More than 60% of anaplastic large-cell lymphomas (Ki-1 lymphoma) are associated with a t(2;5)(p23;q35) translocation that produces an 80 kDa hyperphosphorylated chimeric protein (p80) derived from the fusion of the anaplastic lymphoma kinase (ALK) with nucleophosmin (NPM). The NPM-ALK chimeric gene is an activated tyrosine kinase that has been shown to be a potent oncogene. We have developed a cellular model for the study of p80 action in rat 1a fibroblasts. Expression of cDNA's encoding NPM-ALK (p80) in rat 1a fibroblasts induces anchorage-independent growth in soft agar and promotes foci formation in culture. Cells expressing exogenous p80 showed significantly increased proliferation characterized by accelerated cell cycle entry into S-phase. Consistent with increased G0/G1 to S-phase transition, there is also marked up-regulation of cyclin A and cyclin D1 expression. In addition, p80 transformed cells showed elevated expression of several immediate early genes involved in cellular proliferation, including fos, jun, and c-myc. DNA binding analysis of nuclear extracts prepared from p80 transformed cells reveal marked up-regulation of AP-1 DNA binding activity. Functional AP-1-specific transfection assays also show up-regulation of AP-1-dependent transcriptional activation. These finding demonstrate that p80 transformed rat 1a fibroblast can be a highly useful model system for the molecular and biochemical characterization of the mechanisms of action of this interesting new oncogene.