A major component of the transcription complex AP-1 is cJun. Although upstream signaling cascades to this transcription factor have been well characterized, its downstream effector genes remain to be characterized. To identify cJun target genes, we established a conditional transformation system of Rat-1a cells using tetracycline-inducible cJun. Under adherent growth conditions, cJun expression was rapidly increased in 4 h, and morphological changes gradually occurred after 24 h (spindle and refractile phenotypes appeared after 24 h; close contact of cells, after 2 days; and piling up of cells, after 3 days). In addition, expression of cJun allowed Rat-1a cells to grow without a substratum (nonadherent growth). We identified differentially expressed genes from cJun-induced cells compared with uninduced Rat-1a cells using differential display, suppression subtractive hybridization and microarray analysis. We identified 27 upregulated and 8 downregulated cDNA fragment clones and confirmed 2- to 28-fold differences by northern blot analysis. Sequence analysis revealed 29 known genes and five unmatched clones in addition to c-jun itself. All 11 genes with known promoters had AP-1 sites, and 5 genes have been reported to be regulated by AP-1. Surprisingly, approximately 50% of the genes were identical to or showed homology with cytoskeleton- and adhesion-related genes, suggesting possible cooperative roles in morphological transformation. Furthermore, growth under nonadherent conditions altered the differential expression of some genes. We are currently investigating the precise roles of these genes.