Molecular cloning of a novel human CC chemokine (eotaxin-3) that is a functional ligand of CC chemokine receptor 3

Previously, we mapped the novel CC chemokine myeloid progenitor inhibitory factor 2 (MPIF-2)/eotaxin-2 to chromosome 7q11.23 (Nomiyama, H., Osborne, L . R., Imai, T., Kusuda, J,, Miura, R., Tsui, L.-C., and Yoshie, O. (1998) G enomics 49, 339-340). Since chemokine genes tend to be clustered, unknown c hemokines may be present in the vicinity of those mapped to new chromosomal loci. Prompted by this hypothesis, we analyzed the genomic region containi ng the gene for MPIF-2/eotaxin-2 (SCYA24) and have identified a novel CC ch emokine termed eotaxin-3. The genes for MPIF-2/eotaxin-2 (SCYA24) and eotax in-3 (SCYA26) are localized within a region of similar to 40 kilobases, By Northern blot analysis, eotaxin-3 mRNA was constitutively expressed in the heart and ovary. We have generated recombinant eotaxin-3 in a baculovirus e xpression system. Eotaxin-3 induced transient calcium mobilization specific ally in CC chemokine receptor 3 (CCR3)-expressing L1.2 cells with an EC50 o f 3 nM. Eotaxin-3 competed the binding of I-125-eotaxin to CCR3-expressing L1.2 cells with an IC50 of 13 nM. Eotaxin-3 was chemotactic for normal peri pheral blood eosinophils and basophils at high concentrations. Collectively , eotaxin-3 is yet another functional ligand for CCR3. The potency of eotax in-3 as a CCR3 ligand seems, however, to be similar to 10-fold less than th at of eotaxin, Identification of eotaxin-3 will further promote our underst anding of the control of eosinophil trafficking and other CCR3-mediated bio logical phenomena. The strategy used in this study may also be applicable t o identification of other unknown chemokine genes.