The CCL6 chemokine gene was identified as a direct positive target of the L-Myc oncoprotein in interleukin 3-dependent 32D myeloid cells. A mutant form of c-Myc, lacking a region of the NH(2)-terminal domain necessary for transcriptional repression (c-MycDeltaMBII), also up-regulated CCL6. Chromatin immunoprecipitation showed that L-Myc, c-MycDeltaMBII, and full-length c-Myc all bound the CCL6 promoter, although the latter was inactive in transcriptional up-regulation. Exogenously added CCL6 induced marked apoptosis in some cell types. However, in 32D cells, the coexpression of c-Myc and CCL6 abrogated interleukin 3 dependence and produced a highly leukemogenic phenotype. In two solid tumor models, CCL6 overexpression also accelerated tumor growth, and/or enhanced local and metastatic spread in association with marked apoptosis of the tumor capsule and adjacent normal tissues. Our results show that CCL6 can be either a positive or negative target for Myc oncoproteins. The chemokine may alter tumor behavior by relieving its growth factor dependency and by promoting invasiveness as a result of local tissue apoptosis.