Identification of C-C Chemokine Receptor 1 (CCR1) as the Monocyte Hemofiltrate C-C Chemokine (HCC)-1 Receptor

Hemofiltrate C-C chemokine (HCC)-1 is a recently cloned C-C chemokine that is structurally similar to macrophage inflammatory protein (MIP)-1α. Unlike most chemokines, it is constitutively secreted by tissues and is present at high concentrations in normal human plasma. Also atypical for chemokines, HCC-1 is reported not to be chemotactic for leukocytes. In this paper, we have investigated the chemokine receptor usage and downstream signaling pathways of HCC-1. Cross-desensitization experiments using THP-1 cells suggested that HCC-1 and MIP-1α activated the same receptor. Experiments using a panel of cloned chemokine receptors revealed that HCC-1 specifically activated C-C chemokine receptor (CCR)1, but not closely related receptors, including CCR5. HCC-1 competed with MIP-1α for binding to CCR1-transfected cells, but with a markedly reduced affinity (IC₅₀ = 93 nM versus 1.3 nM for MIP-1α). Similarly, HCC-1 was less potent than MIP-1α in inducing inhibition of adenylyl cyclase in CCR1-transfected cells. HCC-1 induced chemotaxis of freshly isolated human monocytes, THP-1 cells, and CCR1-transfected cells, and the optimal concentration for cell migration (100 nM) was ∼100-fold lower than that of MIP-1α (1 nM). These data demonstrate that HCC-1 is a chemoattractant and identify CCR1 as a functional HCC-1 receptor on human monocytes.