Chemokines have been shown to chemoattract and activate different leukocyte populations. Here we report the in vitro effect of macrophage inflammatory protein (MIP)-1a, MIP-1b, regulated on activation, normal T-cells, expressed and secreted (RANTES), monocyte chemotactic protein-1 (MCP-1), interleukin-8 (IL-8), interferon inducible protein-10 (IP-10), neutrophil-activating peptide-2 (NAP-2), growthrelated protein (GRO)-a and GRO-g, on the migration of 3 human breast carcinoma cell lines, MCF-7, T47D and ZR-75-1, using a microchemotaxis chamber to assess migration across fibronectin-coated polycarbonate membranes. MCF-7 cells responded chemotactically to all chemokines tested in a pattern which was dose and time dependent, although responses to the different chemokines were variable. ZR-75-1 responded to MIP-1b and GRO-a, giving maximum migration indices of 3.7 and 5.3, respectively, and exhibited a migratory response to MIP-1a, IL-8 and MCP-1 although to a lower degree. T47D was unresponsive to the chemokines tested, but both MCF-7 and T47D cells bound radiolabelled ligands with binding constants (Kd) ranging from 0.6 to 2.2 nM and 0.6 to 2.1 nM, respectively. The specificity of the chemotactic response of MCF-7 to MIP-1a and MIP-1b was confirmed using chemokine-specific neutralising antibodies and heat denaturation, and was demonstrated to involve G protein and cyclic AMP signalling pathways. MIP-1b and MIP-1a were shown to induce changes in the organisation of the actin cytoskeleton and the level of F-actin in MCF-7 cells, as determined using flow cytometric analysis and confocal microscopy. Our results show that breast carcinoma cells can respond to chemokines, and suggests a potential role for these molecules in the process of tumour cell migration, invasion and metastasis. Int. J. Cancer 71:257-266, 1997.r 1997 Wiley-Liss, Inc.Chemokines are an ever expanding family of proinflammatory cytokines with more than 20 recognised family members, the majority showing between 20 and 80% homology in their amino acid sequences and possessing a conserved 4 cysteine residues motif (Baggiolini et al., 1994). The separation into the a and b subfamilies is based on 2 criteria: the presence or the absence, respectively, of an intervening amino acid residue located between the first 2 of the 4 conserved cysteines, and the clustering of genes encoding the a and b chemokines to human chromosomes 4 and 17, respectively. Murine lymphotactin (Kelner et al., 1994) and the human homologue SCM-1 (Yoshida et al., 1995) contain only 2 of the 4 conserved cysteines found in the other family members and constitute a distant third subfamily (the C or g type subfamily).All chemokine family members have been shown to induce the directional migration of particular inflammatory cell types, including granulocytes, monocytes and lymphocytes (Baggiolini et al., 1994). These proteins have also been shown to be active over a wide concentration range and are produced by a variety of cell types in response to primary proinflammatory mediators such a...