The CCR4-Not complex is a tumor suppressor in Drosophila melanogaster eye cancer models

The CNOT3 protein is a subunit of the CCR4-Not complex, a cytoplasmic protein complex mediating mRNA deadenylation as the first step in mRNA degradation. We recently identified CNOT3 loss-of-function mutations in patients with T-cell acute lymphoblastic leukemia (T-ALL). However, it is not clear yet how loss of this gene is involved in cancer development. Here we use different Drosophila melanogaster eye cancer models to study the potential tumor suppressor function of Not3, the CNOT3 orthologue, as well as other members of the CCR4-NOT complex. We show that not only Not3 but also the structural components Not1 and Not2, as well as the deadenylases Twin and Pop2 all behave as tumor suppressor genes. Moreover, RNA-sequencing analyses revealed that Not3 loss leads to increased expression levels of genes involved in DNA replication and ribosome biogenesis pathways, and that CycB is a Not3 target gene in our cancer models. Furthermore, we were able to confirm those results on human T-ALL cell lines, pointing out the conserved function of Not3 in both model systems and in tumor development. Together, our data establish a critical role for Not3 and the entire CCR4-NOT complex as a tumor suppressor. Overall design: RNA-sequencing in Drosophila Melanogaster and in 2 human cell lines, knock-down of Not3/CNOT3 gene