FBXL12 degrades FANCD2 to regulate replication recovery and promote cancer cell survival under conditions of replication stress
Oncogene-induced replication stress constitutes an early obstacle for pre-cancerous cells to overcome to progress towards malignancy. Fanconi anaemia signalling represents a major genomic maintenance pathway that is activated in response to replication stress, impinging on stalled replication fork stability and recovery. Here, we report that upon replication stress, phosphorylation of the FANCD2 N-terminus by CHK1 triggers FBXL12-dependent proteasomal degradation of FANCD2, facilitating clearance of FANCD2 at stalled replication forks. This mechanism is required to promote efficient and faithful DNA replication under conditions of CYCLIN E- and drug-induced replication stress. Notably, reconstitution of FANCD2 with mutations in the N-terminal phosphodegron fail to re-establish fork progression in FANCD2-deficient human fibroblasts in response to replication stress. In the absence of FBXL12, FANCD2 becomes trapped on chromatin leading to replication stress, excessive DNA damage, and cell death. In human cancers, FBXL12, CYCLIN E, and Fanconi anaemia signalling are positively correlated and upregulation or amplification of FBXL12 is linked to reduced survival in patients with high CYCLIN E expressing breast tumours. Finally, depletion of FBXL12 exacerbated oncogene-induced replication stress and sensitised breast cancer cells to drug-induced replication stress by WEE1 inhibition. Collectively, our results indicate that FBXL12 constitutes a vulnerability of CYCLIN E-overexpressing cancer cells and may represent a novel target for cancer therapy. Overall design: Comparative gene expression profiling analysis of RNA-seq data obtained using MDA-MB-231 basal-like breast cancer cells. Triplicate samples from FBXL12-WT (transduced with scrambled control gRNA) reference cells and two FBXL12-KO clones were profiled.