Of 14 chemokine receptors investigated, only CXCR4 was expressed on ovarian cancer cells [C. J. Scotton et al., Cancer Res., 61: 4961-4965, 2001]. To further understand the role of this chemokine receptor in ovarian tumor biology, we studied the action of its ligand, CXCL12 (stromal cell-derived factor 1), on the CXCR4-expressing ovarian cancer cell lines IGROV. Ligand stimulation of the CXCR4 receptor resulted in sustained activation of Akt/protein kinase B and biphasic phosphorylation of p44/42 mitogen-activated protein kinase in IGROV. When IGROV cells were cultured under suboptimal conditions, CXCL12 stimulated their in vitro growth, an effect that was abrogated by neutralizing antibodies to CXCR4. This increase in cell number was attributable to stimulation of DNA synthesis, not protection from apoptosis. CXCL12 treatment of IGROV cells also induced mRNA and protein for tumor necrosis factor alpha, a cytokine that is expressed by tumor cells in ovarian cancer biopsies. IGROV cells invaded through Matrigel toward a CXCL12 gradient. Invasion was abrogated by the broad spectrum matrix metalloproteinase and TNFalpha converting enzyme inhibitor Marimastat and was partially inhibited by neutralizing antitumor necrosis factor alpha antibodies. These effects were not limited to the IGROV cell line. They could also be demonstrated in the CAOV-3 ovarian cancer cell line and primary ovarian tumor cells isolated from ovarian ascites. These biological effects of CXCL12 on IGROV cells were also inhibited by the small molecular weight CXCR4 antagonist AMD3100. Finally, we found abundant intracellular CXCL12 protein in tumor cells in 15 of 18 ovarian cancer biopsies but not in epithelial cells from normal ovary or borderline disease. The chemokine CXCL12 may have multiple biological effects in ovarian cancer, stimulating cell migration and invasion through extracellular matrix, as well as DNA synthesis and establishment of a cytokine network in situations that are suboptimal for tumor cell growth.