FANCJ helicase promotes DNA end resection by facilitating CtIP recruitment to DNA double-strand breaks.

FANCJ helicase mutations are known to cause hereditary breast and ovarian cancers as well as bone marrow failure syndrome Fanconi anemia. FANCJ plays an important role in the repair of DNA inter-strand crosslinks and DNA double-strand breaks (DSBs) by homologous recombination (HR). Nonetheless, the molecular mechanism by which FANCJ controls HR mediated DSB repair is obscure. Here, we show that FANCJ promotes DNA end resection by recruiting CtIP to the sites of DSBs. This recruitment of CtIP is dependent on FANCJ K1249 acetylation. Notably, FANCJ acetylation is dependent on FANCJ S990 phosphorylation by CDK. The CDK mediated phosphorylation of FANCJ independently facilitates its interaction with BRCA1 at damaged DNA sites and promotes DNA end resection by CtIP recruitment. Strikingly, mutational studies reveal that ATP binding competent but hydrolysis deficient FANCJ partially supports end resection, indicating that in addition to the scaffolding role of FANCJ in CtIP recruitment, its helicase activity is important for promoting end resection. Together, these data unravel a novel function of FANCJ helicase in DNA end resection and provide mechanistic insights into its role in repairing DSBs by HR and in genome maintenance.

FANCJ helicase controls the balance between short- and long-tract gene conversions between sister chromatids.

The FANCJ DNA helicase is linked to hereditary breast and ovarian cancers as well as bone marrow failure disorder Fanconi anemia (FA). Although FANCJ has been implicated in the repair of DNA double-strand breaks (DSBs) by homologous recombination (HR), the molecular mechanism underlying the tumor suppressor functions of FANCJ remains obscure. Here, we demonstrate that FANCJ deficient human and hamster cells exhibit reduction in the overall gene conversions in response to a site-specific chromosomal DSB induced by I-SceI endonuclease. Strikingly, the gene conversion events were biased in favour of long-tract gene conversions in FANCJ depleted cells. The fine regulation of short- (STGC) and long-tract gene conversions (LTGC) by FANCJ was dependent on its interaction with BRCA1 tumor suppressor. Notably, helicase activity of FANCJ was essential for controlling the overall HR and in terminating the extended repair synthesis during sister chromatid recombination (SCR). Moreover, cells expressing FANCJ pathological mutants exhibited defective SCR with an increased frequency of LTGC. These data unravel the novel function of FANCJ helicase in regulating SCR and SCR associated gene amplification/duplications and imply that these functions of FANCJ are crucial for the genome maintenance and tumor suppression.

Characterizing replisome disassembly in human cells.

To ensure timely duplication of the entire eukaryotic genome, thousands of replication machineries (replisomes) act on genomic DNA at any time during S phase. In the final stages of this process, replisomes are unloaded from chromatin. Unloading is driven by polyubiquitylation of MCM7, a subunit of the terminated replicative helicase, and processed by p97/VCP segregase. Most of our knowledge of replication termination comes from model organisms, and little is known about how this process is executed and regulated in human somatic cells. Here we show that replisome disassembly in this system requires CUL2LRR1-driven MCM7 ubiquitylation, p97, and UBXN7 for unloading and provide evidence for "backup" mitotic replisome disassembly, demonstrating conservation of such mechanisms. Finally, we find that small-molecule inhibitors against Cullin ubiquitin ligases (CULi) and p97 (p97i) affect replisome unloading but also lead to induction of replication stress in cells, which limits their usefulness to specifically target replisome disassembly processes.

Dexamethasone Alters the Appetite Regulation via Induction of Hypothalamic Insulin Resistance in Rat Brain.

Elevated levels of glucocorticoid, a steroid hormone released in response to stress, have been implicated in the pathophysiology of diabetes, which is now known to extend its effect on brain functions. Hence, we aimed to investigate the status of brain insulin signaling in response to dexamethasone (a synthetic glucocorticoid) treatment in female Charles Foster rat. This model exhibited pronounced hyperinsulinemia and glucose intolerance with loss in appetite and body weight. Immunoblotting of insulin receptor (INSR)-PI3kinase-AKT demonstrated reduced insulin signaling in hypothalamus but no change in hippocampus, cortex, and cerebellum in dexamethasone-treated rats as compared to vehicle-treated rats, signifying the diversity of distribution and function of insulin in different brain regions. These results also correlated with appetite change, a key function governed by hypothalamus. Hence, we further explored the hypothalamic feeding circuit and found altered levels of neuropeptide genes (Agrp, Npy, Pomc) and candidate nutrient sensors (GLUT1, SirT1, and PPARγ). There was also a considerable reduction in glycogen content and appetite-regulating neurotransmitters (GABA, glutamate, dopamine) in dexamethasone-treated rats. Thus, concluding that dexamethasone not only induces peripheral insulin resistance but also impairs hypothalamic function of appetite regulation via the interwoven cascade of insulin signaling, neurotransmitters, and neuropeptides. Graphical Abstract Reduced insulin signaling as well as elevated glucocorticoid levels in hypothalamus modulates the key appetite regulating neuropeptides, neurotransmitters, and nutrient sensors resulting into reduced appetite and bodyweight.