A natural CCL5/RANTES variant antagonist for CCR1 and CCR3

Development of tolerance to chemokine receptor antagonists: current paradigms and the need for further investigation

Chemokine G-protein coupled receptors are validated drug targets for many diseases, including cancer, neurological, and inflammatory disorders. Despite much time and effort spent on therapeutic development, very few chemokine receptor antagonists are approved for clinical use. Among potential reasons for the slow progress in developing chemokine receptor inhibitors, antagonist tolerance, a progressive reduction in drug efficacy after repeated administration, is likely to play a key role. The mechanisms leading to antagonist tolerance remain poorly understood. In many cases, antagonist tolerance is accompanied by increased receptor concentration on the cell surface after prolonged exposure to chemokine receptor antagonists. This points to a possible role of altered receptor internalization and presentation on the cell surface, as has been shown for agonist (primarily opioid) tolerance. In addition, examples of antagonist tolerance in the context of other G-protein coupled receptors suggest the involvement of noncanonical signal transduction in opposing the effects of the antagonists. In this review, we summarize the available progress and challenges in therapeutic development of chemokine receptor antagonists, describe the available knowledge about antagonist tolerance, and propose new avenues for future investigation of this important phenomenon. Furthermore, we highlight the modern methodologies that have the potential to reveal novel mechanisms leading to antagonist tolerance and to propel the field forward by advancing the development of potent "tolerance-free" antagonists of chemokine receptors.

Increased joint loading induces subchondral bone loss of the temporomandibular joint via the RANTES-CCRs-Akt2 axis

Early-stage temporomandibular joint osteoarthritis (TMJOA) is characterized by excessive subchondral bone loss. Emerging evidence suggests that TMJ disc displacement is involved, but the pathogenic mechanism remains unclear. Here, we established a rat model of TMJOA that simulated disc displacement with a capacitance-based force-sensing system to directly measure articular surface pressure in vivo. Micro-CT, histological staining, immunofluorescence staining, IHC staining, and Western blot were used to assess pathological changes and underlying mechanisms of TMJOA in the rat model in vivo as well as in RAW264.7 cells in vitro. We found that disc displacement led to significantly higher pressure on the articular surface, which caused rapid subchondral bone loss via activation of the RANTES-chemokine receptors-Akt2 (RANTES-CCRs-Akt2) axis. Inhibition of RANTES or Akt2 attenuated subchondral bone loss and resulted in improved subchondral bone microstructure. Cytological studies substantiated that RANTES regulated osteoclast formation by binding to its receptor CCRs and activating the Akt2 pathway. The clinical evidence further supported that RANTES was a potential biomarker for predicting subchondral bone loss in early-stage TMJOA. Taken together, this study demonstrates important functions of the RANTES-CCRs-Akt2 axis in the regulation of subchondral bone remodeling and provides further knowledge of how disc displacement causes TMJOA.

The multilayered complexity of the chemokine receptor system

The chemokines receptor family are membrane-expressed class A-specific seven-transmembrane receptors linked to G proteins. Through interaction with the corresponding ligands, the chemokines, they induce a wide variety of cellular responses including cell polarization, movement, immune and inflammatory responses, as well as the prevention of HIV-1 infection. Like a Russian matryoshka doll, the chemokine receptor system is more complex than initially envisaged. This review focuses on the mechanisms that contribute to this dazzling complexity and how they modulate the signaling events triggered by chemokines. The chemokines and their receptors exist as monomers, dimers and oligomers, their expression pattern is highly regulated, and the ligands can bind distinct receptors with similar affinities. The use of novel imaging-based technologies, particularly real-time imaging modalities, has shed new light on the very dynamic conformations that chemokine receptors adopt depending on the cellular context, and that affect chemokine-mediated responses. This complex scenario presents both challenging and exciting opportunities for drug discovery.

Gene transfer of the S24F regulated on activation normal T-cell expressed and secreted-chemokine ligand 5 variant attenuates cardiac allograft rejection

BACKGROUND

Regulated on activation normal T-cell expressed and secreted (RANTES)-chemokine ligand 5 plays a key role in mediating heart transplant rejection. Suppression of RANTES-mediated signals can reduce leukocyte recruitment and mitigate transplant rejection severity. The present study describes the construction of an adenovirus overexpression vector encoding a natural S24F RANTES variant as a means of reducing leukocyte recruitment, resulting in the prevention of allograft rejection.

METHODS

The in vitro transendothelial chemotaxis assay was used to compare RANTES-induced transmigration of peripheral blood mononuclear cells across human umbilical vein endothelial cells cultured on the upper Transwell chamber. Intracoronary delivery of Ad-S24F, Ad-Null, or phosphate-buffered saline was performed in BALB/c donor hearts that were transplanted into the abdominal cavity of C57BL/6 recipients as a measure of allograft survival. Intragraft inflammatory cell infiltrates and associated proinflammatory cytokine expression profiles were detected by immunohistochemistry and quantitative real-time polymerase chain reaction on day 6 after transplantation, respectively.

RESULTS

Regulated on activation normal T-cell expressed and secreted-induced peripheral blood mononuclear cell transendothelial chemotaxis is inhibited by S24F (Ad-S24F, 9.2%±0.02%; Ad-Null, 17.7%±0.02%; medium control, 15.1%±0.01%; P<0.05). Cardiac allograft survival was prolonged after delivery of 1×10 plaque-forming units of Ad-S24F (13.00±0.33 days compared with 9.38±0.60 and 9.00±0.38 days after Ad-Null or phosphate-buffered saline treatment, respectively, P<0.05). S24F gene transfer reduced the number of intragraft CD8 T lymphocytes, monocyte-macrophages, and T-cell receptor αβ cell infiltrates (P<0.05) and decreased transcripts for RANTES and interferon-γ (P<0.05).

CONCLUSION

S24F is an important component of the chemokine network involved in regulating the biologic activity of RANTES, and its expression can be used in the prevention and treatment of cardiac allograft rejection.

CCL5 secreted by senescent aged fibroblasts induces proliferation of prostate epithelial cells and expression of genes that modulate angiogenesis

There is increased interest in the effects of secretory products from aged cells on promoting both benign and malignant cell growth. We identified a human fibroblast line, AG04382, from an aged donor that naturally demonstrated senescence-associated features and whose conditioned media significantly induced proliferation of benign prostatic hyperplasia (BPH1) cells. Candidate cytokines mediating this effect were identified with protein arrays and validated by ELISA. We found that the AG04382 fibroblast line secreted high levels of CXCL5, CCL5, and CCL2, but relative to the other lines, its conditioned media was unique in its increased expression of CCL5. Blocking studies using specific antibodies against CXCL5, CCL5, and CCL2 in the conditioned media of AG04382 showed that only CCL5 contributed significantly to BPH1 proliferation. Stimulation of BPH1 cells with rhuCCL5 resulted in increased proliferation and migration, as well as significant changes in the expression of genes that influence angiogenesis. These data suggest that CCL5 is a candidate chemokine secreted by aged cells that promotes prostate growth and regulates angiogenesis.

Time- and temperature-dependent acetylation of the chemokine RANTES produced in recombinant Escherichia coli

The S24F mutant of the chemokine RANTES was found to be partly acetylated when produced in recombinant Escherichia coli BL21(DE3)(pDIA17)(CCL5-S24F-pET-26b). Mass spectrometry and Edman sequencing of peptides generated by lys-C endopeptidase indicated that Lys-26, Lys-34, Lys-46, and Lys-57 were susceptible to acetylation. The extent of acetylation of the RANTES S24F polypeptide increased with temperature and with the time during which the culture was incubated after adding the inducer isopropyl-beta-D-thiogalactoside (IPTG). These findings suggest that induction at low temperature and for a short period of time should be preferred when spurious acetylation is a problem for the production of genuine recombinant polypeptides. Acetylation of the polypeptide was not affected by deleting acs, yfiQ, or speG, which encode acetyl-CoA synthetase, acetyl-CoA synthetase acetylase, and spermidine acetyl transferase, respectively, nor by the presence or absence of the pDIA17 plasmid, which harbours the cat gene encoding chloramphenicol acetyl transferase. By contrast, spontaneous acetylation of RANTES could be demonstrated by incubating either the purified polypeptide or inclusion bodies derived from an induced culture in the presence of acetyl-CoA.