investigated. Expression of CCR5 on the surface of freshly isolated human monocytes was virtually undetectable by flow cytometry with the monoclonal antibody 5C7. However, after culture of monocytes for 48 h in serum-free medium, approximately 30% of the resulting macrophages expressed CCR5 and the cells were susceptible to infection by macrophage-tropic HIV-1. Addition of either macrophage colony-stimulating factor (M-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) to the cultures markedly increased both the extent of HIV-1 entry and replication as well as surface expression of CCR5. In contrast, addition of the T-helper 2 (Th2) cell-derived cytokine interleukin-4 (IL-4) or IL-13 prevented the expression of CCR5 induced by culture in medium alone, and IL-4 inhibited virus entry, replication, and cytopathicity under these conditions. IL-4 or IL-13 also prevented the stimulatory effects of M-CSF or GM-CSF on CCR5 expression as well as HIV-1 entry and replication. In addition, IL-4 reversed the increase in CCR5 expression induced by pretreatment of cells with M-CSF. Although IL-10 also inhibits HIV-1 replication in macrophages, it did not suppress surface CCR5 expression induced by colony-stimulating factors. These results indicate that the cytokine environment determines the susceptibility of macrophages to HIV-1 infection by various mechanisms, one of which is the regulation of HIV-1 coreceptor expression.

Processing by CD26/dipeptidyl-peptidase IV reduces the chemotactic and anti-HIV-1 activity of stromal-cell-derived factor-1alpha

The chemokine stromal-cell-derived factor-1alpha (SDF-1alpha) chemoattracts lymphocytes and CD34+ haematopoietic progenitors and is the ligand for CXCR4 (CXC chemokine receptor 4), the main co-receptor for T-tropic HIV-1 strains. SDF-1alpha was NH2-terminally cleaved to SDF-1alpha(3-68) by dipeptidyl-peptidase IV (CD26/DPP IV), which is present in blood in soluble and membrane-bound form. SDF-1alpha(3-68) lost both lymphocyte chemotactic and CXCR4-signaling properties. However, SDF-1alpha(3-68) still desensitized the SDF-1alpha(1-68)-induced Ca2+ response. In contrast to CD26/DPP IV-processed RANTES(3-68), SDF-1alpha(3-68) had diminished potency to inhibit HIV-1 infection. Thus, CD26/DPP IV impairs the inflammatory and haematopoietic potency of chemokines but plays a dual role in AIDS.

Negative regulation of the anti-human immunodeficiency virus and chemotactic activity of human stromal cell-derived factor 1alpha by CD26/dipeptidyl peptidase IV

Stromal cell-derived factor 1alpha (SDF-1alpha) is a chemokine that has been shown to prevent infection of T-tropic HIV strains and is a possible substrate of CD26/dipeptidyl peptidase IV (DPPIV). In this study, we show that SDF-1alpha was cleaved at the N-terminal region by CD26/DPPIV and as a result the inhibitory activity of SDF-1alpha against HIV infection disappeared. Moreover, the chemotactic activity of SDF-1alpha also disappeared specifically by DPPIV activity of recombinant soluble CD26. These results suggested that dissemination of T-tropic HIV strains in vivo may be facilitated by CD26/DPPIV via inactivation of functional SDF-1alpha.

Anti-arthritic effects of the novel dipeptidyl peptidase IV inhibitors TMC-2A and TSL-225

We evaluated the immunopharmacological effects of two novel dipeptidyl peptidase IV (DP IV) inhibitors, TMC-2A [(2S,2S',2S'')-2-[2'-[2''-amino-3''-(-indol-3'''-yl)-1''-oxopropyl]-1',2 ',3',4'-tetrahydro-6',8'-dihydroxy-7'-methoxyisoquinol-3-yl-car bonylamino]-4-hydroxymethyl-5-hydroxypentanoic acid] and TSL-225 (tryptophyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid). TMC-2A, produced by Aspergillus sp. A374, inhibited rat kidney DP IV uncompetitively, with a Ki value of 5.3 microM. In vivo, TMC-2A suppressed alkyldiamine (N,N-dioctadecyl-N',N-bis(2-hydroxyethyl)propanediamine)-induced arthritis. We developed a chemically modified inhibitor, TSL-225, with potency similar to that of TMC-2A. TSL-225 inhibited DP IV uncompetitively, with a Ki value of 3.6 microM. TSL-225 was also effective against adjuvant-induced arthritis. These results suggest that TMC-2A and its derivatives may have therapeutic potential for the treatment of inflammatory diseases such as rheumatoid arthritis.

Chemokine receptors and chemokines in HIV infection

Suppression of HIV by chemokines represents a special case in virology and immunology where soluble molecules other than antibodies inhibit infection by a specific virus. The basis for this inhibition is that HIV has evolved to use certain chemokine receptors as "coreceptors" for entry into host cells. Human genotypes that reduce or prevent coreceptor expression are strongly associated with protection against infection and slower disease progression. We suggest that local production of certain chemokines can produce a similar modulation of coreceptor expression, and mounting evidence indicates that chemokine release is a major determinant of protection from HIV infection. Here we review this evidence and explore future avenues for investigating the role of chemokines in controlling HIV infection.

Increased rate of HIV-1 entry and its cytopathic effect in CD4+/CXCR4+ T cells expressing relatively high levels of CD26

The role of the T-cell activation antigen CD26 was evaluated in viral entry and infection of CD4(+)/CXCR4(+) cells by the lymphotropic HIV-1 Lai isolate. For this purpose, CEM T cells, which are permissive to HIV infection and express low levels of CD26, were used to establish by transfection four groups of cell clones expressing either low, high, and very high levels of CD26, or expressing the anti-sense RNA of CD26. Entry was monitored by the detection of proviral DNA synthesis and the kinetics of virus production, whereas the cytopathic effect was demonstrated by the occurrence of apoptosis. HIV entry and infection were consistently accelerated by at least 24 to 48 h in clones expressing high levels of CD26 compared to the parental cells or to the clones expressing low levels of CD26. Interestingly, infection of clones expressing very high levels of CD26 was not accelerated and showed a kinetics of infection similar to that of low CD26 expressing clones. Moreover, HIV infection was significantly reduced in the clones expressing CD26 anti-sense RNA. In the different clones, apoptosis was dependent on the severity of virus infection and occurred after the accumulation of HIV envelope glycoproteins. Our results demonstrate that with equivalently expressed levels of CD4 and CXCR4 in cell lines established from CEM cells, relatively high levels of CD26 contribute to an increased rate of HIV entry, infection, and apoptosis. Furthermore, they point out that overexpression of CD26 in a given cell line may lead to a negative effect on HIV infection. Consequently, CD26 appears to regulate HIV entry and apoptosis, processes which are critical for viral pathogenesis.

Chemokines, lymphocytes and viruses: what goes around, comes around

Chemokines are believed to be the long-sought soluble mediators of selective lymphocyte recruitment. As most selectin-integrin interactions are nonselective, it is thought that the discrimination seen during lymphocyte infiltration into tissues is brought about by the actions of distinct chemokines. Developments over the past year have demonstrated the expanding roles of these factors in lymphocyte chemoattraction, normal trafficking, and viral immunity.

Anti-HIV-1 and chemotactic activities of human stromal cell-derived factor 1alpha (SDF-1alpha) and SDF-1beta are abolished by CD26/dipeptidyl peptidase IV-mediated cleavage

CD26 is a leukocyte-activation antigen that is expressed on T lymphocytes and macrophages and possesses dipeptidyl peptidase IV (DPPIV) activity, whose natural substrates have not been identified yet. CXC chemokines, stromal cell-derived factor 1alpha (SDF-1alpha) and 1beta (SDF-1beta), sharing the receptor CXCR-4, are highly efficacious chemoattractants for resting lymphocytes and CD34(+) progenitor cells, and they efficiently block the CXCR-4-mediated entry into cells of T cell line tropic strains of HIV type 1 (HIV-1). Here we show that both the chemotactic and antiviral activities of these chemokines are abrogated by DPPIV-mediated specific removal of the N-terminal dipeptide, not only when the chemokines are produced in transformed mouse L cell line to express human CD26 but also when they were exposed to a human T cell line (H9) physiologically expressing CD26. Mutagenesis of SDF-1alpha confirmed the critical requirement of the N-terminal dipeptide for its chemotactic and antiviral activities. These data suggest that CD26-mediated cleavage of SDF-1alpha and SDF-1beta likely occurs in human bodies and promotes HIV-1 replication and disease progression. They may also explain why memory function of CD4(+) cells is preferentially lost in HIV-1 infection. Furthermore, CD26 would modulate various other biological processes in which SDF-1alpha and SDF-1beta are involved.