ZFP36L1 is the key mediator of preserving genome stability during aphidicolin-induced replication stress

RNA binding proteins are the heart of post transcriptional regulation of gene expression. Dysregulation of mRNA stability has been linked to a range of diseases due to overexpression of genes encoding, growth factors, inflammatory cytokines and proto-oncogenes. The small group of remarkably similar ZFP36 proteins have been linked to a plethora of roles in regulation of immunity and cell differentiation. In particular, ZFP36L1, an ARE-binding protein, plays a pivotal role in cell fate determination underlying normal physiological processes and in disease. Despite the existence of considerable proportion of scientific literature, several questions around the multiple targets and location-specific roles played by this protein largely remains unclear. Our laboratory has recently developed a CRISPR KO system of ZFP36L1 in osteosarcoma cells and demonstrated vividly the requirements of ZFP36L1 in preserving genome instability in the presence of replication stress. The study presented here aims at conclusively showing whether these proteins can compensate for the deficiency of one or more of the others. Most importantly, filling in these gaps in knowledge will be crucial to demonstrate and to successfully harness ZFP36L1 as a cancer vulnerability drug target for therapeutic applications. In this direction, we have developed a streamlined approach for generation of CRISPR ZFP36L1 knockouts in a tetracycline-inducible U-2OS system. We show that loss of ZFP36L1 resulted in increased levels of hallmarks of RS-associated genomic instability that could be attributed to the defects in phosphorylation of the master cell cycle regulator CHK2 exhibiting increased mitotic defects including: chromosome breaks, DNA double strand breaks, chromosome mis-segregation, micronuclei, 53BP1 G1-nuclear bodies and CFS fragility. Interestingly, we also demonstrate that ZFP36L1 binds chromatin independently of replication stress implicating potential roles of ZFP36L1 in events associated with DNA replication/repair. We show that inducible expression of ZFP36L1 resulted in the reversal of phenotype associated with ZFP36L1 loss suggesting ZFP36L1 is essential in limiting the impact of replication-stress. Taken together our studies propose that ZFP36L1 is crucial for preserving the genome and that loss of ZFP36L1 results in defective DNA repair at CFS through deficiencies in CHK2 activation resulting in genomic instability.