Harvey, K.; Mitchell, K.; Vissers, J. H. A.; Pojer, J. M.; Brooks, E.; Hilmi, A. J. S.; Papenfuss, A. T.; Schroder, J.

Epithelial organs maintain their integrity and prevent tumour initiation by actively removing defective cells, such as those that have lost apicobasal polarity. Here, we identify how transcription factors of two key signalling pathways, Jun-N-terminal kinase (JNK) and Hippo, regulate epithelial integrity by controlling transcription of an overlapping set of target genes. Targeted DamID experiments reveal that in proliferating cells of the Drosophila melanogaster eye, the AP-1 transcription factor Jun, and the Hippo pathway transcription regulators Yorkie and Scalloped bind to a common suite of target genes that regulate organ growth. In defective neoplastic cells, AP-1 transcription factors repress transcription of growth genes together with the CtBP co-repressor. If gene repression by AP-1/CtBP fails, neoplastic tumour growth ensues, driven by Yorkie/Scalloped. Thus, AP-1/CtBP eliminates defective cells and prevents tumour initiation by acting in parallel to Yorkie/Scalloped to repress expression of a shared transcriptome. These findings shed new light on the maintenance of epithelial integrity and tumour suppression.