Essential Roles for Polymerase θ-Mediated End Joining in the Repair of Chromosome Breaks.

DNA polymerase theta (Pol θ)-mediated end joining (TMEJ) has been implicated in the repair of chromosome breaks, but its cellular mechanism and role relative to canonical repair pathways are poorly understood. We show that it accounts for most repairs associated with microhomologies and is made efficient by coupling a microhomology search to removal of non-homologous tails and microhomology-primed synthesis across broken ends. In contrast to non-homologous end joining (NHEJ), TMEJ efficiently repairs end structures expected after aborted homology-directed repair (5' to 3' resected ends) or replication fork collapse. It typically does not compete with canonical repair pathways but, in NHEJ-deficient cells, is engaged more frequently and protects against translocation. Cell viability is also severely impaired upon combined deficiency in Pol θ and a factor that antagonizes end resection (Ku or 53BP1). TMEJ thus helps to sustain cell viability and genome stability by rescuing chromosome break repair when resection is misregulated or NHEJ is compromised.

Quality control autophagy degrades soluble ERAD-resistant conformers of the misfolded membrane protein GnRHR.

Molecular chaperones triage misfolded proteins via action as substrate selectors for quality control (QC) machines that fold or degrade clients. Herein, the endoplasmic reticulum (ER)-associated Hsp40 JB12 is reported to participate in partitioning mutant conformers of gonadotropin-releasing hormone receptor (GnRHR), a G protein-coupled receptor, between ER-associated degradation (ERAD) and an ERQC autophagy pathway. ERQC autophagy degrades E90K-GnRHR because pools of its partially folded and detergent-soluble degradation intermediates are resistant to ERAD. S168R-GnRHR is globally misfolded and disposed of via ERAD, but inhibition of p97, the protein retrotranslocation motor, shunts S168R-GnRHR from ERAD to ERQC autophagy. Partially folded and grossly misfolded forms of GnRHR associate with JB12 and Hsp70. Elevation of JB12 promotes ERAD of S168R-GnRHR, with E90K-GnRHR being resistant. E90K-GnRHR elicits association of the Vps34 autophagy initiation complex with JB12. Interaction between ER-associated Hsp40s and the Vps34 complex permits the selective degradation of ERAD-resistant membrane proteins via ERQC autophagy.

Thromboembolic risk in patients with lung cancer receiving systemic therapy.

In this retrospective study, we investigated the influence of chemotherapy and immunotherapy on thromboembolic risk among United States Veterans with lung cancer during their first 6 months (180 days) following initiation of systemic therapy. Included patients received treatment with common front-line agents that were divided into four groups: chemotherapy alone, immunotherapy alone, combination of chemo- and immunotherapies, and molecularly targeted therapies (control group). The cohort experienced a 7·4% overall incidence of thrombosis, but the analysis demonstrated significantly different rates among the different groups. We explored models incorporating multiple confounding variables as well as the competing risk of death, and these results indicated that both chemo- and immunotherapies were associated with an increased incidence of thrombosis, either alone or combined, compared with the control group (7·56%, P = 2.2 × 10-16 ; 10·2%, P = 2.2 × 10-16 ; and 7·87%, P = 2.4 × 10-14 respectively vs. 4·10%). The Khorana score was found to be associated with increased risk, as were vascular disease and metastases. We found an association between risk of thrombosis and the use of anticoagulation, accounting for several confounders, including history of thrombosis. Further study is warranted to better determine the drivers of thromboembolic risk and to identify ways to mitigate this risk for patients.

Ureteroscopic evaluation and treatment of benign essential hematuria: a systematic review.

INTRODUCTION The advent of ureteroscopy has revolutionized the treatment many urologic diseases, including benign essential hematuria. This systematic review examines the treatment of benign essential hematuria (BEH) with ureteroscopic interventions. MATERIALS AND METHODS: We performed a systematic review of the literature from 1977 to May 2020. We included studies that evaluated the use of ureteroscopy to diagnose or treat BEH. Demographics, follow up, findings, treatment method and success rate were extracted from each identified paper. Quality analysis was performed independently by both authors. RESULTS: Our search resulted in 587 articles. Fifteen of these studies met inclusion criteria and were included in the final analysis. No randomized controlled trials were found. All 15 studies were case series. Nine studies were graded as good, five as fair, and one as poor. Follow up ranged from 2 to 108 months. A total of 307 patients underwent ureteroscopy for suspected BEH; 223 (73%) were diagnosed with a discrete lesion, 33 (11%) with a diffuse lesion, and 44 (14%) had no lesions seen on ureteroscopy. Of those diagnosed with discrete lesions, the most common was minute venous ruptures (35%), followed by hemangiomas (26%). Ureteroscopic treatment successfully relieved the hematuria and symptoms in most patients, and was more successful in those treated for discrete lesion (115/120, 96%) than diffuse (10/19, 53%). CONCLUSIONS: Ureteroscopic treatment of BEH yields excellent outcomes. In this systematic review, 96% of patients with discrete lesions and 53% of patients with diffuse lesions had resolution of their hematuria after ureteroscopic interventions.

Bridging of double-stranded breaks by the nonhomologous end-joining ligation complex is modulated by DNA end chemistry.

The nonhomologous end-joining (NHEJ) pathway is the primary repair pathway for DNA double strand breaks (DSBs) in humans. Repair is mediated by a core complex of NHEJ factors that includes a ligase (DNA Ligase IV; L4) that relies on juxtaposition of 3΄ hydroxyl and 5΄ phosphate termini of the strand breaks for catalysis. However, chromosome breaks arising from biological sources often have different end chemistries, and how these different end chemistries impact the way in which the core complex directs the necessary transitions from end pairing to ligation is not known. Here, using single-molecule FRET (smFRET), we show that prior to ligation, differences in end chemistry strongly modulate the bridging of broken ends by the NHEJ core complex. In particular, the 5΄ phosphate group is a recognition element for L4 and is critical for the ability of NHEJ factors to promote stable pairing of ends. Moreover, other chemical incompatibilities, including products of aborted ligation, are sufficient to disrupt end pairing. Based on these observations, we propose a mechanism for iterative repair of DSBs by NHEJ.

Unconventional Bladder Preservation: Factors Predicting Failure to Receive Definitive Surgery following Chemotherapy for Nonmetastatic Muscle Invasive Bladder Cancer in the National Cancer Database.

PURPOSE: Neoadjuvant chemotherapy is an important adjunct to cystectomy for managing muscle invasive bladder cancer. Using the National Cancer Database we investigated factors that predict failure to undergo surgery following multi-agent chemotherapy for nonmetastatic muscle invasive bladder cancer. MATERIALS AND METHODS: We performed a cohort study in patients diagnosed with cT2-4aN0M0 urothelial cell carcinoma of the bladder between 2004 and 2013 who underwent multi-agent chemotherapy. We excluded those with surgery prior to chemotherapy, clinical T4b disease and those who received radiotherapy. Socioeconomic and clinical predictors, including time from diagnosis to treatment, were analyzed using logistic regression for the receipt of surgery after chemotherapy. Cox proportional hazards modeling was applied to perform time dependent analysis. RESULTS: Of the 4,640 patients who met our study inclusion and exclusion criteria 4,244 (91%) proceeded to surgery. Negative predictors of surgery included African American or Hispanic race (OR 0.58, p = 0.007 and 0.48, p = 0.002, respectively), increasing age (OR 0.44, p <0.001) and greater time between diagnosis and chemotherapy initiation (fourth quartile greater than 59 days, OR 0.51, p <0.001). African American race (HR 0.79, p <0.001), Medicare (HR 0.86, p <0.001) and other government insurance (HR 0.73, p <0.001) were associated with delayed chemotherapy. CONCLUSIONS: Increasing age, African American or Hispanic race and longer time to chemotherapy predicted failure to undergo surgery. Furthermore, African American race was associated with delayed chemotherapy. Chemotherapy was also delayed in patients on Medicare or other government insurance. Longer time to neoadjuvant chemotherapy is a modifiable risk factor that should be closely observed in multimodal cancer treatment.

Higher outcomes of vasectomy reversal in men with the same female partner as before vasectomy.

PURPOSE: We reviewed fertility outcomes of vasectomy reversal at a high surgical volume center in men with the same female partner as before vasectomy. MATERIALS AND METHODS: We retrospectively studied a prospective database. All vasectomy reversals were performed by a single surgeon (EFF). Patients who underwent microsurgical vasectomy reversal and had the same female partner as before vasectomy were identified from 1978 to 2011. Pregnancy and live birth rates, procedure type (bilateral vasovasostomy, bilateral vasoepididymostomy, unilateral vasovasostomy or unilateral vasoepididymostomy), patency rate, time from reversal and spouse age were evaluated. RESULTS: We reviewed the records of 3,135 consecutive microsurgical vasectomy reversals. Of these patients 524 (17%) who underwent vasectomy reversal had the same female partner as before vasectomy. Complete information was available on 258 patients (49%), who had a 94% vas patency rate. The clinical pregnancy rate was 83% by natural means compared to 60% in our general vasectomy reversal population (p <0.0001). On logistic regression analysis controlling for female partner and patient ages, years from vasectomy and vasectomy reversal with the same female partner the OR was 2 (p <0.007). Average time from vasectomy was 5.7 years. Average patient and female partner age at reversal was 38.9 and 33.2 years, respectively. CONCLUSIONS: Outcomes of clinical pregnancy and live birth rates are higher in men who undergo microsurgical vasectomy reversal with the same female partner. These outcomes may be related to a shorter interval from vasectomy, previous fertility and couple motivation.

Impact on Pregnancy of Gross and Microscopic Vasal Fluid during Vasectomy Reversal.

PURPOSE: We compared fertility outcomes with gross and microscopic fluid findings at vasectomy reversal at a high volume vasectomy reversal center. MATERIALS AND METHODS: A retrospective study of a prospective database was performed. All vasectomy reversals were performed by a single surgeon (EFF) between 1978 and 2011. The clinical pregnancy rate was self-reported or determined via patient mailers. Patient and operative findings were determined through database review. We classified vasal fluid as opalescent, creamy, pasty or clear. Intraoperative light microscopy was used to determine if sperm or sperm parts were present and if they were motile. Multivariate analysis was performed evaluating patient age, partner age, years after vasectomy, type of surgery, and gross and microscopic fluid analysis. RESULTS: A total of 2,947 microsurgical vasectomy reversals were reviewed after we excluded reversals performed for post-vasectomy pain. We determined the pregnancy status of 902 (31%) cases. On univariate analysis with respect to pregnancy the presence of motile sperm at vasovasostomy neared statistical significance (p=0.075) and there was no difference between bilateral vs unilateral motile sperm. Gross fluid appearance was not statistically significant but we found the order of pregnancy success to be opalescent, creamy, clear then pasty fluid. On multivariate analysis only female partner age and sperm heads only or no sperm seen on light microscopy had statistical significance (p <0.05). CONCLUSIONS: The presence of motile sperm at vasectomy reversal approaches statistical significance on univariate analysis as a factor that affects clinical pregnancy rates. On multivariate analysis female partner age and microscopic findings of sperm heads only or no sperm are inversely related to pregnancy rates. These data will help counsel couples after vasectomy reversal and reinforce the importance of female partner age.

Timing, incidence and risk factors for venous thromboembolism in patients undergoing radical cystectomy for malignancy: a case for extended duration pharmacological prophylaxis.

PURPOSE: Patients undergoing radical cystectomy for bladder cancer are at high risk for venous thromboembolism. Recent data have demonstrated that the risk of venous thromboembolism often extends beyond hospital discharge in nonurological surgical populations. To our knowledge the timing of venous thromboembolism in patients who have undergone radical cystectomy during a 30-day postoperative period has not been assessed. Therefore, we evaluated the timing, incidence and risk factors for venous thromboembolism for patients undergoing radical cystectomy for malignancy. MATERIALS AND METHODS: In this descriptive, observational, retrospective study data from 1,307 patients who underwent radical cystectomy for malignancy from 2005 to 2011 were collected using the American College of Surgeons NSQIP (National Surgical Quality Improvement Program) database. Venous thromboembolism occurrences were evaluated by postoperative day and whether they occurred while an inpatient or after discharge home. Univariate and multivariate Cox regression and logistic regression models were used to evaluate risk factors associated with venous thromboembolism. RESULTS: Of 1,307 patients 78 (6%) were diagnosed with venous thromboembolism. The mean time to venous thromboembolism diagnosis was 15.2 days postoperatively. Of all venous thromboembolism events 55% were diagnosed after patient discharge home. The 30-day mortality rate from venous thromboembolism was 6.4%. Risk factors for the development of venous thromboembolism on multivariate analysis were age (p = 0.024), operative time (p = 0.004) and sepsis or septic shock (p = 0.0001). CONCLUSIONS: More than half of all venous thromboembolisms (55%) in patients undergoing radical cystectomy for malignancy occurred after discharge home and the mean time to venous thromboembolism diagnosis was 15.2 days postoperatively. It is reasonable to consider extended duration pharmacological prophylaxis (4 weeks) in this high risk surgical population.

A single dose of a non-steroidal anti-inflammatory drug (NSAID) prevents severe pain after ureteric stent removal: a prospective, randomised, double-blind, placebo-controlled trial.

OBJECTIVES: To determine the incidence of severe pain after ureteric stent removal. To evaluate the efficacy of a single dose of a non-steroidal anti-inflammatory drug (NSAID) in preventing this complication. PATIENTS AND METHODS: A prospective, randomised, double-blind, placebo-controlled trial was performed at our institution. Adults with an indwelling ureteric stent after ureteroscopy were randomised to receive either a single dose of placebo or an NSAID (rofecoxib 50 mg) before ureteric stent removal. Pain was measured using a visual analogue scale (VAS) just before and 24 h after stent removal Pain medication use after ureteric stent removal was measured using morphine equivalents. RESULTS: In all, 22 patients were enrolled and randomised into the study before ending the study after interim analysis showed significant decrease in pain level in the NSAID group. The most common indication for ureteroscopy was urolithiasis (14 patients). The proportion of patients with severe pain (VAS score of ≥7) during the 24 h after ureteric stent removal was six of 11 (55%) in the placebo group and it was zero of 10 in the NSAID group (P < 0.01). There were no complications related to the use of rofecoxib. CONCLUSIONS: We found a 55% incidence of severe pain after ureteric stent removal. A single dose of a NSAID before stent removal prevents severe pain after ureteric stent removal.

Alemtuzumab induction with tacrolimus monotherapy in 25 pediatric renal transplant recipients.

ALA induction in transplantation has been shown to reduce the need for maintenance immunosuppression. We report the outcome of 25 pediatric renal transplants between 2007 and 2010 using ALA induction followed by tacrolimus maintenance monotherapy. Patient ages were 1-19 yr (mean 14 ± 4.1 yr). Time of follow-up was 7-51 months (mean 26 ± 13 months). Tacrolimus monotherapy was maintained in 48% of patients, and glucocorticoids were avoided in 80% of recipients. Mean plasma creatinine and GFR at one yr post-transplant were 0.88 ± 0.3 mg/dL and 104.4 ± 25 mL/min/1.73m(2) , respectively. One, two, and three-yr actuarial patient and graft survival rates were 100%. The incidence of early AR (<12 months after transplantation) was 12%, while the incidence of late AR (after 12 months) was 16%. Forty-four percent of the recipients recovered normal, baseline renal function after an episode of AR, and 44% had persistent renal dysfunction (plasma creatinine 1.0-1.8 mg/dL). One graft was lost four yr after transplantation due to medication non-compliance. Four (16%) patients developed BK or CMV infection. In our experience, ALA induction with tacrolimus monotherapy resulted in excellent short- and mid-term patient and graft survival in low-immunologic risk pediatric renal transplant recipients.

Increased risk of head and neck cancer in Agent Orange exposed Vietnam Era veterans.

IMPORTANCE: United States military personnel during the Vietnam Era were potentially exposed to Agent Orange, a known carcinogen. The link between Agent Orange and head and neck cancers is largely unknown; laryngeal cancer is currently the only subsite with sufficient evidence of an Agent Orange association. OBJECTIVE: We aim to determine the relationship between Agent Orange exposure and the incidence of head and neck cancers in Vietnam Era veterans as well as any relationship with head and neck cancer survival. MATERIALS AND METHODS: The present study utilizes the Veterans Affairs Corporate Data Warehouse (VA CDW) to identify Vietnam Era veterans, their Agent Orange exposure status, limited demographic data, presence of head and neck cancer, and survival data. RESULTS: Of 8,877,971 Vietnam Era veterans, 22% self-reported exposure to Agent Orange, and 54,717 had a diagnosis of head and neck cancer. Agent Orange exposure significantly predicted upper aerodigestive tract carcinoma, with a relative risk (RR) of 1.10. On subsite analysis, Agent Orange exposure (as well as race, gender, and substance use) was significantly associated with oropharyngeal (RR 1.16), nasopharyngeal (RR 1.22), laryngeal (1.11), and thyroid (1.24) cancers. Agent Orange exposure was associated with improved 10-year overall survival in upper aerodigestive tract cancer patients. CONCLUSIONS AND RELEVANCE: Self-reported Agent Orange exposure correlated with increased risks of oropharyngeal, nasopharyngeal, laryngeal, and thyroid cancers, and predicted improved survival in upper aerodigestive tract cancer patients. These findings broaden our understanding of the risks of Agent Orange exposure.

Risk of Head and Neck Cancer in Patients With Prior Hematologic Malignant Tumors.

Importance: More than 1.3 million people in the United States have a hematologic malignant tumor currently or in remission. Previous studies have demonstrated an increased risk of secondary neoplasms in patients with hematologic malignant tumors, but research specifically on the risk of head and neck solid tumors in patients with prior hematologic malignant tumors is limited. Objectives: To examine a possible association between prior hematologic malignant tumors and risk of head and neck cancer and to assess the overall survival (OS) among these patients. Design, Setting, and Participants: This retrospective analysis used the Veterans Affairs (VA) Corporate Data Warehouse (CDW) to identify patients with diagnoses of hematologic malignant tumors and head and neck cancers. All patients in the VA CDW with a birthdate between January 1, 1910, and December 31, 1969, were included, for a cohort of 30 939 656 veterans. Data analysis was performed from August 15, 2018, to January 31, 2019. Exposures: Outpatient problem lists were queried for diagnoses of hematologic malignant tumor and associated malignant tumors using International Classification of Diseases, Ninth Revision (ICD-9) and International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) codes to categorize patients by history of hematologic malignant tumors. Main Outcomes and Measures: Presence of head and neck cancer was determined from ICD-9 and ICD-10 codes of outpatient problem lists, and cancers were grouped by subsite. The OS was determined from date of death or last outpatient visit date. Results: Of 30 939 656 patients (27 636 683 [89.3%] male; 13 971 259 [45.2%] white), 207 322 patients had a hematologic malignant tumor, of whom 1353 were later diagnosed with head and neck cancer. A history of hematologic malignant tumors was significantly associated with overall aerodigestive tract cancer, with a relative risk (RR) of 1.6 (95% CI, 1.5-1.7), as well as oral cavity (RR, 1.7; 95% CI, 1.5-1.9), oropharynx (RR, 1.7; 95% CI, 1.5-1.9), larynx (RR, 1.3; 95% CI, 1.2-1.5), nasopharynx (RR, 2.8; 95% CI, 2.1-3.9), sinonasal (RR, 3.0; 95% CI, 2.2-4.1), salivary gland (RR, 2.8; 95% CI, 2.4-3.3), and thyroid (RR, 2.1; 95% CI, 1.9-2.4) tumors on subsite analysis. A prior hematologic malignant tumor was also negatively associated with 2-year and 5-year OS for multiple subsites. Conclusions and Relevance: A prior diagnosis of hematologic or associated malignant tumors was associated with an increased risk of solid head and neck cancers in a range of subsites. In addition, for several head and neck cancer subsites, patients with prior hematologic malignant tumors had worse 2-year and 5-year OS. These results indicate that a prior hematologic malignant tumor may be an adverse risk factor in the development and progression of head and neck cancer.

Elevated incidence of head and neck cancer in solid organ transplant recipients.

BACKGROUND: Solid organ transplant recipients are known to be at an increased risk of cancer development, but research on head and neck cancer in transplant recipients has been limited and prior risk assessments may not be accurate. METHODS: A retrospective review using a national Veterans Administration database to query outpatient problem lists for ICD codes indicating solid organ transplant and subsequent diagnosis of head and neck cancer. RESULTS: In a study of 30 939 656 patients (37 969 solid organ transplants and 113 995 head and neck cancers), history of transplant significantly predicted head and neck cancer, with relative risks ranging from 1.85 (thyroid) to 2.91 (salivary gland). Worse overall survival (OS) was seen for head and neck cancer patients with prior transplants. CONCLUSIONS: In a large case-control study, prior transplant was a risk factor for head and neck cancer development and worse OS for head and neck cancer patients.

The safety and efficacy of transurethral microwave therapy in high-risk catheter-dependent men.

OBJECTIVE: Previous studies have demonstrated the efficacy of transurethral microwave therapy (TUMT) in the management of high-risk catheter-dependent men, although few have assessed safety in high-risk patients, including those continuing anticoagulation therapy during treatment. Our goal was to assess the safety and effectiveness of TUMT in a population of high-risk catheter-dependent men. MATERIAL AND METHODS: A retrospective analysis of patients who underwent TUMT at a single Veterans Affairs facility for the treatment of benign prostatic hyperplasia was completed. The primary outcome was 30-day postprocedural complications by Clavien-Dindo grade, including bleeding events. The secondary outcome was success in catheter removal. RESULTS: We performed TUMT in 157 men, 105 of whom had urinary retention-requiring an indwelling urethral catheter or clean intermittent catheterization. Overall, 86% of patients underwent TUMT while on anticoagulant therapy and 25% were treated while taking warfarin. The median age of the patients was 76.9 years (95% CI 74.9-78.8) median ASA-score was 3, and median follow-up was 26 months (range 1-65). Only two men experienced hematuria requiring treatment postoperatively and no transfusions were required. Only two patients (1.9%) required readmission within 30 days after treatment. There were 24 (22.9%) Clavien-Dindo grade I-II complications without grade III or higher complications. Urinary retention resolved in 63.7% of men after treatment. CONCLUSION: Our results suggest that TUMT is a safe and reasonably effective treatment for high-risk catheter-dependent men. Furthermore, the low incidence of adverse bleeding events suggests that TUMT is a safe treatment modality for men requiring uninterrupted anticoagulation.

The estimated prevalence of missed positive lymph nodes based on extent of lymphadenectomy at radical prostatectomy.

PURPOSE: To determine practice patterns for the extent of lymphadenectomy at radical prostatectomy and associations with detection of pN1 prostate cancer, as well as the impact of lymphadenectomy extent on underdetection of pN1 disease and overall survival. MATERIALS AND METHODS: Prostatectomy cases in the NCDB from 2004 to 2013 were included. Lymphadenectomy extent was defined by the number of nodes examined. Logistic regression was used to identify risk factors for the top quartile of lymph node count and pN1 disease. This model was created to estimate the expected prevalence of pN1, and generated observed over expected ratios. A Cox regression model was used to evaluate the effect of lymph node count on overall survival. RESULTS: Lymphadenectomy was performed in 209,789 (60%) of 358,522 surgeries, with pN1 in 6,428 (3.08%). Increasing quartiles for lymph node count was associated with pN1 (3-5 nodes OR 2.11; 6-8 nodes OR 3.12; ≥9 nodes OR 5.91, all P< 0.001). The logistic regression model suggested that 59% of pN1 cases are missed due to low lymph node count. Increased lymph node count was associated with increasing pN1 detection (O/E: 1-2 nodes = 0.18; 3-5 nodes = 0.37; 6-8 nodes = 0.56; ≥9 nodes = 1.01). Cox proportional hazards modeling demonstrated that the top quartile for lymph node count had improved overall survival (HR 0.93, CI 0.87-0.99, P= 0.03). CONCLUSIONS: Increasing lymphadenectomy extent was associated with pN1 disease on multivariate analysis, and logistic regression modeling suggested a substantial proportion of pN1 were missed due to low lymphadenectomy extent across all risk groups.

Update on flexible ureteroscopy.

OBJECTIVE: An update on ureteroscopy with focus on current technology and newer instrumentation is presented. METHODS: A literature search through Medline-indexed journals as well as personal comments are included in this review. Topics such as new semirigid and flexible ureteroscopes, lasers, ureteral access sheats, wires and stone extraction devices are outlined. RESULTS: Thanks to the continuous advances of technology and miniaturization of instruments, ureteroscopy is an ever-expanding field. A clear outline of the available instruments and techniques with reference to published results catches the status of this dynamic field. CONCLUSIONS: Urologists are faced with a host of new products related to ureteroscopy every year. This review serves to identify the most useful and proven advances in the field and helps in selecting the equipment needed for a successful minimally invasive approach to upper urinary tract pathologies.

Ribonucleotide incorporation enables repair of chromosome breaks by nonhomologous end joining.

The nonhomologous end-joining (NHEJ) pathway preserves genome stability by ligating the ends of broken chromosomes together. It employs end-processing enzymes, including polymerases, to prepare ends for ligation. We show that two such polymerases incorporate primarily ribonucleotides during NHEJ-an exception to the central dogma of molecular biology-both during repair of chromosome breaks made by Cas9 and during V(D)J recombination. Moreover, additions of ribonucleotides but not deoxynucleotides effectively promote ligation. Repair kinetics suggest that ribonucleotide-dependent first-strand ligation is followed by complementary strand repair with deoxynucleotides, then by replacement of ribonucleotides embedded in the first strand with deoxynucleotides. Our results indicate that as much as 65% of cellular NHEJ products have transiently embedded ribonucleotides, which promote flexibility in repair at the cost of more fragile intermediates.