Proper CycE-Cdk2 activity in endocycling tissues requires regulation of the cyclin-dependent kinase inhibitor Dacapo by dE2F1b in Drosophila.

Polyploidy is an integral part of development and is associated with cellular stress, aging, and pathological conditions. The endocycle, comprised of successive rounds of G and S phases without mitosis, is widely employed to produce polyploid cells in plants and animals. In Drosophila, maintenance of the endocycle is dependent on E2F-governed oscillations of Cyclin E (CycE)-Cdk2 activity, which is known to be largely regulated at the level of transcription. In this study, we report an additional level of E2F-dependent control of CycE-Cdk2 activity during the endocycle. Genetic experiments revealed that an alternative isoform of Drosophila de2f1, dE2F1b, regulates the expression of the p27CIP/KIP-like Cdk inhibitor Dacapo (Dap). We provide evidence showing that dE2F1b-dependent Dap expression in endocycling tissues is necessary for setting proper CycE-Cdk2 activity. Furthermore, we demonstrate that dE2F1b is required for proliferating cell nuclear antigen expression that establishes a negative feedback loop in S phase. Overall, our study reveals previously unappreciated E2F-dependent regulatory networks that are critical for the periodic transition between G and S phases during the endocycle.

PRPS-Associated Disorders and the Drosophila Model of Arts Syndrome.

While a plethora of genetic techniques have been developed over the past century, modifying specific sequences of the fruit fly genome has been a difficult, if not impossible task. clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9 truly redefined molecular genetics and provided new tools to model human diseases in Drosophila melanogaster. This is particularly true for genes whose protein sequences are highly conserved. Phosphoribosyl pyrophosphate synthetase (PRPS) is a rate-limiting enzyme in nucleotide metabolism whose missense mutations are found in several neurological disorders, including Arts syndrome. In addition, PRPS is deregulated in cancer, particularly those that become resistant to cancer therapy. Notably, Drosophila PRPS shares about 90% protein sequence identity with its human orthologs, making it an ideal gene to study via CRISPR/Cas9. In this review, we will summarize recent findings on PRPS mutations in human diseases including cancer and on the molecular mechanisms by which PRPS activity is regulated. We will also discuss potential applications of Drosophila CRISPR/Cas9 to model PRPS-dependent disorders and other metabolic diseases that are associated with nucleotide metabolism.

Pleiotropic role of Drosophila phosphoribosyl pyrophosphate synthetase in autophagy and lysosome homeostasis.

Phosphoribosyl pyrophosphate synthetase (PRPS) is a rate-limiting enzyme whose function is important for the biosynthesis of purines, pyrimidines, and pyridines. Importantly, while missense mutations of PRPS1 have been identified in neurological disorders such as Arts syndrome, how they contribute to neuropathogenesis is still unclear. We identified the Drosophila ortholog of PRPS (dPRPS) as a direct target of RB/E2F in Drosophila, a vital cell cycle regulator, and engineered dPRPS alleles carrying patient-derived mutations. Interestingly, while they are able to develop normally, dPRPS mutant flies have a shortened lifespan and locomotive defects, common phenotypes associated with neurodegeneration. Careful analysis of the fat body revealed that patient-derived PRPS mutations result in profound defects in lipolysis, macroautophagy, and lysosome function. Significantly, we show evidence that the nervous system of dPRPS mutant flies is affected by these defects. Overall, we uncovered an unexpected link between nucleotide metabolism and autophagy/lysosome function, providing a possible mechanism by which PRPS-dysfunction contributes to neurological disorders.

Estimating hazard ratios from published Kaplan-Meier survival curves: A methods validation study.

OBJECTIVE: Various statistical methods have been developed to estimate hazard ratios (HRs) from published Kaplan-Meier (KM) curves for the purpose of performing meta-analyses. The objective of this study was to determine the reliability, accuracy, and precision of four commonly used methods by Guyot, Williamson, Parmar, and Hoyle and Henley. DESIGN: Pivotal randomized controlled trials (RCTs) in oncology were identified from the pan-Canadian Oncology Drug Review (pCODR) database (primary analysis) and the Food and Drug Administration's (FDA) drug approvals page (secondary analysis) between January 2012 and May 2016. Two reviewers independently reconstructed HRs using each method on KM curves extracted from each trial and compared them with reported HRs (gold standard). Bland-Altman plots and summary statistics were calculated to assess accuracy and precision of these methods. Interrater reliability was assessed using intraclass correlation coefficient (ICC). These four methods were also applied to KM curves of different structures (ie, flat versus steep curves). RESULTS: A total of 118 KM curves (55 RCTs) and 77 KM curves (46 RCTs) were extracted from pCODR and FDA, respectively. In the primary analysis, the Guyot method was the most accurate with the lowest mean error (0.0094; 95% CI, -0.0012-0.020). All four methods had excellent interrater reliability. The Guyot method showed the smallest bias and greatest precision on the Bland-Altman plots. The Guyot method was consistently superior in both the secondary and all sensitivity analyses. CONCLUSION: In the absence of reported HRs, we recommend that researchers consider the Guyot method to reconstruct HRs from KM curves when performing aggregate data meta-analyses.

Neoadjuvant treatments for locally advanced, resectable esophageal cancer: A network meta-analysis.

The relative survival benefits and postoperative mortality among the different types of neoadjuvant treatments (such as chemotherapy only, radiotherapy only or chemoradiotherapy) for esophageal cancer patients are not well established. To evaluate the relative efficacy and safety of neoadjuvant therapies in resectable esophageal cancer, a Bayesian network meta-analysis was performed. MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials were searched for publications up to May 2016. ASCO and ASTRO annual meeting abstracts were also searched up to the 2015 conferences. Randomized controlled trials that compared at least two of the following treatments for resectable esophageal cancer were included: surgery alone, surgery preceded by neoadjuvant chemotherapy, neoadjuvant radiotherapy or neoadjuvant chemoradiotherapy. The primary outcome assessed from the trials was overall survival. Thirty-one randomized controlled trials involving 5496 patients were included in the quantitative analysis. The network meta-analysis showed that neoadjuvant chemoradiotherapy improved overall survival when compared to all other treatments including surgery alone (HR 0.75, 95% CR 0.67-0.85), neoadjuvant chemotherapy (HR 0.83. 95% CR 0.70-0.96) and neoadjuvant radiotherapy (HR 0.82, 95% CR 0.67-0.99). However, the risk of postoperative mortality increased when comparing neoadjuvant chemoradiotherapy to either surgery alone (RR 1.46, 95% CR 1.00-2.14) or to neoadjuvant chemotherapy (RR 1.58, 95% CR 1.00-2.49). In conclusion, neoadjuvant chemoradiotherapy improves overall survival but may also increase the risk of postoperative mortality in patients locally advanced resectable esophageal carcinoma.

A network meta-analysis of the sequencing and types of systemic therapies with definitive radiotherapy in locally advanced squamous cell carcinoma of the head and neck (LASCCHN)☆.

OBJECTIVES: The current standard therapy for locally advanced squamous cell carcinoma of the head and neck (LASCCHN) is platinum-based chemotherapy plus concurrent radiotherapy (CRT), but several systemic therapies have been evaluated. We performed a Bayesian network meta-analysis (NMA) with random effects to enable direct and indirect comparisons of all existing treatment modalities for LASCCHN simultaneously. MATERIAL AND METHODS: A systematic review was conducted using MEDLINE, EMBASE, ASCO abstracts, ASTRO abstracts and the Cochrane Central of Registered Trials using Cochrane methodology to identify randomized controlled trials (RCTs) up to June 2016. Only abstracts that involved the same definitive radiotherapy in the arms for the RCT were included. RESULTS: Sixty-five RCTs involving 13,574 patients and 16 different treatment strategies were identified. Chemotherapy plus concurrent radiation (CRT) was superior to RT with a HR of 0.74 (95%CR 0.69-0.79) for OS in the NMA. Only 3 trials compared RT alone to concurrent therapy with an EGFR antibody (ERT), demonstrating a superior OS (HR 0.75, 95% CR 0.60-0.94), but this difference was not statistically significant when interpreted in a NMA (HR 0.84, 95%CR 0.65-1.08). ERT was not superior to CRT (HR 1.19, 95%CR 0.93-1.54), and the addition of neo-adjuvant taxane-based chemotherapy to CRT was not beneficial (HR 0.86, 95% CR 0.70-1.07). CONCLUSION: The addition of either adjuvant or neoadjuvant chemotherapy to the CRT backbone does not confer an OS benefit in the treatment of LASCCHN. Similarly, ERT does not confer an OS benefit for patients who are eligible for CRT.