Multiple pathways of amino terminal processing produce two truncated variants of RANTES/CCL5

Abstract

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The CC chemokine regulated on activation, normal T cell expressed and secreted (RANTES)/CC chemokine ligand 5 (CCL5) is expressed by macrophages, endothelial cells, keratinocytes, and T cells during a wide variety of immune responses. Post-translational proteolysis is expected to play an important role in regulating such broad-based expression; however, the rates and modes of RANTES processing by primary cell systems remain poorly understood. Here, we show that peripheral blood mononuclear cells (PBMC) secrete RANTES as an intact molecule that is subject to three post-translational processing pathways. One occurs in the presence of serum or plasma and rapidly generates a RANTES variant lacking two N-terminal residues (3-68 RANTES). Such processing is mainly attributable to soluble CD26. A second pathway, which is evident in the absence of serum or plasma, generates 3-68 RANTES in concert with the expression of cell-surface CD26. The third pathway is unique and generates a novel variant lacking three N-terminal residues (4-68 RANTES). This variant binds CC chemokine receptor 5, exhibits reduced chemotactic and human immunodeficiency virus (HIV)-suppressive activity compared with 1-68 and 3-68 RANTES, and is generated by an unidentified enzyme associated with monocytes and neutrophils. Overall, these results indicate that the production of RANTES by primary cells is regulated by multiple processing pathways which produce two variants with different functional properties. Such findings have important implications for understanding the immunological and HIV-suppressive activities of native RANTES.